Abstract
BACKGROUND: Leisure activity is associated with a wide range of physical and mental health outcomes. Nonetheless, the causal basis for these associations is uncertain and we do not fully understand why some individuals are active while others are sedentary. METHODS: We investigated genetic and environmental contributions to individual differences in frequencies of social, physical, and intellectual leisure activities and their relationship to depressive symptoms, using data from the Interplay of Genes and Environment across Multiple Studies consortium. The sample consisted of 31 596 like-sex twins (44.1% monozygotic, 31.4% women, age range 32-99 years) representing 11 studies from Sweden, Denmark, United States, and Australia. RESULTS: Results indicated moderate contributions of genetic factors to social (a2 = 0.26, 95% CI = 0.16; 0.35), physical (a2 = 0.39, CI = 0.28; 0.51), and intellectual (a2 = 0.47, CI = 0.33; 0.61) activities. The contribution of shared environmental factors (c2) was trivial, ranging from -0.03 to 0.02, while estimates of nonshared environmental factors (e2) were consistently substantial, ranging from 0.52 to 0.68. There was no evidence that estimates varied by age and limited evidence that they varied by sex and country. Co-twin control analyses revealed a significant negative within-pair association of depressive symptoms with each activity domain. CONCLUSIONS: Although genetic factors contribute importantly to mid-to-late-life activity levels, associations of leisure activity levels with depressive symptoms remained significant when controlling for (unmeasured) genetic and shared environmental confounding. These findings are consistent with, albeit not proof of, a causal effect of leisure activities on depressive symptoms.