Independent and joint associations of intrinsic capacity and frailty index with incident disability and all-cause mortality among older Chinese adults

Abstract

Background Intrinsic capacity (IC) and the frailty index (FI) constitute two conceptually distinct frameworks for evaluating health status in later life; however, their comparative and combined prognostic utility for incident disability and all-cause mortality has not been fully elucidated. Methods This prospective cohort study included 7,168 adults aged ≥60 years from the 2014 wave of the Chinese Longitudinal Healthy Longevity Survey. IC was evaluated across five domains and aggregated into a composite score ranging from 0 to 10. FI was derived using a deficit accumulation approach. Incident disability was defined as new-onset limitation in at least one of six basic activities of daily living in 2018. All-cause mortality was ascertained during follow-up. Multivariable logistic regression and Cox proportional hazards models were applied, together with joint association and incremental predictive analyses. Results In fully adjusted models, higher IC was independently associated with lower odds of incident disability [odds ratio (OR) = 0.79, 95% confidence interval (CI): 0.74–0.84], whereas higher FI was associated with greater odds of disability (OR per 0.1 increase = 1.93, 95% CI: 1.67–2.23). Similarly, higher IC was associated with reduced risk of all-cause mortality [hazard ratio (HR) = 0.84, 95% CI: 0.82–0.85], whereas higher FI was associated with increased mortality risk (HR per 0.1 increase = 1.25, 95% CI: 1.19–1.31). After mutual adjustment, both IC and FI remained significantly associated with incident disability, whereas only IC remained significantly associated with all-cause mortality. Participants with concomitantly lower IC and higher FI exhibited the greatest risks of both disability (OR = 4.31, 95% CI: 2.65–7.04) and mortality (HR = 2.66, 95% CI: 2.32–3.04). Conclusion Both IC and FI were significantly associated with incident disability and all-cause mortality among older Chinese adults. The combination of IC and FI identified distinct profiles of functional and mortality risk, while IC showed a stronger association with mortality than FI.