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These are the most-read science news stories of 2020.

When squeezed to high pressure between two diamonds (shown), a material made of carbon, sulfur and hydrogen can transmit electricity without resistance at room temperature. The discovery ranked among Science News ' most popular in 2020.

Adam Fenster

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By Cassie Martin

December 31, 2020 at 8:00 am

Science News drew over 22 million visitors to our website this year. Our COVID-19 coverage was most popular. Here’s a recap of the other most-read news stories and long reads of 2020.

Top news stories

1. In a first, a person’s immune system fought HIV — and won

Scientists analyzed billions of cells from two people with HIV who don’t require medication to keep the virus under control. What the team found was astonishing: One person had no working copies of HIV in any of the cells, while the other person had just one working copy. What’s more, that one copy was imprisoned in tightly wound DNA.

2. The first room-temperature superconductor has finally been found

Up to 15° Celsius, a material made of carbon, sulfur and hydrogen can conduct electricity without resistance. While the room-temperature superconductor works only at high pressures, the discovery brings scientists a step closer to realizing a more energy-efficient future .

3. Astronomers have found the edge of the Milky Way at last

Computer simulations and observations of nearby galaxies have revealed that the Milky Way stretches 1.9 million light-years across. The measurement could help tease out how massive the galaxy is and exactly how many galaxies orbit it .

4. More ‘murder hornets’ are turning up. Here’s what you need to know

An invasion of Asian giant hornets into North America could spell trouble for honeybees. But the threat that the world’s largest hornet species poses to people is minimal .

5. A star orbiting the Milky Way’s black hole validates Einstein

The odd orbit of a star around the supermassive black hole at the Milky Way’s center confirms Albert Einstein’s general theory of relativity. Rather than tracing out a single ellipse, the star’s orbit rotates over time — the result of the black hole warping spacetime .

Favorite visualization

“ A new 3-D map illuminates the ‘little brain’ within the heart ” ( SN: 6/2/20 ) enthralled online readers. An unprecedented view of the heart’s nerve cell cluster could help scientists better understand what those cells do and perhaps lead to targeted therapies for heart diseases.

Top feature stories

1. After the Notre Dame fire, scientists get a glimpse at the cathedral’s origins

A fire that ripped through Paris’ Notre Dame cathedral in April 2019 gave scientists the opportunity to dig into the cathedral’s history and study the building’s materials , including to learn more about climate change.

2. New fleets of private satellites are clogging the night sky

SpaceX and other private companies are planning to launch thousands of internet satellites into orbit around Earth. Hundreds of the satellites already in outer space are obstructing the view of ground-based telescopes and interfering with astronomers’ research .

3. It’s time to stop debating how to teach kids to read and follow the evidence

Research has identified the most effective approaches for teaching children how to read. Those findings could help resolve a long-standing debate that pits phonics against methods that emphasize understanding the meaning of words .

4. To fight discrimination, the U.S. census needs a different race question

The U.S. census has failed to accurately count certain minority groups. As a result, some sociologists are calling for more nuanced census questions that better reflect how respondents view themselves, as well as how society views them — a clearer metric for measuring discrimination .

5. What lifestyle changes will shrink your carbon footprint the most?

Individual actions around shelter, transportation and food can create ripple effects in society to help mitigate the effects of climate change. But to have the most impact, people need to tailor their efforts to their own circumstances .

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Pandemic post

Science News has reported on the COVID-19 pandemic since it began, but none of those stories were included in our most-read lists of 2020. That’s because we think the coverage is in a league of its own.

Stories about when, during an infection, the coronavirus is most contagious and debunking the claim that the virus was made in a lab are among our most-read stories of all time. Readers also were drawn to stories about how the coronavirus spreads and C­OVID-19 v­accines .

As Feedback editor, I review every e-mail we receive from Science News readers. In 2020, more than a third of the thousands of e-mails that filled our inbox were about COVID-19. Hunger for information, for certainty in an uncertain time, has been insatiable.

We’ve strived to answer readers’ pandemic-related questions accurately, given the rapid pace of scientific research into the coronavirus and its effects. Some of those questions have been featured in the pages of this magazine, as well as in the Science News Coronavirus Update newsletter — a weekly e-mail that highlights the l­atest research, data and articles on the c­oronavirus and COVID-19.

Everyone at Science News thanks you, our readers, for your sharp, insightful comments and your continued support. We look forward to answering your many science questions, coronavirus-related and not, in the year ahead.

“ Radiation measurement could help guide lengthy lunar missions ” ( SN: 11/7/20, p. 5 ) incorrectly stated that the average daily exposure to cosmic radiation on the moon is 1.5 million times as high as the average daily exposure on Earth. The average daily exposure on the moon is 1,500 times as high as the average daily exposure on Earth.

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This paper is in the following e-collection/theme issue:

Published on 3.9.2020 in Vol 22 , No 9 (2020) : September

Effects of COVID-19 on College Students’ Mental Health in the United States: Interview Survey Study

Authors of this article:

Original Paper

• Changwon Son 1 , BS, MS   ; 
• Sudeep Hegde 1 , BEng, MS, PhD   ; 
• Alec Smith 1 , BS   ; 
• Xiaomei Wang 1 , BS, PhD   ; 
• Farzan Sasangohar 1, 2 , BA, BCS, MASc, SM, PhD  

1 Department of Industrial and Systems Engineering, Texas A&M University, College Station, TX, United States

2 Center for Outcomes Research, Houston Methodist Hospital, Houston, TX, United States

Corresponding Author:

Farzan Sasangohar, BA, BCS, MASc, SM, PhD

Department of Industrial and Systems Engineering

Texas A&M University

College Station, TX, 77843

United States

Phone: 1 979 458 2337

Email: [email protected]

Background: Student mental health in higher education has been an increasing concern. The COVID-19 pandemic situation has brought this vulnerable population into renewed focus.

Objective: Our study aims to conduct a timely assessment of the effects of the COVID-19 pandemic on the mental health of college students.

Methods: We conducted interview surveys with 195 students at a large public university in the United States to understand the effects of the pandemic on their mental health and well-being. The data were analyzed through quantitative and qualitative methods.

Results: Of the 195 students, 138 (71%) indicated increased stress and anxiety due to the COVID-19 outbreak. Multiple stressors were identified that contributed to the increased levels of stress, anxiety, and depressive thoughts among students. These included fear and worry about their own health and of their loved ones (177/195, 91% reported negative impacts of the pandemic), difficulty in concentrating (173/195, 89%), disruptions to sleeping patterns (168/195, 86%), decreased social interactions due to physical distancing (167/195, 86%), and increased concerns on academic performance (159/195, 82%). To cope with stress and anxiety, participants have sought support from others and helped themselves by adopting either negative or positive coping mechanisms.

Conclusions: Due to the long-lasting pandemic situation and onerous measures such as lockdown and stay-at-home orders, the COVID-19 pandemic brings negative impacts on higher education. The findings of our study highlight the urgent need to develop interventions and preventive strategies to address the mental health of college students.

Introduction

Mental health issues are the leading impediment to academic success. Mental illness can affect students’ motivation, concentration, and social interactions—crucial factors for students to succeed in higher education [ 1 ]. The 2019 Annual Report of the Center for Collegiate Mental Health [ 2 ] reported that anxiety continues to be the most common problem (62.7% of 82,685 respondents) among students who completed the Counseling Center Assessment of Psychological Symptoms, with clinicians also reporting that anxiety continues to be the most common diagnosis of the students that seek services at university counseling centers. Consistent with the national trend, Texas A&M University has seen a rise in the number of students seeking services for anxiety disorders over the past 8 years. In 2018, slightly over 50% of students reported anxiety as the main reason for seeking services. Despite the increasing need for mental health care services at postsecondary institutions, alarmingly, only a small portion of students committing suicide contact their institution counseling centers [ 3 ], perhaps due to the stigma associated with mental health. Such negative stigma surrounding mental health diagnosis and care has been found to correlate with a reduction in adherence to treatment and even early termination of treatment [ 4 ].

The COVID-19 pandemic has brought into focus the mental health of various affected populations. It is known that the prevalence of epidemics accentuates or creates new stressors including fear and worry for oneself or loved ones, constraints on physical movement and social activities due to quarantine, and sudden and radical lifestyle changes. A recent review of virus outbreaks and pandemics documented stressors such as infection fears, frustration, boredom, inadequate supplies, inadequate information, financial loss, and stigma [ 5 ]. Much of the current literature on psychological impacts of COVID-19 has emerged from the earliest hot spots in China. Although several studies have assessed mental health issues during epidemics, most have focused on health workers, patients, children, and the general population [ 6 , 7 ]. For example, a recent poll by The Kaiser Family Foundation showed that 47% of those sheltering in place reported negative mental health effects resulting from worry or stress related to COVID-19 [ 8 ]. Nelson et al [ 9 ] have found elevated levels of anxiety and depressive symptoms among general population samples in North America and Europe. However, with the exception of a few studies, notably from China [ 10 - 12 ], there is sparse evidence of the psychological or mental health effects of the current pandemic on college students, who are known to be a vulnerable population [ 13 ]. Although the findings from these studies thus far converge on the uptick of mental health issues among college students, the contributing factors may not necessarily be generalizable to populations in other countries. As highlighted in multiple recent correspondences, there is an urgent need to assess effects of the current pandemic on the mental health and well-being of college students [ 14 - 17 ].

The aim of this study is to identify major stressors associated with the COVID-19 pandemic and to understand their effects on college students’ mental health. This paper documents the findings from online interview surveys conducted in a large university system in Texas.

Study Design

A semistructured interview survey guide was designed with the purpose of assessing the mental health status of college students both quantitatively and qualitatively. In addition, the interview aimed to capture the ways that students have been coping with the stress associated with the pandemic situation. First, our study assesses participants’ general stress levels using the Perceived Stress Scale-10 (PSS) [ 18 ]. PSS is a widely used instrument to measure overall stress in the past month [ 19 ]. Second, participants were asked if their own and peers’ (two separate questions) stress and anxiety increased, decreased, or remained the same because of the COVID-19 pandemic. For those who indicated increased stress and anxiety during the pandemic, we questioned their stress coping strategies and use of available mental health counseling services. We then elicited pandemic-specific stressors and their manifestations across 12 academic-, health-, and lifestyle-related categories of outcomes such as effects on own or loved ones’ health, sleeping habits, eating habits, financial situation, changes to their living environment, academic workload, and social relations. Students were also asked about the impact of COVID-19 on depressive and suicidal thoughts. These constructs were derived from existing literature identifying prominent factors affecting college students’ mental health [ 20 , 21 ]. Feedback on the severity of COVID-19’s impact on these aspects were elicited using a 4-point scale: 0 (none), 1 (mild), 2 (moderate), and 3 (severe). Participants were asked to elaborate on each response. Third, participants were guided to describe stressors, coping strategies, and barriers to mental health treatment during a typical semester without associating with the COVID-19 pandemic. Although multiple analyses of the collected data are currently under progress, PSS results and the COVID-19–related findings are presented in this paper.

Participants

Participants were recruited from the student population of a large university system in Texas, United States. This particular university closed all their campuses on March 23, 2020, and held all its classes virtually in response to the COVID-19 pandemic. In addition, the state of Texas issued a stay-at-home order on April 2, 2020. Most interviews were conducted about 1 month after the stay-at-home order in April 2020. Figure 1 illustrates the trend of cumulative confirmed cases and a timeline of major events that took place in the university and the state of Texas. Participants were recruited by undergraduate student researchers through email, text messaging, and snowball sampling. The only inclusion criteria for participation was that participants should have been enrolled as undergraduate students in the university at the time of the interviews.

The interviews were conducted by 20 undergraduate researchers trained in qualitative methods and the use of the interview survey guide described above. None of the authors conducted the interviews. All interviews were conducted via Zoom [ 22 ] and were audio recorded. The recordings were later transcribed using Otter.ai [ 23 ], an artificial intelligence–based transcription service, and verified for accuracy manually. Prior to the interview, participants were provided an information document about the study approved by the university’s Institutional Review Board (No 2019-1341D). Upon verbal consent, participants were asked to respond to a questionnaire about their demographic information such as age, gender, year of college, and program of study before completing the interview. Participation was voluntary and participants were not compensated.

Data Analysis

First, descriptive statistics were compiled to describe participants’ demographics (eg, age, gender, academic year, and major) and the distribution of the ratings on PSS-10 survey items. A total PSS score per participant was calculated by first reversing the scores of the positive items (4-7, 9, and 10) and then adding all the ten scores. A mean (SD) PSS score was computed to evaluate the overall level of stress and anxiety among the participants during the COVID-19 pandemic. Second, participants’ answers to 12 academic-, health-, and lifestyle-related questions were analyzed to understand relative impacts of the pandemic on various aspects of college students’ mental health. Percentages of participants who indicated negative ratings (ie, mild, moderate, or severe influence) on these questions were calculated and ranked in a descending order. Qualitative answers to the 12 stressors and coping strategies were analyzed using thematic analysis [ 24 , 25 ] similar to the deductive coding step in the grounded theory method [ 26 ]. A single coder (CS), trained in qualitative analysis methods, analyzed the transcripts and identified themes using an open coding process, which does not use a priori codes or codes created prior to the analysis and places an emphasis on information that can be extracted directly from the data. Following the identification of themes, the coder discussed the codes with two other coders (XW and AS) trained in qualitative analysis and mental health research to resolve discrepancies among related themes and discuss saturation. The coders consisted of two Ph.D. students and one postdoctoral fellow at the same university. MAXQDA (VERBI GmbH) [ 27 ] was used as a computer software program to carry out the qualitative analysis.

Of the 266 university students initially recruited by the undergraduate researchers, 17 retreated and 249 participated in this study. There were 3 graduate students and 51 participants who had missing data points and were excluded, and data from 195 participants were used in the analysis. The average age was 20.7 (SD 1.7) years, and there were more female students (111/195, 57%) than male students (84/195, 43%). Approximately 70% of the participants were junior and senior students. About 60% of the participants were majoring in the college of engineering, which was the largest college in the university population ( Table 1 ). The mean PSS score for the 195 participants was 18.8 (SD 4.9), indicating moderate perceived stress in the month prior to the interview ( Table 2 ).

a PSS: Perceived Stress Scale-10.

Challenges to College Students’ Mental Health During COVID-19

Out of 195 participants, 138 (71%) indicated that their stress and anxiety had increased due to the COVID-19 pandemic, whereas 39 (20%) indicated it remained the same and 18 (9%) mentioned that the stress and anxiety had actually decreased. Among those who perceived increased stress and anxiety, only 10 (5%) used mental health counseling services. A vast majority of the participants (n=189, 97%) presumed that other students were experiencing similar stress and anxiety because of COVID-19. As shown in Figure 2 , at least 54% (up to 91% for some categories) of participants indicated negative impacts (either mild, moderate, or severe) of COVID-19 on academic-, health-, and lifestyle-related outcomes. The qualitative analysis yielded two to five themes for each category of outcomes. The chronic health conditions category was excluded from the qualitative analysis due to insufficient qualitative response. Table 3 presents the description and frequency of the themes and select participant quotes.

a Not every participant provided sufficient elaboration to allow for identification of themes, so the frequency of individual themes does not add up to the total number of participants who indicated negative impacts of the COVID-19 outbreak.

b The five-digit alphanumeric value indicates the participant ID.

c TA: teaching assistant.

Concerns for One’s Own Health and the Health of Loved Ones

A vast majority of the participants (177/195, 91%) indicated that COVID-19 increased the level of fear and worry about their own health and the health of their loved ones. Over one-third of those who showed concern (76/177, 43%) were worried about their families and relatives who were more vulnerable, such as older adults, those with existing health problems, and those who are pregnant or gave birth to a child recently. Some of the participants (26/177, 15%) expressed their worry about their family members whose occupation increased their risk of exposure to COVID-19 such as essential and health care workers. Some participants (19/177, 11%) specifically mentioned that they were worried about contracting the virus.

Difficulty With Concentration

A vast majority of participants (173/195, 89%) indicated difficulty in concentrating on academic work due to various sources of distraction. Nearly half of them (79/173, 46%) mentioned that their home is a distractive environment and a more suitable place to relax rather than to study. Participants mentioned that they were more prone to be interrupted by their family members and household chores at home. Other factors affecting students’ concentration were lack of accountability (21/173, 12%) and social media, internet, and video games (19/173, 11%). Some (18/173, 10%) stated that online classes were subject to distraction due to lack of interactions and prolonged attention to a computer screen. Additionally, monotonous life patterns were mentioned by some to negatively affect concentration on academic work (5/173, 3%).

Disruption to Sleep Patterns

A majority of participants (168/195, 86%) reported disruptions to their sleep patterns caused by the COVID-19 pandemic, with over one-third (38%) reporting such disruptions as severe. Half of students who reported some disruption (84/168, 50%) stated that they tended to stay up later or wake up later than they did before the COVID-19 outbreak. Another disruptive impact brought by the pandemic was irregular sleep patterns such as inconsistent time to go to bed and to wake up from day to day (28/168, 17%). Some (12/168, 7%) reported increased hours of sleep, while others (10/168, 6%) had poor sleep quality.

Increased Social Isolation

A majority of participants answered that the pandemic has increased the level of social isolation (167/195, 86%). Over half of these students (91/167, 54%) indicated that their overall interactions with other people such as friends had decreased significantly. In particular, about one-third (52/167, 31%) shared their worries about a lack of in-person interactions such as face-to-face meetings. Others (9/167, 5%) stated that disruptions to their outdoor activities (eg, jogging, hiking) have affected their mental health.

Concerns About Academic Performance

A majority of participants (159/195, 82%) showed concerns about their academic performance being impacted by the pandemic. The biggest perceived challenge was the transition to online classes (61/159, 38%). In particular, participants stated their concerns about sudden changes in the syllabus, the quality of the classes, technical issues with online applications, and the difficulty of learning online. Many participants (36/159, 23%) were worried about progress in research and class projects because of restrictions put in place to keep social distancing and the lack of physical interactions with other students. Some participants (23/159, 14%) mentioned the uncertainty about their grades under the online learning environment to be a major stressor. Others (12/159, 8%) indicated their reduced motivation to learn and tendency to procrastinate.

Disruptions to Eating Patterns

COVID-19 has also negatively impacted a large portion of participants’ dietary patterns (137/195, 70%). Many (35/137, 26%) stated that the amount of eating has increased, including having more snacks since healthy dietary options were reduced, and others (27/137, 20%) addressed that their eating patterns have become inconsistent because of COVID-19, for example, irregular times of eating and skipping meals. Some students (16/137, 12%) reported decreased appetite, whereas others (7/137, 5%) were experiencing emotional eating or a tendency to eat when bored. On the other hand, some students (28/195, 14%) reported that they were having healthier diets, as they were cooking at home and not eating out as much as they used to.

Changes in the Living Environment

A large portion of the participants (130/195, 67%) described that the pandemic has resulted in significant changes in their living conditions. A majority of these students (89/130, 68%) referred to living with family members as being less independent and the environment to be more distractive. For those who stayed in their residence either on- or off-campus (18/130, 14%), a main change in their living environment was reduced personal interactions with roommates. Some (9/130, 7%) mentioned that staying inside longer due to self-quarantine or shelter-in-place orders was a primary change in their living circumstances.

Financial Difficulties

More than half of the participants (115/195, 59%) expressed their concerns about their financial situations being impacted by COVID-19. Many (44/115, 38%) noted that COVID-19 has impacted or is likely to impact their own current and future employment opportunities such as part-time jobs and internships. Some (21/115, 18%) revealed the financial difficulties of their family members, mostly parents, getting laid off or receiving pay cuts in the wake of COVID-19.

Increased Class Workload

The effect of COVID-19 on class workload among the college students was not conclusive. Although slightly over half of participants (106/195, 54%) indicated their academic workload has increased due to COVID-19, the rest stated the workload has remained the same (70/195, 36%) or rather decreased (19/195, 10%). For those who were experiencing increased workloads, nearly half (51/106, 48%) thought they needed to increase their own efforts to catch up with online classes and class projects given the lack of in-person support from instructors or teaching assistants. About one-third of the participants (33/106, 31%) perceived that assignments had increased or became harder to do. Some (6/106, 6%) found that covering the remainder of coursework as the classes resumed after the 2-week break to be challenging.

Depressive Thoughts

When asked about the impact of the COVID-19 pandemic on depressive thoughts, 44% (86/195) mentioned that they were experiencing some depressive thoughts during the COVID-19 pandemic. Major contributors to such depressive thoughts were loneliness (28/86, 33%), insecurity or uncertainty (10/86, 12%), powerlessness or hopelessness (9/86, 10%), concerns about academic performance (7/86, 8%), and overthinking (4/86, 5%).

Suicidal Thoughts

Out of 195 participants, 16 (8%) stated that the pandemic has led to some suicidal thoughts with 5% (10/16) reporting these thoughts as mild and 3% (6/16) as moderate. There were 6 participants (38%) that attributed their suicidal thoughts to the presence of depressive thoughts. Other reasons were related to academic performance (1/16, 6%), problems with family as they returned home (1/16, 6%), and fear from insecurity and uncertainty (1/16, 6%).

Coping Mechanism During COVID-19

To cope with stress and anxiety imposed by COVID-19, college students reported seeking support from others but were mainly using various self-management methods.

Self-Management

The majority of the participants (105/138, 76%) with increased stress due to the outbreak of COVID-19 explained that they were using various means to help themselves cope with stress and anxiety during the pandemic. Some (24/105, 23%) relied on negative coping methods such as ignoring the news about COVID-19 (10/105), sleeping longer (7/105), distracting themselves by doing other tasks (5/105), and drinking or smoking (2/105). Approximately one-third (30/105, 29%) used positive coping methods such as meditation and breathing exercises (18/105), spiritual measures (7/105), keeping routines (4/105), and positive reframing (2/105). A majority of the participants (73/105, 70%) who used self-management mentioned doing relaxing hobbies including physical exercise (31/105), enjoying streaming services and social media (22/105), playing with pets (7/105), journaling (5/105), listening to music (4/105), reading (2/105), and drawing (2/105). Finally, some participants (15/105, 14%) stated that they were planning activities (eg, drafting to-do lists) for academic work and personal matters as a self-distraction method.

Seeking Support From Others

Approximately one-third of the participants (47/138, 34%) mentioned that communicating with their families and friends was a primary way to deal with stress and anxiety during COVID-19. Some explicitly stated that they were using a virtual meeting application such as Zoom frequently to connect to friends and family. Only 1 participant claimed to be receiving support from a professional therapist, and another participant was using Sanvello, a mobile mental health service app provided by the university.

Barriers to Seeking Professional Support During COVID-19

Despite the availability of tele-counseling and widespread promotion of such services by the university, a vast majority of participants who indicated an increase in stress and anxiety (128/138, 93%) claimed that they had not used school counseling services during the pandemic. Reasons for such low use included the condition not being perceived as severe enough to seek the services (4/128, 3%), not comfortable interacting with unfamiliar people (1/128, 0.8%), not comfortable talking about mental health issues over the phone (1/128, 0.8%), and lack of trust in the counseling services (1/128, 0.8%).

Principal Findings

College students comprise a population that is considered particularly vulnerable to mental health concerns. The findings of this study bring into focus the effects of pandemic-related transitions on the mental health and well-being of this specific population. Our findings suggest a considerable negative impact of the COVID-19 pandemic on a variety of academic-, health-, and lifestyle-related outcomes. By conducting online survey interviews in the midst of the pandemic, we found that a majority of the participants were experiencing increased stress and anxiety due to COVID-19. In addition, results of the PSS showed moderate levels of stress among our participants. This is in line with a recent pre–COVID-19 survey conducted in the United Kingdom (mean PSS score 19.79, SD 6.37) [ 28 ]; however, the administration of PSS as interview questions (compared to allowing participants to read and respond to the 10 questions) might have introduced bias and resulted in underreporting.

Among the effects of the pandemic identified, the most prominent was worries about one’s own health and the health of loved ones, followed by difficulty concentrating. These findings are in line with recent studies in China that also found concerns relating to health of oneself and of family members being highly prevalent among the general population during the pandemic. Difficulty in concentrating, frequently expressed by our participants, has previously been shown to adversely affect students’ confidence in themselves [ 29 ], which has known correlations to increased stress and mental health [ 30 ]. In comparison with stress and anxiety in college students’ general life, it appears that countermeasures put in place against COVID-19, such as shelter-in-place orders and social distancing practices, may have underpinned significant changes in students’ lives. For example, a vast majority of the participants noted changes in social relationships, largely due to limited physical interactions with their families and friends. This is similar to recent findings of deteriorated mental health status among Chinese students [ 10 ] and increased internet search queries on negative thoughts in the United States [ 31 ]. The findings on the impact of the pandemic on sleeping and eating habits are also a cause for concern, as these variables have known correlations with depressive symptoms and anxiety [ 20 ].

Although a majority of participants expressed concerns regarding academic performance, interestingly, almost half of the participants reported lower stress levels related to academic pressure and class workload since the pandemic began. This may be due, in part, to decisions taken by professors and the university to ease the students’ sudden transition to distance learning. For instance, this university allowed students to choose a pass/fail option for each course instead of a regular letter grade. Additionally, actions taken by professors, such as reduced course loads, open book examinations, and other allowances on grading requirements, could also have contributed to alleviating or reducing stress. Although participants who returned to their parental home reported concerns about distractions and independence, students might have benefited from family support and reduced social responsibilities. Therefore, the increased stress due to the pandemic may have been offset, at least to some extent.

Alarmingly, 44% (86/195) of the participants reported experiencing an increased level of depressive thoughts, and 8% (16/195) reported having suicidal thoughts associated with the COVID-19 pandemic. Previous research [ 32 ] reported about 3%-7% of the college student population to have suicidal thoughts outside of the pandemic situation. Furthermore, with the exception of high-burnout categories, depression levels among students, reported in several recent studies [ 33 - 35 ], have varied between 29% and 38%, which may suggest an uptick in pandemic-related depressive symptoms among college students similar to recent studies in China [ 10 , 11 ]. Although our participants specifically mentioned several factors such as feelings of loneliness, powerlessness, as well as financial and academic uncertainties, other outcomes that were perceived to be impacted by the COVID-19 pandemic may also act as contributors to depressive thoughts and suicidal ideation. In particular, both difficulty concentrating and changes in sleeping habits are associated with depression [ 20 , 29 , 36 ].

Our study also identifies several coping mechanisms varying between adaptive and maladaptive behaviors. The maladaptive coping behaviors such as denial and disengagement have been shown to be significant predictors of depression among young adults [ 37 ]. In contrast, adaptive coping such as acceptance and proactive behaviors are known to positively impact mental health. Our findings suggest that the majority of our participants exhibited maladaptive coping behaviors. Identifying students’ coping behavior is important to inform the planning and design of support systems. In this regard, participatory models of intervention development can be used, in which researchers’ and psychologists’ engagement with the target population to adapt interventional programs to their specific context has shown promise [ 37 , 38 ]. For instance, Nastasi et al [ 37 ] used a participatory model to develop culture-specific mental health services for high school students in Sri Lanka. Similar approaches can be adopted to engage college students as well to develop a mental health program that leverages their natural positive coping behaviors and addresses their specific challenges.

Participants described several barriers to seeking help, such as lack of trust in counseling services and low comfort levels in sharing mental health issues with others, which may be indicative of stigma. Perceiving social stigma as a barrier to seeking help and availing counseling services and other support is common among students [ 29 ]. One study showed that only a minor fraction of students who screened positive for a mental health problem actually sought help [ 39 ]. Although overcoming the stigma associated with mental health has been discussed at length, practical ways of mitigating this societal challenge remains a gap [ 40 , 41 ]. Our findings suggest that self-management is preferred by students and should be supported in future work. Digital technologies and telehealth applications have shown some promise to enable self-management of mental health issues [ 42 ]. For instance, Youn et al [ 43 ] successfully used social media networks as a means to reach out to college students and screen for depression by administering a standardized scale, the Patient Health Questionnaire-9. Digital web-based platforms have also been proposed to enhance awareness and communication with care providers to reduce stigma related to mental health among children in underserved communities [ 44 ]. For instance, one of the online modules suggested by the authors involves providing information on community-identified barriers to communicating with care providers. Technologies such as mobile apps and smart wearable sensors can also be leveraged to enable self-management and communication with caregivers.

In light of the aforementioned projections of continued COVID-19 cases at the time of this writing [ 45 ] and our findings, there is a need for immediate attention to and support for students and other vulnerable groups who have mental health issues [ 17 ]. As suggested by a recent study [ 46 ] based on the Italian experience of this pandemic, it is essential to assess the population’s stress levels and psychosocial adjustment to plan for necessary support mechanisms, especially during the recovery phase, as well as for similar events in the future. Although the COVID-19 pandemic seems to have resulted in a widespread forced adoption of telehealth services to deliver psychiatric and mental health support, more research is needed to investigate use beyond COVID-19 as well as to improve preparedness for rapid virtualization of psychiatric counseling or tele-psychiatry [ 47 - 49 ].

Limitations and Future Work

To our knowledge, this is the first effort in documenting the psychological impacts of the COVID-19 pandemic on a representative sample of college students in the United States via a virtual interview survey method in the middle of the pandemic. However, several limitations should be noted. First, the sample size for our interview survey was relatively small compared to typical survey-only studies; however, the survey interview approach affords the capture of elaboration and additional clarifying details, and therefore complements the survey-based approaches of prior studies focusing on student mental health during this pandemic [ 10 , 11 , 50 ]. Second, the sample used is from one large university, and findings may not generalize to all college students. However, given the nationwide similarities in universities transitioning to virtual classes and similar stay-at-home orders, we expect reasonable generalizability of these findings. Additionally, a majority of our participants were from engineering majors. Therefore, future work is needed to use a stratified nationwide sample across wider disciplines to verify and amend these findings. Third, although a vast majority of participants answered that they have not used the university counseling service during the pandemic, only a few of them provided reasons. Since finding specific reasons behind the low use is a key to increasing college students’ uptake of available counseling support, future research is warranted to unveil underlying factors that hinder college students’ access to mental health support. Finally, we did not analyze how student mental health problems differ by demographic characteristics (eg, age, gender, academic year, major) or other personal and social contexts (eg, income, religion, use of substances).

Future work could focus on more deeply probing the relationships between various coping mechanisms and stressors. Additionally, further study is needed to determine the effects of the pandemic on students’ mental health and well-being in its later phases beyond the peak period. As seen in the case of health care workers in the aftermath of the severe acute respiratory syndrome outbreak, there is a possibility that the effects of the pandemic on students may linger for a period beyond the peak of the COVID-19 pandemic itself [ 51 ].

Acknowledgments

This research was partly funded by a Texas A&M University President’s Excellence (X-Grant) award.

Conflicts of Interest

None declared.

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• Zivin K, Eisenberg D, Gollust SE, Golberstein E. Persistence of mental health problems and needs in a college student population. J Affect Disord 2009 Oct;117(3):180-185. [ CrossRef ] [ Medline ]
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• Torous J, Jän Myrick K, Rauseo-Ricupero N, Firth J. Digital mental health and COVID-19: using technology today to accelerate the curve on access and quality tomorrow. JMIR Ment Health 2020 Mar 26;7(3):e18848 [ FREE Full text ] [ CrossRef ] [ Medline ]
• Youn SJ, Trinh N, Shyu I, Chang T, Fava M, Kvedar J, et al. Using online social media, Facebook, in screening for major depressive disorder among college students. Int J Clin Health Psychol 2013 Jan;13(1):74-80. [ CrossRef ]
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• Shore JH, Waugh M, Calderone J, Donahue A, Rodriguez J, Peters D, et al. Evaluation of telepsychiatry-enabled perinatal integrated care. Psychiatr Serv 2020 May 01;71(5):427-432. [ CrossRef ] [ Medline ]
• Huckins JF, daSilva AW, Wang W, Hedlund E, Rogers C, Nepal SK, et al. Mental health and behavior of college students during the early phases of the COVID-19 pandemic: longitudinal smartphone and ecological momentary assessment study. J Med Internet Res 2020 Jun 17;22(6):e20185 [ FREE Full text ] [ CrossRef ] [ Medline ]
• McAlonan GM, Lee AM, Cheung V, Cheung C, Tsang KW, Sham PC, et al. Immediate and sustained psychological impact of an emerging infectious disease outbreak on health care workers. Can J Psychiatry 2007 Apr;52(4):241-247. [ CrossRef ] [ Medline ]

Abbreviations

Edited by G Eysenbach, G Fagherazzi, J Torous; submitted 10.06.20; peer-reviewed by T Liu, V Hagger; comments to author 28.07.20; revised version received 01.08.20; accepted 15.08.20; published 03.09.20

©Changwon Son, Sudeep Hegde, Alec Smith, Xiaomei Wang, Farzan Sasangohar. Originally published in the Journal of Medical Internet Research (http://www.jmir.org), 03.09.2020.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in the Journal of Medical Internet Research, is properly cited. The complete bibliographic information, a link to the original publication on http://www.jmir.org/, as well as this copyright and license information must be included.

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Nih research matters.

December 22, 2020

2020 Research Highlights — Human Health Advances

Disease prevention, diagnosis, and treatment .

With NIH support, scientists across the United States and around the world conduct wide-ranging research to discover ways to enhance health, lengthen life, and reduce illness and disability. Groundbreaking NIH-funded research often receives top scientific honors. In 2020, these honors included one of NIH’s own scientists and another NIH-supported scientist who received Nobel Prizes . Here’s just a small sample of the NIH-supported research accomplishments in 2020.

Full 2020 NIH Research Highlights List

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COVID-19 vaccines and treatments

Since first appearing in China late last year, COVID-19 has become an ongoing global pandemic. NIH researchers quickly began testing potential treatments to help reduce the severity of the disease. Remdesivir, a broad-spectrum antiviral treatment, showed early promise . Results from the completed trial in October showed that it shortened recovery time for patients hospitalized with COVID-19 . NIH research was also instrumental in determining which treatments, such as hydroxychloroquine , were ultimately not effective. Meanwhile, NIH researchers began developing vaccine candidates to protect against the disease. The first COVID-19 vaccine candidate tested in people , co-developed by NIH and the biotech company Moderna, Inc., triggered an immune response against the virus without serious side effects. An analysis in November found the vaccine was safe and well-tolerated, with a vaccine efficacy rate of 94.5% . The FDA approved it for emergency use in December. NIH also launched the Rapid Acceleration of Diagnostics (RADx SM ) initiative to speed innovation in COVID-19 testing. An NIH-funded COVID-19 home test was the first to receive over-the-counter authorization from the FDA.

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Comparing heart disease treatments

People with moderate to severe but stable heart disease may undergo invasive procedures, such as bypass surgery and stenting, or manage their condition with medication and lifestyle changes alone. A study showed that invasive procedures may offer better symptom relief and quality of life for some patients with chest pain. But for those who didn't have any symptoms, it was safe to begin treatment with non-invasive approaches. The findings may change clinical practice and official guidelines for treating patients.

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Combining tests more accurately diagnoses prostate cancer

The type of biopsy traditionally used to diagnose prostate cancer takes systematically spaced tissue samples from the prostate gland. This method isn’t targeted and can lead to uncertainty about whether a man has aggressive prostate cancer. Researchers found that adding MRI-targeted biopsies to the traditional prostate biopsy created a more accurate diagnosis and prediction of the course of prostate cancer. The approach is poised to help reduce both overtreatment and undertreatment of the disease.

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Early detection of Alzheimer’s disease

Having a simple blood test to detect Alzheimer’s disease before symptoms develop would aid the study of treatments to slow or stop its progression. Studies found that a protein called ptau181, which can be measured in the blood, was as good as invasive or expensive tests at diagnosing Alzheimer’s early . Another protein, called ptau217, was even better at predicting who would later develop the disease .  A type of brain imaging could also play a role in tracking disease development. These approaches could help identify people to participate in trials of early treatments or preventive strategies.

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Number of steps per day more important than step intensity

Walking is an easy way for many inactive people to ease into better health. A goal of 10,000 steps a day is common. A study found that adults who took at least 8,000 steps a day had a reduced risk of death over the following decade than those who only walked 4,000 steps a day. Step intensity (number of steps per minute) didn’t influence the risk of death, suggesting that the total number of steps per day is more important than intensity.

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Harnessing the health benefits of bacteria

Some types of bacteria cause disease, but others can help protect human health. A strain of bacteria called Lactobacillus crispatus was used as a treatment to prevent recurring bacterial vaginosis . In another study, treatment with the bacterium  Roseomonas mucosa,  taken from healthy human skin, improved eczema in children . These findings show the potential of harnessing the healthy human microbiome to prevent or treat disease.

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Multifocal contact lenses slow myopia progression in children

Myopia, also called nearsightedness, is a common vision problem, where close objects can be seen clearly but objects farther away appear blurry. In the U.S., myopia typically begins in childhood. Researchers found that children who wore certain multifocal contact lenses had slower progression of their myopia, or nearsightedness, over three years. The findings support using multifocal contacts to treat myopia in children, which could also help prevent other vision problems later in life.

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Biomarkers predict recovery from brain injury

More than a million people in the U.S. experience a mild traumatic brain injury, or concussion, every year. Researchers found that military veterans with higher blood levels of a protein released by injured neurons were more likely to report long-term symptoms. More study is needed to confirm whether this could be used to predict who is at risk of long-term health problems after concussion. Two blood proteins were linked to the time needed by college athletes to return to play following a concussion. These biomarkers may help doctors predict which athletes need additional time to recover.

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ROLAND GRAD, MD, MSc, AND MARK H. EBELL, MD, MS

Am Fam Physician. 2021;104(1):41-48

Related letter: Should Muscle Relaxants Be Used as Adjuvants in Patients With Acute Low Back Pain?

Published online June 9, 2021.

Author disclosure: Dr. Grad has no relevant financial affiliations. Dr. Ebell is cofounder and editor-in-chief of Essential Evidence Plus; see Editor's Note.

This article summarizes the top 20 research studies of 2020 identified as POEMs (patient-oriented evidence that matters), including the two most highly rated guidelines of the year on gout and chronic obstructive pulmonary disease (COPD). Regarding COVID-19, handwashing and social distancing through stay-at-home orders or quarantine measures are effective at slowing the spread of illness. Use of proper face masks (not gaiters or bandanas) is also effective at preventing transmission. This is important because the virus can infect others during the presymptomatic phase. Aspirin can no longer be recommended for the primary prevention of cardiovascular disease. Human papillomavirus vaccination is strongly associated with reduced risk of invasive cervical cancer, especially in women who were vaccinated before 17 years of age. When a woman who is postmenopausal has a screening bone mineral density test, rechecking the test after three years does not help to identify those who will have a fragility fracture. A higher daily step count is associated with lower all-cause mortality. After one year of follow-up, physical therapy is preferred to glucocorticoid injections for osteoarthritis of the knee; acetaminophen is ineffective for acute low back pain or pain due to knee or hip osteoarthritis; and adding a muscle relaxant to ibuprofen does not improve functional outcomes or pain in people reporting moderate to severe back pain one week after starting treatment. Although short-term antibiotics and steroids are effective in treating acute exacerbations of COPD, not much else is. Successful communication with patients seeking an antibiotic for a flulike illness can be achieved with combinations of messaging, including information on antibiotic resistance and the self-limiting nature of the illness. A new prediction rule effectively identifies patients with a history of penicillin allergy who have a low likelihood of positive findings on allergy testing. Low-value screening tests in asymptomatic, low-risk patients often lead to further testing, diagnostic procedures, or referrals. A new tool helps determine the amount of change needed to signify a real difference between two laboratory values in the same person over time. Finally, a pillar of our specialty, continuity of care, is associated with decreased all-cause mortality.

Annually for 22 years, a team of clinicians has systematically reviewed English-language medical journals to identify original research most likely to change and improve primary care practice. The team includes experts in family medicine, pharmacology, hospital medicine, and women's health. 1 , 2

The goal of this process is to identify POEMs (patient-oriented evidence that matters). A POEM must report at least one patient-oriented outcome, such as improvement in symptoms, morbidity, or mortality. It should also be free of important methodologic bias, making the results valid and trustworthy. Finally, if applied in practice, the results would change what some physicians do by prompting them to adopt a new practice or discontinue an old one that has been shown to be ineffective or harmful. Adopting POEMs in clinical practice should improve patient outcomes. Of more than 20,000 research studies published in 2020 in the journals reviewed by the POEMs team, 306 met criteria for validity, relevance, and practice change. These POEMs are emailed daily to subscribers of Essential Evidence Plus (Wiley-Blackwell, Inc.).

The Canadian Medical Association purchases a POEMs subscription for its members, many of whom receive the daily POEM. As these physicians read a POEM, they can rate it using a validated questionnaire. This process is called the Information Assessment Method ( https://www.mcgill.ca/iam ). POEM ratings address the domains of clinical relevance, cognitive impact, use of this information in practice, and expected health benefits if that POEM is applied to a specific patient. 3 , 4 In 2020, each of the 306 daily POEMs was rated by an average of 1,230 physicians.

In this article, we present the 20 most clinically relevant POEMs as rated by Canadian Medical Association members in 2020. This is the 10th installment of our annual series ( https://www.aafp.org/afp/toppoems ). As we write this article, the pandemic rolls on. However, beyond COVID-19, our patients continue to face the usual (and unusual) health problems of everyday life. Thus, we summarize the clinical question and bottom-line answer for research studies identified as a top 20 POEM, organized by topic and followed by a brief discussion. This set of 20 POEMs includes the two most relevant practice guidelines of the year. The full POEMs are available online at https://www.aafp.org/afp/poems2020 .

The year 2020 saw the emergence of SARS-CoV-2, a novel coronavirus that causes the COVID-19 illness, and 54 POEMs addressed the epidemiology, diagnosis, treatment, and prognosis of patients with COVID-19. Not surprisingly, the four most highly rated POEMs of the year and five in the top 20 provided evidence regarding preventive measures ( Table 1 ) . 5 – 10 These were published early in the pandemic and provided important evidence for family physicians to share with their patients.

The most highly rated POEM was originally published in 2015 and reissued in 2020 after the content was updated for COVID-19. The study was a large pragmatic trial in the United Kingdom that randomized participants to a brief online hand-washing intervention or usual care. Those who completed the intervention had fewer respiratory tract infections over the next four months (51% vs. 59%; P < .001; number needed to treat = 12). 5

The next COVID-19 POEM was a Cochrane review. 6 The authors reviewed the results of modeling studies of COVID-19 and previous coronavirus pandemics, as well as four observational studies. They concluded that quarantine measures are effective in slowing the spread of infection, especially when implemented early and in conjunction with other public health measures.

The third POEM summarized the results of two ecologic studies. The first compared COVID-19 incidence rates in eight Iowa counties that did not have stay-at-home orders with seven neighboring Illinois counties that had such orders in place. 7 The second compared a Georgia county that implemented stay-at-home orders approximately two weeks before the rest of Georgia with seven surrounding counties. 8 In both studies, earlier implementation of stay-at-home orders was associated with a lower incidence of COVID-19.

Another POEM summarized the results of one of the earliest studies to evaluate the effectiveness of different kinds of masks for preventing the spread of respiratory droplets. 9 Using laser technology, 14 types of masks were evaluated. Gaiters and bandanas were essentially useless, polypropylene and surgical masks were much better, and N95 masks were best.

An important factor in the rapid spread of COVID-19 was transmission by asymptomatic people. One of the first publications to report this was described in the next POEM. Chinese researchers studying infector-infectee transmission pairs found that the peak of infectiousness occurs about one day before symptom onset, and that 44% of secondary cases occur during the presymptomatic period. 10 Another study (not among the top 20 POEMs) reviewed cohorts in which the entire group was tested for COVID-19 during an outbreak and found that the rates of asymptomatic or presymptomatic infection are 75% or higher in young adult populations and approximately 40% overall. 11

Prevention and Screening

POEMs addressing prevention topics are summarized in Table 2 . 12 – 15 The first was a meta-analysis of randomized trials comparing aspirin with placebo as primary prevention. It compared four studies that recruited patients since 2005, with older studies that largely recruited patients in the 1980s and 1990s. The newer studies no longer found that patients taking aspirin for primary prevention have significant reductions in cancer incidence or mortality, cardiovascular mortality, or nonfatal myocardial infarction. Any benefits were countered by harms, such as increased gastrointestinal bleeding. 12 Perhaps we are doing a better job of screening for cancer and preventing cardiovascular events through use of statins and antihypertensives, lessening the need for aspirin in prevention.

We often tell our patients to walk more, but does walking affect mortality? The next POEM used data from a national sample of U.S. residents whose daily steps were measured between 2003 and 2006. 13 All-cause mortality was 77 per 1,000 person-years for those with less than 4,000 steps per day; 21 per 1,000 for those with 4,000 to 7,999 steps per day; 7 per 1,000 for those with 8,000 to 11,999 steps per day; and 4.8 per 1,000 for those with at least 12,000 steps per day. Step intensity was not significantly associated with mortality after controlling for total daily steps. Bottom line? Higher step counts are associated with lower all-cause mortality, suggesting our patients should keep walking. 13

When a woman who is postmenopausal has a screening bone mineral density test, the question arises about whether to repeat the test and, if so, how often? The third POEM in this group is a cohort study from the Women's Health Initiative, which showed that information gained from a second test three years after the first does not add predictive value beyond the first test result. Because bone density changes little over time, one bone mineral density test at around 65 years of age is likely to be sufficient for the purpose of screening to prevent a fragility fracture. 14

Studies have shown that human papillomavirus (HPV) vaccination can reduce the likelihood of precancerous abnormalities identified on a Papanicolaou (Pap) test. The next POEM is a Swedish study that used data from a national health registry to compare the risk of invasive cervical cancer in 527,871 vaccinated women vs. 1,145,112 unvaccinated women. 15 After adjusting for differences between groups, the incidence rate ratio (IRR; the ratio of the incidence of cancer in vaccinated people to that in unvaccinated people) for invasive cervical cancer was 0.37 (95% CI, 0.21 to 0.57). For women who were vaccinated before 17 years of age, the IRR was only 0.12 (95% CI, 0.00 to 0.34), whereas for those vaccinated between 17 and 30 years of age, the IRR was 0.47 (95% CI, 0.27 to 0.75). HPV vaccination is strongly associated with a lower risk of invasive cervical cancer, especially when given early.

Musculoskeletal

Three POEMs addressing musculoskeletal topics are summarized in Table 3 . 16 – 19 The first is a study that randomized adults with knee osteoarthritis to up to three corticosteroid injections or up to eight physical therapy sessions in the first six weeks, with additional sessions as needed. 16 The rapid and large improvement in the first month for both groups is somewhat surprising, with relatively little further improvement the rest of the year. This suggests regression to the mean may have contributed to the observed improvement (i.e., patients were identified when their arthritis was flaring up and would have improved no matter what). Also, the open-label design may have contributed to a Hawthorne effect (alteration of behavior by the participants of a study who know they are being observed) for those in the physical therapy group and a placebo effect for those in the injection group. A Cochrane review concluded that glucocorticoid injections are effective, although primarily in the two to four weeks following injection. 17 Overall, the physical therapy group did better at one year, with continued improvement, whereas the injection group plateaued after the first month. 16

The next POEM is a systematic review of randomized controlled trials of acetaminophen compared with placebo for pain relief in adults. 18 It showed that acetaminophen is more effective than placebo in providing some pain relief in patients with acute migraine and might be more beneficial than placebo (which also works well) for tension headaches. A single dose of acetaminophen is about twice as likely as placebo to reduce postpartum perineal pain, and it may be effective (but not as effective as other treatments) for acute renal colic. Importantly, acetaminophen is ineffective for patients with acute low back pain or pain due to knee or hip osteoarthritis.

The last POEM in this category addresses a drug class often prescribed for back pain. In people with moderate to severe low back pain who are taking a nonsteroidal anti-inflammatory drug, such as ibuprofen (up to 600 mg three times per day), does the addition of a muscle relaxant improve function or reduce pain? No. 19 This finding reminds us of an earlier randomized controlled trial from the same author that was a top POEM of 2015. At that time, we advised not adding cyclobenzaprine to naproxen for patients with acute low back pain. 20

Respiratory

Two top POEMs on respiratory topics are summarized in Table 4 . 21 , 22 One is a meta-analysis of randomized controlled trials of treatment in patients with an exacerbation of chronic obstructive pulmonary disease. 21 This shows that antibiotics and corticosteroids are effective in treating acute exacerbations in outpatient and inpatient settings, regardless of the severity of the exacerbation. Current research does not provide good guidance on which antibiotic is best or on the optimal dose or duration of corticosteroid treatment. Notably, studies performed in critically ill patients were not included in this analysis.

The other POEM addresses the tricky issue of communicating with patients who appear to be seeking an antibiotic for a flulike illness. It is a randomized trial conducted online in the United Kingdom showing that patients receiving the combination of a fear-based message about increased antibiotic resistance and an empowering message are less likely to visit a physician for their next respiratory tract infection (45.1% to 46.1% vs. 29.2%; P < .001) and less likely to request an antibiotic (52.5% to 54.7% vs. 42.3%; P < .001) than those receiving only fear-based messaging. 22

Miscellaneous

Four top POEMs do not fall easily into a single category ( Table 5 ) . 23 – 26 The first is about a new clinical prediction rule to identify patients who report a penicillin allergy but are unlikely to have a true allergy if tested. The FAST rule is as follows—five years or less since the reaction: 2 points; anaphylaxis, angioedema, or severe cutaneous reaction: 2 points; treatment required for reaction: 1 point. Patients with a score of 0 have a less than 1% likelihood of a positive result on allergy testing, and those with a score of 1 or 2 have a 5% likelihood. 23

The COVID-19 pandemic upended medical practice, leading to large reductions in the use of health care services. For example, the Canadian Urological Association recommended the cessation of prostate-specific antigen screening for prostate cancer until the resolution of the pandemic. 27 In this context, the next POEM reminds us to avoid low-value screening tests in asymptomatic, low-risk patients because they often lead to further testing, diagnostic procedures, or referrals. 24 Specifically, screening tests in low-risk patients, such as chest radiography and electrocardiography in adults as part of an annual health examination and Pap tests in those younger than 21 years or older than 69 years, should be avoided.

How many patients still ask for annual blood tests despite physicians counseling them on the low yield for doing this? The next POEM was the top non–COVID-related POEM of 2020 for clinical relevance. 25 This POEM describes a new online tool ( https://www.bmj.com/content/368/bmj.m149 ) to illustrate the variability in a single laboratory value (such as the A1C test) and the amount of change needed to signify a real difference between two values in the same person over time. For example, given the variability inherent in total cholesterol measurements, it is difficult to detect a clinically important change within a one-year period.

Our final miscellaneous POEM is a systematic review of the value of a pillar of family medicine—personal continuity of care. This is defined by an ongoing relationship with a physician that builds the physician-patient relationship and promotes the healing power of interactions. This core principle of family medicine stands up to scientific scrutiny by demonstrating an associated reduction in mortality. 26

Practice Guidelines

POEMs sometimes summarize high-impact clinical practice guidelines. Key messages from the two highest rated guidelines, addressing gout and chronic obstructive pulmonary disease, are summarized in Table 6 . 28 , 29

The full text of the POEMs discussed in this article is available at https://www.aafp.org/afp/poems2020 .

A list of top POEMs from previous years is available at https://www.aafp.org/afp/toppoems .

Editor's Note: This article was cowritten by Dr. Mark Ebell, deputy editor for evidence-based medicine for AFP and cofounder and editor-in-chief of Essential Evidence Plus, published by Wiley-Blackwell, Inc. Because of Dr. Ebell's dual roles and ties to Essential Evidence Plus, the concept for this article was independently reviewed and approved by a group of AFP 's medical editors. In addition, the article underwent peer review and editing by three of AFP 's medical editors. Dr. Ebell was not involved in the editorial decision-making process.—Sumi Sexton, MD, Editor-in-Chief

The authors thank Wiley-Blackwell, Inc., for giving permission to excerpt the POEMs; Drs. Allen Shaughnessy, Henry Barry, David Slawson, Nita Kulkarni, and Linda Speer for selecting and writing the original POEMs; the academic family medicine fellows and faculty of the University of Missouri–Columbia for their work as peer reviewers; Joulé, Inc., for supporting the POEMs CME program in Canada; Pierre Pluye, PhD, for codeveloping the Information Assessment Method; and Maria Vlasak for her assistance with copyediting the POEMs.

Shaughnessy AF, Slawson DC, Bennett JH. Becoming an information master: a guidebook to the medical information jungle. J Fam Pract. 1994;39(5):489-499.

Ebell MH, Barry HC, Slawson DC, et al. Finding POEMs in the medical literature. J Fam Pract. 1999;48(5):350-355.

Grad RM, Pluye P, Mercer J, et al. Impact of research-based synopses delivered as daily e-mail: a prospective observational study. J Am Med Inform Assoc. 2008;15(2):240-245.

Pluye P, Grad RM, Johnson-Lafleur J, et al. Evaluation of email alerts in practice: part 2. Validation of the information assessment method. J Eval Clin Pract. 2010;16(6):1236-1243.

Little P, Stuart B, Hobbs FDR, et al. An internet-delivered handwashing intervention to modify influenza-like illness and respiratory infection transmission (PRIMIT): a primary care randomised trial [published correction appears in Lancet . 2015;386(10004):1630]. Lancet. 2015;386(10004):1631-1639.

Nussbaumer-Streit B, Mayr V, Dobrescu AI, et al. Quarantine alone or in combination with other public health measures to control COVID-19: a rapid review. Cochrane Database Syst Rev. 2020(4):CD013574.

Lyu W, Wehby GL. Comparison of estimated rates of coronavirus disease 2019 (COVID-19) in border counties in Iowa without a stay-at-home order and border counties in Illinois with a stay-at-home order. JAMA Netw Open. 2020;3(5):e2011102.

Ebell MH, Bagwell-Adams G. Mandatory social distancing associated with increased doubling time: an example using hyperlocal data. Am J Prev Med. 2020;59(1):140-142.

Fischer EP, Fischer MC, Grass D, et al. Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Sci Adv. 2020;6(36):eabd3083.

He X, Lau EHY, Wu P, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19 [published correction appears in Nat Med . 2020;26(9):1491–1493]. Nat Med. 2020;26(5):672-675.

Oran DP, Topol EJ. Prevalence of asymptomatic SARSCoV-2 infection: a narrative review. Ann Intern Med. 2020;173(5):362-367.

Moriarty F, Ebell MH. A comparison of contemporary versus older studies of aspirin for primary prevention. Fam Pract. 2020;37(3):290-296.

Saint-Maurice PF, Troiano RP, Bassett DR, et al. Association of daily step count and step intensity with mortality among US adults. JAMA. 2020;323(12):1151-1160.

Crandall CJ, Larson J, Wright NC, et al. Serial bone density measurement and incident fracture risk discrimination in postmenopausal women. JAMA Intern Med. 2020;180(9):1232-1240.

Lei J, Ploner A, Elfström KM, et al. HPV vaccination and the risk of invasive cervical cancer. N Engl J Med. 2020;383(14):1340-1348.

Deyle GD, Allen CS, Allison SC, et al. Physical therapy versus glucocorticoid injection for osteoarthritis of the knee. N Engl J Med. 2020;382(15):1420-1429.

Jüni P, Hari R, Rutjes AWS, et al. Intra-articular corticosteroid for knee osteoarthritis. Cochrane Database Syst Rev. 2015(10):CD005328.

Saragiotto BT, Abdel Shaheed C, Maher CG. Paracetamol for pain in adults. BMJ. 2019;367:l6693.

Friedman BW, Irizarry E, Solorzano C, et al. A randomized, placebo-controlled trial of ibuprofen plus metaxalone, tizanidine, or baclofen for acute low back pain. Ann Emerg Med. 2019;74(4):512-520.

Friedman BW, Dym AA, Davitt M, et al. Naproxen with cyclobenzaprine, oxycodone/acetaminophen, or placebo for treating acute low back pain: a randomized clinical trial. JAMA. 2015;314(15):1572-1580.

Dobler CC, Morrow AS, Beuschel B, et al. Pharmacologic therapies in patients with exacerbation of chronic obstructive pulmonary disease: a systematic review with meta-analysis. Ann Intern Med. 2020;172(6):413-422.

Roope LSJ, Tonkin-Crine S, Herd N, et al. Reducing expectations for antibiotics in primary care: a randomised experiment to test the response to fear-based messages about antimicrobial resistance. BMC Med. 2020;18(1):110.

Trubiano JA, Vogrin S, Chua KYL, et al. Development and validation of a penicillin allergy clinical decision rule. JAMA Intern Med. 2020;180(5):745-752.

Bouck Z, Calzavara AJ, Ivers NM, et al. Association of low-value testing with subsequent health care use and clinical outcomes among low-risk primary care outpatients undergoing an annual health examination. JAMA Intern Med. 2020;180(7):973-983.

McCormack JP, Holmes DT. Your results may vary: the imprecision of medical measurements. BMJ. 2020;368:m149.

Baker R, Freeman GK, Haggerty JL, et al. Primary medical care continuity and patient mortality: a systematic review. Br J Gen Pract. 2020;70(698):e600-e611.

Kokorovic A, So AI, Hotte SJ, et al. A Canadian framework for managing prostate cancer during the COVID-19 pandemic: recommendations from the Canadian Urologic Oncology Group and the Canadian Urological Association. Can Urol Assoc J. 2020;14(6):163-168.

FitzGerald JD, Dalbeth N, Mikuls T, et al. 2020 American College of Rheumatology Guideline for the Management of Gout [published correction appears in Arthritis Rheumatol . 2021;73(3):413]. Arthritis Rheumatol. 2020;72(6):879-895.

Nici L, Mammen MJ, Charbek E, et al. Pharmacologic management of chronic obstructive pulmonary disease. An official American Thoracic Society Clinical Practice Guideline [published correction appears in Am J Respir Crit Care Med. 2020;202(6):910]. Am J Respir Crit Care Med. 2020;201(9):e56-e69.

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The 5 most popular scientific papers of August 2020 in the Nature Index journals

A gruesome escape artist and ingenious dolphin behaviour feature in these stand-out studies from August.

The Indo-Pacific bottlenose dolphin ( Tursiops aduncus ). Credit: Blue Planet Archive/Alamy Stock Photo

27 October 2020

Blue Planet Archive/Alamy Stock Photo

The Indo-Pacific bottlenose dolphin ( Tursiops aduncus ).

Animals adapt to their environments in remarkable ways. Whether they’re figuring out how to pass through the digestive systems of predators unscathed, or sharing clever methods for ferreting out a snack, these newly discovered behaviours demonstrate how much there is left to discover, even about the most widely-studied species.

Understanding certain adaptions, such as how disease-carrying animals respond to landscapes that are being progressively developed into farmland, can be crucial to human survival too.

These findings feature among the most popular natural sciences studies of August, published in the 82 high-quality journals tracked by the Nature Index.

Also included below are two studies that offer insights into the body’s immune response to COVID-19.

1. “Selective and cross-reactive SARS-CoV-2 T cell epitopes in unexposed humans”

Immune cells called memory T cells remain in the body long after an infection has been eliminated. This ‘memory’ is thought to give the cells a head-start in recognizing and fighting off repeat invaders.

A widely read study published in Science found that memory T cells that recognize common cold coronaviruses also appear to recognize elements of SARS-CoV-2, the virus that causes COVID-19.

The team behind the research, co-led by Daniela Weiskopf and Alessandro Sette from the Center for Infectious Disease and Vaccine Research at the La Jolla Institute for Immunology in California, found that some people who have not been exposed to SARS-CoV-2 have pre-existing reactivity to SARS-CoV-2 sequences.

“The immunological mechanisms underlying this preexisting reactivity are not clear, but previous exposure to widely circulating common cold coronaviruses might be involved,” the study states.

The researchers suggest that this could explain why some people have milder COVID-19 cases than others, but emphasized that more data is needed to know for sure.

The study has more than double the Altmetric score of the second most-discussed paper in this list. It has been covered by more than 200 news outlets so far, and has reached an audience of roughly 25 million people on Twitter.

2. “Active escape of prey from predator vent via the digestive tract”

Current Biology

It’s one thing for prey to evade a predator’s attacks. It’s quite another to escape from the predator after being digested.

This study, authored solely by Sugiura Shinji, an ecologist from Kobe University in Japan, describes how the Japanese water scavenger beetle ( Regimbartia attenuate ) manages to extricate itself from inside several species of frog within 6 hours of being swallowed.

While some prey animals unwittingly hitch a ride through their predator’s gut to be ultimately excreted through the vent (or cloaca) with the the faeces (referred to as “passive”), this aquatic beetle appears to take a more “active” approach.

“Swallowed beetles likely used their legs to move through the digestive tract toward the frog vent, hastening their escape,” the paper describes.

Remarkably, the strategy results in significantly more escapes than failures:

Credit: Sugiura Shinji

The paper reached an audience of almost 10 million on Twitter, and was covered by publications such as The New York Times and NPR.

3. “Sex differences in immune responses that underlie COVID-19 disease outcomes”

There is increasing evidence that COVID-19 produces more severe symptoms and higher mortality among men than among women. This study set out to investigate whether immune responses against the virus SARS-CoV-2 (which causes COVID-19) differ by gender, and whether such differences can help explain the progression of COVID-19 in male and female patients.

Led by a team at Yale University in New Haven, Connecticut, the study analyzed nasal, saliva, and blood samples from COVID-19 patients and a control (non-infected) group and found key differences in the immune response between male and female patients during the early phases of infection.

“We now have clear data suggesting that the immune landscape in COVID-19 patients is considerably different between the sexes and that these differences may underlie heightened disease susceptibility in men,” one of the study authors, Akiko Iwasaki, from the Howard Hughes Medical Institute in Maryland, said in a press statement.

“Collectively, these data suggest we need different strategies to ensure that treatments and vaccines are equally effective for both women and men.”

The paper has been covered by 145 online news outlets to date, and has reached an audience of more than 7 million on Twitter, according to Altmetric.

4. “Integrating Genetic, Environmental, and Social Networks to Reveal Transmission Pathways of a Dolphin Foraging Innovation”

Observations of Indo-Pacific bottlenose dolphins ( Tursiops aduncus ) in Shark Bay, Western Australia have shown that they can learn foraging techniques outside the mother-calf bond, which suggests they have a similar cultural nature to great apes.

Researchers observed young dolphins learning ‘shelling’ behaviour – using their beaks to bring empty shells to the surface and shaking out the prey hiding within – from their peers.

The study, led by Sonja Wild when she was a PhD candidate at the University of Leeds in the United Kingdom, challenges conventional wisdom about how dolphins pass on knowledge.

"These results were quite surprising, as dolphins tend to be conservative, with calves following a 'do-as-mother-does' strategy for learning foraging behaviours,” Wild, now at the Centre for the Advanced Study of Collective Behaviour at the University of Konstanz, Germany, said in a press statement.

“This opens the door to a new understanding of how dolphins may be able to behaviourally adapt to changing environments, as learning from one's peers allows for a rapid spread of novel behaviour across populations." The paper has been covered by 269 online news outlets to date, according to Altmetric.

5. “Zoonotic host diversity increases in human-dominated ecosystems”

Animals that carry disease-causing micro-organisms, or pathogens, thrive in human habitats, according to this paper led by a team at University College London, in the United Kingdom.

The study, based on a dataset of 184 studies incorporating almost 7,000 species, 376 of which are known to carry human-shared pathogens, found that the disruptions caused by global changes in land use appear to benefit disease-carrying species. Changes in land use include clearing natural forest to make space for farmland or housing developments.

“We … show that mammal species that harbour more pathogens overall (either human-shared or non-human-shared) are more likely to occur in human-managed ecosystems,” the paper concludes.

“Our results suggest that global changes in the mode and the intensity of land use are creating expanding hazardous interfaces between people, livestock and wildlife reservoirs of zoonotic [pathogen-caused] disease.”

The paper has been covered by more than 150 online news outlets, and reached more than 5 million people on Twitter.

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Research Roundup: How the Pandemic Changed Management

• Mark C. Bolino,
• Jacob M. Whitney,
• Sarah E. Henry

Lessons from 69 articles published in top management and applied psychology journals.

Researchers recently reviewed 69 articles focused on the management implications of the Covid-19 pandemic that were published between March 2020 and July 2023 in top journals in management and applied psychology. The review highlights the numerous ways in which employees, teams, leaders, organizations, and societies were impacted and offers lessons for managing through future pandemics or other events of mass disruption.

The recent pandemic disrupted life as we know it, including for employees and organizations around the world. To understand such changes, we recently reviewed 69 articles focused on the management implications of the Covid-19 pandemic. These papers were published between March 2020 and July 2023 in top journals in management and applied psychology.

• Mark C. Bolino is the David L. Boren Professor and the Michael F. Price Chair in International Business at the University of Oklahoma’s Price College of Business. His research focuses on understanding how an organization can inspire its employees to go the extra mile without compromising their personal well-being.
• JW Jacob M. Whitney is a doctoral candidate in management at the University of Oklahoma’s Price College of Business and an incoming assistant professor at Kennesaw State University. His research interests include leadership, teams, and organizational citizenship behavior.
• SH Sarah E. Henry is a doctoral candidate in management at the University of Oklahoma’s Price College of Business and an incoming assistant professor at the University of South Florida. Her research interests include organizational citizenship behaviors, workplace interpersonal dynamics, and international management.

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Scientists Discover 100 New Marine Species in New Zealand

The findings, from the largely uncharted waters of Bounty Trough, show that “we’ve got a long way to go in terms of understanding where life is found in the ocean,” a researcher said.

By Rebecca Carballo

A team of 21 scientists set off on an expedition in the largely uncharted waters of Bounty Trough off the coast of the South Island of New Zealand in February hoping to find a trove of new species.

The expedition paid off, they said on Sunday, with the discovery of 100 new species, a number that was likely to grow, said Alex Rogers, a marine biologist who was a leader of the expedition.

“I expect that number to increase as we work through more and more of the samples,” Dr. Rogers said. “I think that number is going to be in the hundreds instead of just 100.”

Dozens of mollusks, three fish, a shrimp and a cephalopod that is a type of predatory mollusk were among the new species found in the expedition, which was led by Ocean Census, a nonprofit dedicated to the global discovery of ocean life, the National Institute of Water and Atmospheric Research in New Zealand, and the Museum of New Zealand Te Papa Tongarewa.

One creature that caused a “lot of head-scratching” is a star-shaped animal, about a centimeter across, but researchers have not managed to identify it, Dr. Rogers said. They believe it may possibly be a coral.

Two million-plus species are estimated to live in the oceans, but only 10 percent of ocean life is known. It is vital to learn more about the aquatic life because marine ecosystems carry out functions that support life on Earth, such as creating food for billions, storing carbon and regulating climate, Dr. Rogers said.

“We’re dealing with a situation where we know marine life is in decline,” he said. “In order to try to manage human activities to prevent this continuing decline, we need to understand the distribution of marine life better than we currently do.”

Ocean Census was founded last year by the Nippon Foundation, a Japanese philanthropic organization, and the U.K.-based ocean exploration foundation Nekton. When it began its work, Ocean Census set a goal of finding at least 100,000 new marine species in a decade.

The group is focused on exploring some of the most under-sampled bodies of water.

In the February expedition, researchers first mapped the area with an imaging system and video cameras to check that it would be safe for their equipment and to ensure that there were no vulnerable animal communities that potentially could be harmed.

Then, they deployed what is known as the Brenke sled , a sampling device that has two nets, one close to the seabed, and the other a meter above it. As it drags along the floor, it churns up animals living close to the sea floor. To find larger animals, the researchers used other methods, such as baited nets.

Trawling the depths at 4,800 meters — or roughly the equivalent to Mont Blanc, the highest peak in the Alps — researchers collected 1,791 samples.

Given its depth, Bounty Trough is not of great interest to fisheries and therefore is poorly sampled, Dr. Rogers said. Geologists have surveyed this area but biologists have not.

Worldwide, about 240,000 marine species have been discovered and named to date but only 2,200 species are discovered each year on average, according to Ocean Census.

In many bodies of water there is still a lot that scientists have to learn, Dr. Rogers said.

“It’s probably the equivalent of a space mission,” he said. “We’re still in early days, but the number of species that we found in the Bounty Trough really indicates to us that we’ve got a long way to go in terms of understanding where life is found in the ocean.”

Rebecca Carballo is a reporter based in New York. More about Rebecca Carballo

Explore the Animal Kingdom

A selection of quirky, intriguing and surprising discoveries about animal life..

Aside from chimps and humans, researchers have found clear evidence of menopause in only five species — all of them whales. A new study looks at the possible causes for it .

Scientists never imagined that the blind cave salamanders called olms willingly left their caves. Then, they discovered several at aboveground springs in northern Italy .

According to a common narrative that male mammals tend to be larger than female ones. A new study paints a more complex picture .

Daddy longlegs, the group of splendidly leggy arachnids also known as harvestmen, have been thought to have just two eyes. New research has uncovered four more vestigial ones .

The means by which some whales sing underwater has long been a mystery. A contraption that forced air through the larynxes of three carcasses puts forth an explanation .

Here’s how a male elephant seal, not usually possessed with a paternal instinct, prevented a younger animal from drowning in an unlikely act of altruism .

8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death

An analysis of over 20,000 U.S. adults found that people who limited their eating across less than 8 hours per day, a time-restricted eating plan, were more likely to die from cardiovascular disease compared to people who ate across 12-16 hours per day, according to preliminary research presented at the American Heart Association's Epidemiology and Prevention Lifestyle and Cardiometabolic Scientific Sessions 2024, March 18- 21, in Chicago. The meeting offers the latest science on population-based health and wellness and implications for lifestyle.

Time-restricted eating, a type of intermittent fasting, involves limiting the hours for eating to a specific number of hours each day, which may range from a 4- to 12-hour time window in 24 hours. Many people who follow a time-restricted eating diet follow a 16:8 eating schedule, where they eat all their foods in an 8-hour window and fast for the remaining 16 hours each day, the researchers noted. Previous research has found that time-restricted eating improves several cardiometabolic health measures, such as blood pressure, blood glucose and cholesterol levels.

"Restricting daily eating time to a short period, such as 8 hours per day, has gained popularity in recent years as a way to lose weight and improve heart health," said senior study author Victor Wenze Zhong, Ph.D., a professor and chair of the department of epidemiology and biostatistics at the Shanghai Jiao Tong University School of Medicine in Shanghai, China. "However, the long-term health effects of time-restricted eating, including risk of death from any cause or cardiovascular disease, are unknown."

In this study, researchers investigated the potential long-term health impact of following an 8-hour time-restricted eating plan. They reviewed information about dietary patterns for participants in the annual 2003-2018 National Health and Nutrition Examination Surveys (NHANES) in comparison to data about people who died in the U.S., from 2003 through December 2019, from the Centers for Disease Control and Prevention's National Death Index database.

The analysis found:

• People who followed a pattern of eating all of their food across less than 8 hours per day had a 91% higher risk of death due to cardiovascular disease.
• The increased risk of cardiovascular death was also seen in people living with heart disease or cancer.
• Among people with existing cardiovascular disease, an eating duration of no less than 8 but less than 10 hours per day was also associated with a 66% higher risk of death from heart disease or stroke.
• Time-restricted eating did not reduce the overall risk of death from any cause.
• An eating duration of more than 16 hours per day was associated with a lower risk of cancer mortality among people with cancer.

"We were surprised to find that people who followed an 8-hour, time-restricted eating schedule were more likely to die from cardiovascular disease. Even though this type of diet has been popular due to its potential short-term benefits, our research clearly shows that, compared with a typical eating time range of 12-16 hours per day, a shorter eating duration was not associated with living longer," Zhong said.

"It's crucial for patients, particularly those with existing heart conditions or cancer, to be aware of the association between an 8-hour eating window and increased risk of cardiovascular death. Our study's findings encourage a more cautious, personalized approach to dietary recommendations, ensuring that they are aligned with an individual's health status and the latest scientific evidence," he continued. "Although the study identified an association between an 8-hour eating window and cardiovascular death, this does not mean that time-restricted eating caused cardiovascular death." Study details and background:

• The study included approximately 20,000 adults in the U.S. with an average age of 49 years.
• Study participants were followed for a median length of 8 years and maximum length of 17 years.
• The study included data for NHANES participants who were at least 20 years old at enrollment, between 2003-2018, and had completed two 24-hour dietary recall questionnaires within the first year of enrollment.
• Approximately half of the participants self-identified as men, and half self-identified as women. 73.3% of the participants self-identified as non-Hispanic white adults, 11% self-identified as Hispanic adults, 8% self-identified as non-Hispanic Black adults and 6.9% of adults self-identified as another racial category, including mixed-race adults and adults of other non-Hispanic races.

The study's limitations included its reliance on self-reported dietary information, which may be affected by participant's memory or recall and may not accurately assess typical eating patterns. Factors that may also play a role in health, outside of daily duration of eating and cause of death, were not included in the analysis.

Future research may examine the biological mechanisms that underly the associations between a time-restricted eating schedule and adverse cardiovascular outcomes, and whether these findings are similar for people who live in other parts of the world, the authors noted.

"Overall, this study suggests that time-restricted eating may have short-term benefits but long-term adverse effects. When the study is presented in its entirety, it will be interesting and helpful to learn more of the details of the analysis," said Christopher D. Gardner, Ph.D., FAHA, the Rehnborg Farquhar Professor of Medicine at Stanford University in Stanford, California, and chair of the writing committee for the Association's 2023 scientific statement, Popular Dietary Patterns: Alignment with American Heart Association 2021 Dietary Guidance.

"One of those details involves the nutrient quality of the diets typical of the different subsets of participants. Without this information, it cannot be determined if nutrient density might be an alternate explanation to the findings that currently focus on the window of time for eating. Second, it needs to be emphasized that categorization into the different windows of time-restricted eating was determined on the basis of just two days of dietary intake," he said.

"It will also be critical to see a comparison of demographics and baseline characteristics across the groups that were classified into the different time-restricted eating windows -- for example, was the group with the shortest time-restricted eating window unique compared to people who followed other eating schedules, in terms of weight, stress, traditional cardiometabolic risk factors or other factors associated with adverse cardiovascular outcomes? This additional information will help to better understand the potential independent contribution of the short time-restricted eating pattern reported in this interesting and provocative abstract."

• Eating Disorder Research
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• Diet and Weight Loss
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How teens and parents approach screen time, most teens at least sometimes feel happy and peaceful when they don’t have their phone, but 44% say this makes them anxious. half of parents say they have looked through their teen’s phone.

Pew Research Center conducted this study to better understand teens’ and parents’ experiences with screen time. 

The Center conducted an online survey of 1,453 U.S. teens and parents from Sept. 26 to Oct. 23, 2023, through Ipsos. Ipsos invited one parent from each of a representative set of households with parents of teens in the desired age range from its KnowledgePanel . The KnowledgePanel is a probability-based web panel recruited primarily through national, random sampling of residential addresses. Parents were asked to think about one teen in their household (if there were multiple teens ages 13 to 17 in the household, one was randomly chosen). At the conclusion of the parent’s section, the parent was asked to have this chosen teen come to the computer and complete the survey in private.

The survey is weighted to be representative of two different populations: 1) parents with teens ages 13 to 17 and 2) teens ages 13 to 17 who live with parents. For each of these populations, they survey is weighted to be representative by age, gender, race and ethnicity, household income and other categories.

This research was reviewed and approved by an external institutional review board (IRB), Advarra, an independent committee of experts specializing in helping to protect the rights of research participants.

Here are the questions among parents and among teens used for this report, along with responses, and its methodology ­­­.

Today’s teenagers are more digitally connected than ever. Most have access to smartphones and use social media , and nearly half say they are online almost constantly. But how are young people navigating this “always on” environment?  

To better understand their experiences, we surveyed both teens and parents on a range of screen time-related topics. Our questions explored the emotions teens tie to their devices, the impact of smartphones on youth, and the challenges parents face when raising children in the digital age.

Key findings from the survey:

• Phone-less: 72% of U.S. teens say they often or sometimes feel peaceful when they don’t have their smartphone; 44% say it makes them feel anxious.
• Good for hobbies, less so for socialization: 69% of teens say smartphones make it easier for youth to pursue hobbies and interests; fewer (30%) say it helps people their age learn good social skills.
• Parental snooping: Half of parents say they have looked through their teen’s phone.
• Smartphone standoffs: About four-in-ten parents and teens report regularly arguing with one another about time spent on their phone.
• Distracted parenting: Nearly half of teens (46%) say their parent is at least sometimes distracted by their phone when they’re trying to talk to them.

This Pew Research Center survey of 1,453 U.S. teens ages 13 to 17 and their parents was conducted Sept. 26-Oct. 23, 2023. 1

Jump to read about views among teens on: Screen time | Feelings when disconnected from phones | Thoughts on smartphones’ impact

Jump to read about views among parents on: Parenting in the smartphone age | Their own screen time struggles

Teens’ views on screen time and efforts to cut back

Fully 95% of teens have access to a smartphone, and about six-in-ten say they use TikTok, Snapchat or Instagram . But do teens think they spend too much time in front of screens?

More teens say they spend too much time on their phone or social media than say they don’t spend enough time on them. We found that 38% of teens say they spend too much time on their smartphone. About a quarter say the same regarding their social media use. 2

But the largest shares say the amount of time they spend on their phone (51%) or on social media (64%) is about right. Relatively few teens say they don’t spend enough time with these technologies.

Views on this differ by gender. Teen girls are more likely than boys to say they spend too much time on their smartphone (44% vs. 33%) or social media (32% vs. 22%).

Teens’ efforts to curb their screen time

A minority of teens have taken steps to reduce their screen time. Roughly four-in-ten teens (39%) say they have cut back on their time on social media. A similar share says the same about their phone (36%).

Still, most teens have not limited their smartphone (63%) or social media (60%) use.

How teens’ behaviors vary by gender

About four-in-ten or more girls say they have cut back on their smartphone or social media use. For boys, those figures drop to roughly one-third.

How teens’ behaviors vary based on their screen time

Teens who report spending too much time on social media and smartphones are especially likely to report cutting back on each. For instance, roughly six-in-ten teens who say they are on social media too much say they have cut back (57%). This is far higher than the 32% among those who say they are on social media too little or the right amount.

How teens feel when they don’t have their phone

Teens encounter a range of emotions when they don’t have their phones, but we asked them about five specific ones. Roughly three-quarters of teens say it often or sometimes makes them feel happy (74%) or peaceful (72%) when they don’t have their smartphone.

Smaller but notable shares of teens equate not having their phone with more negative emotions. Teens say not having their phone at least sometimes makes them feel anxious (44%), upset (40%) and lonely (39%).

It is worth noting that only a minority of teens – ranging from 7% to 32% – say they often feel these emotions when they’re phone-less.

Teens’ feelings on this differ by some demographic factors:

• Age and gender: Older girls ages 15 to 17 (55%) are more likely than younger girls (41%) and teen boys who are younger (41%) and older (40%) to say they feel anxious at least sometimes when they don’t have their smartphone.
• Gender: 45% of teen girls say not having their phone makes them feel lonely regularly, compared with 34% of teen boys.

Do teens think smartphones are negatively impacting young people?

As smartphones have become a universal part of teen life, many have asked what impact, if any, phones are having on today’s youth.

Teens shared their perspectives on smartphones’ impact on people their age and whether these devices have made certain aspects of growing up more or less challenging.

Most teens think the benefits of smartphones outweigh the harms for people their age. Seven-in-ten teens say smartphones provide more benefits than harms for people their age, while a smaller share (30%) take the opposing view, saying there are more harms than benefits.

Teens’ views, by gender and age

Younger girls ages 13 and 14 (39%) are more likely than older teen girls (29%) and teen boys who are younger (29%) and older (25%) to say that the harms of people their age using smartphones outweigh the benefits.

The survey also shows that teens see these devices’ impacts on specific aspects of life differently.

More teens believe smartphones make it easier, rather than harder, to be creative, pursue hobbies and do well in school. Majorities of teens say smartphones make it a little or a lot easier for people their age to pursue hobbies and interests (69%) and be creative (65%). Close to half (45%) say these devices have made it easier for youth to do well in school.

Views are more mixed when it comes to developing healthy friendships. Roughly four-in-ten teens say smartphones make it easier for teens to develop healthy friendships, while 31% each say they make it harder or neither easier nor harder.

But they think smartphones have a more negative than positive impact on teens’ social skills. A larger percentage of teens say smartphones make learning good social skills harder (42%) rather than easier (30%). About three-in-ten say it neither helps nor hurts.

How parents navigate raising teens in the smartphone age

With the rise of smartphones, today’s parents must tackle many questions that previous generations did not. How closely should you monitor their phone use? How much screen time is too much? And how often do phones lead to disagreements?

We developed a set of parallel questions to understand the perspectives of both parents and teens. Here’s what we found:

It’s common for parents to look through their teen’s phone – and many of their teens know it. Half of parents of teens say they look through their teen’s phone. When we asked teens if they thought their parents ever look through their phones, 43% believed this had happened.

Whether parents report looking through their child’s smartphone depends on their kid’s age. While 64% of parents of 13- to 14-year-olds say they look through their teen’s smartphone, this share drops to 41% among parents of 15- to 17-year-olds.

Teens’ accounts of this also vary depending on their age: 56% of 13- to 14-year-olds say their parent checks their smartphone, compared with 35% of teens ages 15 to 17.

How often do parents and teens argue about phone time?

Parents and teens are equally likely to say they argue about phone use. Roughly four-in-ten parents and teens (38% each) say they at least sometimes argue with each other about how much time their teen spends on the phone. This includes 10% in each group who say this happens often .

Still, others say they never have these types of disagreements. One-quarter of parents say they never argue with their teen about this, while 31% of teens say the same.

Teens’ and parents’ views, by race and ethnicity

Hispanic Americans stand out for reporting having these disagreements often. While 16% of Hispanic teens say they often argue with their parent about how much time they’re spending on their phone, that share drops to 9% for White teens and 6% for Black teens. 3

A similar pattern is present among parents. Hispanic parents (19%) are more likely than White (6%) or Black (7%) parents to say they often argue with their teen about this.

Teens’ views, by frequency of internet use

The amount of time teens report being online is also a factor. About half (47%) of teens who report being online almost constantly say they at least sometimes argue with their parent about the amount of time they spend on their phone, compared with those who are online less often (30%). 

How much do parents prioritize tracking their teen’s phone use?

Most parents prioritize managing the amount of time their teen spends on the phone. Roughly three-quarters of parents (76%) say managing how much time their teen spends on the phone is an important or a top priority.  Still, 19% of parents don’t consider this a priority.

Parents’ views, by race and ethnicity

Majorities of parents across racial and ethnic groups think of this as a priority. But some groups stand out for how much they prioritize this. For example, Hispanic (25%) or Black (24%) parents are more likely to say managing how much time their teen is on the phone is a top priority. That share drops to 10% among White parents.

Parents’ views, by household income

We also see differences between the lowest and highest income households: 22% of parents whose annual household income is less than $30,000 consider managing the amount of time their teen is on the phone a top priority, compared with 14% of those whose household income is $75,000 or more a year. Those whose household income is $30,000 to $74,999 a year do not meaningfully differ from either group.

Do parents set time limits on their teen’s phone use?

There’s a nearly even split between parents who restrict their teen’s time on their phone and those who don’t. About half of parents (47%) say they limit the amount of time their teen can be on their phone, while a similar share (48%) don’t do this.

Parents’ views, by teen’s age

Parents of younger teens are far more likely to regulate their child’s screen time. While 62% of parents of 13- to 14-year-olds say they limit how much time their teen can be on their phone, that share drops to 37% among those with a 15- to 17-year-old.

How difficult is it for parents to keep up with their teen’s phone use?

Managing screen time can feel like an uphill battle for some parents. About four-in-ten say it’s hard to manage how much time their teen spends on their phone. A smaller share (26%) says this is easy to do. 

Another 26% of parents fall in the middle – saying it’s neither easy nor hard.

Higher-income parents are more likely to find it difficult to manage their teen’s phone time. Roughly half (47%) of parents living in households earning $75,000 or more a year say managing the amount of time their teen is on their phone is hard. These shares are smaller among parents whose annual household income falls below $30,000 (38%) or is between $30,000 and $74,999 (32%).

Parents’ own struggles with device distractions, screen time

Teens aren’t the only ones who can be glued to their phones. Parents, too, can find themselves in an endless cycle of checking emails , text messages and social media.

With that in mind, we asked parents to think about their own screen time – both the time they spend on their phone, and if it ever gets in the way of connecting with their teen.

Do parents think they spend too much time on their phone?

Like teens, parents are far more likely to say they spend too much rather than not enough time on their phone. About half of parents (47%) say they spend too much time on their smartphone. Just 5% think they spend too little time on it. And 45% believe they spend the right amount of time on their phone.

Parents’ views differ by:

• Household Income: 50% of parents with annual household incomes of $75,000 or more say they spend too much time on their phone. This share drops to 41% among those living in households earning $30,000 to $74,999 a year and 38% among those earning under $30,000.
• Race and ethnicity: 57% of White parents believe they spend too much time on their phone, compared with 38% of Black parents and 34% of Hispanic parents.

How often are parents distracted by their phone when talking with their teen?

When it comes to distracted parenting, parents paint a rosier picture than teens. Nearly half of teens (46%) say their parent is at least sometimes distracted by their phone when they’re trying to talk to them, including 8% who say this happens often.

But when parents were asked to assess their own behavior, fewer – 31% – say this happens regularly.

• Throughout this report, “teens” refers to those ages 13 to 17 and “parents” refers to those with a child ages 13 to 17. ↩
• A  2018 Center survey  also asked U.S teens some of the same questions about experiences and views related to smartphone and social media. Direct comparisons cannot be made across the two surveys due to mode, sampling and recruitment differences. Please read the Methodology section  to learn more about how the current survey was conducted. ↩
• There were not enough Asian respondents in the sample to be broken out into a separate analysis. As always, their responses are incorporated into the general population figures throughout the report. ↩

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Table of contents, teens and internet, device access fact sheet, teens and social media fact sheet, a declining share of adults, and few teens, support a u.s. tiktok ban, teens, social media and technology 2023, about 1 in 5 u.s. teens who’ve heard of chatgpt have used it for schoolwork, most popular.

About Pew Research Center Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research. Pew Research Center does not take policy positions. It is a subsidiary of The Pew Charitable Trusts .

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Original research article, carbon conduction effect and multi-scenario carbon emission responses of land use patterns transfer: a case study of the baiyangdian basin in china.

• 1 School of Public Administration, Hebei University of Economics and Business, Shijiazhuang, China
• 2 Hebei Collaborative Innovation Center for Urban-Rural Integrated Development, Hebei University of Economics and Business, Shijiazhuang, China
• 3 Center for Urban Sustainability and Innovation Development (CUSID), Hebei University of Economics and Business, Shijiazhuang, China

Carbon pooling and release occur all the time in all corners of the earth, where the land use factor is key to influencing the realization of carbon peaking and neutrality. Land use patterns and carbon emissions change under different scenarios and analyzing the correlation will help formulate scientific land use policies for the future. In this study, through remote sensing data, we investigated the changes in land use patterns and carbon emissions in the Baiyangdian basin in China from 2000 to 2020 and analyzed the carbon conduction effect with the help of a land transfer matrix. The geographical simulation and optimization system-future land use simulation (GeoSOS-FLUS) and Markov models were used to predict the land use changes and carbon emissions under the four different scenarios for the region in 2035. The results indicated that 1) the net land use carbon emissions increased from 52,163.03 × 10 3 to 260,754.91.28 × 10 3  t from 2000 to 2020, and the carbon source-sink ratio exhibited a general uptrend; 2) the net carbon emissions due to terrestrial transfers increased over time. The carbon conduction effects due to the transfer of forests, grasslands, water areas, and unused lands to built-up lands also showed a rising trend, albeit the latter two exhibited only small changes; 3) in 2035, the net carbon uptake under the four development scenarios was predicted to be 404,238.04 × 10 3 , 402,009.45 × 10 3 , 404,231.64 × 10 3 , and 404,202.87×10 3  t, respectively, with all values much higher than that of the study area in 2020. The maximum carbon sink capacity was 817.88 × 10 3  t under the double-carbon target scenario, and the maximum carbon source emission was 405,033.61 × 10 3  t under the natural development scenario. The above results provide an essential reference for low carbon-based urban land use regulations for the Baiyangdian basin and other similar projects in the future.

1 Introduction

Global climate change poses a significant threat to sustainable development and the survival of humans ( Rong et al., 2022 ). The terrestrial carbon system is an important component of the global carbon cycle, which plays a critical role in mitigating global warming by effectively regulating the regional climate through the absorption and release of greenhouse gases from the atmosphere ( Yu et al., 2022 ). Land use activities primarily affect the carbon cycle of the ecosystem ( Mendelsohn and Sohngen, 2019 ), with their carbon emissions being second only to the burning of fossil fuels ( Wang Z. et al., 2022 ). Thus, regulating land use activities to reduce carbon emissions is an important means of promoting carbon neutrality from a practical perspective ( Carpio et al., 2021 ). Therefore, several studies have aimed to demonstrate how carbon emissions from land use can help achieve a range of low carbon development goals, particularly carbon peak and neutrality ( Yang and Liu, 2022 ).

Most studies on land use carbon emissions focus on accounting, mechanisms and consequences, projections, and impact factors ( Le Quéré et al., 2012 ; Houghton and Nassikas, 2017 ; Yu et al., 2022 ). The accounting of land use carbon emissions mainly involves assessing the emissions by using bookkeeping, the Intergovernmental Panel on Climate Change (IPCC) inventory, the Carnegie-Ames-Stanford approach (CASA) model, the global production efficiency model (GLO-PEM), and the integrated valuation of ecosystem services and tradeoffs (InVEST) model ( Piao et al., 2022 ; Raihan et al., 2022 ; Walker et al., 2022 ). Houghton and Nassikas (2017) used a bookkeeping model and estimated the average global net carbon fluxes induced by land use and coverage change (LUCC) from 2006 to 2015 to be 1.11 ± 0.35 Pg C yr –1 ; Ghosh et al. (2022) proposed a method to establish a low-carbon city by extensively analyzing land use carbon emissions and sequestration potential using the InVEST model. Regarding the land use carbon emission effects, it primarily investigates the impact of vegetation and soil carbon storage, as well as the dynamic evolution characteristics ( Wang et al., 2020 ; Wolswijk et al., 2022 ). Affuso and Hite (2013) showed that participatory decision-making on land use can triple the net energy value of biofuels and reduce carbon emissions by 20%; Ghorbani et al. (2023) showed that soil carbon storage and atmospheric carbon dioxide (CO 2 ) emissions were directly affected by the changes in the soil characteristics and land use; rising pastures and forests increased the soil organic carbon and microbial biomass carbon in both topsoil and subsoil. For the prediction of land use carbon emissions, Cellular Automata-Markov (CA-Markov), Conversion of Land Use and its Effects at Small regional extent (CLUE-S), Future Land Use Simulation (FLUS), and Patch-generating Land Use Simulation (PLUS) models were used to predict the land use spatial layout for carbon emission analysis ( Wang H. et al., 2022 ; Wu et al., 2022 ). Liu et al. (2018) used a system dynamics approach to establish a multi-perspective integrated measurement model to quantitatively predict new towns on a sector-by-sector basis. They showed that cities need to rely on regional green spaces to mitigate carbon emissions; Yao et al. (2023) proposed a bottom-up cadastral land scale carbon emission prediction framework based on vector cellular automata. Although the aforementioned works serve as excellent examples for the study of land use carbon emissions, only a few studies have focused on carbon emission conduction due to the change in land type ( Li et al., 2023 ). Investigating the effects of land type changes on carbon emissions under various scenarios can provide new perspectives to formulate appropriate land regulation and carbon emission reduction policies ( Ke Y. et al., 2022 ). However, most of the existing research is based on past land use data, and there remains a lack of studies predicting changes in future land use patterns under multiple scenarios and the resultant carbon emissions ( Chuai et al., 2019 ).

Therefore, the objectives of this study were 1) Based on the land use data, combined with the carbon emission estimation model, obtain the carbon emission characteristics of the Baiyangdian basin from 2000 to 2020. 2) Use the land transfer matrix to analyze the carbon transfer effect caused by land use transfer in each period 3) Predict the land use pattern under four different development scenarios in 2035, as well as the resulting carbon emissions, to provide a reference for the city to assess the pressure of carbon emission reduction ( Harper et al., 2018 ).

The rest of the paper is as follows: Section 2 presents an overview of the study area and data sources, Section 3 describes the empirical methodology, Section 4 is the results and analyses section, and Section 5 provides the discussion and conclusions.

2 Study area overview and data sources

2.1 study area overview.

The Xiong’an New Area, China, as a hub to relieve Beijing of non-capital functions, is critical to accelerating the synergistic development of the Beijing-Tianjin-Hebei region, with its land use changes being typical of the current era ( Zhou et al., 2021 ). The Baiyangdian basin, as the ecological hinterland of the Xiong’an New Area, is a prime example of healthy synergies between the carbon system and the development of the city ( Li et al., 2008 ; Zhao et al., 2021 ; Xia et al., 2023 ). The study area is situated in the northern part of the North China Plain, between 113°45′–116°26′ eastern longitudes and 37°51′–40°39′ northern latitudes ( Figure 1 ), which belongs to a warm-temperate monsoon climate. The Baiyangdian basin in this study refers to the administrative area of Hebei Province flowing through nine branches such as the Zuma Long River, the Cao River, and the Zhao Wang Xin River, involving 35 counties (cities and districts) under the jurisdiction of Baoding City, Zhangjiakou City, Shijiazhuang City and Cangzhou City, with a total land area of 34,353.07 km 2 . The basin exhibits an intricate geography, with highlands in the west (mountains) and lowlands in the east (plains). The mountainous area mainly comprises forests and grasslands (17.79% and 19.69% of the total basin area, respectively), and the plains are primarily cultivable land (46.25% of the total basin area).

FIGURE 1 . Spatial location of the study area. (A) China scope; (B) Hebei Province; (C) Baiyangdian Basin.

2.2 Data sources

In this study, we employed remote sensing image data, Digital Elevation Model (DEM) data, slope data, meteorological data, and fossil energy data as follows:

(1) The Landsat4-5/Thematic Mapper (TM) and Landsat8/Operational Land Imager (OLI) remote sensing images used in this study were obtained from the Chinese Academy of Sciences Geospatial Data Cloud ( https://www.gscloud.cn/ ). The data identifiers and dates of the selected images are LT51230332000145BJC00 2000-05-24, LT51230322010156IKR00 2010-06-05, and LC81230332020120LGN00 2020-4-29, respectively. Concerning previous classification standards and combined with research needs, the land was divided into cultivable land, forest, grassland, built-up land, unused land, and water area, with a 30-m spatial resolution.

(2) The DEM data were obtained from the Chinese Academy of Sciences Geospatial Data Cloud ( https://www.gscloud.cn/ ), and further, the slope data was extracted from the DEM data, with an initial resolution of 30 m.

(3) Annual average precipitation and average temperature for the basin study area were collected from the China Meteorological Data Network ( https://data.cma.cn/ ), the spatial resolution is 0.5° × 0.5°.

(4) Data on the consumption of the eight main fossil energy sources used to indirectly estimate carbon emissions from built-up land were obtained from the statistical yearbooks of counties and cities and the National Bureau of Statistics ( http://www.stats.gov.cn/ ) for the years 2000–2020. The corresponding energy carbon emission coefficients were the missing values recommended by the Intergovernmental Panel on Climate Change (IPCC).

3 Research methods

3.1 land use carbon emission calculations.

Carbon sinks include grasslands, forests, unused lands, and water areas ( Guo and Fang, 2021 ). Cultivable land can act as both a carbon source and sink due to its different functions ( Ma and Wang, 2015 ). Therefore, this paper accurately measured the carbon emission values for these five land use types by the direct estimation method. Equation 1 is calculated as follows:

where i = 1, 2, 3, 4, and 5 represent cultivatable land, forest, grassland, water area, and unused land, respectively ( Yue et al., 2020 ); C i   is  i  land type carbon emissions ;   S i is i land type area; and V i is i land type carbon emission coefficient ( Table 1 ).

TABLE 1 . Land use carbon emission coefficients.

Carbon emissions from built-up land occur mainly from human activities and the energy production and industrial processes they host ( Zhang et al., 2021 ). This paper indirectly estimated the carbon emissions of the eight main fossil fuel sources through their consumption. Equation 2 is calculated as follows:

where E c  is built − up land carbon emission , j is the energy source type; E j is the energy consumption; θ j is the energy to standard coal factor; and f j is the carbon emission ( Lu et al., 2022 ) ( Table 2 ).

TABLE 2 . Standard coal conversion and carbon emission coefficients for the energy sources.

According to the principle of indicator system construction, this paper selects five indicators, including population, carbon emission intensity, gross domestic product (GDP), historical carbon emissions, and the proportion of the tertiary industry, to construct the Baiyangdian Basin Carbon Emission Indicator System from the perspective of fairness, efficiency, and feasibility ( Table 3 ). The entropy value technique was initially applied to calculate the weights of individual indicators. Subsequently, this method was supplemented by a total carbon emission measurement model to ultimately quantify the indirect carbon emissions originating from the different land types in the study region ( Tang et al., 2022 ).

TABLE 3 . Indicator system for the allocation of carbon emissions.

3.2 Estimation of land transfer-based carbon emission conduction

Land use changes can cause carbon transfer, which is defined as the carbon conduction effect of land use carbon emissions. Two factors, the difference between the level of carbon sequestration and carbon emissions following a change in land class and the area of change, mainly determine the amount of carbon emissions they transmit ( Qiao et al., 2016 ). The area of land class conversion can be calculated from a land use transfer matrix indicating the amount of change and the direction of transfer, and its Eq. 3 is:

where N is the number of land use types; and S i j is the area transferred from land type i to land type j. The carbon transmission due to the interconversion between land categories other than built-up land ( C t ) can be estimated from the transfer matrix and the difference between the carbon emission coefficients ( δ i 1 − δ i 2 ) of each category using Eq. 4 :

This paper considers the built-up land within the Baiyangdian basin to be spatially homogeneous, neglecting the carbon emission differences that may arise in distinct spatial scenarios per unit area. Therefore, during the study period T1∼T2, the carbon emissions transferred from built-up land to the other types of land can be calculated by Eq. 5 :

In contrast, Eq. 6 is used to calculate the transfer of carbon emissions from other land types to built-up land:

Where C t is the Carbon emission transmission; δ i is the carbon emission coefficient ( δ i 1 ) or carbon absorption coefficient ( δ i 2 ) for land use types other than built-up land; δ T 1 and δ T 2 are the carbon emission generated on the unit area of built-up land in T1 and T2 years, respectively ( Zhang et al., 2014b ), and the unit is t·(km 2 ·a) −1 . E b 1 and E b 2 are the carbon emissions generated by built-up land in T1 and T2 years, respectively; S bi and S ib are the areas of built-up land in years T1 and T2; S bi and S ib are the areas of interconversion of built-up land and other land types, respectively ( Zhang et al., 2014a ).

3.3 GeoSOS-FLUS model

In this study, the GeoSOS-FLUS model was used to simulate future land use change in the Baiyangdian basin. The model has two main components, scenario setting and model building ( Sun et al., 2021 ). As a resource on which human activity depends, changes in land use and spatial distribution characteristics essentially depend on a tradeoff between economic development and ecological protection. Therefore, based on previous studies and specific planning policies of each city in the Baiyangdian basin, we established four development scenarios, namely, natural development, balanced development, cultivable land protection, and double-carbon target, and analyzed their effects ( Tao et al., 2015 ; Hong et al., 2021 ; Wang Z. et al., 2022 ). The different scenario settings and corresponding scenario descriptions are shown in Table 4 .

TABLE 4 . Land use change rules for different scenarios.

The GeoSOS-FLUS model includes the following two framework contents:

(1) The study identified six key factors, namely, elevation, slope, temperature, precipitation, distance to the road, and distance to the railway, responsible for driving land use changes in the Baiyangdian basin. To evaluate the probability of each land use type suitability, we employed an artificial neural network (ANN) algorithm ( Wang et al., 2019 ). To verify the accuracy of the calculations, we simulated a land use distribution map for 2020 using the land use types of the study region in 2010 and matched the findings with the land use distribution map for the same year. The Kappa coefficient is 0.7464 and has an overall accuracy of 84.20%, demonstrating good simulation results.

(2) The model sampled the first-stage land use distribution data and proposed an adaptive inertia competitive roulette mechanism to simulate the land use scenario distribution. A degree of uncertainty and complexity in land use conversion remained, influenced by a variety of factors. Due to the application of the sampling method and competitive mechanism, the proposed model could effectively avoid error transmission, along with the adverse effects of uncertainty and complexity. In other words, the GeoSOS-FLUS model exhibited good accuracy and enabled the simulation predictions to be consistent with the actual data.

3.4 Markov prediction

The Markov process can predict the possible state of an event at any particular instance in the future according to the current state of the event by following the “no aftereffect” principle ( Yang et al., 2020 ). In this study, the transfer probability matrix was solved by a Markov process according to the change relation of time series to make an energy knot prediction. The Markov model was employed to predict future land use patterns in the Baiyangdian basin energy structure based on historical energy data from 2000 to 2020. Let us assume that at time m , the state vector of the energy consumption structure in the basin can be expressed as Eq. 7 :

where S r ( m ), S c ( m ), S o ( m ), S g ( m ), S k ( m ), S d ( m ), S f ( m ), and S n ( m ) are the proportions of raw coal, coke, crude oil, gasoline, kerosene, diesel, fuel oil, and natural gas in energy consumption, respectively. The transition matrix at time m∼m+1 can be expressed as Eq. 8 :

where i and j are energy types; and P i − j m is the probability of energy i conversion to energy j . The model effect coefficient, w , was used as the criterion to judge the quality of prediction results, which can be computed as Eq. 9 :

where S r is the real value, S p is the predicted value, and S r ¯ is the average of the actual values. If the value is closer to 1, the prediction results are close to the actual values and the prediction accuracy is high.

4 Results and analysis

4.1 changes in land use carbon emissions.

Based on the calculations, Table 5 shows land use carbon emissions in the Baiyangdian basin for the years 2000, 2010, and 2020. The net land use carbon emissions in the basin were found to steadily increase over the past two decades, with a total amount of 208,591.88 × 10 3  t and an average annual increase of 10,429.59 × 10 3  t. Grasslands, forests, water areas, and unused lands acted as carbon sinks, increasing the total carbon absorption by 9.59 × 10 3  t. The combined carbon emissions from cultivable and built-up lands as carbon sources increased by 208,601.48 × 10 3  t. The carbon source emission to sink absorption ratio in the basin increased, especially reaching the highest value of 330.21 in 2020, 4.9 times higher than in 2000. This indicated that the carbon sources in the basin were continuously rising, and the carbon sink was continuously declining.

TABLE 5 . Changes in carbon source emissions, sink absorption, and its ratio in the Baiyangdian basin.

Specifically, carbon emissions from built-up lands were on an upward trend, along with carbon sequestration in forests and water areas were on an upward trend, other land types steadily declined as carbon sources or sinks ( Figure 2 ). In the case of building sites, from 2000 to 2010, rapid urbanization, enhanced land intensification, and a mass of cultivable lands, forests, and grasslands were transformed into built-up lands, resulting in an expansion trend of built-up land, which is manifested in the fact that the rate of transferring in is 18.5 times higher than the rate of transferring out. The land use dynamic attitude (k) reached 0.0087, with the land area expanding by 268.36 km 2 . This increase accounted for 94.52% of carbon emissions in 2000, rising to 98.72% in 2020, representing the largest contribution to carbon emissions ( Figure 2 ). Due to the minimal net conversion of land from other categories to built-up land within their respective land usage dynamics between 2000 and 2010, the proportion of carbon emissions attributed to built-up land was the lowest during the entire research period, in 2020 ( Table 6 ). The area of cultivated land has been decreasing from 2000 to 2010, with 637.45 km 2 of cultivated land being transferred out at a rate 12.67 times faster than the rate of transfer in, making it the land category with the largest reduction in area share of any land category.

FIGURE 2 . Change and proportion of carbon emissions from land use. (A,B) Land use carbon emissions; (C) Proportion of carbon emissions.

TABLE 6 . Land use changes in the Baiyangdian basin from 2000 to 2020.

Among the carbon sinks, grassland and unused land demonstrated a marginal reduction in carbon sequestration, with the corresponding proportion decreasing from 0.54% in 2000 to 0.49% in 2020 ( Figure 2B ). The fluctuating trends in the carbon uptake ratios of grasslands and unused lands could be attributed to their continued transfer to built-up and cultivable lands. In 2000–2010, 86.64 km 2 of grassland and 5.14 km 2 of unused land were transferred, and in 2010–2020, 1,390.75 km 2 of grassland and 17.98 km 2 of unused land were transferred.

4.2 Carbon conduction effects due to land type changes

To determine the carbon emissions after each stage of land type transfer, we combined the land use transfer matrix with the carbon source/sink capacity of the land type. The values with an asterisk in Table 7 indicate the net carbon emissions from land use transfer at each period of the study period and increased over time. Throughout the entire study period, carbon emissions were determined by the carbon source category. The key role of built-up land was highlighted by the study’s finding that built-up land accounted for most carbon emissions from total carbon sources. The transfer of cultivable lands and grasslands to built-up lands had the most significant effect on carbon transfer through the conversion of carbon sinks into sources. This impact is due to the release of carbon stored in the soil, ecosystem, and biomass. This transformation of cultivated land and grassland into built-up land accounted for 84.05% of the total carbon emissions ( Table 7 ). The carbon conduction from cultivable to built-up land was 1.02 × 10 3  t from 2000 to 2010, which increased to 42.44 × 10 3  t from 2010 to 2020. The carbon conduction from forests, and grasslands, to built-up land also showed an increasing trend. The carbon conduction effect caused by water area and unused land transfer is the same as that caused by grassland cultivation, which also shows an increasing trend.

TABLE 7 . Carbon conduction effect of land type transfer in the Baiyangdian basin from 2000 to 2020 (10 3  t).

4.3 Multi-scenario simulation and prediction of land use structure

In this paper, four scenarios were simulated using the GeoSOS-FLUS model for the prediction of the Baiyangdian basin land use in 2035 ( Figure 3 ). The 2035 balanced development, cultivable land protection, and double-carbon target scenarios were largely consistent, but with differences in certain regions.

FIGURE 3 . Land use change simulation for the Baiyangdian basin in 2035 under different scenarios (The total land area is 34,353.07 km 2 ). (A) Natural development; (B) Balanced development; (C) Cultivable land protection; (D) double-carbon target.

In the natural development scenario, the area of forests, water area, grasslands, cultivable lands, and unused lands in 2035 was 12,118.94, 462.03, 1626.05, 15,009.93, and 10.98 km 2 , respectively. Compared to 2020, the water area increased by 54.17 km 2 at most; the forest area increased by 39.68 km 2 ; and the cultivable land reduced by 5.03%, with a reduction of 795 km 2 . In the balanced development scenario, compared to 2020, the area of built-up lands, forests, and water bodies increased by 918.30, 260.43, and 119.7 km 2 , respectively. Accordingly, the area of the cultivable lands and grasslands was reduced by 1096.82 km 2 and 218.22 km 2 , respectively. As urbanization converts large parts of farmlands, food security will be further threatened if the focus remains only on economic development. In the cultivable land protection scenario, the built-up land area was relatively small, close to 5104.76 km 2 . Compared with the natural development scenario, the area of forests and grasslands increased by 41.48 and 38.61 km 2 , respectively, while the area of cultivable lands and grassland decreased by 65.88 and 10.43 km 2 , respectively, indicating a severe deterioration of the Baiyangdian basin ecology. This also suggested that even in the cultivable land protection scenario, only a small portion of cultivable land, grassland, and water area were expanded. It also demonstrated the need to place a higher priority on environmental preservation, rather than economic development in the Baiyangdian basin. In the double-carbon target scenario, the area of cultivable lands, forests, grasslands, water area, unused lands, and built-up lands changed to 14705.15 km 2 , 12438.86 km 2 , 1615.62 km 2 , 527.85 km 2 , 6.17 km 2 , and 5007.5 km 2 , respectively. In comparison to 2020, the grassland area decreased by 190.96 km 2 and the carbon-emitting cultivable land decreased by 1099.78 km 2 . Moreover, the area of water area rose by 119.99 km 2 , while that of the forests expanded by 359.6 km 2 ( Table 8 ).

TABLE 8 . Area of each land use type under multi-scenario modeling (km 2 ).

4.4 Prediction of land use carbon emissions

4.4.1 direct land use carbon emissions.

The cultivable land carbon emissions in the Baiyangdian Basin in 2020 were calculated to be 666.97 × 10 3  t, compared to which the emissions in the four scenarios set in 2035 were predicted to decrease slightly ( Table 9 ). In particular, the cultivable land carbon emissions for the balanced development and double-carbon target scenarios were likely to decrease more about 7%. Regarding the carbon sinks, the maximum carbon uptake of the forests under the double-carbon target scenario was 801.26 × 10 3  t, an increase of 3.1% compared with that in 2020, followed by 794.68 × 10 3  t under the balanced development scenario. The carbon uptake of grasslands remained largely unchanged, with an average value was about 3.5 × 10 3  t. Water areas exhibited the largest carbon uptake in the double-carbon target scenario. Compared with 2020, the water area carbon emissions increased for all four scenarios, with a growth ratio of 23.71%. The unused land area was relatively small, which also remained largely unchanged. The predicted results for the different scenarios are shown in Table 9 .

TABLE 9 . Prediction results of direct carbon emissions from land use under multi-scenario simulation (10 3 t).

4.4.2 Indirect land use carbon emissions

We chose the energy consumption data of the Baiyangdian basin in 2019 as the initial value and combined it with the average transfer probability matrix P obtained by Eq. 9 . We subsequently utilized the Markov model for forecasting the energy composition in 2020 and verified the accuracy by comparing the predictions with the actual data ( Figure 4 ).

FIGURE 4 . Share of energy consumption in the Baiyangdian Basin by energy source and projections.

According to Eq. 9 , the model effect coefficient w is 0.999 close to 1, indicating a good prediction result, and hence, a reasonable and reliable prediction model. Therefore, the energy consumption in 2020 was selected as the initial vector and combined with the average transfer probability matrix, P , obtained from historical energy data from 2000 to 2020, and the energy consumption structure of the Baiyangdian basin in 2035 was predicted ( Figure 4 ).

Using the carbon emissions data from 2000 to 2020 for the Baiyangdian basin, we employed the grey prediction GM (1,1) model to forecast the 2035 emissions and assess the model precision. The carbon emissions due to built-up lands in the basin in 2035 were expected to reach 404,400.19 × 10 3  t.

4.4.3 Summary of land use carbon emissions in the Baiyangdian basin

In this study, we built a Markov model to forecast total terrestrial carbon emissions in the Baiyangdian basin ( Table 10 ). The land use carbon sinks were primarily related to the land type area, and the carbon sources were primarily related to the continuous growth of energy consumption. Compared with 2020, the net land use carbon emissions in the basin were predicted to increase in 2035 for the four scenarios by 143,483.14 × 10 3 , 143,454.55 × 10 3 , 143,476.74 × 10 3 , and 143,447.97 × 10 3  t, respectively. All values were much higher than the net carbon emissions of the study area in 2020. In the natural development scenario, the carbon source emission peaked at 405,033.61 × 10 3  t, increasing by 143,486.62 × 10 3  t, about 55.03%. The lowest carbon sink absorption out of the four scenarios was 795.57 × 10 3  t, with a slight increase of 3.48 × 10 3  t compared with 2020. In the balanced development and cultivable land protection scenarios, carbon emissions increased significantly, carbon sink absorptions increased by 19.34 × 10 3  t and 7.11 × 10 3  t, and carbon source emissions increased by 143,473.89 × 10 3  t and 143,483.84 × 10 3  t, respectively. In the double-carbon target scenario, the lowest carbon source emission was 405,020.75 × 10 3  t and the highest carbon sink absorption was 817.88 × 10 3  t in the fourth scenario, which has a significant increase compared to the other three scenarios. Generally, land use carbon emissions in the natural development scenarios were the highest, followed by the balanced development, cultivable land protection, and double-carbon target scenarios. Therefore, it is worth thinking about how to balance carbon emission and absorption in the Baiyangdian Basin to achieve healthy development ( Chuai et al., 2016 ).

TABLE 10 . Total land use carbon emissions prediction results under multi-scenario simulations (10 3  t).

5 Conclusion and discussion

5.1 discussion.

The macro-scale carbon sinks in the study area could be rapidly accounted for using the direct carbon emission coefficients of the different land types. The relevant national-scale or regional studies by Fang Jingyun and other scholars (2023) served as the basis for the direct carbon emission coefficients of land use employed in this study. The next step should be to improve the monitoring of ecosystem carbon fluxes across countries and the investigation of carbon density across the various land types to correct the coefficients in a localized manner. Additionally, the GeoSOS-PLUS model combines the transformation, as well as pattern analysis strategies, which can effectively uncover the causes of land type changes and compare the simulation results for various scenarios. This can offer guidance for decision-making and future policy planning. In contrast to Zhou et al. (2020) who used the conventional CA-Markov model to simulate the land use in the built-up land of the urban Shanghai area, our experimental results demonstrated that the GeoSOS-PLUS model significantly improved the simulation and predictions of land use patterns in the Baiyangdian basin, with an overall accuracy of 99%. This addressed the issue of the conventional CA model not adequately accounting for the connection between the influencing variables and spatial changes.

Based on the goal of carbon neutrality, this study makes the following suggestions:

a) The government should strictly regulate the unchecked growth of built-up in developing areas; moderately resume plowing in forests, lakes, and grasslands; and boost the capacity of forests as carbon sinks. They must realize the concept of increasing sinks and reducing sources through the creation of rational and scientific land use policies.

b) Improving the industrial and energy consumption structures; investing more in clean energy resources; and creating a green, diversified energy supply system should be prioritized.

c) When creating the national “dual carbon” roadmap, the unbalanced distribution of regional carbon sources and sinks must be considered and objectively examined for their growth potential.

It should be noted that this paper uses fixed coefficients to calculate carbon emissions, and the coefficients can be optimized by combining the localized measured data or by using multi-source remote sensing image data to improve the accuracy of the calculation. When analyzing the transmission effect of carbon emissions, this paper does not consider the difference in carbon emission coefficients of the same land use type in different counties and cities, and the same land type in different regions may have differences in carbon emission capacity due to factors such as the degree of land intensification. In the future, we will carry out in-depth research on the refinement of the carbon transmission effect due to the internal transformation of land use types. In addition, there is a long way to go to achieve the goal of “double carbon,” and the carbon emission accounting and prediction model established for the characteristics of China’s land use has clarified the important paths affecting China’s carbon emissions from land use and has been widely applied in cities in the central and eastern parts of China as well as in northern China. For regions outside of China, it is necessary to combine regional characteristics, add more factors describing land characteristics, and continuously improve the accuracy of the model, which can also be committed to the study of carbon emissions in other regions.

5.2 Conclusion

In this study, we first analyzed the land use carbon emissions and subsequent transmissions caused by land use changes in the Baiyangdian basin. We then simulated four scenarios based on the GeoSOS-FLUS model, namely, natural development, balanced development, cultivable land protection, and double-carbon target ( Yang et al., 2022 ), and finally predicted the land use carbon emissions in the Baiyangdian basin in 2035 using a Markov model. The double-carbon target scenario further illustrated the critical position of ecological conservation ( Ke N. et al., 2022 ). In general, from the new direction of carbon emission control, combined with regional land use, our study makes outstanding contributions to regional land rational planning and ecological protection ( Chen et al., 2022 ). The primary conclusions of the study are as follows:

1. The ratio of the Baiyangdian basin carbon source emission to sink absorption has been steadily increasing, especially rapidly in 2020, reaching a maximum of 330.21, 4.9 times higher than in 2000. This shows that the carbon sources (sinks) are consistently rising (declining). Over the past 20 years, the net land use carbon emissions in the basin increased by 208,591.88 × 10 3  t, with an average yearly rise of 10,429.59 × 10 3  t.

2. The net carbon emissions from land transfer in the basin exhibit a clear rising trend between 2000 and 2020. The carbon conduction effect due to forests and grasslands being converted to built-up land also shows an increasing trend, whereas the reverse transfer from built-up land to carbon sinks increases only slightly.

3. After simulating four scenarios in the Baiyangdian basin in 2035, it was found that the net land use carbon emissions under the natural development, balanced development, cultivable land protection, and double-carbon target scenarios are predicted to be 404,238.04 × 10 3 , 402,009.45 × 10 3 , 404,231.64 × 10 3 , and 404,202.87 × 10 3  t, respectively, much higher than the values in 2020. However, carbon emissions from cultivable lands show a decreasing trend; the rate of increase of carbon emissions from built-up lands slowed down, and the carbon absorption by forests and grasslands gradually increased. These trends establish the carbon source-sink ratio as a highly suitable parameter for the future planning of ecological vs economic development.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

XG: Writing–original draft, Writing–review and editing. MiZ: Writing–original draft, Writing–review and editing. MnZ: Writing–original draft, Writing–original draft. ZG: Writing–review and editing. XL: Writing–review and editing. ZY: Writing–review and editing.

The authors declare that financial support was received for the research, authorship, and/or publication of this article. This project is supported by the National Natural Science Foundation of China (NSFC): Research on Safety Resilience Evaluation of Critical Infrastructure Systems in Urban Cities and Optimization of Operation (72374063); the National Natural Science Foundation of China (NSFC): Realization Mechanisms, Influencing Factors and Optimization of Urban Ecosystem Service Delivery: A Case Study of Beijing and its Surrounding Areas (42371279); the Social Science Foundation of Hebei Province: Research on Optimization of Ecological Spatial Pattern and Quality Improvement of Baiyangdian Basin Based on Multi-source Data (HB22GL030) Funding Support.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: land use, carbon source-sink ratio, carbon conduction effects, Markov prediction, Baiyangdian basin

Citation: Gao X, Zhao M, Zhang M, Guo Z, Liu X and Yuan Z (2024) Carbon conduction effect and multi-scenario carbon emission responses of land use patterns transfer: a case study of the Baiyangdian basin in China. Front. Environ. Sci. 12:1374383. doi: 10.3389/fenvs.2024.1374383

Received: 22 January 2024; Accepted: 05 March 2024; Published: 13 March 2024.

Reviewed by:

Copyright © 2024 Gao, Zhao, Zhang, Guo, Liu and Yuan. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Meiran Zhao, [email protected]

† These authors have contributed equally to this work and share first authorship

This article is part of the Research Topic

Dynamics of Land Use and Carbon Emissions in the Context of Carbon Neutrality and Carbon Peaking

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The key findings in this article are based on McKinsey’s fourth global survey of customer care executives. This survey was our largest yet, gathering the views of more than 340 leaders at the director, senior director, vice president, and C-suite levels. Respondents came from companies with annual revenues of $100 million to $10 billion-plus, representing every major industry segment.

The majority of respondents said that the companies they worked for were headquartered in North America (just over 50 percent) or Western Europe (almost 25 percent), with 10 percent headquartered in India and 4 percent in China. Most respondents said their organizations operated in multiple regions: 75 percent reported operating in North America, 58 percent in Europe, 57 percent in Asia–Pacifc, 39 percent in the Middle East and Africa, and 37 percent in Latin America. We plan to expand future research to include more organizations headquartered outside North America and Western Europe.

To make matters worse, executives say that most of the challenges highlighted in our last survey  are still present today (see sidebar, “Customer care in the spotlight”). Those challenges include rising call volumes, high levels of employee attrition, and persistent talent shortages. Meanwhile, some of the largest consumer-facing technology organizations in the world have become exceptional at digitally enabled customer care, which is lifting customer expectations everywhere, piling further pressure onto customer care staff and leadership at other companies.

Our survey reveals three major themes that are top of mind for customer care leaders. First, their priorities are shifting, from an overwhelming focus on customer experience to a multidimensional approach that also emphasizes revenue goals and technology transformation. Second, they are working hard to build future-ready AI-enabled ecosystems for their operations. Finally, they are boosting their capabilities by investing in employee upskilling programs and building stronger outsourcing relationships.

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Reprioritizing core operations.

When we began monitoring the sentiment of customer care leaders in 2016, their priorities were clear. Customer experience came first, followed at a distance by operational improvement, technology transformation, and revenue generation—in that order.

Over the past seven years, those priorities have converged (Exhibit 1). Revenue generation, which was mentioned by about one in 20 customer care leaders in our first survey, has been rising steadily in importance ever since. It is now a priority for a third of customer care leaders. But over the past two years, technology enhancements and operational improvements have seen the fastest increases. The expectation that customer care functions can do it all and do it well has never been higher.

Leaders also understand that they need to engage with their customers to delight them. Currently, only 11 percent of respondents say reducing contact volume is important to them, a 20-percentage-point drop over 12 months. Indeed, 57 percent of leaders expect call volumes to increase by as much as one-fifth over the next one or two years.

Separate research suggests that these leaders are right to stay focused on direct personal interaction, even when many of their customers are young digital natives. In a recent McKinsey survey of 3,500 consumers, respondents of all ages said that live phone conversations were among their most preferred methods of contacting companies for help and support. That finding held true even among 18- to 28-year-old Gen Z consumers, a cohort that favors text and social messaging for interpersonal communications.

There’s also evidence that younger consumers are getting tired of the digital self-service paradigm. One financial-services company reports that its Gen Z customers are 30 to 40 percent more likely to call than millennials, and they use the phone as often as baby boomers. Premium-segment customers of all ages also prefer the phone, with many saying that live phone support is part of the premium service they are paying for.

These findings don’t point to a future of phone-only customers, however. While customers of all generations prioritize support from a real person, they also want the flexibility to use different channels according to their needs. Digital-chat services have achieved a high level of acceptance across generations, and email remains important, especially for older consumers (Exhibit 2).

The need to excel in service across multiple channels creates extra challenges for customer care leaders, especially when budgets are tight. And 37 percent of respondents in our survey say that cost is still a key priority. This tension is driving companies to look for ways to control the customer care costs that go beyond call volume reduction, with automation and outsourcing the most frequently cited levers.

Creating a future-ready AI ecosystem

The tensions in modern customer care are clearly seen in companies’ approaches to advanced digital technologies. Our survey demonstrates that digital has already become a decisive differentiator. Among respondents who report that their operations are delivering better-than-expected performance, more than half have high levels of digital integration. Banking, telecommunications, and travel and logistics are among the leading industries in this regard.

Those high performers are in the minority, however. Only 8 percent of respondents from North America report greater-than-expected satisfaction with their customer performance. In Africa, Europe, and the Middle East, the figure is 5 percent. Among organizations reporting that performance was in line with or lower than expected, more than 80 percent also say their levels of digital integration are partial or low.

Leaders agree that they need to get digital right. More than half of the respondents to our survey expect the share of inbound contacts that take place through digital channels to exceed 40 percent in the next three years.

Artificial intelligence will play a decisive role in future customer care ecosystems. Respondents to our survey are already deploying AI tools in a variety of applications, including chatbots and automated email response systems, training and support for call center agents, back-office analytics, and decision making.

Over the past 12 months, the availability of powerful generative AI (gen AI) tools, especially large language models (LLMs) that can parse and respond to unstructured text or speech, has opened new possibilities for technology in customer care. More than 80 percent of respondents are already investing in gen AI, or expect to do so in the coming months, with leaders highlighting a wide range of potential applications.

One European subsidiary of a global bank replaced its well-established rules-based customer chatbot with a new system based on gen AI technology. Seven weeks after launch, the AI chatbot was 20 percent more effective at successfully answering customer queries than the old tool. The bank has already identified a road map of improvements that could double its performance in the coming months.

Early adopters are extremely ambitious about the potential of gen AI. The executive in charge of customer care at one major global organization told us that they expect 100 percent of customer interactions to be AI-enabled in the coming years, using a combination of technologies including new virtual assistants, agent-assist tools, and AI-powered voice analytics.

For most companies, however, the gen AI customer care revolution is still in its early stages. Leaders highlight multiple issues that are making it hard for them to integrate these technologies into their existing processes and workflows. The issues include technical challenges regarding deployment and scaling; concerns about safety, security, and governance; and difficulties in defining the desired outcomes from, or business case for, gen AI investments (Exhibit 3).

Learn more about Customer Care

Rethinking skills.

Today, customer care organizations lack many of the critical skills they need to deliver excellent service and navigate the transition to a digitally mediated, AI-enabled world. In part, that’s because customer care leaders have been running to stand still. Record levels of staff attrition following the COVID-19 pandemic meant that supervisors spent much of their time interviewing and bringing new staff up to speed. They spent less time mentoring their established teams, a problem exacerbated by the introduction of hybrid and remote working arrangements. Some agents and team leaders have spent years working with little interaction or coaching from their managers.

Staff turnover has now slowed, and two in three leaders in our latest survey say upskilling and reskilling are critical priorities. Companies highlight a range of benefits that accrue from effective upskilling and reskilling programs, including improvements to employee morale, increased productivity, and faster adoption of new technologies and working methods. Meanwhile, technology is changing upskilling programs. Twenty-one percent of leaders tell us that they are already using AI-based tools to train and support their customer care staff.

AI-based agent support systems are already becoming a key tool for companies seeking to offer extremely effective personal service to demanding customers. These systems can help agents resolve complex queries the first time, simultaneously reducing care costs and boosting customer experience.

One global construction equipment company, for example, uses a gen AI system to help its call center staff navigate thousands of pages of technical-support documentation. The system selects the appropriate steps to resolve a customer’s problem in seconds, based on free text questions entered by the agent and background information such as the serial numbers of vehicles and parts. The tool has cut average call resolution times from around 125 minutes to a few seconds, and it is currently saving customers €150,000 to €300,000 per day in reduced asset downtime.

Elsewhere, companies are using AI to transform the way they manage and support their customer care agents. New AI-based tools can optimize call volume forecasting, for example. This approach helped one company improve forecast accuracy by seven percentage points, while halving the work required to manage team capacities and schedules. The change improved customer service levels by more than 10 percent, while cutting staffing and overtime costs by more than 5 percent.

Companies are also looking outside their organizations for innovative ways to fill capability gaps. Outsourcing, once viewed primarily as a way to reduce costs, is increasingly seen as an effective source of additional skilled capacity and innovation capabilities. Fifty-five percent of the companies in our survey currently outsource part of their customer care operations, and 47 percent of those organizations expect to increase their outsourcing over the next two years.

Outsourcing relationships are becoming deeper too, with respondents telling us that they are now using their business process outsourcing for a range of activities that extends far beyond traditional call and email handling. They include content management and digital-marketing services, payments handling, and the development of AI-based customer care tools. Following the blueprint established by major players in the industrial products, medical device, software, and e-commerce sectors, some companies are now working with outsourcing partners to set up global innovation hubs that will drive the development of next-generation customer care technologies.

Our survey suggests that customer care organizations are running at two different speeds. In the fast lane, top performers have seized the opportunities presented by advances in digital technologies. With ruthless prioritization, they are investing capital to drive efficiency and service excellence across the customer journey. The best have already reshaped their organizations around highly integrated digital platforms. One high-performing company with more than 5,000 service agents is on track to deliver 75 digital-experience improvements this year, for example.

Other companies are still in the slow lane, struggling to fit a patchwork of digital point solutions into legacy care ecosystems. Unsure where to put their dollars, they are trapped in a cycle of continual system adaptation with no clear destination or road map.

In 2024, both types of organizations may need to shift their positions on the road. Gen AI is raising the bar for performance, productivity, and personalization in customer care, and tomorrow’s fully AI-enabled care organizations will operate very differently from those of today. It’s time for companies to look at their care ecosystems with fresh eyes. They should formulate an independent perspective on the changing expectations of their customers and the role of advanced AI in their organization. The future of customer care is calling. Leaders should answer with a bold vision and an aggressive time line for change.

Eric Buesing is a partner in McKinsey’s Charlotte office, where Paul Hurst is an associate partner; Maximilian Haug is an associate partner in the Boston office; Vivian Lai is a consultant in the New York office; Subhrajyoti Mukhopadhyay is an expert in the Chicago office; and Julian Raabe  is a partner in the Munich office.

The authors wish to thank Jorge Amar, Brian Blackader, Marcela Guaqueta, Suryansha Gupta, and Josh Wolff for their contributions to this article.

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More than six in 10 US abortions in 2023 were done by medication — a significant jump since 2020

FILE - A patient prepares to take the first of two combination pills, mifepristone, for a medication abortion during a visit to a clinic in Kansas City, Kan., on, Oct. 12, 2022. More than six in 10 of the abortions in the United States last year were done through medication, up from 53% in 2020, according to research released Tuesday, March 19, 2024. The Guttmacher Institute, a research group that supports abortion rights, said about 642,700 medication abortions took place in the first full calendar year after the U.S. Supreme Court overturned Roe v. Wade. Medication abortion accounted for 63% of abortions in the formal health care system. (AP Photo/Charlie Riedel, File)

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More than six in 10 of the abortions in the United States last year were done through medication, up from 53% in 2020, new research shows.

The Guttmacher Institute, a research group that supports abortion rights, said about 642,700 medication abortions took place in the first full calendar year after the U.S. Supreme Court overturned Roe v. Wade. Medication abortion accounted for 63% of abortions in the formal health care system.

The data was released Tuesday, a week before the high court will hear arguments in a case that could impact how women get access to mifepristone, which is usually used with another pill in medication abortions.

Guttmacher researcher Rachel Jones said the increase wasn’t a surprise.

“For example, it is now possible in some states, at least for health care providers, to mail mifepristone to people in their homes,” Jones said, “so that saves patients travel costs and taking time off work.”

Guttmacher’s data, which is collected by contacting abortion providers, doesn’t count self-managed medication abortions that take place outside the health care system or abortion medication mailed to people in states with abortion bans.

Dr. Grace Ferguson, an OB-GYN and abortion provider in Pittsburgh who isn’t involved with the research, said the COVID-19 pandemic and the overturning of Roe v. Wade “really opened the doors” for medication abortions done through telehealth.

Ferguson said “telehealth was a really good way of accommodating that increased volume” in states where abortion remained legal and saw an increase in people who traveled from more restrictive states.

Guttmacher data shows that medication abortions have risen steadily since mifepristone was approved by the Food and Drug Administration in 2000. The drug, which blocks the hormone progesterone, also primes the uterus to respond to the contraction-causing effect of another drug, misoprostol. The two-drug regimen is used to end a pregnancy through 10 weeks gestation.

The case in front of the Supreme Court could cut off access to mifepristone by mail and impose other restrictions, even in states where abortion remains legal.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.

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Dementia prevention, intervention, and care: 2020 report of the Lancet Commission

Gill livingston.

a Division of Psychiatry, University College London, London, UK

d Camden and Islington NHS Foundation Trust, London, UK

Jonathan Huntley

Andrew sommerlad.

f National Ageing Research Institute and Academic Unit for Psychiatry of Old Age, University of Melbourne, Royal Melbourne Hospital, Parkville, VIC, Australia

Clive Ballard

g University of Exeter, Exeter, UK

Sube Banerjee

h Faculty of Health: Medicine, Dentistry and Human Sciences, University of Plymouth, Plymouth, UK

Carol Brayne

i Cambridge Institute of Public Health, University of Cambridge, Cambridge, UK

Alistair Burns

j Department of Old Age Psychiatry, University of Manchester, Manchester, UK

Jiska Cohen-Mansfield

k Department of Health Promotion, School of Public Health, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel

l Heczeg Institute on Aging, Tel Aviv University, Tel Aviv, Israel

m Minerva Center for Interdisciplinary Study of End of Life, Tel Aviv University, Tel Aviv, Israel

Claudia Cooper

Sergi g costafreda.

n Department of Preventive and Social Medicine, Goa Medical College, Goa, India

b Dementia Research Centre, UK Dementia Research Institute, University College London, London, UK

o Institute of Neurology, National Hospital for Neurology and Neurosurgery, University College London Hospitals NHS Foundation Trust, London, UK

Laura N Gitlin

p Center for Innovative Care in Aging, Johns Hopkins University, Baltimore, MA, USA

Robert Howard

Helen c kales.

r Department of Psychiatry and Behavioral Sciences, UC Davis School of Medicine, University of California, Sacramento, CA, USA

Mika Kivimäki

c Department of Epidemiology and Public Health, University College London, London, UK

Eric B Larson

s Kaiser Permanente Washington Health Research Institute, Seattle, WA, USA

Adesola Ogunniyi

t University College Hospital, Ibadan, Nigeria

Vasiliki Orgeta

Karen ritchie.

u Inserm, Unit 1061, Neuropsychiatry: Epidemiological and Clinical Research, La Colombière Hospital, University of Montpellier, Montpellier, France

v Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK

Kenneth Rockwood

w Centre for the Health Care of Elderly People, Geriatric Medicine Dalhousie University, Halifax, NS, Canada

Elizabeth L Sampson

e Barnet, Enfield, and Haringey Mental Health Trust, London, UK

Quincy Samus

q Department of Psychiatry and Behavioral Sciences, Johns Hopkins University, Baltimore, MA, USA

Lon S Schneider

x Department of Psychiatry and the Behavioural Sciences and Department of Neurology, Keck School of Medicine, Leonard Davis School of Gerontology of the University of Southern California, Los Angeles, CA, USA

Geir Selbæk

y Norwegian National Advisory Unit on Ageing and Health, Vestfold Hospital Trust, Tønsberg, Norway

z Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway

aa Geriatric Department, Oslo University Hospital, Oslo, Norway

ab Department Psychosocial and Community Health, School of Nursing, University of Washington, Seattle, WA, USA

Naaheed Mukadam

Associated data, executive summary.

The number of older people, including those living with dementia, is rising, as younger age mortality declines. However, the age-specific incidence of dementia has fallen in many countries, probably because of improvements in education, nutrition, health care, and lifestyle changes. Overall, a growing body of evidence supports the nine potentially modifiable risk factors for dementia modelled by the 2017 Lancet Commission on dementia prevention, intervention, and care: less education, hypertension, hearing impairment, smoking, obesity, depression, physical inactivity, diabetes, and low social contact. We now add three more risk factors for dementia with newer, convincing evidence. These factors are excessive alcohol consumption, traumatic brain injury, and air pollution. We have completed new reviews and meta-analyses and incorporated these into an updated 12 risk factor life-course model of dementia prevention. Together the 12 modifiable risk factors account for around 40% of worldwide dementias, which consequently could theoretically be prevented or delayed. The potential for prevention is high and might be higher in low-income and middle-income countries (LMIC) where more dementias occur.

Our new life-course model and evidence synthesis has paramount worldwide policy implications. It is never too early and never too late in the life course for dementia prevention. Early-life (younger than 45 years) risks, such as less education, affect cognitive reserve; midlife (45–65 years), and later-life (older than 65 years) risk factors influence reserve and triggering of neuropathological developments. Culture, poverty, and inequality are key drivers of the need for change. Individuals who are most deprived need these changes the most and will derive the highest benefit.

Policy should prioritise childhood education for all. Public health initiatives minimising head injury and decreasing harmful alcohol drinking could potentially reduce young-onset and later-life dementia. Midlife systolic blood pressure control should aim for 130 mm Hg or lower to delay or prevent dementia. Stopping smoking, even in later life, ameliorates this risk. Passive smoking is a less considered modifiable risk factor for dementia. Many countries have restricted this exposure. Policy makers should expedite improvements in air quality, particularly in areas with high air pollution.

We recommend keeping cognitively, physically, and socially active in midlife and later life although little evidence exists for any single specific activity protecting against dementia. Using hearing aids appears to reduce the excess risk from hearing loss. Sustained exercise in midlife, and possibly later life, protects from dementia, perhaps through decreasing obesity, diabetes, and cardiovascular risk. Depression might be a risk for dementia, but in later life dementia might cause depression. Although behaviour change is difficult and some associations might not be purely causal, individuals have a huge potential to reduce their dementia risk.

In LMIC, not everyone has access to secondary education; high rates of hypertension, obesity, and hearing loss exist, and the prevalence of diabetes and smoking are growing, thus an even greater proportion of dementia is potentially preventable.

Amyloid-β and tau biomarkers indicate risk of progression to Alzheimer's dementia but most people with normal cognition with only these biomarkers never develop the disease. Although accurate diagnosis is important for patients who have impairments and functional concerns and their families, no evidence exists to support pre-symptomatic diagnosis in everyday practice.

Our understanding of dementia aetiology is shifting, with latest description of new pathological causes. In the oldest adults (older than 90 years), in particular, mixed dementia is more common. Blood biomarkers might hold promise for future diagnostic approaches and are more scalable than CSF and brain imaging markers.

Wellbeing is the goal of much of dementia care. People with dementia have complex problems and symptoms in many domains. Interventions should be individualised and consider the person as a whole, as well as their family carers. Evidence is accumulating for the effectiveness, at least in the short term, of psychosocial interventions tailored to the patient's needs, to manage neuropsychiatric symptoms. Evidence-based interventions for carers can reduce depressive and anxiety symptoms over years and be cost-effective.

Keeping people with dementia physically healthy is important for their cognition. People with dementia have more physical health problems than others of the same age but often receive less community health care and find it particularly difficult to access and organise care. People with dementia have more hospital admissions than other older people, including for illnesses that are potentially manageable at home. They have died disproportionately in the COVID-19 epidemic. Hospitalisations are distressing and are associated with poor outcomes and high costs. Health-care professionals should consider dementia in older people without known dementia who have frequent admissions or who develop delirium. Delirium is common in people with dementia and contributes to cognitive decline. In hospital, care including appropriate sensory stimulation, ensuring fluid intake, and avoiding infections might reduce delirium incidence.

Key messages

• • New evidence supports adding three modifiable risk factors—excessive alcohol consumption, head injury, and air pollution—to our 2017 Lancet Commission on dementia prevention, intervention, and care life-course model of nine factors (less education, hypertension, hearing impairment, smoking, obesity, depression, physical inactivity, diabetes, and infrequent social contact).
• • Modifying 12 risk factors might prevent or delay up to 40% of dementias.
• • Prevention is about policy and individuals. Contributions to the risk and mitigation of dementia begin early and continue throughout life, so it is never too early or too late. These actions require both public health programmes and individually tailored interventions. In addition to population strategies, policy should address high-risk groups to increase social, cognitive, and physical activity; and vascular health.
• • Aim to maintain systolic BP of 130 mm Hg or less in midlife from around age 40 years (antihypertensive treatment for hypertension is the only known effective preventive medication for dementia).
• • Encourage use of hearing aids for hearing loss and reduce hearing loss by protection of ears from excessive noise exposure.
• • Reduce exposure to air pollution and second-hand tobacco smoke.
• • Prevent head injury.
• • Limit alcohol use, as alcohol misuse and drinking more than 21 units weekly increase the risk of dementia.
• • Avoid smoking uptake and support smoking cessation to stop smoking, as this reduces the risk of dementia even in later life.
• • Provide all children with primary and secondary education.
• • Reduce obesity and the linked condition of diabetes. Sustain midlife, and possibly later life physical activity.
• • Addressing other putative risk factors for dementia, like sleep, through lifestyle interventions, will improve general health.
• • Many risk factors cluster around inequalities, which occur particularly in Black, Asian, and minority ethnic groups and in vulnerable populations. Tackling these factors will involve not only health promotion but also societal action to improve the circumstances in which people live their lives. Examples include creating environments that have physical activity as a norm, reducing the population profile of blood pressure rising with age through better patterns of nutrition, and reducing potential excessive noise exposure.
• • Dementia is rising more in low-income and middle-income countries (LMIC) than in high-income countries, because of population ageing and higher frequency of potentially modifiable risk factors. Preventative interventions might yield the largest dementia reductions in LMIC.

For those with dementia, recommendations are:

• • Post-diagnostic care for people with dementia should address physical and mental health, social care, and support. Most people with dementia have other illnesses and might struggle to look after their health and this might result in potentially preventable hospitalisations.
• • Specific multicomponent interventions decrease neuropsychiatric symptoms in people with dementia and are the treatments of choice. Psychotropic drugs are often ineffective and might have severe adverse effects.
• • Specific interventions for family carers have long-lasting effects on depression and anxiety symptoms, increase quality of life, are cost-effective and might save money.

Acting now on dementia prevention, intervention, and care will vastly improve living and dying for individuals with dementia and their families, and thus society.

Introduction

Worldwide around 50 million people live with dementia, and this number is projected to increase to 152 million by 2050, 1 rising particularly in low-income and middle-income countries (LMIC) where around two-thirds of people with dementia live. 1 Dementia affects individuals, their families, and the economy, with global costs estimated at about US$1 trillion annually. 1

We reconvened the 2017 Lancet Commission on dementia prevention, intervention, and care 2 to identify the evidence for advances likely to have the greatest impact since our 2017 paper and build on its work. Our interdisciplinary, international group of experts presented, debated, and agreed on the best available evidence. We adopted a triangulation framework evaluating the consistency of evidence from different lines of research and used that as the basis to evaluate evidence. We have summarised best evidence using, where possible, good- quality systematic reviews, meta-analyses, or individual studies, where these add important knowledge to the field. We performed systematic literature reviews and meta-analyses where needed to generate new evidence for our analysis of potentially modifiable risk factors for dementia. Within this framework, we present a narrative synthesis of evidence including systematic reviews and meta-analyses and explain its balance, strengths, and limitations. We evaluated new evidence on dementia risk in LMIC; risks and protective factors for dementia; detection of Alzheimer's disease; multimorbidity in dementia; and interventions for people affected by dementia.

Nearly all the evidence is from studies in high-income countries (HIC), so risks might differ in other countries and interventions might require modification for different cultures and environments. This notion also underpins the critical need to understand the dementias related to life-course disadvantage—whether in HICs or LMICs.

Our understanding of dementia aetiology is shifting. A consensus group, for example, has described hippocampal sclerosis associated with TDP-43 proteinopathy, as limbic-predominant age-related TDP-43 encephalopathy (LATE) dementia, usually found in people older than 80 years, progressing more slowly than Alzheimer's disease, detectable at post-mortem, often mimicking or comorbid with Alzheimer's disease. 3 This situation reflects increasing attention as to how clinical syndromes are and are not related to particular underlying pathologies and how this might change across age. More work is needed, however, before LATE can be used as a valid clinical diagnosis.

The fastest growing demographic group in HIC is the oldest adults, those aged over 90 years. Thus a unique opportunity exists to focus on both human biology, in this previously rare population, as well as on meeting their needs and promoting their wellbeing.

Prevention of dementia

The number of people with dementia is rising. Predictions about future trends in dementia prevalence vary depending on the underlying assumptions and geographical region, but generally suggest substantial increases in overall prevalence related to an ageing population. For example, according to the Global Burden of Diseases, Injuries, and Risk Factors Study, the global age-standardised prevalence of dementia between 1990 and 2016 was relatively stable, but with an ageing and bigger population the number of people with dementia has more than doubled since 1990. 4

However, in many HIC such as the USA, the UK, and France, age-specific incidence rates are lower in more recent cohorts compared with cohorts from previous decades collected using similar methods and target populations 5 ( figure 1 ) and the age-specific incidence of dementia appears to decrease. 6 All-cause dementia incidence is lower in people born more recently, 7 probably due to educational, socio-economic, health care, and lifestyle changes. 2 , 5 However, in these countries increasing obesity and diabetes and declining physical activity might reverse this trajectory. 8 , 9 In contrast, age-specific dementia prevalence in Japan, South Korea, Hong Kong, and Taiwan looks as if it is increasing, as is Alzheimer's in LMIC, although whether diagnostic methods are always the same in comparison studies is unclear. 5 , 6 , 7

Incidence rate ratio comparing new cohorts to old cohorts from five studies of dementia incidence 5

IIDP Project in USA and Nigeria, Bordeaux study in France, and Rotterdam study in the Netherlands adjusted for age. Framingham Heart Study, USA, adjusted for age and sex. CFAS in the UK adjusted for age, sex, area, and deprivation. However, age-specific dementia prevalence is increasing in some other countries. IID=Indianapolis–Ibadan Dementia. CFAS=Cognitive Function and Ageing Study. Adapted from Wu et al, 5 by permission of Springer Nature.

Modelling of the UK change suggests a 57% increase in the number of people with dementia from 2016 to 2040, 70% of that expected if age-specific incidence rates remained steady, 10 such that by 2040 there will be 1·2 million UK people with dementia. Models also suggest that there will be future increases both in the number of individuals who are independent and those with complex care needs. 6

In our first report, the 2017 Commission described a life-course model for potentially modifiable risks for dementia. 2 Life course is important when considering risk, for example, obesity and hypertension in midlife predict future dementia, but both weight and blood pressure usually fall in later life in those with or developing dementia, 9 so lower weight and blood pressure in later life might signify illness, not an absence of risk. 11 , 12 , 13 , 14 We consider evidence on other potential risk factors and incorporate those with good quality evidence in our model.

Figure 2 summarises possible mechanisms of protection from dementia, some of which involve increasing or maintaining cognitive reserve despite pathology and neuropathological damage. There are different terms describing the observed differential susceptibility to age-related and disease-related changes and these are not used consistently. 15 , 16 A consensus paper defines reserve as a concept accounting for the difference between an individual's clinical picture and their neuropathology. It, divides the concept further into neurobiological brain reserve (eg, numbers of neurones and synapses at a given timepoint), brain maintenance (as neurobiological capital at any timepoint, based on genetics or lifestyle reducing brain changes and pathology development over time) and cognitive reserve as adaptability enabling preservation of cognition or everyday functioning in spite of brain pathology. 15 Cognitive reserve is changeable and quantifying it uses proxy measures such as education, occupational complexity, leisure activity, residual approaches (the variance of cognition not explained by demographic variables and brain measures), or identification of functional networks that might underlie such reserve. 15 , 16 , 17 , 18 , 19 , 20

Possible brain mechanisms for enhancing or maintaining cognitive reserve and risk reduction of potentially modifiable risk factors in dementia

Early-life factors, such as less education, affect the resulting cognitive reserve. Midlife and old-age risk factors influence age-related cognitive decline and triggering of neuropathological developments. Consistent with the hypothesis of cognitive reserve is that older women are more likely to develop dementia than men of the same age, probably partly because on average older women have had less education than older men. Cognitive reserve mechanisms might include preserved metabolism or increased connectivity in temporal and frontal brain areas. 17 , 18 , 19 , 20 , 21 People in otherwise good physical health can sustain a higher burden of neuropathology without cognitive impairment. 22 Culture, poverty, and inequality are important obstacles to, and drivers of, the need for change to cognitive reserve. Those who are most deprived need these changes the most and will derive the highest benefit from them.

Smoking increases air particulate matter, and has vascular and toxic effects. 23 Similarly air pollution might act via vascular mechanisms. 24 Exercise might reduce weight and diabetes risk, improve cardiovascular function, decrease glutamine, or enhance hippocampal neurogenesis. 25 Higher HDL cholesterol might protect against vascular risk and inflammation accompanying amyloid-β (Aβ) pathology in mild cognitive impairment. 26

Dementia in LMIC

Numbers of people with dementia in LMIC are rising faster than in HIC because of increases in life expectancy and greater risk factor burden. We previously calculated that nine potentially modifiable risk factors together are associated with 35% of the population attributable fraction (PAFs) of dementia worldwide: less education, high blood pressure, obesity, hearing loss, depression, diabetes, physical inactivity, smoking, and social isolation, assuming causation. 2 Most research data for this calculation came from HIC and there is a relative absence of specific evidence of the impact of risk factors on dementia risk in LMIC, particularly from Africa and Latin America. 27

Calculations considering country-specific prevalence of the nine potentially modifiable risk factors indicate PAF of 40% in China, 41% in India and 56% in Latin America with the potential for these numbers to be even higher depending on which estimates of risk factor frequency are used. 28 , 29 Therefore a higher potential for dementia prevention exists in these countries than in global estimates that use data predominantly from HIC. If not currently in place, national policies addressing access to education, causes and management of high blood pressure, causes and treatment of hearing loss, socio-economic and commercial drivers of obesity, could be implemented to reduce risk in many countries. The higher social contact observed in the three LMIC regions provides potential insights for HIC on how to influence this risk factor for dementia. 30 We could not consider other risk factors such as poor health in pregnancy of malnourished mothers, difficult births, early life malnutrition, survival with heavy infection burdens alongside malaria and HIV, all of which might add to the risks in LMIC.

Diabetes is very common and cigarette smoking is rising in China while falling in most HIC. 31 A meta-analysis found variation of the rates of dementia within China, with a higher prevalence in the north and lower prevalence in central China, estimating 9·5 million people are living with dementia, whereas a slightly later synthesis estimated a higher prevalence of around 11 million. 30 , 32 These data highlight the need for more focused work in LMIC for more accurate estimates of risk and interventions tailored to each setting.

Specific potentially modifiable risk factors for dementia

Risk factors in early life (education), midlife (hypertension, obesity, hearing loss, traumatic brain injury, and alcohol misuse) and later life (smoking, depression, physical inactivity, social isolation, diabetes, and air pollution) can contribute to increased dementia risk ( table 1 ). Good evidence exists for all these risk factors although some late-life factors, such as depression, possibly have a bidirectional impact and are also part of the dementia prodrome. 33 , 34

PAF for 12 dementia risk factors

Data are relative risk (95% CI) or %. Overall weighted PAF=39·7%. PAF=population attributable fraction.

In the next section, we briefly describe relevant newly published and illustrative research studies that add to the 2017 Commission's evidence base, including risks and, for some, mitigation. We have chosen studies that are large and representative of the populations, or smaller studies in areas where very little evidence exists. We discuss them in life-course order and within the life course in the order of magnitude of population attributable factor.

Education and midlife and late-life cognitive stimulation

Education level reached.

Higher childhood education levels and lifelong higher educational attainment reduce dementia risk. 2 , 35 , 36 , 37 New work suggests overall cognitive ability increases, with education, before reaching a plateau in late adolescence, when brain reaches greatest plasticity; with relatively few further gains with education after age 20 years. 38 This suggests cognitive stimulation is more important in early life; much of the apparent later effect might be due to people of higher cognitive function seeking out cognitively stimulating activities and education. 38 It is difficult to separate out the specific impact of education from the effect of overall cognitive ability, 38 , 39 and the specific impact of later-life cognitive activity from lifelong cognitive function and activity. 39 , 40

Cognitive maintenance

One large study in China tried to separate cognitive activity in adulthood from activities for those with more education, by considering activities judged to appeal to people of different levels of education. 40 It found people older than 65 years who read, played games, or bet more frequently had reduced risk of dementia (n=15 882, odds ratio [OR]=0·7, 95% CI 0·6–0·8). The study excluded people developing dementia less than 3 years after baseline to reduce reverse causation.

This finding is consistent with small studies of midlife activities which find them associated with better late-life cognition; so for example, in 205 people aged 30–64 years, followed up until 66–88 years, travel, social outings, playing music, art, physical activity, reading, and speaking a second language, were associated with maintaining cognition, independent of education, occupation, late-life activities, and current structural brain health. 41 Similarly, engaging in intellectual activity as adults, particularly problem solving, for 498 people born in 1936, was associated with cognitive ability acquisition, although not the speed of decline. 42

Cognitive decline

The use it or lose it hypothesis suggests that mental activity, in general, might improve cognitive function. People in more cognitively demanding jobs tend to show less cognitive deterioration before, and sometimes after retirement than those in less demanding jobs. 43 , 44 One systematic review of retirement and cognitive decline found conflicting evidence. 45 Subsequently, a 12-year study of 1658 people found older retirement age but not number of years working, was associated with lower dementia risk. 46 Those retiring because of ill health had lower verbal memory and fluency scores than those retiring for other reasons. 47 Another study found a two-fold increase in episodic memory loss attributable to retirement (n=18 575, mean age 66 years), compared to non-retirees, adjusting for health, age, sex, and wealth. 48 Similarly, in a cohort of 3433 people retiring at a mean age of 61 years, verbal memory declined 38% (95% CI 22–60) faster than before retirement. 44 In countries with younger compared to higher retirement ages, average cognitive performance drops more. 49

Cognitive interventions in normal cognition and mild cognitive impairment

A cognitive intervention or cognition-orientated treatment comprises strategies or skills to improve general or specific areas of cognition. 50 Computerised cognitive training programmes have increasingly replaced tasks that were originally paper-and-pencil format with computer-based tasks for practice and training. 51

Three systematic reviews in the general population found no evidence of generalised cognition improvement from specific cognitive interventions, including computerised cognitive training, although the domain trained might improve. 52 , 53 , 54

A meta-analysis of 17 controlled trials of at least 4 hours of computerised cognitive training, (n=351, control n=335) for mild cognitive impairment, found a moderate effect on general cognition post-training (Hedges' g=0·4, 0·2–0·5); 55 however few high quality studies and no long-term high quality evidence about prevention of dementia currently exists. A meta-analysis of 30 trials of computerised, therapy-based and multimodal interventions for mild cognitive impairment found an effect on activities of daily living (d=0·23) and metacognitive outcomes (d=0·30) compared to control. 56 A third systematic review identified five high quality studies, four group-delivered and one by computer, and concluded the evidence for the effects of cognitive training in mild cognitive impairment was insufficient to draw conclusions. 53 A comprehensive, high quality, systematic overview of meta-analyses of cognitive training in healthy older people, those with mild cognitive impairment and those with dementia, found that most were of low standard, were positive and most reached statistical significance but it was unclear whether results were of clinical value because of the poor standard of the studies and heterogeneity of results ( figure 3 ). 51

Pooled results of meta-analyses investigating objective cognitive outcomes of cognition-oriented treatment in older adults with and without cognitive impairment

K represents the number of primary trials included in the analysis. If a review reported several effect sizes within each outcome domain, a composite was created and k denotes the range of the number of primary trials that contributed to the effect estimate. AMSTAR=A MeaSurement Tool to Assess systematic Reviews (max score 16). Adapted from Gavelin et al, 51 by permission of Springer Nature.

In the only randomised controlled trial (RCT) of behavioural activation (221 people) for cognition in amnestic mild cognitive impairment, behavioural activation versus supportive therapy was associated with a decreased 2-year incidence of memory decline (relative risk [RR] 0·12, 0·02–0·74). 57

Hearing impairment

Hearing loss had the highest PAF for dementia in our first report, using a meta-analysis of studies of people with normal baseline cognition and hearing loss present at a threshold of 25 dB, which is the WHO threshold for hearing loss. In the 2017 Commission, we found an RR of 1·9 for dementia in populations followed up over 9–17 years, with the long follow-up times making reverse causation bias unlikely. 2 A subsequent meta-analysis using the same three prospective studies measuring hearing using audiometry at baseline, found an increased risk of dementia (OR 1·3, 95% CI 1·0–1·6) per 10 dB of worsening of hearing loss. 58 A cross-sectional study of 6451 individuals designed to be representative of the US population, with a mean age of 59·4 years, found a decrease in cognition with every 10 dB reduction in hearing, which continued to below the clinical threshold so that subclinical levels of hearing impairment (below 25 dB) were significantly related to lower cognition. 59

Although the aetiology still needs further clarification, a small US prospective cohort study of 194 adults without baseline cognitive impairment, (baseline mean age 54·5 years), and at least two brain MRIs, with a mean of 19 years follow-up, found that midlife hearing impairment measured by audiometry, is associated with steeper temporal lobe volume loss, including in the hippocampus and entorhinal cortex. 60

Hearing aids

A 25-year prospective study of 3777 people aged 65 years or older found increased dementia incidence in those with self-reported hearing problems except in those using hearing aids. 61 Similarly, a cross–sectional study found hearing loss was only associated with worse cognition in those not using hearing aids. 62 A US nationally representative survey of 2040 people older than 50 years, tested every two years for 18 years, found immediate and delayed recall deteriorated less after initiation of hearing aid use, adjusting for other risk factors. 63 Hearing aid use was the largest factor protecting from decline (regression coefficient β for higher episodic memory 1·53; p<0·001) adjusting for protective and harmful factors. The long follow-up times in these prospective studies suggest hearing aid use is protective, rather than the possibility that those developing dementia are less likely to use hearing aids. Hearing loss might result in cognitive decline through reduced cognitive stimulation.

Traumatic brain injury (TBI)

The International Classification of Disease (ICD) defines mild TBI as concussion and severe TBI as skull fracture, oedema, brain injury or bleed. Single, severe TBI is associated in humans, and mouse models, with widespread hyperphosphorylated tau pathology, and mice with APOE ε4 compared to APOE ε3 allele have more hippocampal hyper-phosphorylated tau after TBI. 64 , 65 TBI is usually caused by car, motorcycle, and bicycle injuries; military exposures; boxing, horse riding, and other recreational sports; firearms; and falls. 66 A nationwide Danish cohort study of nearly 3 million people aged 50 years or older, followed for a mean of 10 years, found an increased dementia (HR 1·2, 95% CI 1·2–1·3) and Alzheimer's disease risk (1·2, 1·1–1·2). 67 Dementia risk was highest in the 6 months after TBI (4·1, 3·8–4·3) and increased with number of injuries in people with TBI (one TBI 1·2, 1·2–1·3; ≥5 TBIs 2·8, 2·1–3·8). Risk was higher for TBI than fractures in other body areas (1·3, 1·3–1·3) and remained elevated after excluding those who developed dementia within 2 years after TBI, to reduce reverse causation bias. 67

Similarly, a Swedish cohort of over 3 million people aged 50 years or older, found TBI increased 1-year dementia risk (OR 3·5, 95% CI 3·2–3·8); and risk remained elevated, albeit attenuated over 30 years (1·3, 1·1–1·4). 68 ICD defined single mild TBI increased the risk of dementia less than severe TBI and multiple TBIs increased the risk further (OR 1·6, 95% CI 1·6–1·7 for single TBI; 2·1, 2·0–2·2 for more severe TBI; and 2·8, 2·5–3·2 for multiple TBI). A nested case control study of early onset clinically diagnosed Alzheimer's disease within an established cohort also found TBI was a risk factor, increasing with number and severity. 69 A stronger risk of dementia was found nearer the time of the TBI, leading to some people with early-onset Alzheimer's disease.

Military veterans have a high risk of occupational TBI, and formal record keeping allows long-term follow-up. A study of 178 779 veterans with TBI with propensity-matched veterans without TBI found dementia risk was associated with TBI severity (HR 2·4, 95% CI 2·1–2·7 for mild TBI without loss of consciousness; 2·5, 2·3–2·8 for mild TBI with loss of consciousness; and 3·8, 3·6–3·9 for moderate to severe TBI). 70 Similarly women veterans with TBI had increased risk of dementia compared to those without TBI (1·5, 1·0–2·2). 71

A cohort study of 28 815 older adults with concussion, found the risk of dementia doubled, with 1 in 6 developing dementia over a mean follow-up of 3·9 years, although those taking statins had a 13% reduced risk of dementia compared to those who were statin-free. They suggest future RCTs as statins might mitigate injury-related brain oedema, oxidative stress, amyloid protein aggregation, and neuroinflammation. 72

The term chronic traumatic encephalopathy describes sports head injury, which is not yet fully characterised and covers a broad range of neuropathologies and outcomes, with current views largely conjecture. 73 The evidence has subsequently been strengthened by a study on Scottish former soccer players reporting that they are more likely than controls to have Alzheimer's disease specified on their death certificates (HR 5·1, 95% CI 2·9–8·8) and to have been prescribed any dementia-related medications (OR 4·9, 95% CI 3·8–6·3) but not on medical records. 74 The study controlled for socio-economic class based on residential address, which in footballers might be less linked to level of education.

Hypertension

Persistent midlife hypertension is associated with increased risk of a late life dementia. In the Framingham Offspring cohort comprising 1440 people, elevated systolic blood pressure (≥140 mm Hg in midlife; mean age 55 years) was associated with an increased risk of developing dementia (HR 1·6, 95% CI 1·1–2·4) over an 18 year follow-up period. 12 In this study risk increased further if hypertension persisted into later life (mean age 69 years; HR 2·0, 95% CI 1·3–3·1). In the same cohort, people in late midlife (mean age 62 years) with ideal cardiovascular parameters (current non-smoker, body mass index [BMI] 18·5–25 kg/m 2 , regular physical activity, healthy diet, optimum blood pressure <120/<80 mm Hg, cholesterol, and normal fasting blood glucose) were compared to people with at least one of these risks. 75 Those with ideal cardiovascular parameters had a lower 10-year risk of all-cause dementia (HR 0·8, 95% CI 0·1–1·0), vascular dementia (0·5, 0·3–0·8) and clinically diagnosed Alzheimer's disease (0·8, 0·6–1·0). In a UK cohort study of 8639 civil servants, a single measure of systolic blood pressure of 130 mm Hg or higher at age 50 years but not at age 60 or 70 years was associated with increased risk of dementia (1·4, 1·1–1·7). 13 In those with persistent systolic blood pressure of 130 mm Hg or higher, from mean age 45 to 61 years, dementia risk is increased even if free of cardiovascular disease relative to those without hypertension (1·3, 1·0–1·7).

A further cohort study has provided potential insights into mechanisms, reporting that midlife hypertension, defined as from age 40 years, was associated with reduced brain volumes and increased white matter hyperintensity volume but not amyloid deposition. 76 Of note, blood pressure declines in later life and this decline is associated with and, potentially caused by, dementia development (HR 2·4, 95% CI 1·4–4·2). 12 , 13 , 77

Antihypertensive drugs, aspirin, and statins

The US and Puerto Rico Systolic Blood Pressure Intervention Trial (SPRINT) in 9361 hypertensive adults aged 50 years and older, was stopped early because of significantly fewer cardiovascular events and deaths occurring in the intensive treatment arm (aiming for systolic <120 mm Hg, n=4678) in comparison with standard treatment (systolic <140 mm Hg, n=4683). 78 Cognitive assessment continued after stopping the trial intervention in SPRINT MIND. 79 In the intensive compared with the standard treatment group, there were 7·2 dementia cases as opposed to 8·6 cases/1000 person-years (HR 0·8; 95% CI 0·7–1·0) within on average 2 years from the end of the intervention period and 5 years after baseline. Pre-specified secondary outcomes were also reduced in the intensive arm for mild cognitive impairment (14·6 vs 18·3 cases/1000 person-years; HR 0·8, 95% CI 0·7–1·0), combined mild cognitive impairment or dementia (20·2 vs 24·1 cases/1000 person-years; HR 0·9, 95% CI 0·7–1·0) 79 making this the first trial to suggest reduction of risk for mild cognitive impairment. Those who were lost to follow-up were at greater risk of dementia than those who continued but follow-up rates did not differ according to intervention group. 80

Four meta-analyses of blood pressure medications to lower high blood pressure with six studies overlap have provided combined estimates of effects. All meta-analyses suggest reduced dementia in those in the interventions arms for outcomes of any dementia as well as clinically diagnosed Alzheimer's disease. The first included randomised controlled trials (RCTs) of any drug to lower blood pressure and reported a reduction in risk of around 10% at marginal significance (RR 0·9, 95% CI 0·9–1·0). 81 Meta-regression showed risk lowered more if the achieved systolic pressure differential was larger between the intervention and control group. The second included 15 trials and observational studies of diuretics involving 52 599 people (median age 76 years) with 6·1 years median follow-up (dementia HR 0·8, 95% CI 0·8–0·9 and Alzheimer's disease 0·8, 0·7–0·9). 82 The third included used individual participant data from six observational studies; (dementia 0·9, 0·8–1·0 and Alzheimer's disease 0·8, 0·7–1·0; figure 4 ). 83 The fourth focused on people prescribed calcium channel blocker only, included 10 RCTs and observational studies comprising 75 239 hypertensive older adults (median age 72 years, median follow-up 8·2 years) found lowered dementia risk (RR 0·7, 95% CI 0·6–0·9). 84 A 2019 meta-analysis addressing which class of anti-hypertensive drug to use to lower risk of either incident dementia or cognitive decline, found over 50 000 participants in 27 studies and reported no consistent difference in effect according to which class of drug was used. 85

Associations of antihypertensive medication use with incident dementia in those with high blood pressure

Adapted from Ding et al, 83 by permission of Elsevier.

A Cochrane review reported good evidence that statins given to older people at risk of vascular disease do not prevent cognitive decline or dementia. 86 One RCT found 100 mg aspirin versus placebo in 19 114 healthy adults older than 65 years did not reduce dementia (HR 1·0, 95% CI 0·8–1·2), death, physical disability, or cardiovascular disease over a period of 4·7 years. 87

Physical inactivity, exercise, and fitness

Studies of physical activity are complex. Patterns of physical activity change with age, generation, and morbidity and are different across sex, social class, and cultures. The studies suggest a complicated relationship with the potential for both risk reduction and reverse causation.

Meta-analyses of longitudinal observational studies of 1–21 years duration showed exercise to be associated with reduced risk of dementia. 2 A further overview of systematic reviews concluded that there is convincing evidence for physical activity protecting against clinically diagnosed Alzheimer's disease. 88

Since the 2017 Commission, the HUNT study of 28 916 participants aged 30–60 years has been published, reinforcing the previous literature in this area. At least weekly midlife moderate-to-vigorous physical activity (breaking into a sweat) was associated with reduced dementia risk over a 25-year period of follow-up (HR 0·8, 95% CI 0·6–1·1) but the confidence intervals were wide. 89 In contrast the Whitehall Study reporting on the 28-year follow-up of 10 308 people, found that more than 2·5 hours of self-reported moderate-to-vigorous physical activity per week, lowered dementia risk over 10, but not 28 years. 33 Very long-term studies are unusual; however, one 44-year study recruited 191 women (mean age 50) purposively to be representative of the Swedish population and reported that 32% of the participants with low baseline peak fitness, 25% with medium, and 5% with high fitness developed dementia (high vs medium HR 0·1, 95% CI 0·03–0·5, low vs medium 1·4, 0·7–2·8). 90

An individual-level meta-analysis of 19 observational studies of relatively younger adults included 404 840 participants' data (mean baseline age 45·5 years; mean follow-up duration 14·9 years), reporting an increased incidence of all-cause dementia (HR 1·4, 95% CI 1·2–1·7) and clinically diagnosed Alzheimer's disease (1·4, 1·1–1·7) in those who were physically inactive in the 10-year period before diagnosis. 91 Notably, however, no difference in dementia risk measured 10–15 years before time of dementia incidence was found except in those with comorbid cardio-metabolic disease (RR 1·3, 95% CI 0·8–2·1).

People might stop exercising due to prodromal dementia so inactivity might be either a consequence or a cause or both in dementia and might be more of a risk in those with cardiovascular morbidity. As with other outcomes, exercise might be required to be sustained and continue nearer the time of risk. 92

Trials of exercise

Since the 2017 Commission several meta-analyses and systematic reviews have been published with three high quality meta-analyses which we include. The first included 39 RCTs with an unclear total number of participants examining moderate or vigorous exercise of any frequency lasting 45–60 min per session in cognitively normal adults aged older than 50 years. This analysis reported global cognitive improvements (standard mean difference [SMD]=0·3, 95% CI 0·2–0·4) for moderate or vigorous resistance (13 studies) or aerobic exercise (18 studies) lasting 45–60 min per session with no difference between them but no effect found for yoga. 93 A second meta-analysis of RCTs in people with mild cognitive impairment found global cognition improved in the intervention group (0·3, 0·1–0·5) with aerobic exercise having a higher effect (0·6, 0·5–0·6). 94 This study did not have dementia as an outcome measure. A third meta-analysis of RCTs of longer term exercise found five studies (four lasting 12 months and one 24 months) with 2878 participants with normal baseline cognition. 95 The incidence of dementia was 3·7% (n=949) for exercisers and 6·1% (n=1017) for controls (random effect RR 0·6, 95% CI 0·3–1·1; fixed effect as no evidence of heterogeneity 0·7, 0·4–1·0). The authors concluded that the study showed no significant effect of exercise for reducing dementia, mild cognitive impairment, or clinically significant cognitive decline but was underpowered. WHO guidelines have been published since the 2017 Commission, suggesting specific activity levels drawing on these, and one further systematic review which considered sex differences on the effect of exercise. 96 , 97 It concluded the evidence points towards physical activity having a small, beneficial effect on normal cognition, with a possible effect in mild cognitive impairment, mostly due to aerobic exercise. 97 Evidence about the effect of specific types of exercise, such as progressive muscle resistance training, on dementia risk is scarce.

In the 2017 Commission we reported on diabetes as a risk factor for dementia. Distinguishing between treated and untreated diabetes as a risk factor for dementia is challenging in observational studies. In a pooled meta-analysis from over 2·3 million individuals with type 2 diabetes across 14 cohort studies, including 102 174 with dementia, diabetes was associated with an increased risk of any dementia (RR 1·6, 95% CI 1·5–1·8 for women and 1·6, 1·4–1·8 for men). 98 The risk of dementia increased with the duration and severity of diabetes. The effect of different diabetic medications on cognition or dementia outcomes remains unclear as few studies have investigated this area. 99 However, one meta-analysis of cohort studies of diabetes reported that, cross sectionally, people with diabetes taking metformin had lower prevalence of cognitive impairment (three studies OR 0·6, 95% CI 0·4–0·8) and, longitudinally, reduced dementia incidence (six studies HR 0·8, 95% CI 0·4–0·9) compared with those taking other medications or no medication. 100 However another analysis did not find a protective effect of metformin for incident dementia (three studies, RR 1·1, 95% CI 0·5–2·4) with possible harm with insulin therapy (1·2, 1·1–1·4); but this did not account for severity of diabetes of those with type 2 diabetes on insulin. 99 A Cochrane review reported intensive compared to standard diabetes control trials with 5 year follow up (n=11 140), showing no impact on cognitive decline (1·0, 95% CI 0·9–1·1) or dementia (1·3, 0·9–1·9). 101

Overall type 2 diabetes is a clear risk factor for development of future dementia; however, whether any particular medication ameliorates this risk is unclear. Intensive diabetic control does not decrease the risk of dementia.

Combined cardiovascular risk factors

Studies of individual cardiovascular risk factors usually control for other cardiovascular risks, which cluster in individual people. This does not take into account the combinations and contexts in which risk occurs. A UK study of 7899 people aged 50 years followed up for 25 years, calculated a cardiovascular health score based on four behaviour-related (smoking, diet, physical activity, BMI) and three biological (fasting glucose, blood cholesterol, blood pressure) metrics each coded on a three-point scale (0, 1, 2). 100 A better score was associated with a lower risk of dementia (HR 0·9, 95% CI 0·9–1·0 per 1 point scale increment), for both behaviour-related (HR/1 point increment in subscales 0·9, 95% CI 0·8–0·9) and biological subscales (0·9, 0·8–1·0), maintained in people free of cardiovascular disease over the follow-up (0·9, 95% CI 0·8–1·0). These authors also reported an association of the score on the scale with hippocampal atrophy and total brain volume but not white matter hyperintensities. This finding underlines the importance of clustering of cardiovascular risk factors in midlife, as studies of individual risk factors in this sample had not shown a significant association, when controlling for other individual risks. 33

Excessive alcohol consumption

Heavy drinking is associated with brain changes, cognitive impairment, and dementia, a risk known for centuries. 102 An increasing body of evidence is emerging on alcohol's complex relationship with cognition and dementia outcomes from a variety of sources including detailed cohorts and large-scale record based studies. Alcohol is strongly associated with cultural patterns and other sociocultural and health-related factors, making it particularly challenging to understand the evidence base.

A French 5-year longitudinal study of over 31 million people admitted to hospital, found alcohol use disorders (harmful use or dependence as defined in ICD) were associated with increased dementia risk, calculated separately for men and women (women HR 3·3, 95% CI 3·3–3·4, men 3·4, 3·3–3·4). 103 The relationship of dementia with alcohol use disorders was particularly clear in the earlier onset dementias (age less than 65 years) in which 56·6% had an alcohol use disorder noted in their records (n=57 353; 5·2% all dementias).

A systematic review incorporating 45 studies of light to moderate drinking using a variety of definitions reported a reduced risk of dementia compared with not drinking (RR 0·7; 95% CI 0·6–0·91). 104 Risk was not reported separately for men and women. Drinking less than 21 units of alcohol per week (1 unit of alcohol=10 mL or 8 g pure alcohol) might be associated with a lower risk of dementia. 105 , 106 A 5-year follow-up study of 13 342 men and women volunteers from UK biobank aged 40–73 years who drank, included few heavy drinkers and did not analyse abstainers. 106 The study reported that those who drank more than 12 units per week declined slightly more in reaction time in a perceptual matching task than those who drank less (β2=−0·07, 95% CI −0·09 to −0·04). 106 The UK Whitehall study with 23 years follow-up, included 9087 participants aged 35–55 years at baseline. 107 Drinking more than 21 units per week and long-term abstinence were both associated with a 17% (95% CI 4–32 and 13–23 respectively) increase in dementia compared to drinking less than 14 units. Drinking more than 14 units was also associated with right sided hippocampal atrophy on MRI. 108

Weight control and obesity

Overweight is an emerging concern, given the changing BMI across the world's ageing population. New evidence supports the relationship between increased BMI and dementia from a review of 19 longitudinal studies including 589 649 people aged 35 to 65 years, followed up for up to 42 years. It reported obesity (BMI ≥30; RR 1·3, 95% CI 1·1–1·6) but not being overweight (BMI 25–30; 1·1, 1·0–1·2) was associated with late-life dementia. 109 In a further meta-analysis of individual level data from 1·3 million adults (aged ≥18 years), which included two studies from the meta-analysis cited above, 109 higher body mass measured before probable preclinical and prodromal dementia was associated with increased dementia risk (RR 1·3, 1·1–1·7/5-unit increase in BMI). 11

Weight loss in midlife and dementia risk

A meta-analysis of seven RCTs (468 participants) and 13 longitudinal studies (551 participants) of overweight and obese adults without dementia, mean age 50 years, found weight loss of 2 kg or more in people with BMI greater than 25 was associated with a significant improvement in attention and memory. All but one of the studies included participants aged younger than 65 years. The RCTs reported memory improvement over 8–48 weeks (SMD=0·4, 95% CI 0·2–0·6) and short-term longitudinal studies found improvement over a median of 24 weeks (SMD=0·7, 95% CI 0·5–0·8); however, data about the long-term effects or the effect of weight loss in preventing dementia are absent. 110

Smokers are at higher risk of dementia than non-smokers, 2 and at a higher risk of premature death before the age at which they might have developed dementia, introducing some bias and uncertainty in the association between smoking and risk of dementia. 111 , 112 Stopping smoking, even when older, reduces this risk. Among 50 000 men aged older than 60 years, stopping smoking for more than 4 years, compared to continuing, substantially reduced dementia risk over the subsequent 8 years (HR 0·9; 95% CI 0·7–1·0). 113 Worldwide, 35% of non-smoking adults and 40% of children are estimated to be exposed to second-hand smoke; 114 although literature on the impact of this exposure and dementia risk is scarce. One study indicated that in women aged 55–64 years, second-hand smoke exposure was associated with more memory deterioration and the risk increased with exposure duration even after controlling for other confounding factors. 115

Depression is associated with dementia incidence, with a variety of possible psychological or physiological mechanisms. It is also part of the prodrome and early stages of dementia. Reverse causation is possible whereby depressive symptoms result from dementia neuropathology that occurs years before clinical dementia onset. These explanations are not mutually exclusive. As in diabetes, few studies considering depression as a risk factor for dementia have distinguished between treated and untreated depression. In a meta-analysis of 32 studies, with 62 598 participants, with follow-up from 2 to 17 years, a depressive episode was a risk factor for dementia (pooled effect size 2·0, 95% CI 1·7–2·3). 116 Meta-regression analysis revealed a non-significant trend for the association between depression and incident dementia to be weaker when the length of follow-up was longer. The Norwegian HUNT study, suggested that symptoms of psychological distress predicted dementia 25 years later however with wide bounds of uncertainty (HR 1·3, 95% CI 1·0–1·7). 89 Two further studies differentiate between late-life and earlier life depressive symptoms. The UK Whitehall study, in a follow-up of 10 189 people, reports that in late life these symptoms increase dementia risk but not at younger ages (follow-up 11 years HR 1·7; 95% CI 1·2–2·4; follow-up 22 years 1·0, 0·7–1·4). 34 , 117 A 14-year longitudinal study of 4922 initially cognitively healthy men, aged 71–89 years, found depression was associated with 1·5 (95% CI 1·2- 2·0) times the incidence of dementia but this association was accounted for by people developing dementia within 5 years of depression. 118 The use of antidepressants did not decrease this risk.

A study of 755 people with mild cognitive impairment and with a history of depression from the Australian longitudinal Alzheimer's Disease Neuroimaging Initiative, considered the effect of selective serotonin-reuptake inhibitor (SSRI) treatment, such as citalopram, known to reduce amyloid plaque generation and plaque formation in animal models. 119 The study found that more than 4 years of such treatment was associated with delayed progression to clinically diagnosed Alzheimer's disease. People treated with antidepressants seem likely to differ from those who are not treated. Thus, the question of whether antidepressant treatment mitigates dementia risk remains open.

Social contact

Social contact, now an accepted protective factor, enhances cognitive reserve or encourages beneficial behaviours, although isolation might also occur as part of the dementia prodrome. Several studies suggest that less social contact increases the risk of dementia. Although most people in mid and later life are married, by the time they reach older age, disproportionate numbers of women are widowed as they outlive their husbands, thus reducing their social contact. In these generations, marital status is therefore an important contributor to social engagement. Additionally, most marriages are in the relatively young, and married people usually have more interpersonal contact than do single people—this gives a long-term estimate of the effect of social contact. A systematic review and meta-analysis including 812 047 people worldwide found dementia risk to be elevated in lifelong single (RR 1·4, 95% CI 1·1–1·9) and widowed people (1·2, 1·0–1·4), compared with married people and the association was consistent in different sociocultural settings. 120 Studies adjusted for sex and we do not know if a differential risk between men and women exists. Differences persisted in studies that adjusted for education and physical health so might be attributable to married people having more social contact, rather than solely because they tend to have better physical health and more education, although residual confounding is possible. A systematic review and meta-analysis of 51 longitudinal cohort studies of social isolation and cognition included 102 035 participants aged 50 or more years at baseline, with follow-up of 2–21 years. 121 High social contact (measured through either or both of social activity and social network) was associated with better late-life cognitive function (r=0·05, 95% CI: 0·04–0·065) and no differences according to sex or length of time followed up.

A new meta-analysis found that in long-term studies (≥10 years), good social engagement was modestly protective (n=8876, RR=0·9, 95% CI 0·8–1·0); but loneliness was not associated with dementia risk. 122 No long term (>10 years) studies of loneliness and dementia outcomes have been done.

A UK 28-year follow-up study of 10 308 people found that more frequent social contact at age 60 years was associated with lower dementia risk over 15 years of follow-up (HR for one standard deviation social contact frequency 0·9, 95% CI 0·8–1·0). This finding suggests more frequent social contact during late middle age is associated with a modest reduction in dementia risk, independent of socio-economic and other lifestyle factors. 123 A Japanese longitudinal cohort study of 13 984 adults aged older than 65 years with a mean of 10 years follow-up calculated a five-point social contact scale based on: marital status; exchanging support with family members; having contact with friends; participating in community groups; and engaging in paid work. It found the score to be linearly associated with reduced dementia risk; those who scored highest on the five-point scale were 46% less likely to develop incident dementia compared with those in the lowest category. 124

Despite clear cultural variation in the meaning and perception of social isolation, findings of protective effect of more social contact are largely consistent in different settings and for either sex across the studies and meta-analyses. 118 , 120 , 121

Social interventions

Little evidence of the effects of social interventions on dementia exists but a systematic review of low quality RCTs of 576 adults aged 60 or more years with normal cognition found facilitated meeting and discussion groups were associated with improved global cognition and increased brain volume at follow-up. 118

Air pollutants

Air pollution and particulate pollutants are associated with poor health outcomes, including those related to non-communicable diseases. Attention has turned to their potential effect on the brain. Animal models suggest airborne particulate pollutants accelerate neurodegenerative processes through cerebrovascular and cardiovascular disease, Aβ deposition, and amyloid precursor protein processing. 125 , 126 Although the higher levels of dementia from air pollutants are still subject to the potential for residual confounding, the effects on animal models are evidence of physiological effects over and above those driven by life-course deprivation.

High nitrogen dioxide (NO 2 ) concentration (>41·5 μg/m 3 ; adjusted HR 1·2, 95% CI 1·0–1·3), fine ambient particulate matter (PM) 2·5 from traffic exhaust (1·1, 1·0–1·2) 127 , 128 , 129 and PM 2·5 from residential wood burning (HR=1·6, 95% CI 1·0–2·4 for a 1 μg/m 3 increase) are associated with increased dementia incidence. Traffic often produces NO 2 and PM 2·5 and it is hard to separate their effects, although evidence for additive effects of different pollutants exists. 127 , 128 , 129 A systematic review of studies until 2018 including 13 longitudinal studies with 1–15 years follow-up of air pollutants exposure and incident dementia, found exposure to PM 2·5, NO 2 , and carbon monoxide were all associated with increased dementia risk. 24 The attributable burden of dementia and excess death from PM 2·5 in one large 10-year US study was particularly high in Black or African American individuals and socio-economically disadvantaged communities and related to particulate PM 2·5 concentrations above the US guidelines. 130

Mechanisms by which sleep might affect dementia remain unclear, but sleep disturbance has been linked with β-amyloid (Aβ) deposition, 131 , 132 reduced glymphatic clearance pathways activation, 133 low grade inflammation, increased Tau, hypoxia 132 , 134 and cardiovascular disease. 135 Sleep disturbance is hypothesised to increase inflammation which raises Aβ burden, leading to Alzheimer's disease and further sleep disturbance. 136

Two meta-analyses showed similar findings. The first was a synthesis of longitudinal studies with an average of 9·5 years follow-up and the second reported cross-sectional and prospective cohort studies of mixed quality with different methods of measuring sleep. Sleep disturbances were defined broadly, often self-reported and including short and long sleep duration, poor sleep quality, circadian rhythm abnormality, insomnia, and obstructive sleep apnoea. All these disturbances were associated with a higher risk of all-cause dementia (RR 1·2; 95% CI 1·1–1·3) 137 and clinically diagnosed Alzheimer's disease (1·6, 1·3–1·9) compared with no sleep disturbance, although not all cohort studies excluded those with cognitive impairment or dementia at baseline from their analyses. 138 A U-shaped association has been reported between sleep duration and risk of mild cognitive impairment or dementia with higher risks of dementia with less than 5 hours (HR=2·6; 95% CI 1·4–5·1) compared with more than 5 and less than 7 and more than 10 hours sleep (2·2, 1·4–3·5) and risks for all-cause dementia and clinically diagnosed Alzheimer's disease being similar. 135 , 139 , 140 , 141

The postulated mechanisms of reduced sleep leading to accumulation of Alzheimer's type pathology is inconsistent with the evidence that both more sleep and less sleep are associated with increased risk of dementia. New onset late-life sleep disturbance, a few years before clinical dementia, might be part of the natural history of the dementia syndrome, appearing to be a risk factor, or reflect other disorders, for example, mood disturbances or cardiovascular disease. 135 , 142 Hypnotic use might increase risks although this is unclear and a 2018 study 139 suggests that findings of a connection were related to reverse causality and confounders. 143 When benzodiazepine use was considered, in one study, sleep length was no longer significant 139 but not in all studies. 135 Those taking hypnotics were at greater risk of dementia than those who did not regardless of sleep duration. 139 Medication for sleep disturbance might be harmful and benzodiazepines are associated with falls, hospital admissions, and possibly dementia. 139 , 144

Nutrition and dietary components are challenging to research with controversies still raging around the role of many micronutrients and health outcomes in dementia. Observational studies have focused on individual components ranging from folate and B vitamins, Vitamin C, D, E, and selenium amongst others as potential protective factors. 88 There has been a move towards considering the evidence base for whole diets in the last 5 years, particularly high plant intake such as in the Mediterranean diet (high intake of vegetables, legumes, fruits, nuts, cereals, and olive oil; low intake of saturated lipids and meat) or the similar Nordic diet, rather than individual nutrients, which might reduce cognitive decline and dementia. 145 One example is a longitudinal cohort study of 960 participants, ages 58–99 years, in which those reporting the highest intake of green leafy vegetables, equivalent to 1·3 servings per day, had less cognitive decline over 4·7 years than those reporting the lowest intake (β=0·05 standardised units 95% CI 0·02–0·07). 146 The authors report this difference as being equivalent to being 11 years younger. A further prospective cohort study with three midlife dietary assessments in 8255 people, followed up for a mean of nearly 25 years, found neither healthy dietary pattern nor Mediterranean diet protected from dementia, except in those with cardiovascular disease, suggesting that diet might influence dementia risk by protecting from the excess risk of cardiovascular risk factors. 147

Dietary interventions

As well as whole diets, there has been some interest in multi-nutrient interventions. A systematic review and a Cochrane review including RCTs of supplements (A, B, C, D, and E; calcium, zinc, copper, and multivitamins trials, n-3 fatty acids, antioxidant vitamins, and herbs) found a lack of evidence for supplement use to preserve cognitive function or prevent dementia in middle-aged (45–64 years) or older people (aged 65 years and older). 148 , 149 Cochrane reviews found no evidence for beneficial effects on cognition of those with mild cognitive impairment of supplementation with B vitamins for 6 to 24 months 150 or with vitamin E in preventing progression from mild cognitive impairment to dementia. 151 A 24-month RCT of 311 people of a multi-nutrient drink containing docosahexaenoic acid, vitamins B12, B6, folic acid, and other nutrients; found no significant effect on preventing cognitive deterioration in prodromal Alzheimer's disease. 152 The authors comment that the control group's cognitive decline was much lower than expected, leading to an inadequately powered trial.

Meta-analysis of two RCTs with 471 participants with normal cognition found the Mediterranean diet improved global cognition compared to controls (SMD 0·2, 95% CI 0·0–0·4). 153 A further meta-analysis identified five RCTs (n=1888) with a weak effect on global cognition (SMD 0·2, 95% Cl 0·0–0·5) 154 but no benefit of Mediterranean diet for incident cognitive impairment or dementia.

The WHO guidelines recommend a Mediterranean diet to reduce the risk of cognitive decline or dementia, as it might help and does not harm, but conclude Vitamins B and E, polyunsaturated fatty acid, and multicomplex supplementation should not be recommended. 97

Trials of combination strategies to prevent dementia

The FINGER RCT was a 2-year multidomain intervention to prevent cognitive decline and dementia in 1260 people with cardiovascular risk factors aged 60–77 years, recruited from a Finnish national survey. Similar multidomain studies were discussed in the 2017 Commission. 2 FINGER found a small group reduction in cognitive decline in the intervention group compared with control (comprehensive neuropsychological test battery Z score 0·02, 95% Cl 0·00–0·04) regardless of baseline sociodemographic, socio-economic, cognitive, or cardiovascular status. 155 However, in a subgroup analysis, greater beneficial effects were observed on processing speed in individuals with higher baseline cortical thickness in Alzheimer's disease areas. 156

The Healthy Ageing Through Internet Counselling in the Elderly (HATICE) study recruited 2724 older people (≥65 years) in the Netherlands, Finland, and France with two or more cardiovascular risk factors. 157 , 158 It compared an interactive internet platform plus remote support by a coach, aiming to improve self-management of vascular risk factors, with a non-interactive control platform with basic health information. A small improvement in the cardiovascular risk composite primary outcome was observed in the intervention group compared with the control group at 18 months, mainly through weight loss, and the dementia risk score was slightly lower in those who received the intervention (mean difference −0·15, 95% CI −0·3 to −0·0). A larger effect was observed in the younger age group (65–70 years) and those with the lowest level of education, who had a higher baseline risk, suggesting that targeting high-risk populations might be more effective. Several multidomain preventive trials are ongoing—for example, World Wide FINGERS .

Total PAF calculation

We incorporated excessive alcohol consumption, TBI, and air pollution into our life-course model of dementia, as well as the original nine risk factors, because of the updated evidence. To calculate new RRs for excessive alcohol consumption, TBI and air pollution, we systematically reviewed the literature and did new meta-analyses for excessive alcohol consumption and TBI. For the other nine factors, we used values for RR and risk factors prevalence from our previous analysis and calculated communality using the same method as in the 2017 Commission. 2

PAF calculation

We used a representative sample of over 10 000 UK community-dwelling adults, to calculate communality (clustering of risk factors) of 11 risk factors for which data existed, 159 to allow calculation of each factor's unique risk. As we could find no datasets measuring TBI, with the other 11 risk factors of interest, we could not calculate its communality. We therefore used the mean of the other 11 communalities to calculate a weighted PAF, so we could include TBI. We used cohabitation as a proxy measure for social contact, and urbanicity for air pollution exposure. Our analysis found four principal components, explaining 55% of the total variance between the eleven risk factors, suggesting substantial overlap. The appendix (p 2) shows the PAF formula and the steps in calculating communality and we detail our new meta-analyses next, which we used to update the figure and perform our new calculations.

Incorporation of the new chosen risks in new systematic reviews

We searched, from inception to Oct 29, 2019, Embase, Allied, and Complementary Medicine, MEDLINE, and PsycINFO terms “dementia” OR “dement*” OR “AD” OR “VaD”, “Alzheimer*” AND “alcohol” OR “ethanol” OR “alcohol*” OR “drink*” OR “drunk*” to update an earlier review. 160 We used inclusion criteria: original population-based cohort studies measuring drinking during midlife, as alcohol intake tends to fall with age; 161 alcohol consumption quantified at baseline by units or number of drinks (one drink, 1·5 units) per week; and all-cause dementia ascertained at follow-up using validated clinical measures. We contacted authors for additional data. 162 Three studies met our inclusion criteria. 107 , 162 , 163 We converted HRs to RRs 164 and used raw data 162 to calculate RR, 165 for our random effects meta-analysis using Generic Inverse Variance Methods. The RR associated with drinking—more than 21 units (168 g) of alcohol weekly—compared with lighter drinking was 1·18 (95% Cl 1·06–1·31; figure 5 ). We used Health Survey England figures for heavier drinking prevalence to calculate PAF as we could not find a worldwide estimate. The weighted PAF was 0·8.

Meta-analysis of relative risk of dementia associated with drinking more than 21 units of alcohol per week in midlife compared to lighter consumption of alcohol

To estimate the RR of TBI of all severities for all cause dementia, we searched Embase, Medline, and PsycINFO from Jan 1, 2016, to Oct 21, 2019, updating an earlier search, 166 using terms (“traumatic brain injury” or “head injury” or “brain injury” or TBI) AND (neurodegeneration or “cognitive dysfunction” or dementia or “Alzheimer's disease” or “Parkinson's disease” or “frontotemporal dementia”). We converted HR figures to RR. 164 , 167 We used inclusion criteria: original population-based cohort studies, baseline TBI of all severities reported, and all-cause dementia ascertained at follow-up using validated clinical measures. We combined four new studies meeting inclusion criteria 67 , 68 , 71 , 168 with the four studies meeting criteria from the original review in a random effects meta-analysis. 166 The pooled RR was 1·84 (95% CI 1·54–2·20) for all cause dementia from all severities of TBI ( figure 6 ) although there was heterogeneity in study-specific estimates, possibly because of different populations. We used the TBI adult population prevalence of 12·1% from a meta-analysis to calculate PAF. 173 The weighted PAF was 3·4.

Meta-analysis of relative risk of all-cause dementia associated with all severity midlife traumatic brain injury

A 2019 systematic review synthesised observational studies, finding consistently increased risk of dementia from air pollution, but heterogeneous comparator groups precluded meta-analysis. 24 We updated the search, using the same search terms and searching MEDLINE, Embase, and PsycINFO from Sept 20, 2018, (the end date of the last search) to Oct 22, 2019. We included longitudinal studies with assessment of all cause air pollution exposure; use of formal assessment of cognitive function at baseline; report of incident all-cause dementia, data from adults (age ≥18 years); and a minimum follow-up of 6 months. As meta-analysis was not possible, we used data from the only study of all-cause air pollution with the outcome of all-cause dementia, with low-moderate risk of bias. This population-based, observational cohort was from Canada, where pollutant concentrations are among the lowest in the world and examined 2 066 639 people, with a mean baseline age of 67 years. 174 We calculated the RR of dementia for those in the three highest quartiles compared to the lowest was 1·09 (1·07–1·11). The attributable fraction for exposure to the highest three quartiles versus the lowest quartile of PM 2·5 and NO 2 was 6·1% (4·8–7·5). The weighted PAF was 2·3.

Table 1 displays the prevalence, communality, relative risk, unweighted and weighted PAFs adjusted for communality. Figure 7 shows the updated life-course model of potentially modifiable risk factors for dementia, including the three new risk factors.

Population attributable fraction of potentially modifiable risk factors for dementia

Strengths and limitations

This Commission is the most comprehensive analysis to date and updates the 2017 Commission with emerging risk factor evidence convincing enough to calculate PAF for potentially reversible risk factors. We reviewed the literature systematically for the chosen risk factors and provided illustrative new literature to update our synthesis and identify data to calculate communality. We find a hopeful picture with an estimate of around 40% of all cases of dementia being associated with 12 potentially modifiable risk factors.

We have made assumptions to calculate this new model. We used global figures for dementia risk although we know the risk factors prevalence varies between countries and most global research is from HIC, so LMIC are under-represented because of lack of data. We have assumed a causal relationship between risk factors and dementia, although we have been cautious and not included risk factors with less good evidence. No single database exists with all 12 risk factors together, but we found 11 of the factors in a UK database and used the mean figure for communality calculations for TBI. We calculated communality for the other 11. We do not know how far findings of communality in other geographical populations might differ, or in those with a differing distribution of age groups or sex. We found that social isolation was not explicitly measured and had to use proxies, such as cohabitation when considering prevalence, which are approximate.

Specifically, evidence for the association of alcohol misuse with dementia comes from HIC and future studies from LMIC are needed to complete the picture. Exposure to air pollution changes over a lifetime and is inextricably linked to poverty and deprivation. However, the effects on animal models suggests specific physiological effects over and above those driven by life-course deprivation. We also considered the overlap with education for this and other risk factors and the correction for education, strongly inversely linked to deprivation, will address at least some of the confounding. However, the results in one study which reported the effect of air pollution on incident dementia showed very little difference in estimates before and after adjustment for education and other risk factors, suggesting little residual confounding exists. 174 We were also unable to meta-analyse data on pollution and thus unlike the other relative risks, the figure comes from only one study, from an area of low pollution so is likely to be an underestimate.

The longitudinal evidence linking potentially modifiable risk factors to dementia generally fulfils causality criteria in observational data (strength, consistency, biological plausibility, temporality, dose–response, coherence, and quasi-experimental studies, for example, more education or using hearing aids). When measuring a risk nearer to the age of dementia onset, then it is more likely that prodromal change affects, or even causes it. Alternatively, a risk factor might act on preclinical pathology or even cause dementia near the time of exposure. Thus, excessive alcohol, and TBI are particularly important in young-onset dementia, although many early onset dementias relate to genetic risks. Risk factors might also matter more at a time of higher biological vulnerability, which the studies we have drawn on cannot establish. The length of exposure required for risk or protection effect, and their inter-relationships as they change across life is unclear—it seems probable that longer or more intense exposure has stronger effects. Additionally, as our communality figures show, risk factors overlap. We cannot establish from these data if having multiple risk factors has an additive or synergistic effect. Association does not prove causation, however, as already noted, the reductions in prevalence and incidence in several HIC suggests that at least some of the risk factors estimated here do have a causal relationship with the clinical expression of dementia.

Key points and recommendations

We judge that sufficient new evidence supports adding three additional modifiable risk factors for dementia to our 2017 Commission model (excessive alcohol, traumatic brain injury, and air pollution). We have been able to add updated evidence on the nine risk factors implicated in the 2017 Commission (education, hypertension, hearing impairment, smoking, obesity, depression, inactivity, diabetes, and social contact). Reduction of these risk factors might be protective for people with or without a genetic risk, although study findings have not been entirely consistent. 175 , 176 , 177 , 178 As we noted in the 2017 Commission, others have previously calculated an estimate of the risk associated with APOε4 at 7% taking into account some other risk factors and this estimate highlights how relatively important potentially modifiable risk factors are in dementia. 2 , 179

For some risk factors, the pattern of risk and the individual's other health, both physical and mental, might be especially important. Currently, the evidence suggests a Mediterranean or Scandinavian diet might have value in preventing cognitive decline in people with intact cognition, particularly as one component of a healthy lifestyle, although how long the exposure has to be or during which ages is unclear. We do not recommend taking additional vitamins, oils, or mixed dietary supplements as a means of preventing dementia as extensive testing in trials has not led to signals of beneficial effects.

Data from RCTs on interventions to prevent cognitive decline, all-cause dementia, or Alzheimer's disease are few. For some key life influences, only observational data, particularly related to natural experiments such as changing the statutory education age, are possible. These influences should be investigated systematically wherever possible. Others can theoretically be investigated but the long follow-up required for midlife risk and protective factors and non-random attrition in longer studies are challenging. Using intermediate endpoints, such as cognition, and dementia onset in research remains uncertain because no intermediate markers with such a close relationship to dementia outcomes exist that it would be possible to predict with certainty for any given individual, age, and sex. Overall, the evidence for treating hypertension is strongest and high blood pressure throughout midlife increases the risk of dementia even without stroke.

Although a need for more evidence is apparent, recommendations should not wait, as clear indications of ways to reduce the chances of developing dementia without causing harm will also lead to other health and wellbeing benefits.

Our recommended strategies for dementia risk reduction include both population-wide and targeted interventions ( panel ). It is important to remember that more socially disadvantaged groups, including Black, Asian, and minority ethnic groups, are particularly at risk.

Recommended strategies for dementia risk reduction

Risks are particularly high in more socially disadvantaged populations including in Black, Asian, and minority ethnic groups.

Population-wide

• • Prioritise childhood education for all, worldwide
• • Implement social public health policies that reduce hypertension risk in the entire population
• • Develop policies that encourage social, cognitive, and physical activity across the life course for all (with no evidence for any specific activities being more protective)
• • Scrutinise the risks for hearing loss throughout the life course, to reduce the risk of exposure to this risk factor
• • Reduce the risk of serious brain trauma in relevant settings, including occupational and transport
• • National and international policies to reduce population exposure to air pollution
• • Continue to strengthen national and international efforts to reduce exposure to smoking, both for children and adults, and to reduce uptake and encourage cessation

Targeted on individuals

• • Treat hypertension and aim for SBP <130 mm Hg in midlife
• • Use hearing aids for hearing loss; we need to help people wear hearing aids as many find them unacceptable, too difficult to use, or ineffective
• • Avoid or discourage drinking 21 or more units of alcohol per week
• • Prevent head trauma where an individual is at high risk
• • Stopping smoking is beneficial regardless of age
• • Reduce obesity and the linked condition of diabetes by healthy food availability and an environment to increase movement
• • Sustain midlife, and possibly late-life physical activity

Although we have more to learn about effectiveness, avoiding or delaying even a proportion of potentially modifiable dementias should be a national priority for all.

Interventions and care in dementia

Not all dementia will be preventable and we present the latest evidence on intervention and care for dementia. To date the emphasis has been on specific subtypes of dementia, most notably on Alzheimer's disease, which has been conceptualised over the years in a variety of changing diagnostic criteria—eg, DSM IV and DSM V. 180 , 181 Intense efforts have been put into biomarkers for early preclinical detection of the disease process before it becomes dementia. Biomarkers need to show reliability and validity, and for dementias they also need to be very closely and clearly related to clinical syndrome outcomes in the way that, for example, human papillomavirus is for cervical cancer, and hypertension has been for stroke.

Biomarkers and detection of Alzheimer's disease

Markers of neurodegeneration linked to clinical dementia include brain volume loss—ie, hippocampal volume loss and entorhinal cortex and medial temporal cortical thinning—seen in structural imaging. The most studied molecular markers are in Alzheimer's disease and are amyloid and tau, which PET and CSF detect clinically. The prevalence of particular pathologies at different ages is important in interpretation of such studies. So, for example, population derived studies show increases in plaques in the population from less than 3% at age 50–59 years to around 40% at age 80–89 years. 182

Amyloid imaging

Amyloid imaging detects amyloid in the brain with high sensitivity and specificity in both cognitively normal and people with Alzheimer's disease when the gold-standard comparison is either neuropathology or clinical diagnosis, distinguishing Alzheimer's disease from other neurodegenerative conditions. 183 Amyloid imaging is not a diagnostic test for dementia. A US study of randomly selected older people from the community recruited 1671 people (mean age of 71 years). 182 The prevalence of PET detected amyloid positivity increased from 2·7% (95% CI 0·5–4·9) of people without cognitive impairment aged 50–59 years to 41·3% (95% CI 33·4–49·2%) aged 80–89 years. 182 In 10-year follow-up PET positivity was associated with a higher probability of developing Alzheimer's disease compared with those who were amyloid negative (HR 2·6, 95% CI 1·4–4·9). In participants with mild cognitive impairment who were amyloid positive the probability (HR 1·9, 95% CI 0·9–3·9) was not very different to those who were amyloid negative (1·6, 0·8–3·4).

Similarly, an 8-year follow-up study of 599 volunteers (average age 70 years) in Australia found that cognitively normal PET amyloid-positive people had an elevated risk of developing Alzheimer's disease compared with amyloid negative (17·7% vs 8·1%; OR 2·4, 95% CI 1·5–4·0). 184 Over 80% of the 266 people who were PET amyloid-positive did not go onto develop a cognitive impairment within 8 years, showing positive status does not predict impairment for most people in a timeframe that might be a useful prognostic window. Follow-up at 5 years of amyloid-positive participants with normal cognition or mild cognitive impairment versus amyloid negative people found the same pattern of increased risk (2·6, 1·4–4·9). Risk also increases per 1 year of age (HR 1·05, 95% CI 0·55–2·0/year), and APOEε4 status (2·6, 1·4–5·0). 184

Most people who are amyloid positive with no other markers have not developed Alzheimer's disease dementia during their lifetime. A model of lifetime risks of people who are amyloid positive without any other biomarkers finds it to be 8·4% for a 90-year-old woman who is cognitively normal at baseline, 23·5% for a 75-year-old woman and 29·3% for a 65-year-old woman. 185 The 10-year risk is considerably less, so a 65-year-old woman with only amyloid biomarkers but who is cognitively normal and has no neurodegeneration has a 10-year Alzheimer's disease risk of 2·5% and a man 2·3%, but the risk is higher with accompanying neurodegeneration ( table 2 ). 185

Ten-year risks by age of developing Alzheimer's disease for women based on amyloidosis alone and in the presence of neurodegeneration and mild cognitive impairment

Data are relative risk (95% CI) or %. Reproduced from Brookmeyer and Abdalla 185 by permission of Elsevier.

Overall, the knowledge of PET-measured amyloid and tau status and MRI-derived cortical thickness in a general population derived sample, only adds a small improvement, which might not be clinically important for predicting memory decline over a model with clinical and genetic variables. 186

Using amyloid PET in patients with cognitive impairment of uncertain causes, results in changes to the clinical diagnosis of Alzheimer's disease 187 and sometimes to medication prescription. We do not know whether PET use improves patient care or decreases care costs. Many people have a mixed cause of dementia and a positive result does not indicate only Alzheimer's disease.

Fluid biomarkers

PET imaging is very costly (US$3000 in the USA) and although used in some clinical settings remains the topic of research to understand its usefulness in broader populations. Fluid biomarkers—ie, blood and cerebrospinal fluid tests—have become a more practical focus of interest since it has become possible to measure specific proteins linked to the proteins associated with the neuropathologies of Alzheimer's disease. 188 A composite blood biomarker for amyloid tested in a discovery dataset and then a validation cohort of participants aged 60–90 years who were already taking part in studies in Japan or Australia had areas under the receiver operating characteristic curves of 96·7% for discovery and 94·1% for validation. The blood biomarker had sensitivity and specificity above 80% against amyloid PET measurement 188 and correlated with CSF concentrations of Aβ1–42. These results are similar to other amyloid blood biomarkers 189 , 190 and harmonisation to a common reference standard is now vital. Although CSF Aβ1–42/1–40 ratio and amyloid PET are now considered interchangeable, 191 CSF tau biomarkers have only correlated weakly with brain tau as currently measured by radioligands. 192 Neurofilament light protein is measured in many cohorts; however, it is non-specific. People with Huntington's disease, multiple sclerosis, mild cognitive impairment, and Alzheimer's disease might have raised blood neurofilament light concentrations, which are a marker of neurodegeneration. 193 , 194 , 195

Key points and conclusions

To be useful in clinical practice biomarkers must be well understood in the populations to which they are going to be applied, including the effects of age and sex on results. There is now reasonable evidence that amyloid and tau measured by PET or in fluid indicate increased risk for development of cognitive impairment in older adults but at the individual level prognostication is not possible as most cognitively normal people with these markers do not develop dementia within a clinically relevant timeframe. Negative amyloid results can be useful for ruling out current Alzheimer's pathology in people with cognitive impairment when the cause is uncertain and show an individual is unlikely to develop Alzheimer's disease during the next few years. High neurofilament light concentrations indicate a neurodegenerative process but not its cause. The value of biomarkers, in terms of diagnostic value, has not been addressed in different representative populations and particularly not in those from LMIC. The potential advantages of blood biomarkers are their low cost and their wider acceptability and applicability in many settings. In many areas of medicine more reliable diagnostic tests have improved research, including epidemiological and public health research and trials, to help distinguish cause from symptom (tuberculosis from a fever) or assess risk factor and disease (hypercholesterolaemia and ischaemic heart disease). Those biomarkers developed for the underlying biology of the dementia syndrome are subject to the same assessment of value.

Principles of intervention in people with dementia

In the 2017 Commission, we discussed that when concerns are raised by patients or family, an accurate diagnosis is helpful. Such a diagnosis provides a gateway to intervention and services where available, for planning for possible futures, and support for family, as well as to research. Unfortunately, these services are not always available. National plans for dementia support timely diagnosis and offer help to individuals and their families.

We did not address screening of those not presenting with concerns but rigorous systematic reviews by the US Task Force on Prevention have found an absence of evidence of benefit and harm. 196 The first trial of population screening took place in the USA, screening 4005 primary care patients aged 65 years or older. No clear benefit or harm in terms of quality of life, mood, or increasing diagnostic rates was found. 197 Other strategies might become more valuable in time such as sensitive awareness of risk factors, when routine records suggest an individual might be deteriorating cognitively. 198

People with dementia have complex problems with symptoms in many domains. Those providing support and any interventions must consider the person as a whole, as well as their context and their close carers, whether family or friends. Individuals' medical, cognitive, psychological, environmental, cultural, and social needs must be given consideration. 2 In the context of under provision of services, this notion is and will continue to be a challenge. Dementia, as an illness which affects cognition by definition, affects the ability to organise activities and people with dementia often need help to do what they enjoy—for example, listen to music, or go to gardens and parks. Wellbeing is one of the goals of dementia care.

Interventions once a diagnosis has been made

Cholinesterase inhibitors have a useful, modest role in improving cognition and activities of daily living in patients with mild-to-moderate Alzheimer's disease and memantine can be prescribed in combination or each drug used separately for moderate and severe Alzheimer's disease. 2 , 199 , 200 However, although available in most countries these drugs are no longer remunerated in France because it is felt that they offer only a small benefit while shifting clinician's attention from other interventions. Whether non-prescribing of this drug will help patients by removing an intervention with known benefit or be detrimental to them is unknown. 201 No advances have been reported in Aβ therapeutics, with negative results from phase 3 trials of monoclonal antibodies (eg, solanezumab, crenezumab) and inhibitors of β-secretase, a protease involved in the production of Aβ peptides. 202 Aducanumab previously abandoned as futile now has further unpublished results. Three 5HT6 antagonists and the calcium channel blocker nilvadipine 203 , 204 have also been ineffective. These drugs also show substantial impact during treatments at so-called therapeutic concentrations on the leakiness of blood vessels. The long-term impact of such side-effects is unknown. Anti-tau, anti-amyloid, and anti-inflammatory drugs continue to be in focus and some argue that pre-symptomatic interventions are necessary, especially if targeting Aβ production, but no evidence of efficacy 205 and some evidence of worsening target symptoms currently exists. 206

Cognitive training in people with dementia

A meta-analysis of 12 controlled trials of 389 people with mild dementia, completing 4 or more hours of group-based computerised cognitive training (mean age 66–81 years, 63·5% female participants), found a small, statistically significant beneficial effect on overall cognition, driven by two trials of virtual reality or Video games (SMD=0·3, 95% CI 0·0–0·5), one with a low and one with a high risk of bias. 55

A Cochrane review 207 found 33 trials of cognitive training, only one of which overlapped with the study above, with around 2000 participants with mild-to-moderate dementia, most with a high or uncertain risk of bias. 207 People completing cognitive training, compared with usual treatment or non-specific activities, had small-to-moderate effects on overall cognition (SMD 0·4, 95% CI 0·2–0·6) and specific cognitive abilities such as verbal fluency and improvements lasted for a few months to 1 year. No direct evidence was observed to suggest that cognitive training was better than cognitive stimulation therapy.

Exercise and physical activity

The Dementia and Physical Activity RCT 208 found moderate-to-high intensity aerobic and strength exercise training did not slow cognitive impairment in people with mild-to-moderate dementia but improved physical fitness. The US Reducing Disability in Dementia study 209 implemented an at-home multicomponent intervention including exercise education, training to increase pleasant events, and activator-behaviour-consequence problem-solving approach over 6 weeks by case managers in 255 community dwelling people with dementia older than 60 years and their family carer and were able to follow up 140 (54·9%). The study found increased physical activity; days of taking 30 or more minutes of exercise (effect size 0·6, 95% CI 0·4–0·8 after the treatment and 0·3, 0·1–0·5 at 13 months) in a before and after intervention comparison.

Interventions for neuropsychiatric symptoms of dementia

Neuropsychiatric symptoms are common and often clustered in people with dementia. These symptoms might precede dementia and are associated with tau and amyloid neuropathology. 210 This suggests that underlying neurobiological mechanisms might underpin neuropsychiatric symptoms. However, other drivers relating to the personal history and the environment of the person with dementia are also likely to exist. Neurodegeneration could lead to increased vulnerability to stressors or triggers. Genetics, cognitive reserve, resilience, medical comorbidities, and environment including responses of carers might modify these relationships. Needs and responses will also be individual and relate to a person's own social, cultural, and historical context. First-line assessment and management of neuropsychiatric symptoms should focus on basic health: describe and diagnose symptoms; look for causes such as pain (using validated pain assessments might help), illness, discomfort, hunger, loneliness, boredom, lack of intimacy and worry that could cause the behaviours and alleviate these while considering risks of harm. 2

No new evidence of medication effectiveness for these symptoms exists; risperidone in low doses (0·5 mg daily) and some other antipsychotics are sometimes effective but often ineffective and have adverse effects. 2 Specific initiatives have led to a decrease in antipsychotic prescriptions for people with dementia, although often replaced with other psychotropics ( figure 8 ), such as benzodiazepines, antidepressants, and mood stabilisers. 211 These psychotropics lack evidence of efficacy for neuropsychiatric symptoms but show clear evidence of possible harm; for example, trazodone and benzodiazepines increase fall-related injuries. 144 Major policy changes should be assessed carefully, within and across countries for unintended consequences (and perhaps unexpected benefits) and their costs.

Proportion of patients with a diagnosis of dementia prescribed an antipsychotic drug (A) and those prescribed an anxiolytic, hypnotic, or antidepressant (B)

CPRD=Clinical Practice Research Datalink. Reproduced from Donegan et al, 211 by permission of Elsevier.

Evidence is slowly accumulating for the effectiveness, at least in the short term, of person-centred evidence-based psychosocial interventions. In Germany, a 6-month cluster RCT of nurse-delivered, supervised dementia care management used a computer-assisted nurse assessment to determine personalised intervention modules, then a multi-disciplinary team discussion and agreement with the physician for 634 people (mean age 80 years) with dementia living at home with a primary carer or alone. 212 The mean mini mental state examination (MMSE) was 23, only 38% had a formal diagnosis of dementia; the majority of participants (51%) had mild dementia but some had moderate and some severe dementia. The intervention consisted of psychosocial management of treatment and care, medication management and carer support, and education and discussion with a psychiatrist or neurologist. The intervention, compared with care as usual, was associated with better outcomes for neuropsychiatric symptoms (Neuropsychiatric Inventory [NPI] score −7·5, 95% CI −11·1 to −3·8), however this effect could be because of deterioration in care as usual (in the care as usual group NPI increased from 7·2 to 15·2; in the intervention group NPI increased from 7·6 to 8·2). This between-group reduction in neuropsychiatric symptoms was greater than that expected, extrapolating from other study results, with antipsychotic medication. Effects on quality of life were only apparent for those people living with a carer.

An eight-session home-based tailored activity programme RCT, tailored both to the person with dementia living at home and to a family member compared with eight telephone-based education sessions, recruited 160 participants with 64% follow-up, imputing values for the rest. 213 The study reported a large reduction in overall neuropsychiatric symptoms immediately after the intervention, which were better in the group receiving home-based tailored activity programme on the neuropsychiatric inventory (mean difference in score 24·3, 95% CI 3·1–45·6), and on functional dependence and pain but this was not sustained 4 months later. Non-completers had more severe neuropsychiatric symptoms.

Since the 2017 Commission two new systematic reviews of antidepressants to treat depression in dementia reported moderate quality evidence that antidepressant treatment for people with dementia does not lead to better control of symptomatology compared with placebo. 214 , 215

Agitation is distressing for people with dementia and those around them, and contributes substantially to the overall costs as the level of agitation increases. 216 The body of evidence on this key behaviour is growing, mostly focused on care-home settings. These findings are valuable as these populations are most affected; however, because many people with dementia reside at home a major gap in knowledge remains.

Care home residents with agitation often find sitting still difficult and therefore might not be included in activities. 217 , 218 Two new cluster RCTs of professionals delivering multicomponent, interdisciplinary, interventions in care homes successfully reduced agitation. The WHELD study 219 included participants with or without neuropsychiatric symptoms and provided person-centred care, aiming to improve communication with people with dementia. It implemented social, sensory experiences or other activities; educated about antipsychotic review; and addressed physical problems, finding lower Cohen Mansfield Agitation Inventory (CMAI) at 9 months (MD −4·3 points, 95% CI −7·3 to −1·2). 219 The TIME study 220 for people with moderate-to-high levels of agitation consisted of a manual-based comprehensive assessment of the resident and structured case conference for the staff and doctor, to create a tailored plan, and then implement it. This intervention led to reduced agitation at 8 weeks (NPI −1·1 points, 95% CI −0·1 to −2·1; CMAI −4·7 points, −0·6 to −8·8) and 12 weeks (NPI −1·6, −0·6 to −2·7; CMAI −5·9, −1·7 to −10·1). 220 These effect sizes are similar to those seen for medications, but without harmful side-effects. 2 , 221 A further RCT studied a six-session intervention with staff in groups, teaching staff to understand agitation as related to medical, psychological, or social unmet needs and to implement strategies to meet these needs, using the describe, investigate, create, and evaluate approach. 222 The intervention did not reduce agitation symptoms, although it was cost-effective, improving quality of life. 223 Overall, the current evidence for agitation in care homes favours multi-component interventions by clinical staff, including considering if drugs might harm, and not drug interventions. Thus a major gap remains in knowledge about people living at home who comprise the majority of those with dementia.

Psychotic symptoms in dementia

People with dementia might be wrongly thought to have delusions when they misremember, and new psychotic symptoms are often due to delirium, thus thorough assessment of symptoms is essential. 2 Management of psychosis in dementia should start with non-pharmacological interventions; however, evidence for effectiveness of these interventions for psychosis in dementia is weaker than for agitation. 224 Antipsychotics for psychosis in dementia should be prescribed in as low a dose and for the shortest duration possible. 2 However, a Cochrane review of antipsychotics withdrawal found two trials with participants with dementia who had responded to antipsychotic treatment. These reported that stopping antipsychotics was associated with symptomatic relapse 225 suggesting the need for caution in any medication withdrawal in this group. There was low-quality evidence that, in general, discontinuation might make little or no difference to overall neuropsychiatric symptoms, adverse events, quality of life or cognitive function. 226

Apathy might be conceptualised as the opposite of engagement, comprising reduced interest, initiative, and activity. Like people without dementia, those with dementia engage more in preferred activities, but require additional support to do so. 227 A study in care homes observed engagement increased during activities in those who attended the groups. 228 A Cochrane review of the few people who had been in drug RCTs of methylphenidate versus placebo for apathy in dementia found small improvements on the apathy evaluation scale (MD −5·0, 95% CI −9·6 to−0·4, n=145, three studies, low-quality evidence) but not on the NPI apathy subscale (MD −0·1, 95% CI −3·9 to 3·7, n=85, two studies). 229

There is no evidence that medication for sleep in dementia is effective 230 and considerable evidence for harm—ie, earlier death, increased hospitalisation, and falls—exists. 139 , 144 Testing of non-pharmacological interventions is ongoing. 231

Carer distress related to neuropsychiatric symptoms rather than the dementia symptoms was associated in one study with increased use and costs of health services, 232 highlighting the need for effectively identifying, educating, and supporting distressed carers. An RCT 233 reporting 6-year follow-up after the eight session STrAtegies for RelaTives intervention—manual-based coping intervention delivered by supervised psychology graduates—found continuing effectiveness for depressive symptoms in carers (adjusted MD −2·00; 95% CI −3·4 to −0·6) and risk of case-level depression, with patient-related cost being approximately 3 times lower than those who did not receive the intervention (median £5759 vs £16 964 in the final year; p=0·07). 233 Another US study 234 followed up 663 people, mean age 77 years, 55% women. Caregiver depression rather than symptoms of people with dementia predicted emergency department use for people with dementia, with a 73% (RR 1·73, 95% CI 1·3–2·3) increase. 234

Functioning

A UK RCT of 14 sessions of cognitive rehabilitation focused on individual goal attainment with therapy delivered at home by an occupational therapist or nurse to 475 participants with mild-to-moderate dementia (MMSE ≥18 for inclusion; mean 24) and a family carer. 235 Individuals had two or three goals; the most common was engaging in activities (21% of goals). The intervention group reported increased goal attainment over 3 and 9 months compared with usual treatment (effect size 0·8, 95% CI 0·6–1·0 at both 3 and 9 months). 235 The treatment did not improve participants' quality of life, mood, self-efficacy, cognition, carer stress, or health status and was not cost-effective. A systematic review 236 of RCTs without meta-analysis for overall effect size, concluded that all interventions which had improved functioning in people living with dementia in the community have been individual rather than group interventions. These were: in-home physiotherapist delivered aerobic exercise (two studies, larger one positive, 140 people with Alzheimer's disease; smaller study negative, 30 people with Alzheimer's disease), individualised cognitive rehabilitation (mild or moderate dementia; two studies; 257 cognitive reserve intervention groups and 255 controls), and in-home activities-focused occupational therapy (people with mild to moderate dementia, three studies, 201 intervention, 191 controls) reduced functional decline compared to controls but group-exercise and reminiscence therapies were ineffective. 236

People with dementia have other illnesses

Multimorbidity is a huge challenge in dementia, not only because people with dementia have increased rates of other illnesses, but also because they often find it particularly difficult to organise care. People with dementia might forget to tell their family or health professionals of symptoms, struggle to understand or follow agreed plans, and are more likely to forget to drink and eat, increasing falling and infection rates. 237 People with dementia consult primary care less often 238 and have fewer dental visits 239 than those without dementia and their family members, if involved, often feel they lack knowledge to assist. 240 Health-care professionals need education to be more comfortable, understanding, and positive in communicating with people with dementia. 241

Around 70–80% of people diagnosed with dementia in primary care have at least two other chronic illnesses. 242 , 243 People who are physically more frail are more likely to have dementia, but the relationship between pathology and symptoms in these people is comparatively weak suggesting that dementia might be from other causes. 22 Compared to the general older population, people with dementia have increased rates of cerebrovascular disease, 243 , 244 , 245 , 246 stroke, 247 Parkinson's disease, 243 , 245 diabetes, 245 , 247 skin ulcers, anxiety and depression, 243 , 245 pneumonia, incontinence, and electrolyte disturbance. 245 Multimorbidity in people with dementia is associated with faster functional decline 248 and worse quality of life for people with dementia and their family carers. 249

Dementia and COVID-19

Severe acute respiratory syndrome coronavirus 2, was first identified in patients with viral pneumonia in Hubei province, China. 250 Severity and mortality of the associated disease (COVID-19) worsen with increasing age 251 and with pre-existing illnesses such as hypertension and diabetes, 252 and thus many people with dementia are at particular risk. Death certificates from the UK indicate that dementia and Alzheimer's disease were the most common underlying conditions, specified in 11 950 deaths (25·6% of all deaths involving COVID-19) in March to May, 2020. 253 Many charities, practitioners, and academics supporting people with dementia have issued guidance based on current evidence and best practice, including advance consideration of whether people would wish to be hospitalised if they develop severe COVID-19. Concern has been expressed that the illness and consequent distancing might increase family carer stress, loneliness, neuropsychiatric symptoms and use of psychotropic medication, and lead to complications, including future dementia. Interventions delivered remotely through technology have also been implemented in some places. 254 , 255 , 256 , 257

People with dementia might struggle to adhere to measures to reduce virus transmission, as they might not understand or remember about required changes to behaviour, such as physical distancing and hygiene, leading to increased risk to themselves and their carers. 258 They might additionally be vulnerable if they depend on others for daily activities or personal care, as this necessitates close personal contact.

This situation is particularly concerning in those care homes, where many residents have dementia and where many COVID-19 deaths have occurred in many countries 259 , 260 , 261 with reports of more than half of residents being admitted to hospital. In US nursing homes, among 10 576 people with confirmed COVID-19, residents living with dementia made up 52% of COVID-19 cases; yet, accounted for 72% of all deaths (an increased risk of 1·7). 262 The number of people living together in care homes means that the infection of an individual, either staff or resident, could endanger more people than in traditional or family households. Although evidence exists that if staff are sufficiently and rigorously protected they are unlikely to develop COVID-19, many staff have become unwell and some have died. 263 , 264 Illness means that there are fewer people to care for residents at a time when they need particularly high levels of care. This situation is particularly relevant in the care of residents with dementia, if they are expected to remain in their own rooms, rather than eating and participating in activities with others. Staff or residents might also be moved between care homes and increase risk in other homes. 261 Restrictions on visitors to private homes, care homes, and hospitals might cause greater distress for people with dementia and they might not understand why people are wearing masks, recognise who is behind it, or understand speech when lips are covered. Lack of restrictions means that the visitors might also be at elevated risk. 261

The impacts of COVID-19 on people with dementia might be particularly severe in LMICs, due to smaller health budgets for testing and protective equipment, capacity of health-care systems, quality of care home provision and patterns of workforce mobility. 264

Thus, people with dementia are particularly vulnerable to COVID-19 because of their age, multimorbidity, and difficulties in maintaining physical distancing. 250 , 251 , 252

We recommend rigorous public health measures of protective equipment and hygiene, including not moving staff or residents between care homes or admitting new residents when their COVID-19 status is unknown, should mitigate impacts on people with dementia. It is also imperative that there is frequent and regular testing of staff in care homes for infection, ensuring staff have sick pay so that they do not come in when symptomatic and interim care is being set up for people discharged from hospital so that only those who are COVID-19 free come to live in care homes. Resident testing should encompass asymptomatic as well as symptomatic people, when there is exposure within the home to COVID-19. In the future, many homes might be able to start to provide oxygen therapy so that those who do not want to be admitted to hospital are still able to access oxygen therapy. In addition, it is also important to reduce isolation by providing the necessary equipment and a brief training to relatives on how to protect themselves and others from COVID-19; so that they can visit their relatives with dementia in nursing homes safely when it is allowed. Further evidence is needed to inform responses to this and future public health emergencies.

Hospital admissions

Hospitalisation in people with dementia is associated with adverse, unintended consequences, including distress, functional and cognitive decline, and high economic costs. 265 , 266 , 267 People with dementia have 1·4 to 4 times more hospital admissions than others with similar illnesses. 266 , 268 , 269 , 270

A systematic review and meta-analysis including 34 studies of 277 432 people with dementia found that in the six studies which compared the two groups, people with dementia had increased hospital admissions compared with those without dementia, after adjusting for age, sex, and physical comorbidity (RR 1·4, 95% CI 1·2–1·7; figure 9 ). 271 Hospitalisation rates in people with dementia ranged from 0·37 to 1·26 per person-year in high-quality studies. Admissions are often for conditions that might be manageable in the community (potentially preventable hospitalisations). 268 People with dementia experience longer and more frequent admissions and readmissions; health-care expenditure for people with moderate-severe dementia is around double that of people without dementia. 269 , 272 , 273 Early detection and management of physical ill-health in people with dementia, particularly of pain, falls, diabetes, incontinence, and sensory impairment, is important. 199 , 274 , 275 However, no intervention has successfully reduced number of hospital admissions of community-dwelling people with dementia, 276 although education, exercise, rehabilitation, and telemedicine have reduced admissions for older people without dementia. 277

Systematic review and meta-analysis of hospitalisation rates of people with dementia compared to those without dementia controlled for age and sex

Reproduced from Shepherd et al, 271 by permission of Springer Nature.

High-quality care for people with dementia takes longer than caring for others with the same condition. 278 Recognition of dementia in hospital inpatients is necessary for optimum care, 279 but dementia is often undetected or unrecorded. 280 In the UK however, detection rates have increased over the past 10 years. 281

Physical illness, delirium, and dementia

Dementia and delirium frequently occur together. In one hospital inpatients' survey nearly 35% of those older than 80 years experienced delirium; those with prior cognitive impairment had 15 times the risk of developing delirium than those without (OR 15·3, 95% CI 5·2–45·4). 282 People with delirium without known dementia are more likely to be diagnosed with dementia in the future than others, either because of pre-existing undiagnosed dementia or cognitive impairment, present in 20·7% (95% CI 11·9–29·5) and 37·8% (27·3–88·3) respectively of one cohort, or because delirium has neurotoxic effects and so precipitates dementia. 283 People with similar neuropathology show faster cognitive decline if they develop delirium than if they do not. 284 Additionally, older people without dementia declined cognitively more than twice as fast after an emergency hospital admission for any cause, compared with those not admitted, suggesting any severe illness is associated with cognitive decline. 285 Risk factors for delirium in dementia include sensory impairment, pain, polypharmacy, dehydration, intercurrent illnesses, such as urinary tract infections or faecal impaction, and an unfamiliar or changing environment. 286 Delirium in older people should prompt consideration of underlying dementia.

Most research on delirium prevention has been in people without dementia. It suggests targeting hydration, stopping medication predisposing to delirium, monitoring the depth of anaesthesia, and sleep promotion. However, no evidence for medication efficacy, including cholinesterase inhibitors, antipsychotic medication, or melatonin exists. 287 , 288 , 289 The Hospital Elder Life Program 290 —an intervention to prevent delirium in those admitted to hospital—reduces delirium incidence and includes people who are cognitively impaired. This multidisciplinary treatment consists of daily visits, orientation, therapeutic activities, sleep enhancement, early mobilisation, vision and hearing adaptation, fluid repletion, infection prevention and management of constipation, pain, and hypoxia, and feeding assistance. 290

A network meta-analysis of drugs for prevention and treatment of delirium did not include studies of people with dementia, thus we cannot use this to recommend drugs for people with dementia and delirium as this research might be inapplicable to them. 291

Little high-quality research exists on managing delirium in dementia. One RCT compared care at a specialist medical and mental health unit to usual care for 600 confused people older than 65 years, acutely admitted to hospital and found no difference in the primary outcome of days spent at home or in hospital, but increased family satisfaction. 292 A further RCT of cognitively stimulating activities for people with delirium in dementia did not improve the delirium. 293 No definitive evidence that any medication improves delirium in people with dementia exists: cholinesterase inhibitors, antipsychotics, and sedating benzodiazepines are ineffective and antipsychotics and benzodiazepines are associated with mortality and morbidity. 265 , 288 , 294 , 295 , 296 , 297 Given the risk of dementia in people who develop delirium, its prevention, and possibly advances in its management, might offer a means for dementia prevention. 298

Link between very old age, frailty, and dementia

The fastest growing demographic group in most advanced countries are people aged 90 years and older. One well characterised post-mortem cohort of the oldest old (n=1079; mean age 90 years) dying with dementia, found that neuropathological features of Alzheimer's disease account for about half of the cognitive decline seen as people diagnosed with Alzheimer's disease had mixed causes of dementia. 299 Although Alzheimer's disease neuropathology was the commonest cause of dementia, Alzheimer's disease changes rarely occurred on their own, so only 9% of people with dementia had pure Alzheimer's disease pathology. 300 People who have Alzheimer's disease pathology without developing dementia tend to have fewer age-related health deficits than those who develop it with even low concentrations of plaques and tangles. 301 A moderation analysis showed that the relationship between Alzheimer's disease pathology and dementia status differed according to level of frailty (adjusted for age, sex, and education) with increasing frailty weakening the relationship between Alzheimer's disease pathology and dementia ( figure 10 ). 22 As with delirium, some of this additional health risk might be modifiable. This approach suggests a new type of therapy focus on specific age-related processes that underpin many diseases of late life might reduce the incidence or severity of dementia.

Moderation analyses of the relationship between Alzheimer's disease pathology and clinical diagnosis of Alzheimer's dementia (adjusted for age, sex, and education)

As frailty increased, the odds of a neuropathological diagnosis of Alzheimer disease corresponding to a clinical diagnosis decreased. Reproduced from Wallece et al, 22 by permission of Elsevier.

End-of-life care in dementia

The numbers of people dying with dementia are increasing but the evidence for the best end-of-life care is scarce. Trends in age-standardised death rates (3·6%) for dementia increased slightly between 1990–2016, with pronounced increases in the USA and Japan and decreases in western Europe and central Latin America. 4 Dementia is more readily being included on death certificates, which accounts for some of the rise. The increase might be related to dementia manifesting at later ages, with higher physical frailty 22 leading to a faster decline.

Most people with dementia might die while still in the mild-to-moderate stages whereas only about a quarter of those dying with dementia have severe dementia. 302 , 303 The trajectory of dementia is often unpredictable 304 and palliative care initiation should reflect need not prognosis.

Decision making about end of life is complex and simple rules of thumb, co-designed with staff and carers, provided clarity in some small studies. 304 One RCT testing decision-aids about families' and doctors' goals of care for people with advanced dementia led to increased palliative care content in care plans. 305 , 306 In a 9-month UK prospective study, 85 care home residents with advanced dementia from 14 homes were likely to be living with distressing symptoms, specifically agitation (54%) or pain (61% on movement). 304

Capacity to make abstract decisions, including about the future, might be lost early in dementia. 307 Therefore, advance care planning, designed to empower people with dementia and improve quality of dying, might theoretically be something everyone should do before developing dementia. 308 However, people might not be able to predict their future wishes. This might explain why family carer proxies show only low-to-moderate agreement with stated end-of-life treatment preferences of people with dementia. 309 Advance care planning might, however, reduce carers' uncertainty in decision making and improve perceptions of quality of care. 310

Partners of people dying with dementia experience poorer mental health than those facing bereavement from other causes 311 possibly because of long and difficult caring responsibilities. This might be ameliorated through sensitive and timely information, particularly regarding the progression of dementia, 312 individually or through family and staff case-conferencing. 313 , 314

Conclusions

Knowledge about risk factors and potential prevention, detection, and diagnosis of dementia is improving although significant gaps remain. 315 In this Commission report, we have specified policy and individual changes to delay the onset of cognitive impairment and dementia and better ways to support and treat people with dementia and their families and to improve their quality of life.

Interventions, including organisation of the complex physical illness and social needs, to support people affected by dementia can have a huge effect when taken as a whole. Our ambition is for worldwide provision of resources for an adequate level of wellbeing to people with dementia and their carers with a better evidence base to guide individual care and policy making alike. With good quality care, people can live well with dementia and families can feel supported.

Acknowledgments

We are partnered by University College London (UCL), the Alzheimer's Society, UK, the Economic and Social Research Council, and Alzheimer's Research UK, and would like to thank them for financial help. These organisations funded the fares, accommodation, and food for the Commission meeting but had no role in the writing of the manuscript or the decision to submit it for publication. We would like to thank Bernadette Courtney, Jacques Gianino, and Nuj Monowari, from UCL, London, UK, for their administrative help, including managing finances, booking rooms and food, and setting up a website supported by the University College London Hospitals National Institute for Health Research Biomedical Research Centre. We would like thank Henrik Zetterberg for advice on biomarkers and dementia.

Contributors

GL, JH, AS, and NM contributed to literature searches and quality assessments for systematic reviews. JH and NM performed meta-analyses. GL, JH, AS, and NM conceived the new PAF calculation and NM led the statistical analysis. GL, JH, AS, NM, DA, CLB, SB, AB, JC-M, CC, SGC, NF, RH, HCK, EBL, VO, KRi, KRo, ELS, QS, LSS, and GS attended the conference to discuss the content. GL, JH, EBL, AS, DA, and ELS wrote first drafts of sections of the paper. GL wrote the first draft of the whole paper and revisions of drafts. CBa reviewed and contributed to revision of the final drafts. All authors contributed to sections of the reports and all revised the paper for important intellectual content.

Declaration of interests

AS reports grants from Wellcome Trust (200163/Z/15/Z), outside the submitted work. DA reports grants from Eli Lilly, during the conduct of the study. CBa reports grants and personal fees from Aca-dia and Lundbeck; and personal fees from Roche, Otsuka, Biogen, Eli Lilly, and Pfizer, outside the sub-mitted work. SB reports grants and personal fees from AbbVie, personal fees and non-financial sup-port from Eli Lilly, and personal fees from Eleusis, Daval International, Boehringer Ingelheim, Axovant Sciences, Lundbeck, and Nutricia, outside the submitted work; and he has been employed by the Department of Health for England. NF reports non-financial support from Eli Lilly, outside the submitted work. LNG and her institutions (Johns Hopkins University, Baltimore, MD, USA, Drexel University, Philadelphia, PA, USA, and Thomas Jefferson University, Philadelphia, PA, USA) are entitled to receive royalties from fees associated with online training for the tailored activity program, which is an evidence-based program referenced in the Review. RH reports grants from Department of Health, NIHR HTA Programme, outside the submitted work; and he is a Scientific Trustee of the charity Alzheimer's Research UK. MK reports grants from the UK Medical Research Council (S011676, R024227), NordForsk (the Nordic Programme on Health and Welfare, 75021) and the Academy of Finland (311492), outside the submitted work. EBL reports other (royalties) from UpToDate, outside the submitted work. KRo reports personal fees from Clinical Cardio Day-Cape Breton University, Sydney, NS, Canada, CRUIGM-Montreal, Jackson Laboratory, Bar Harbor, MA, USA (speaker fees), MouseAge, Rome, Italy (speaker fees), Lundbeck, Frontemporal Dementia Study-Group, SunLife Insurance, Japan, outside the submitted work. He is a President and Chief Science Officer of DGI Clinical, which in the last 5 years has contracts with pharma and device manufacturers (Baxter, Baxalta, Shire, Hollister, Nutricia, Roche, Otsuka) on individualised outcome measurement. In 2017, he attended an advisory board meeting with Lundbeck. He is also Associate Director of the Canadian Consortium on Neurodegeneration in Aging, which is funded by the Canadian Institutes of Health Research, and with additional funding from the Alzheimer Society of Canada and several other charities, as well as, in its first phase (2013-2018), from Pfizer Canada and Sanofi Canada. He receives career support from the Dalhousie Medical Research Foundation as the Kathryn Allen Weldon Professor of Alzheimer Research, and research support from the Canadian Institutes of Health Research, the QEII Health Science Centre Foundation, the Capital Health Research Fund and the Fountain Family Innovation Fund of the QEII Health Science Centre Foundation. LSS reports grants and personal fees from Eli Lilly, Merck, and Roche/Genentech; personal fees from Avraham, Boehringer Ingelheim, Neurim, Neuronix, Cognition, Eisai, Takeda, vTv, and Abbott; and grants from Biogen, Novartis, Biohaven, and Washington University DIAN-TU, outside the submitted work. The remaining authors declare no conflict of interests.

Supplementary Material

Uncited references.