Association between frailty status and depression among older adults: panel data analysis of three longitudinal cohort studies

Declining physical function and increasing frailty are common in older adults, and physical frailty is associated with psychological disorders. This study examined the association between the Frailty Index (FI) and depression among older adults from three countries. This study utilized data from participants aged 50 and older in three studies: the China Health and Retirement Longitudinal Study (CHARLS), the US Health and Retirement Study (HRS), and the English Longitudinal Study of Ageing (ELSA), comprising 52,211 individuals with 139,513 observations. Frailty was assessed using a 27-item FI, encompassing diseases (excluding heart disease and stroke), symptoms, disabilities, physical function, and cognition, scored from 0 to 1. Depressive symptoms were measured using the Center for Epidemiologic Studies Depression Scale (CES-D). Generalized estimating equations (GEE) with binary logistic regression were used to examine the FI-depression association, adjusting for potential confounders identified via causal directed acyclic graphs. Additionally, curve fitting was applied to explore non-linear relationships, while Poisson binomial regression and subgroup analyses were conducted to test the robustness of the findings. In the fully adjusted model (Model 3), a higher FI (per 0.1-unit increase) was positively associated with greater odds of depression (CHARLS: β = 1.7, 95% CI 1.7–1.8; HRS: β = 2.0, 95% CI 1.9–2.1; ELSA: β = 1.6, 95% CI 1.6–1.6). Compared to the robust group (FI ≤ 0.10), the frail group (FI ≥ 0.25) had significantly higher odds of depression (CHARLS: OR = 4.9, 95% CI 4.5–5.3; HRS: OR = 4.3, 95% CI 3.8–4.9; ELSA: OR = 4.4, 95% CI 4.0–4.8). When FI was categorized into tertiles, the highest tertile (T3) was associated with increased odds of depression compared to the lowest tertile (CHARLS: OR = 3.4, 95% CI 3.2–3.7; HRS: OR = 2.7, 95% CI 2.5–3.0; ELSA: OR = 3.3, 95% CI 3.0–3.6). A positive association was observed between the Frailty Index and depression among older adults in CHARLS, HRS, and ELSA. these findings suggest that maintaining physical robustness is associated with a lower burden of depressionin older populations.