Depression is a significant global problem, affecting the lives of approximately 280 million people and contributing to more than 47 million disability-adjusted life years in 2019 (WHO, 2023). 5% of adults worldwide suffer from depression (WHO, 2023). Its consequences extend beyond mental health, with increased risk of suicide and premature death from other diseases.
Effective prevention of depression requires targeted interventions and changes in factors that increase its risk. Reviews have pointed to the potential of staying physically active as a preventive measure for depression. Although previous research has shown that more active individuals are less likely to be depressed, an important aspect remains unexplored (Mammen & Faulkner, 2013).
To date, no studies have looked in depth to understand the strength of the relationship between physical activity and depression, nor have they identified the most beneficial types of physical activity. Thus, this systematic review and meta-analysis aimed to scrutinize this relationship using a dose-response approach, considering different levels of activity and their impact on depression risk. In addition, it attempted to estimate the potential reduction in the incidence of depression within the population if more individuals adopted higher levels of physical activity.
Can physical activity prevent the development of depression?
Methods
The study used a systematic review and meta-analysis methodology. The authors searched databases including PubMed, SCOPUS, Web of Science, PsycINFO and reference lists of systematic reviews up to 12 November 2020. Articles were reviewed in any language.
Prospective cohort studies that met specific criteria were included in the analysis. These criteria included reporting any aspect of physical activity at three or more exposure levels, providing risk estimates for depression, and having a sample size of 3,000 or more adults with 3 or more years of follow-up. The outcome of interest was depression, 1) the presence of a major depressive disorder as indicated by physician diagnosis, registry data, or self-report of diagnostic interviews, and 2) high depressive symptoms defined using validated cutoffs for a depressive screening instrument.
Two extractors independently extracted the data and a third reviewer checked for errors. A two-stage random-effects dose-response meta-analysis was used to model the dose-response relationship between physical activity and depression. Study-specific associations were estimated using generalized least squares regression, and the pooled association was calculated by pooling 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 populations of the included cohorts.
The authors systematically standardized exposure levels to a universal metric known as marginal metabolic equivalent work-hours per week (mMET-hours/week). This metric measures physical activity volume by capturing energy expended in excess of resting metabolic rate (1 MET). Multiple matching methods were used judiciously, taking into account the availability of reporting data, author data, and validation studies. The matching process significantly improves the comparability of data across studies, which is an essential condition for conducting a comprehensive meta-analysis. This standardization provides a nuanced understanding of the complex dose-response relationship between physical activity and depression.
Sensitivity and subgroup analyzes were performed, heterogeneity factors were investigated. These analyzes tested alternative hypotheses (eg, men and women) and aimed to explain variations in the association between physical activity and depression.
Results
The final meta-analysis included 15 studies with 191,130 participants and 2,110,588 person-years. About 64% of the participants in the studies were women. All but one of the studies were initiated 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, the majority of participants had an exposure level of less than 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 who engage in half the recommended activity have an 18% lower risk of depression and those who meet the recommended level have a 25% lower risk, with reduced potential benefits and higher uncertainty than this exposure level.
In a population risk assessment, researchers found that achieving at least 8.8 mMET hours per week could prevent 11.5% of depression events. The preventive effect was more pronounced for high depressive symptoms than for major depression.
Sensitivity analyzes tested alternative hypotheses and did not significantly alter dose–response associations or population risk estimates. Analysis of heterogeneity factors such as gender and study methods did not significantly explain variation in the association between physical activity and depression.
Engaging in physical activity, even at low levels, is associated with a reduced risk of depressive symptoms.
Results
This meta-analysis of the relationship between physical activity and depression shows significant mental health benefits of being physically active, even at levels below current public health recommendations.
The results highlight the benefits of physical activity in preventing depressive symptoms and informing public health approaches.
Strengths and limitations
The study demonstrates 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 harmonization, facilitated by using mMET-hours/week as a standard metric, ensured consistency in physical activity assessment across studies. Finally, including a Population Impact Fraction analysis, it offered practical insights into the public health consequences of achieving recommended levels of physical activity.
However, several limitations should be considered. First, reliance on self-reported measures introduced potential recall and social desirability biases and could potentially affect the accuracy of reported data. In addition, limited data at higher levels of physical activity may affect the generalizability of findings, particularly for individuals engaging in more intense physical activity. Furthermore, excluding device-based measures may lead to an incomplete representation of individuals' actual activity levels. In addition, 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 range of physical activity patterns and their association with depression over time. These limitations highlight the need for caution in interpreting the results, as factors such as reverse causation, where depression may lead to reduced physical activity, may confound the observed associations. Finally, it should be noted that these findings are observational and causality cannot be directly inferred. Other factors beyond physical activity may contribute to the observed associations.
The results should be interpreted with caution, as other social factors may contribute to the development of depressive symptoms despite being physically active.
Implications for practice
The results have important implications for clinical practice, highlighting the mental health benefits that can be achieved through moderate physical activity. Physicians are urged to individualize recommendations, as even modest levels of activity can significantly contribute to mental well-being. At the same time, there is a need to dispel the misconception that only vigorous exercise benefits mental health. Encouraging individuals to adopt simpler activities such as walking or light exercise can be equally effective in supporting their mental health. This transition shifts the focus from strict exercise routines to embracing manageable, everyday activities as mental health allies. For example, physicians and mental health practitioners can work with their clients to create customized exercise plans that meet their unique needs and goals, fostering motivation and engagement. Additionally, they can encourage clients to start with simple activities, highlighting recent research findings that even brisk walking provides significant health benefits.
In the future, researchers may delve deeper into the complex aspects of the dose-response relationship between physical activity and depression. This involves examining the different effects of different types, frequencies and intensities of physical activity on mental health outcomes. Understanding the contextual factors influencing this association would offer valuable insights, allowing for more personalized recommendations. In addition, future research efforts may prioritize the development of effective strategies to manage problems such as reverse causation and exposure measurement errors. Identifying longer follow-up times in studies would increase the accuracy of the interpretation of the relationship between physical activity and depression. In addition, examination of potential moderating factors such as age, gender, geographic location, and socioeconomic considerations will contribute to a more comprehensive understanding of the complex interactions between physical activity and mental health.
Physicians can make recommendations tailored to their clients' goals and needs, even at low exercise intensities.
Statement of interest
The author of this blog has no conflict of interest.
Links
Primary paper
Pearce, M., Garcia, L., Abbas, A., Stren, T., Schuch, FB, Golubic, R., Kelly, P., Khan, S., Utukuri, M., Laird, Y., Mok , A., Smith, A., Tainio, M., Brage, S., & Woodcock, J. (2023). The Relationship Between Physical Activity and Risk of Depression: A Systematic Review and Meta-analysis. JAMA Psychiatry, 79(6), 550-559.https://doi.org/10.1001/jamapsychiatry.2022.0609
References
Mammen, G., & Faulkner, G. (2013). Physical activity and depression prevention. American Journal of Preventive Medicine, 45(5), 649-657. https://doi.org/10.1016/j.amepre.2013.08.001
World Health Organization. (2023, March 31). Depressive disorder (depression). World Health Organization. https://www.who.int/news-room/fact-sheets/detail/depression