Sleep disorders as a catalyst: exploring the cyclical link between depressive symptoms and instrumental activities of daily living disability in older Chinese (Preprint)

BACKGROUND Depressive symptoms, sleep disorders, and functional disability are interrelated. However, the bidirectional pathways between depression, sleep disorders, and instrumental activities of daily living (IADLs) disability remain underexplored in China. OBJECTIVE We aimed to examine the bidirectional longitudinal relationships between depression and IADLs disability among older Chinese adults, with a focus on elucidating the mediating role of sleep disorders in this dynamic interplay. METHODS The study encompassed 2,667 older adults who provided complete data at T1 (2015), T2 (2018), and T3 (2020) of the China Health and Retirement Longitudinal Study (CHARLS). Depressive symptoms was assessed using the 10-item Centre for Epidemiological Studies Depression Scale (CESD-10), and a 6-item scale was used to measure IADLs disability. Sleep disorders were self-reported. Temporal associations between depressive symptoms and IADLs disability, as well as the longitudinal mediating effect of sleep disorders were examined using a cross-lagged panel model (CLPM). RESULTS Prior depression significantly predicted subsequent IADLs disability at T2 (β=0.070, P<0.001) and T3 (β=0.074, P<0.001) and prior IADLs disability predicted subsequent depression at T2 (β=0.094, P<0.001) and T3 (β=0.100, P<0.001). Additionally, the indirect effect of IADLs disability on depression via sleep disorders (β=0.062, SE 0.010, P<0.001, effect size 50.41%) was significant across all three-time intervals. However, the mediating role of sleep disorders rendered the direct effect of depression on IADLs disability non-significant (β=0.009, SE 0.018, P=0.609), indicating that depression primarily caused IADLs disability through sleep disorders in older adults. CONCLUSIONS Depressive symptoms and IADLs disability are bidirectionally linked, and sleep disorders play a longitudinal mediating role in the bidirectional relationship among older Chinese adults. The potential longitudinal bidirectionality highlights the importance of sleep health for interventions on depression and functional disability in older adults.