Functional social isolation mediates the association between depression and executive function in older women: findings from the Canadian Longitudinal Study on Aging Comprehensive cohort.

Depression and social isolation increase risk for executive function declines and are among the top five modifiable risk factors for dementia. However, the interrelationships between depression, social isolation and executive function are not well established. Further evidence is needed to inform strategies to promote executive function and independence in older age. We examined whether social isolation mediated the association between depression and executive function in community-dwelling middle-aged and older adults and whether this association was modified by age and sex. Adults aged 45 to 85 years from the Canadian Longitudinal Study on Aging (CLSA) Comprehensive cohort were followed over three years (complete case analysis, n = 14,133). Baseline depressive symptoms, a history of clinical depression, and functional social isolation (perceived lack of social support) were self-reported. Executive function at follow-up was a composite measure of five cognitive tests. Conditional process analysis assessed the mediating effects of functional social isolation across age group and sex, adjusted for sociodemographic and health covariates. Functional social isolation significantly mediated the association of depressive symptoms (proportion mediated [P_M] = 8.0%) or clinical depression (P_M = 17.5%) with executive function only among women aged 75+ years. Functional social isolation explains a proportion of the total effect of depressive symptoms or clinical depression on executive function in women aged 75 and older. Although reverse causation cannot be ruled out, our findings suggest that interventions that reduce functional social isolation or depression in older women may promote executive function.