Physical activity and depression, role of familial and genetic confounding in multicohort study

Physical activity is a promising intervention method to treat and prevent depression. Experimental and observational studies have associated physical activity with lower depression risk, but they differ in the reported strength of the association. We used longitudinal multicohort data with twins and siblings to assess the strength of the association while accounting for familial and genetic confounding. The data included 7 cohorts from Finland, Germany, and US (n= 8,205 sibling and dizygotic twin pairs and 843 monozygotic twin pairs). We compared the effect sizes between ordinary regression models with within-sibling pair, and within-twin pair fixed-effect regression models. Results showed a weak association between physical activity and depressive symptoms in unpaired models (~SMD= -.07), which remained similar in within-sibling pair models (SMD=-.05), and in within-twin pair models (SMD= -.08). These results were robust with use of physical activity measured as minutes per week and with different intensities of physical activity. There was no evidence for reverse causality. Our findings suggest that naturally occurring individual differences in leisure-time physical activity may be only weakly associated with later depressive symptoms.