Depression is a significant global challenge, affecting approximately 280 million individuals and contributing to over 47 million disability-adjusted life years in 2019 (World Health Organization, 2023). Globally, 5% of adults suffer from depression (WHO, 2023), with consequences extending beyond mental health to an increased risk of suicide and premature mortality from other illnesses. Effective prevention of depression requires targeted interventions and modifications to risk factors. Reviews suggest that staying physically active may be a preventive measure for depression. While previous studies show that more active individuals have a lower likelihood of developing depression, the strength of this connection and the most beneficial types of physical activity remain unexplored (Mammen & Faulkner, 2013). Therefore, this systematic review and meta-analysis aimed to thoroughly investigate this relationship, considering different activity levels and their impact on depression risk using a dose-response approach. It also aimed to estimate the potential reduction in depression cases within the population if more individuals engaged in higher levels of physical activity.
The study employed a systematic review and meta-analysis methodology, searching databases up to November 12, 2020, and including prospective cohort studies meeting specific criteria. The outcome of interest was depression, with data extracted independently by two reviewers and analysed using a two-stage random-effects dose-response meta-analysis. The findings revealed an inverse curvilinear dose-response relationship between physical activity and depression, with more significant risk reductions observed at lower activity levels. Achieving at least 8.8 mMET hours per week could potentially prevent 11.5% of incident depression cases, particularly for elevated depressive symptoms. Sensitivity and subgroup analyses did not significantly alter the results.
Strengths of the study include a robust methodology, dose-response analysis, comprehensive exposure harmonisation using mMET-h/wk, and Population Impact Fraction analyses. Limitations include reliance on self-reported measures, limited data at higher physical activity levels, and underrepresentation of lower- and middle-income countries.
In conclusion, the study suggests that even modest levels of physical activity can significantly reduce the risk of developing depressive symptoms. Health practitioners are encouraged to personalize recommendations and emphasize the mental health benefits of simple activities like walking or light exercises. Future research should explore the diverse impacts of different types, frequencies, and intensities of physical activity on mental health outcomes and consider contextual factors influencing this association. This will enable more personalized recommendations and effective strategies to manage challenges like reverse causality.
