Physical Activity and Depression and Anxiety Disorders: A Systematic Review of Reviews and Assessment of Causality.

Introduction: Globally, depressive and anxiety disorders are the leading contributors to mental ill health. Physical activity reduces symptoms of depression and anxiety and has been proposed as an adjunct treatment therapy for depression and anxiety. Prospective studies suggest that physical activity may reduce the incidence of depression and anxiety. We conducted a systematic review of reviews with the aim to provide a comprehensive overview of available epidemiologic evidence on the strength of the association between physical activity and incident cases of depression and anxiety and to assess the likelihood of these associations being causal. Methods: We searched Embase and PubMed databases for systematic reviews published between January 1, 2000 and March 19, 2020 that reported findings on the strength of association between physical activity and incidence of depression and anxiety. We updated this search to October 15, 2022. Two reviewers independently assessed the methodologic quality of the included reviews using the Assessment of Multiple Systematic Reviews rating scale. We carried out a narrative synthesis of the evidence. We used the Bradford Hill criteria to assess the likelihood of associations being causal. Results: The initial search yielded 770 articles, of which 4 remained for data extraction. Two of the included reviews were scored as high quality, and 2 were scored as low quality. From the 2 included reviews that reported pooled estimates, people with high physical activity levels were found to have a decreased risk of incident depression (adjusted RR=0.83, 95% CI=0.76, 0.90) and reduced odds of developing anxiety (adjusted OR=0.74,95% CI=0.62, 0.88) when compared with those with low physical activity levels. We assessed physical activity to be probably causally related to both depression and anxiety. Discussion: Our evidence is drawn from systematic reviews of observational data. Further high-quality studies, such as randomized control trials, would help to strengthen the evidence base of the associations between physical activity and depression and anxiety. Nonetheless, our findings provide empirical support for the consideration of physical activity in strategies for the prevention of mental ill health.