Frailty mediates the association between sleep duration and physical, psychological, and cognitive multimorbidity in Chinese middle-aged and older adults

The association between sleep duration and physical, psychological and cognitive multimorbidity (PPC-MM) remains unclear. This study explores whether frailty accounts for part of this association using both cross-sectional and longitudinal analyses. This study utilized data from the China Health and Retirement Longitudinal Study (CHARLS) collected between 2011 and 2018, involving 7,193 participants for cross-sectional and 5,380 for longitudinal analysis. Multivariate logistic regression and Cox proportional hazards models evaluated the association between sleep duration, frailty, and PPC-MM risk. Nonlinear dose-response relationships were assessed with restricted cubic spline (RCS) analysis, and subgroup analyses examined demographic differences. Bootstrap resampling with 1,000 iterations was used to estimate the indirect pathways. In the cross-sectional path analysis, logistic regression analysis showed that sleep duration was negatively associated with PPC-MM (OR = 0.84, 95% CI: 0.80-0.89, P < 0.001). Frailty showed a positive association with PPC-MM (OR = 4.80, 95%CI: 3.92-5.88, P < 0.001). Frailty accounted for 31.61% of the statistical association between sleep duration and PPC-MM. In the longitudinal exploratory mediation analysis, Cox models showed that longer sleep duration was associated with a lower risk of incident PPC-MM (HR = 0.85, 95% CI: 0.80-0.89, P < 0.001). Frailty was positively associated with PPC-MM risk (HR = 5.89, 95% CI: 4.81-7.21, P < 0.001). Exploratory mediation analysis further indicated that the indirect pathway via frailty accounted for 26.99% of the total prospective association between sleep duration and incident PPC-MM. Sleep duration was negatively associated with PPC-MM, while frailty was positively associated with PPC-MM. Exploratory analyses suggested that frailty may serve as a partial intermediary in this association.