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

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).