Cognitive decline before and after incident depression: Evidence from three international prospective cohorts.

BACKGROUND: Depression and cognitive decline frequently co-occur in late life, potentially reflecting shared biological, psychological, or social pathways. However, their temporal relationship remains unclear. Understanding how cognitive deterioration and depression unfold over time may inform prevention and intervention strategies.

METHODS: This cohort study analyzed 40,167 older adults without baseline depression from CHARLS, HRS, and SHARE (2010-2021). Depressive symptoms were assessed using validated scales. Cognitive function was assessed across memory, executive function, and orientation, and standardized as z-scores. Linear mixed models estimated cognitive trajectories before, at, and after depression onset.

RESULTS: Across 401,017.8 person-years, 10530 participants developed depression. Compared with non-depressed individuals, those with depression onset showed faster cognitive decline before onset, acute decline at onset, and accelerated decline thereafter across all cognitive domains (P <0.001).

DISCUSSION: Cognitive decline precedes, accompanies, and accelerates after the onset of depression among older adults. These findings suggest that cognitive impairment may be an early signal associated with depression risk, highlighting the importance of routine cognitive monitoring in preventive mental health strategies.