Joint effects of sleep duration and depression on the risk of cardiovascular disease and mediating role of depression in middle-aged and older Chinese adults: a nationwide prospective cohort study

Background: Cardiovascular diseases (CVD) are the leading cause of mortality in China. Depression and sleep disturbances are recognized as risk factors for CVD, but their interplay and combined effects remain unclear. This study examines how sleep duration and depression interact to influence CVD risk. Methods We analyzed data from five waves of the China Health and Retirement Longitudinal Study (CHARLS) between 2011 and 2020. The final sample included 12,050 individuals aged 45 and above. Sleep duration was categorized as 6 hours or less, 6?8 hours and >8 hours. Depression was assessed using the CESD-10 score and categorized as no depression, mild/moderate depression, and severe depression. Cox proportional hazards models assessed the association between sleep, depression, and CVD. Mediation analysis explored depression?s role in this relationship. Results Short sleep duration was associated with a higher CVD risk (HR 1.19; 95% CI: 1.03?1.38). Restricted cubic spline (RCS) analysis showed a U-shaped association between sleep duration and CVD risk, with the lowest risk observed at 7.61 hours of sleep. Severe depression further increased CVD risk when combined with short sleep duration (HR 2.08; 95% CI: 1.46-2.95) or long sleep duration (HR 2.08; 95% CI: 1.05-5.35). Mediation analysis revealed that depression explained 43.8% of the total effect of short sleep on CVD. Conclusions Both short sleep and depression independently raise the risk of CVD, with depression partially mediating the effect of sleep on cardiovascular health. Interventions targeting both sleep and mental health could reduce CVD risk in high-risk populations.