Sequential link in depression, sleep and cognition: Longitudinal evidence from a serial multiple mediation analysis of older adults in China

Background: A growing body of literature examines the link between depression, sleep and cognition, but little is known regarding the extent to which this relationship holds among older adults over time.Objective: This study examines how sleep duration mediates the relationship between depressive symptoms and cognitive performance, by utilizing partial least squares structural equation modelling (PLS-SEM) estimation.Methods: This study utilizes the 2013-18 China Health and Retirement Longitudinal Study (CHARLS) dataset, of which 3557 participants over the age of 50 satisfied inclusion criteria. Depressive symptoms and cognitive performance are measured by the Center for Epidemiological Studies Depression Scale (CESD) and the Mini-Mental State Examination (MMSE); sleep duration is assessed using the adapted Pittsburgh Sleep Quality Index (PSQI). A serial multiple mediation model was built to assess how depressive symptoms in 2013 and in 2018 are related, in addition to assessing their links with sleep duration and cognitive performance.Findings: Results indicate that early depression positively predicts depression progression (std.8 = 0.564, 95 % Confidence Interval: 0.534, 0.594), but negatively predicts sleep duration (std.8 =-0.081, 95 % CI:-0.128, -0.034) and cognitive performance (std.8 =-0.118, 95 % CI:-0.165,-0.072). The sequential indirect effect of early depression operating via depression progression and sleep duration is evaluated to be-0.083 (95 % CI: -0.110,-0.056), representing as much as 41.29 % of the total effect. Conclusions: Early depressive symptoms are directly associated with increased depressive symptoms and shortened sleep, which are identified as key channels through which early depression is linked with worsened cognition.Clinical implications: Many older adults may underestimate the adverse costs of early depression, since its net effects on cognition could be channeled indirectly and discretely via depression progression and sleep, which is worth highlighting in health guidelines and clinical recommendations.