Independent and interactive associations of physical activity intensity and sleep duration with depressive symptoms among middle-aged and older Chinese adults: evidence from CHARLS 2020

Physical activity and sleep are modifiable behaviours associated with mental health; however, associations with depressive symptoms may differ across physical activity intensity and sleep duration. This study examined the independent and interactive associations of participation in vigorous, moderate, and light physical activity and sleep duration with depressive symptoms among middle-aged and older Chinese adults. This cross-sectional study used data from the 2020 China Health and Retirement Longitudinal Study (CHARLS). Depressive symptoms were assessed using the 10-item Center for Epidemiologic Studies Depression Scale (CESD-10; score ≥ 10). Physical activity was classified as vigorous, moderate, or light, and sleep duration as short (< 6 h/day), normal (6–8 h/day), or long (> 8 h/day). Multivariable logistic regression estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs). Statistical interaction by sleep duration was assessed using interaction terms and adjusted marginal differences. A sensitivity analysis incorporated frequency and daily duration of vigorous physical activity. Among 16,165 participants, 37.6% had depressive symptoms; 15,816 participants were included in complete-case regression analyses. Compared with normal sleep duration, short sleep was associated with higher odds of depressive symptoms (aOR = 2.48, 95% CI: 2.31–2.66), whereas long sleep was not significantly associated (aOR = 1.04, 95% CI: 0.90–1.20). Vigorous physical activity was associated with higher odds of depressive symptoms (aOR = 1.34, 95% CI: 1.24–1.45), whereas light physical activity was associated with lower odds (aOR = 0.91, 95% CI: 0.83–0.99); moderate physical activity was not significantly associated. The sensitivity analysis showed a broadly consistent positive association across higher frequency-duration categories of vigorous physical activity. Sleep duration and physical activity intensity showed distinct associations with depressive symptoms. These findings highlight the importance of considering physical activity intensity and context alongside sleep duration when investigating behavioural correlates of mental health in ageing populations.