Frailty, depressive symptoms, and incident respiratory disease: a CHARLS cohort study

Ageing populations face a rising burden of asthma and chronic lung disease (CLD). We assessed whether frailty and depressive symptoms—and their changes—predict incident respiratory diseases. Adults ≥ 45 years from the China Health and Retirement Longitudinal Study (CHARLS) without asthma or CLD at baseline were followed. Multivariable logistic regression estimated odds ratios (ORs) for baseline frailty (per 0.1-unit increase), CES-D-10 depressive symptoms, and transitions across two waves. Dose–response was examined using smoothed curve fitting and threshold effect analysis. We tested the interaction between frailty and depressive symptoms and performed stratified analyses by depressive status. All models were adjusted for comprehensive covariates, including daily cigarette consumption and history of prior lung disease. Sensitivity analyses were conducted by excluding heavy smokers and using an onset-timing proxy respectively. During follow-up, 258 participants developed asthma and 702 developed CLD. In multivariable models, each 0.1-unit increase in the baseline frailty index was associated with a higher risk of asthma (OR = 1.222, 95% CI 1.081–1.381) and, more strongly, with CLD (OR = 1.291, 95% CI 1.190–1.402). For depressive symptoms, each 1-point increase was significantly associated with an increased risk of CLD (OR = 1.032, 95% CI 1.018–1.047), while the association with asthma was positive in direction but did not reach statistical significance (OR = 1.016, 95% CI 0.994–1.039). The interaction between frailty and depressive symptoms was statistically significant for CLD (p < 0.05) but not for asthma, suggesting a synergistic effect for CLD but independent effects for asthma. Smoothed curve fitting showed an approximately linear gradient for depressive symptoms with both outcomes; for FI, the asthma curve rose at low FI and then plateaued, whereas the FI–CLD curve was monotonically increasing. These associations remained robust in sensitivity analyses excluding heavy smokers. Frailty and depressive symptoms are key risk markers for incident respiratory disease in later life. Incorporating brief frailty assessment and depression screening into routine care may improve risk stratification and support upstream, multidisciplinary prevention for asthma and CLD.