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Depression presents a significant global challenge, affecting the lives of approximately 280 million people and contributing to more than 47 million disability-adjusted life years in 2019 (WHO, 2023). Globally, 5% of adults suffer from depression (WHO, 2023). Its consequences extend beyond mental health and are linked to an increased risk of suicide and premature death from other illnesses.
Effective prevention of depression requires targeted interventions and changes to its risk factors. Reviews suggest the potential of being physically active as a preventive measure for depression. Although previous studies suggest that more active individuals are less likely to develop depression, one key aspect remains unexplored (Mamen & Faulkner, 2013).
No study to date has delved deeper into understanding the strength of the link between physical activity and depression or identified the most beneficial forms of physical activity. Therefore, this systematic review and meta-analysis aimed to explore this relationship closely, taking into account different activity levels and their effect on depression risk, using a dose-response approach. In addition, it attempted to estimate the potential reduction in cases of depression in the population if more people adopted higher levels of physical activity.
Can physical activity prevent the development of depression?
methods
The study used a systematic review and meta-analysis method. The authors searched databases including PubMed, SCOPUS, Web of Science, PsycINFO, and reference lists of systematic reviews up to November 12, 2020. Articles are peer-reviewed and in any language.
Prospective cohort studies meeting specific criteria were included in the analysis. These criteria report any aspect of physical activity at three or more exposure levels, provide risk estimates for depression, and have a sample size of 3,000 or more adults with a follow-up period of 3 years or more. The outcome of interest was depression, 1) presence of major depressive disorder as indicated by physician diagnosis, registry data, or self-report of diagnostic interviews, and 2) elevated depressive symptoms established using validated cut-offs for a depression screening instrument.
Two extractors independently extracted data and a third reviewer cross-checked for errors. A two-stage random-effects dose-response meta-analysis was used to model a dose-response association between physical activity and depression. Study-specific associations were estimated using generalized least-squares regression, and pooled association was calculated by combining study-specific coefficients using restricted maximum likelihood. A population perspective of the relative importance of the estimated dose-response associations was calculated using potential effect fractions (PIFs) based on the exposure prevalence in the population of the included cohorts.
The authors systematically standardized reported exposure levels to a universal metric called marginal metabolic equivalent task hours per week (mMET-h/wk). This metric estimates physical activity volume by summing energy expended above resting metabolic rate (1 MET). Multiple validation methods were thoughtfully used, taking into account the availability of reported information, author data, and validation work. The standardization process significantly improves the comparability of data across different studies, which is an important requirement for conducting a comprehensive meta-analysis. This standardization ensures a nuanced understanding of the complex dose-response relationship between physical activity and depression.
Sensitivity and subgroup analyzes were performed and differentiating factors were explored. These analyzes tested alternative hypotheses (eg, men vs women) and aimed to explain variations in the association between physical activity and depression.
Results
Fifteen studies with 191,130 participants and 2,110,588 individuals were included in the final meta-analysis. About 64% of the participants in the studies were women. All but one of the studies originated in high-income countries, including the United States (n=6), Europe (n=6), Australia (n=1) and Japan (n=1). One study included data from India, Ghana, Mexico and Russia.
Regarding physical activity, most participants had exposure levels below 17.5 mMET hours per week. An inverse curvilinear dose–response relationship was observed between physical activity and depression, with more significant differences in risk at lower activity levels. Adults participating in half of the recommended activity had an 18% lower risk of depression, but those meeting the recommended level had a 25% lower risk, with potential benefits diminishing and greater uncertainty observed beyond that exposure level.
Assessing population risk, the researchers found that achieving at least 8.8 mMET hours per week could prevent 11.5% of depression cases. The preventive effect was greater for elevated depressive symptoms than for major depression.
Sensitivity analyzes tested alternative assumptions and did not materially alter dose–response associations or population risk estimates. Analysis of covariates such as gender and study methods did not significantly explain variations in the association between physical activity and depression.
Physical activity engagement, even at low volumes, reduces the risk of depressive symptoms.
Conclusions
This meta-analysis on associations between physical activity and depression suggests significant mental health benefits from being physically active, even at levels lower than current public health recommendations.
Findings highlight the benefits of physical activity in preventing depressive symptoms and informing public health policies.
Strengths and limitations
The study exhibits several strengths. First, it used a robust methodology characterized by adherence to strict eligibility criteria and reporting guidelines. Second, by using a dose-response analysis, the study provided a more precise understanding of the relationship between physical activity and depression. Third, comprehensive exposure standardization, facilitated by the use of mMET-h/wk as a standard metric, ensures consistency in assessing physical activity across studies. Finally, including population impact fraction analyses, provided practical insights into the public health implications of achieving recommended physical activity levels.
However, several limitations should be considered. First, reliance on self-reported measures may have introduced potential recall and social-desirability biases, potentially affecting the accuracy of reported data. In addition, the limited availability of data at higher physical activity levels affects the generalizability of the findings, particularly to individuals who engage in more vigorous physical activity. Furthermore, exclusion of device-based measures may have resulted in an incomplete representation of individuals’ actual activity levels. Furthermore, the lack of repeated measures for physical activity and the underrepresentation of low- and middle-income countries limit the study’s ability to capture the full spectrum of physical activity patterns and their associations with depression over time. These limitations highlight the need for caution in interpreting the results, as factors such as reverse causality, in which depression leads to reduced physical activity, may confound the observed associations. Finally, it is important to note that these findings are observational and cannot directly infer causation. Other factors beyond physical activity may contribute to the observed associations.
Findings should be interpreted with caution as being physically active but other social factors may contribute to the development of depressive symptoms.
Implications for practice
The findings have important implications for clinical practice, highlighting the significant mental health benefits that can be achieved through moderate physical activity. Acknowledging that even modest activity levels can contribute significantly to psychological well-being, health practitioners are urged to individualize recommendations. At the same time, there is a need to dispel the myth that only vigorous exercise provides mental health benefits. Encouraging people to take up more regular activities such as walking or light exercise can be effective in supporting their mental health. This shift shifts the focus from rigorous exercise routines to embracing manageable, daily activities that are mental health allies. For example, GPs and mental health practitioners can work with their clients to create exercise plans tailored to their specific needs and goals, in a way that promotes motivation and engagement. In addition, they can encourage clients to start with simple activities, underscoring recent research findings that even brisk walking has significant health benefits.
In the future, researchers may delve deeper into the critical aspects of the dose-response relationship between physical activity and depression. This includes exploring the differential effects of different types, frequencies and intensities of physical activity on mental health outcomes. Understanding the contextual factors that influence this association provides valuable insights, enabling more personalized recommendations. Furthermore, future research efforts will prioritize developing effective strategies to manage challenges such as reverse causality and exposure measurement errors. Establishing longer follow-up times in studies increases the precision of describing the relationship between physical activity and depression. In addition, investigating potential moderating factors such as age, gender, geographic location, and socio-economic considerations may contribute to a more comprehensive understanding of the complex interaction between physical activity and mental health.
Health practitioners can tailor recommendations to fit their clients’ goals and needs, even at low exercise intensities.
Declaration of Interests
The author of this blog has no conflicts of interest.
Links
Primary paper
Pierce, M., Garcia, L., Abbas, A., Strain, T., Schuch, FB, Golubic, R., Kelly, P., Khan, S., Utukuri, M., Laird, Y., Mock, , A., Smith, A., Tainio, M., Brage, S., & Woodcock, J. (2023). Association between physical activity and risk of depression: a systematic review and meta-analysis. JAMA Psychiatry, 79(6), 550–559.
References
Mammen, G., & Faulkner, G. (2013). Physical activity and prevention of depression. American Journal of Preventive Medicine, 45(5), 649–657.
World Health Organization. (2023, March 31). Depressive disorder (depression). World Health Organization.