Socioeconomic status and depression in later life: longitudinal mediation effects of activities of daily living

Background Socioeconomic status (SES) is associated with both depression and activities of daily living (ADL and IADL). However, the role of ADL as a biological mechanism in the relationship between SES and late-life depression, examined through longitudinal data, remains understudied. This study explored the longitudinal mediation effects of basic ADL or IADL on the SES-depression link in older adults. Methods Data from the China Health and Retirement Longitudinal Study (N = 4104) were utilized. Mediation analysis was performed using parallel process latent growth curve modeling. Results The average age of participants was 57.76 years, and 55.7% being females. Significant linear growth over time was observed in ADL, IADL, and depression. Adjusting for covariates, SES was positively linked to the initial levels (intercepts) of ADL (beta(iADL)=-0.100[-0.143, -0.057]), IADL (beta(iIADL)=-0.140[-0.185, -0.095]), and depression (beta(iDEP)=-0.103[-0.158, -0.048]). However, SES showed no significant correlation with the rate of change (slopes) in ADL, IADL, or depression (P > 0.05). The intercepts of ADL (beta(iDEP) = 0.566[0.503, 0.629]) and IADL (beta(iDEP) = 0.607[0.544, 0.670]) were positively correlated with the depression intercept but negatively with the depression slope. Conversely, the slopes of ADL and IADL were positively associated with the depression slope. These results suggest a negative indirect relationship between SES and the initial level of depression, but a positive indirect relationship with the rate of increase in depression through ADL (or IADL) intercept. Conclusions Higher SES is associated with a lower initial risk of depression and ADL difficulties. However, this same higher SES may relate to a faster increase in ADL difficulties and depression among middle-aged and older adults. The findings underscore the need for increased governmental healthcare funding and improved healthcare accessibility. Additionally, maintaining adequate sleep and physical activity can help prevent disability and reduce depression risk later in life, particularly among older adults with lower SES.