Depressive symptoms mediate the longitudinal link between sleep duration and subjective well-being in middle-aged and older Chinese adults.

Evidence on how sleep duration affects subjective well-being and depressive symptoms in older Chinese adults remains limited. Data from 10,706 participants aged 45 years and above in the China Health and Retirement Longitudinal Study (CHARLS) were analyzed. Descriptive statistics, restricted cubic spline models, and subgroup analyses were conducted. Mediation analysis with 1,000 bootstrap iterations assessed the statistical role of depressive symptoms. Sleep duration was significantly associated with depression, self-rated health, life satisfaction, and life expectancy. Restricted cubic spline models revealed a non-linear pattern: approximately 6.5 h of sleep was linked to more favorable levels of depressive symptoms and subjective well-being, with the associations plateauing beyond this point. Gender subgroup analyses showed consistent patterns. Mediation analysis suggested that depressive symptoms partially statistically accounted for the association between sleep duration and subjective well-being; however, because the mediator and outcomes were assessed concurrently (both in 2018), these findings should be interpreted as exploratory. Adequate sleep duration, with an observed non-linear pattern around ~ 6.5 h, is associated with lower depressive symptom levels and greater subjective well-being in Chinese middle-aged and older adults. Early screening for sleep and mental health issues in high-risk groups may help promote healthy aging.