The mediating and moderating effects of depressive symptoms on the prospective association between cognitive function and activities of daily living disability in older adults

Objectives: This study aimed to examine to what extent depressive symptoms mediated and moderated the association between cognitive function and activities of daily living (ADL) disability in older adults. Methods: In older participants from the China Health and Longitudinal Retirement Survey (CHARLS), structural equation modeling and multiple regression were performed to examine the mediating and moderating role of depressive symptoms (measured by the 10-item Center for Epidemiologic Studies Depression Scale) in the association between baseline cognitive function (episodic memory, attention, orientation to time, and visuospatial ability) and endpoint disability in basic ADL (BADL) or instrumental ADL (IADL). Results: Over a 2-year follow-up, among 1677 participants (67.5 +/- 6.0 years old) free of BADL disability and 1194 participants (66.9 +/- 5.6 years old) free of IADL disability, 8.3% and 22.9% developed BADL disability and IADL disability, respectively. Good baseline cognitive performance was significantly associated with the reduced incidence of BADL/IADL disability. The indirect effects of baseline depressive symptoms explained 16.9% and 14.5% of the total effect between cognition and BADL and IADL dependency, respectively. The Johnson-Neyman technique identified a threshold of 7.88 for endpoint depressive symptoms, beyond which the protective effect of baseline cognitive function on BADL emerged. Conclusions: In older adults, good cognitive function reduces the risk of BADL/IADL disability. Depressive symptoms downregulate the protective effect of cognitive function on BADL/IADL over time. Intervention techniques focusing on the simultaneous improvement of cognitive dimensions and depression help improve ADL difficulty and prevent disability in older adults.