Bidirectional relationships between cognitive decline and depression: A study of middle-aged and older adults using...

Cognitive decline and depressive symptoms are common in middle-aged and older adults. Two competing theories-Scar Theory and Vulnerability Theory-offer insights into this relationship. Scar Theory suggests depression causes cognitive impairments, while Vulnerability Theory posits cognitive deficits predispose individuals to depression. Understanding these mechanisms is crucial for developing effective interventions, especially in underrepresented regions like China.

We applied cross-lagged panel network (CLPN) analysis to three waves (2015, 2018, 2020) of data from the China Health and Retirement Longitudinal Study (CHARLS), comprising 14,961 participants aged ≥45 years. Cognitive functions were assessed using the MMSE subscales, and depressive symptoms using the CESD-10. Analyses were conducted separately for males and females, and network centrality metrics were used to identify key bridge symptoms.

The results show that cognitive functions (particularly memory and orientation) predicted depressive symptoms at earlier stage, while hopelessness and low energy subsequently contributed to cognitive decline. Centrality analysis found memory and hopelessness emerged as key bridge symptoms. Sex-specific patterns were also observed: cognitive-to-depressive pathways were more prominent in females, whereas depressive-to-cognitive effects were more pronounced in males.

Causal inference is limited by the observational design. COVID-19 in the 2020 wave may have introduced external confounders.

These findings provide empirical support for both the scar and vulnerability hypotheses and underscore the importance of early, symptom-specific interventions-particularly those targeting memory and hopelessness-in mitigating the reciprocal risks of depression and cognitive decline in Chinese aging populations.