Abstract / Summary
Abstract Background Population aging is driving a mental health crisis among older adults that crosses national borders and social strata, and late-life depression poses an unprecedented challenge to public health systems worldwide. How physical activity shapes depressive symptoms over time in older populations, and whether that influence differs across macro-level national contexts, remains to be clarified. This study examines longitudinally the longitudinal association of physical activity on depressive symptoms in older adults. Methods Drawing on two large, nationally representative long panels — the China Health and Retirement Longitudinal Study (CHARLS) and the US Health and Retirement Study (HRS) — we constructed a longitudinal identification strategy integrating individual fixed effects, inverse probability weighting and cross-lagged panel models, and used it for comparative analysis. Results Cross-national fixed-effects models showed that the protective effect of physical activity was substantially moderated and constrained by educational attainment and living arrangements, displaying a clear asymmetry between the two countries: the US sample showed a robust protective effect on mental health (β = −2.734, p < 0.001), whereas the overall Chinese sample showed substantial attenuation (β = −1.338, p < 0.001). Subgroup inverse association and heterogeneity analyses revealed distinct cross-national heterogeneity between China and the United States, social disadvantage was associated with higher levels of depressive symptoms, whereas evidence for formal effect modification of the physical activity–depression association was limited. Conclusions The benefit of physical activity for the mental health of older adults is not universally applicable worldwide; it is constrained both by the macro-level national context and by micro-level social position. To address the mental health crisis of population aging, future public health interventions may benefit from combining opportunities for physical activity with social and environmental supports, particularly for older adults experiencing social disadvantage.