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Depression presents a significant global challenge, affecting the lives of approximately 280 million individuals and contributing to over 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, intertwining with an increased risk of suicide and premature mortality from other illnesses.
Effectively preventing depression requires targeted interventions and modifications to factors that heighten its risk. Reviews have hinted at the potential of staying physically active as a preventive measure for depression. While previous studies indicate that more active individuals have a lower likelihood of developing depression, a crucial aspect remains unexplored (Mammen & Faulkner, 2013).
No study to date has delved deeply into understanding the strength of the connection between physical activity and depression nor identified the most beneficial types of physical activity. Hence, this systematic review and meta-analysis aimed to meticulously explore this relationship, considering varying activity levels and their impact on depression risk, employing a dose-response approach. Additionally, it sought to estimate the potential reduction in depression cases within the population if more individuals embraced higher physical activity levels.
Can physical activity prevent developing depression?
Methods
The study employed a systematic review and meta-analysis methodology. The authors searched databases, including PubMed, SCOPUS, Web of Science, PsycINFO, and the reference lists of systematic reviews up to November 12, 2020. The articles were peer-reviewed and in any language.
Prospective cohort studies meeting specific criteria were included in the analysis. These criteria encompassed 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 a follow-up duration of 3 years or longer. The outcome of interest was depression, encompassing 1) the presence of major depressive disorder indicated by self-report of physician diagnosis, registry data, or diagnostic interviews, and 2) elevated depressive symptoms established using validated cut-offs for a depressive 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 the dose-response association between physical activity and depression. Study-specific associations were estimated using generalised least-squares regression, and the pooled association was calculated by combining the study-specific coefficients using restricted maximum likelihood. The population perspective of the relative importance of the estimated dose-response associations was calculated using potential impact fractions (PIFs) based on the exposure prevalence in the populations of the included cohorts.
The authors systematically standardised reported exposure levels to a universal metric known as marginal metabolic equivalent task hours per week (mMET-h/wk). This metric gauges physical activity volume by capturing energy expended above the resting metabolic rate (1 MET). Multiple harmonisation techniques were thoughtfully employed, considering reported information, author data, and validation work availability. The harmonisation process significantly improves the comparability of data across diverse studies, a critical prerequisite for conducting a comprehensive meta-analysis. This standardisation ensures a nuanced understanding of the intricate dose-response relationship between physical activity and depression.
Sensitivity and subgroup analyses were conducted, and heterogeneity factors were explored. These analyses tested alternative assumptions (e.g., 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 person-years were included in the final meta-analysis. Approximately 64% of 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 engaging in half the recommended activity had an 18% lower depression risk, while those meeting the recommended level had a 25% lower risk, with diminishing potential benefits and higher uncertainty observed beyond that exposure level.
Estimating the population risk, the researchers found that achieving at least 8.8 mMET hours per week could potentially prevent 11.5% of incident depression cases. The preventive effect was more pronounced for elevated depressive symptoms compared to major depression.
Sensitivity analyses tested alternative assumptions and did not materially alter the dose-response associations or population risk estimates. Analysing heterogeneity factors like gender and study methods did not significantly explain variations in the association between physical activity and depression.
Physical activity engagement, even at low volumes, is associated with a reduced risk of depressive symptoms.
Conclusions
This meta-analysis on the associations between physical activity and depression suggests significant mental health benefits from being physically active, even at levels below the current public health recommendations.
The findings highlight the benefits of physical activity in preventing depressive symptoms and informing public health approaches.
Strengths and limitations
The study exhibits several strengths. Firstly, it employed a robust methodology characterised by rigorous eligibility criteria and adherence to reporting guidelines. Secondly, by utilising dose-response analysis, the study provided a more precise understanding of the relationship between physical activity and depression. Thirdly, the comprehensive exposure harmonisation, facilitated by using mMET-h/wk as a standard metric, ensured consistency in assessing physical activity across studies. Lastly, including Population Impact Fraction analyses offered practical insights into the public health implications of achieving recommended physical activity levels.
However, several limitations should be considered. Firstly, reliance on self-reported measures may have introduced potential recall and social-desirability biases, potentially influencing the accuracy of reported data. Additionally, the limited availability of data at higher physical activity levels could impact the generalizability of findings, particularly for individuals engaging in more intensive physical activity. Moreover, excluding device-based measures may have led to an incomplete representation of individuals’ actual activity levels. Furthermore, the lack of repeated measures for physical activity and the underrepresentation of lower- 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, where depression may lead to reduced physical activity, could confound the observed associations. Lastly, it’s important to note that these findings are observational, and causation cannot be directly inferred. Other factors beyond physical activity could contribute to the observed associations.
The findings need to be carefully interpreted, as other social factors could contribute to developing depressive symptoms despite being physically active.
Implications for practice
The findings hold important implications for clinical practice, highlighting the substantial mental health benefits attainable through moderate levels of physical activity. Health practitioners are urged to personalise recommendations, acknowledging that even modest activity levels can contribute significantly to mental well-being. Simultaneously, there’s a need to dispel the misconception that only vigorous exercises yield mental health benefits. Encouraging individuals to adopt more simple activities like walking or light exercises can be just as effective in supporting their mental health. This shift redirects the focus from strict exercise routines to embracing manageable, everyday activities as mental health allies. For instance, GPs and mental health practitioners can work with their clients to create tailored exercise plans that meet their unique needs and objectives, fostering enthusiasm and involvement. Additionally, they can encourage clients to begin with simple activities, emphasising the latest research findings that even brisk walking provides significant health advantages.
In the future, researchers could delve deeper into the intricate aspects of the dose-response relationship between physical activity and depression. This involves exploring the diverse impacts of different types, frequencies, and intensities of physical activity on mental health outcomes. Understanding contextual factors influencing this association would offer valuable insights, enabling more personalised recommendations. Furthermore, upcoming research endeavours could prioritise developing effective strategies to manage challenges like reverse causality and exposure measurement errors. Establishing longer follow-up times in studies would enhance the accuracy of interpreting the relationship between physical activity and depression. Additionally, investigating potential moderating factors, such as age, gender, geographical location, and socio-economic considerations, would contribute to a more comprehensive understanding of the intricate interplay between physical activity and mental health.
Health practitioners can tailor recommendations to match the goals and needs of their clients, even at low exercise intensity.
Statement of interests
The author of this blog has no conflicts of interest.
Links
Primary paper
Pearce, M., Garcia, L., Abbas, A., Strain, T., Schuch, F. B., Golubic, R., Kelly, P., Khan, S., Utukuri, M., Laird, Y., Mok, 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.https://doi.org/10.1001/jamapsychiatry.2022.0609
References
Mammen, G., & Faulkner, G. (2013). Physical Activity and the Prevention of Depression. 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 Organisation. https://www.who.int/news-room/fact-sheets/detail/depression
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