The mediating role of functional impairment on the relationship between socioeconomic status and death among older adults in China

Socioeconomic status (SES) has been shown to have a significant influence on mortality in older adults. However, the specific dimensions and mechanisms of this influence remain unclear. Therefore, this study aimed to explore the relationship between SES and death in older adults and the mediating role of functional impairment between SES and death, using basic activities of daily living (BADL) and instrumental activities of daily living (IADL) as mediating variables. From the five waves of the Chinese Longitudinal Healthy and Longevity Survey (CLHLS) (2002–2014), 28,286 valid samples were selected. An SES index was constructed by a principal component analysis using three variables: education level, primary occupation before retirement and self-assessed economic status. Death was the outcome variable. Older people’s self-care capacity was the mediating variable, which included BADL and IADL. A modified Poisson regression analysis was performed to determine the association between SES and death. A causal mediation analysis based on a counterfactual framework was also performed to analyse the mediating effect of functional impairment on the relationship between SES and death. After adjustment for demographic characteristics, health behaviour characteristics, BADL and IADL, each 1-point increase in the SES index was negatively associated with an 8% lower risk of death at the first follow-up (odds ratio 0.92, 95% confidence interval [CI] 0.90–0.95, P < 0.001). Mediation analysis showed that BADL and IADL mediated the incidence of death at the first follow-up. The relative mediation effect was 13.37% (indirect effect 1.02, 95% CI 1.02–1.03). As with the influence of BADL, IADL mediated the occurrence of death at the first follow-up with an increasing SES index, accounting for 37.25% of the relative mediation effect (indirect effect 1.08, 95% CI 1.07–1.10). Based on the CLHLS cohort, low SES is a risk factor for death in older adults, and this effect is partly explained by the mediating effects of BADL and IADL.