Reference
Chiang HL, Chuang YF, Chen YA, Hsu CT, Ho CC, Hsu HT, Sheu YH, Gau SS, Liang LL. Physical fitness and risk of mental disorders in children and adolescents. JAMA Pediatr. 2024:178(6):595-607.
Study Objective
To determine if there is an association between physical fitness and mental disorders in children and adolescents
Key Takeaway
Physically fit children were at lower risk of mental disorders than their less-fit peers.
Design
This was a nationwide cohort study conducted in Taiwan using data from the Taiwan National Student Fitness Tests Database (NSFTD) and National Health Insurance Research Database (NHIRD) from January 1, 2009, to December 31, 2019.
Participants
Study participants were divided into 2 cohorts, 1 group that targeted anxiety and depression (n=1,996,633 participants) and 1 group that examined attention-deficit/hyperactivity disorder (ADHD; n=1,920,596 participants). At the start of the study, participants were aged 10 to 11 years and were followed for at least 3 years. Average follow-up was 6 years. Gender distribution was nearly equal. Investigators gathered and analyzed the data from October 2022 to February 2024. Individuals were excluded who had been previously diagnosed with cerebral palsy and those diagnosed previously with anxiety-depression and ADHD were excluded from the second cohort.
Intervention
Investigators did not perform an intervention. The study was observational only.
Study Parameters Assessed
This study obtained data from 2 major sources: the National Health Insurance Research Database and the National Student Fitness Tests Database in Taiwan.
The NHIRD contains comprehensive medical-claims data, covering demographics, healthcare-services utilization, diagnostics, prescriptions, and records of tests and medical procedures for approximately 94% of the country’s population.
The NSFTD compiles data from annual physical-fitness assessments and body mass index (BMI) measurements of students nationwide for about 2 million students each year.
The fitness test included 4 components:
- an 800-meter run,
- number of bent-leg curl-ups performed in 1 minute,
- distance of a standing broad jump, and
- distance attained in the 2-leg sit-and-reach test, which measures flexibility.
Primary Outcome
The primary outcome this study was designed to assess was the onset of a mental disorder after the index date, characterized as either anxiety or depression in the anxiety-depression (ANX-DEP) cohort or ADHD in the ADHD cohort.
Investigators used the Kaplan-Meier method to calculate the cumulative incidence of anxiety, depression, and ADHD across fitness quartiles. Additionally, they used multivariable Cox proportional hazards models that included all 4 fitness components and explored sex and income as modifiers.
Key Findings
Across all categories of fitness measured in these children, increases in fitness were associated with lower risk of anxiety, depression, and ADHD in both sexes.
The ANX-DEP cohort had 1,996,633 participants (51.9% were male, and the median age was 10.6 years). The ADHD cohort had 1,920,596 participants (51.9% male), and the median age was 10.6 years.
Cumulative incidence of mental disorders was lower among participants in better-performing fitness quartiles, suggesting a dose-dependent association.
Gender-specific analyses, controlling for confounders, revealed that improved cardiorespiratory fitness (CF), indicated by a 30-second decrease in run times, was associated with reduced risks of anxiety, depression, and ADHD in female participants and lower risks of anxiety and ADHD in male participants (adjusted hazard ratio [aHR] for ADHD risk for female participants, 0.92; 95% CI, 0.90–0.94; P<0.001; for male participants, 0.93; 95% CI, 0.92–0.94; P<0.001).
Enhanced muscular endurance (ME), marked by an increase of 5 curl-ups per minute, was associated with significantly decreased risk of depression and ADHD in female participants and lower anxiety and ADHD risks in male participants (aHR for ADHD risk for female participants, 0.94; 95% CI, 0.92–0.97; P<0.001; for male participants, 0.96; 95% CI, 0.95–0.97; P<0.001).
Improved muscular power (MP), reflected by a 20-cm increase in jump distance, was associated with reduced risks of anxiety and ADHD in female participants and reduced anxiety, depression, and ADHD in male participants (aHR for ADHD risk for female participants, 0.95; 95% CI, 0.91–1.00; P=0.04; for male participants, 0.96; 95% CI, 0.94–0.99; P=0.001).
Transparency
This work was supported in part by the National Science and Technology Council, Far Eastern Memorial Hospital, and Far Eastern Memorial Hospital National Yang Ming Chiao Tung University Joint Research Program. The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript.
Practice Implications & Limitations
Just under 17% of the world’s current population is between the ages of 10 and 19 years. Mental health problems are the leading health-related disability among this age group.1,2 Statistically, 9.8% of these young people have ADHD, 9.4% suffer from anxiety, and 4.4% have depression.3 This has gotten worse in recent years. In 2023 the American Psychiatric Association reported that in the 10-year period that preceded the Covid pandemic, “feelings of persistent sadness and hopelessness—as well as suicidal thoughts and behaviors—increased by about 40% among young people.”4 From 2001 to 2019, ER visits for self-harm increased by 88%.5
In response to this information, in 2021, US Surgeon General Vivek Murthy warned the nation that mental health challenges were leading to “devastating effects” among young people.5 In an interview, Murthy listed several factors behind this mental health crisis. These “… include the growing crisis of loneliness and isolation; the fact that bullying is taking place not only offline but online; the fact that our kids are surrounded by an information environment that is coming at them 24/7 and that often stokes fear and anxiety. It’s also being driven by the fact that young people, when they think about the future, see the profound threats that we are facing today, like violence and racism and climate change, but they don’t see effective solutions.” While he points out the influence of social media and modern cultural attitudes, he did not appear to focus on physical fitness. Murthy continued, “Other experts theorize that heavy screen use has affected adolescent mental health by displacing sleep, exercise and in-person activity, all of which are considered vital to healthy development.”5
The data from this recent study by Chiang et al suggest that shifts in fitness levels may also be part of the problem and possibly part of the solution.
While mental health problems are increasing in adolescents, their levels of physical fitness are falling. A 2020 review of data from the American Heart Association reported that 75% of America’s adolescents no longer meet the minimum amount of recommended physical exercise per week.6
Further, in 2022, the Physical Activity Alliance reported, “21% of U.S. children and youth ages 6 to 17 meet the guideline of 60 minutes of physical activity every day. In addition, physical-activity levels drop significantly as kids get older, with 42% of 6 to 11 year olds meeting those guidelines but only 15% of 12 to 17 year olds doing so.”7
When these 2 trends are viewed together—first, the increasing frequency of mental disorders and, second, the falling levels of fitness—it is easy to conclude that the 2 are inversely linked. This leads to the assumption that interventions that increase physical fitness levels will lower occurrence of mental disabilities. Such an assumption might seem obvious, so we might not pause to ask whether this assumption has been proven to be true.
In other words, does poor fitness cause mental disorders or the opposite: Do mental disorders lead to greater lethargy and a lack of physical fitness?
At this point, these ideas are still pretty much hypothetical. The Chiang study, while not the first to examine these relationships, is important because it does so methodically and rigorously. Investigators gathered data from a very large cohort, levels of fitness were carefully tested in each participant, and the diagnosis of mental disorders were thoroughly vetted via insurance payments and health records. The study, assessing 1.9 million participants in Taiwan, revealed that children and adolescents in better-performing fitness quantiles exhibit lower cumulative incidences of anxiety, depressive, and attention-deficit/hyperactivity disorders. Enhanced cardiorespiratory fitness, muscular endurance, and muscular power were each independently associated with reduced mental-disorder incidences, even after accounting for confounding factors.
That these associations between fitness and mental health appear to be “dose dependent”—that is, the more fit the individual, the less likely he or she is to suffer from mental disorders—is important as it argues that the link between fitness and mental health is causative. Argues but doesn’t prove.
While we can be relatively assured that there is an association between fitness and mental health, it remains less clear whether the relationship is causative. In other words, does poor fitness cause mental disorders or the opposite: Do mental disorders lead to greater lethargy and a lack of physical fitness?
We want to believe it is the former since, if true, it will provide us with an intervention that may allow us to improve the mental health and reduce the suffering of a large segment of the population.
Several earlier reports have been published suggesting that higher levels of physical fitness in children are associated with fewer mental health problems, in particular, of anxiety and depression.8
In a 2019 review of studies that examined physical fitness and adolescent mental health and which involved 18 intervention studies, investigators included 12 of them (3 randomized, controlled trials [RCTs] and 9 nonRCTs) in a data meta-analysis that reported a small but significant overall effect of physical activity on mental health in children and adolescents aged 6 to 18 years (effect size 0.173, 95% CI 0.106–0.239, P<0.001). When the analyses were performed separately for children and adolescents, the results were significant for adolescents but not for children.9
The more important question, though, is whether intervening by increasing exercise will lead first to better fitness and, from there, to better mental health. Only a small number of reports tell us that improving physical fitness in children by intervention is linked to improved cognitive function.
In 2022 Francesco Ortega et al reported on a 20-week RCT of 109 children, aged 8 to 11 years, who were overweight or obese and who were put on an exercise program. While the control group continued their usual routines, the exercise group attended 3 supervised, 90-minute exercise sessions a week. This exercise intervention significantly improved crystallized intelligence, total intelligence, and cognitive flexibility, and there was a positive but small effect of exercise on academic performance.10 The study did not report on whether the kids were less anxious, depressed, or happier.
A clinical trial by María Eugenia Visier-Alfonso et al, published in 2021, suggested that moderate-to-vigorous physical activity in 9- to 11-year-olds leads to improved academic achievement via improved cardiorespiratory function, which leads to improved cognitive flexibility.11
Several papers have reported associations between various measures of physical fitness and mental status or depression in children in various parts of the world.
In a study involving Norwegian adolescents, Åvitsland et al reported that only cardiorespiratory fitness, rather than muscle strength, was inversely and significantly linked/associated with psychological difficulties. “There was a small but significant inverse association between cardiorespiratory fitness and levels of psychological difficulties in Norwegian adolescents. The results suggest that muscular strength is not associated with psychological difficulties in adolescents, when controlling for cardiorespiratory fitness is,” the authors wrote.12
It would seem apparent that lower cardiorespiratory fitness (CRF) is linked to increased depression, but the studies all appear vulnerable to reverse causation. We want to believe that poor CRF leads to depression rather than depression leads to poor CRF. We know the 2 are associated but not what comes first. More importantly, we want to know if interventions that improve CRF will lessen depression.
What these data do not tell us is how much improvement in psychology we might expect with a fitness intervention.
While the data are sparse to support exercise interventions in children improving mental health, there are more abundant data suggesting that this works in adults. Still, this evidence is not as compelling as we might wish. A meta-analysis by Contreras-Osorio et al, published in 2022, is typical. Knowing that “[e]xecutive function is among the most affected cognitive dimensions in depression,” these researchers found and collated data from 7 studies (N=202 men and 457 women) that measured the impact of exercise on executive function. According to the study authors, “For working memory, a small favoring effect was observed in the experimental groups compared with controls…. Compared with the control group, physical exercise had a trivial effect on cognitive flexibility…. In conclusion, physical exercise interventions may improve working memory behavioral measures in adults with mild-to-moderate depression when compared with active and passive control conditions. However, the reduced number of available high-quality studies precludes more lucid conclusions.”13
In a 2019 systematic review, Ayelett, Bower, and Small examined studies that evaluated exercise effect on anxiety. In their paper, they reviewed data from 9 trials with participants diagnosed with anxiety disorders, plus 6 trials in which participants had raised anxiety on a rating scale. Aerobic exercise was effective in the treatment of raised anxiety compared to waiting-list control. High-intensity exercise showed greater effects than low-intensity intervention. Again, “Conclusions were limited by the small number of studies and wide variation in the delivery of exercise interventions,” the authors reported.14
It would appear that, at least in adults, exercise might be a helpful intervention.
The lingering thought in the back of this reader’s mind is that exercise offers a small amount of improvement to what is a very large problem. Lack of exercise might be part of the problem, and exercise just might be part of the solution. At this point, though, the evidence is still lacking that exercise will fix everything. The Mayo Clinic says this tactfully on its website when, in regard to treating anxiety and depression, it suggests that exercise “eases the symptoms.”15
Should we be prescribing exercise regimes along with antidepressants, anti-anxiolytics, or amphetamines? That’s 1 way of looking at it. One might say that exercise is “natural medicine;” after all, this is the Natural Medicine Journal, so I suppose that is how we could see it.
Yet, it may be that we are looking at this the wrong way. Certain elements of life are required for good health. On that list, we would put healthy food, clean water, restful sleep, and enjoyable exercise. People need all the above elements and probably more to be healthy. Yet we are so accustomed to a medicalized approach to health challenges that we want to put these elements through a test so that we can talk about them as a medical intervention and prescribe them (in this case, exercise) as a medical treatment. Shouldn’t we know better by now? There are many aspects to a good and healthy life. Exercise is 1 of them. If deficient or out of balance with other aspects of an individual’s life, something eventually goes amiss. I’d rather think that we are treating a deficiency when teaching patients the value of regular exercise in their lives. Exercise isn’t a therapy or a drug, but rather a necessity.
Conflict of Interest Disclosure
I have no conflict of interest in writing this review.
