Longitudinal Trajectories of Cognitive Function Among Chinese Middle-Aged and Older Adults: The Role of Sarcopenia and Depressive Symptoms

<b>Objectives:</b> The longitudinal relationship between sarcopenia, depression, and cognitive impairment has been insufficiently studied in China. This study aimed to characterize the association between sarcopenia and cognitive impairment and the mediating role of depression using nationally representative data. <b>Methods:</b> 7091 middle-aged and older adults were analyzed from the China Health and Retirement Longitudinal Study (CHARLS) across three waves (2011, 2013, and 2015). Cognitive trajectories were modeled using a group-based trajectory model (GBTM), while multivariable ordinal logistic regression was employed to evaluate the associations with cognitive trajectories. The mediating role of depressive symptoms was assessed through bootstrap mediation analysis and cross-lagged panel modeling (CLPM). <b>Results:</b> Trajectory analysis identified four distinct cognitive function patterns: "High and Stable" trajectory (<i>n</i> = 2563, 36.73%), "Middle and Stable" group (<i>n</i> = 2860, 38.76%), "Middle and Decline" group (<i>n</i> = 1280, 18.62%), and "Low and Decline" group (<i>n</i> = 388, 5.90%). Sarcopenia and depressive symptoms were associated with the "Low and Decline" trajectory of cognitive function [Overall: OR (95%CI) of 0.315 (0.259, 0.382) and 0.417 (0.380, 0.459)]. Mediation analysis indicated that depressive symptoms accounted for 11.78% of the relationship between sarcopenia and cognitive trajectories. The cross-lagged panel modeling demonstrated a significant mediation pathway of "T1 cognitive function → T2 depression → T3 sarcopenia", with T2 depression mediating 5.31% of the total effect. <b>Conclusions:</b> Our study identified four distinct cognitive trajectories, with sarcopenia and depressive symptoms significantly associated with worse cognitive trajectories over time. Depressive symptoms mediated the relationship between sarcopenia and cognitive function. This highlights the importance of integrating mental health and physical health interventions to address the interconnected risks associated with aging.