Associations Between Longitudinal Changes in Frailty and Incident Arthritis: A Multi-Cohort Study

Purpose: To examine the associations between baseline frailty, longitudinal changes in frailty status, and the risk of incident arthritis in older adults across diverse international populations. Methods: We analyzed harmonized longitudinal data from four large ageing cohorts: CHARLS (China), ELSA (England), SHARE (Europe), and MHAS (Mexico). A total of 48,480 participants aged 45 years and older were included in the baseline analysis, among whom 18,820 were included in the longitudinal frailty change analysis. Frailty was assessed using a standardized frailty index. We employed Cox proportional hazards models to estimate the associations of baseline frailty and frailty transitions over two years with subsequent incident arthritis, adjusting for sociodemographic and lifestyle covariates. Results: Higher baseline frailty levels were prospectively associated with an increased risk of incident arthritis, with Hazard Ratios (HRs) for the highest versus lowest frailty tertiles ranging from 1.26 (95% CI 1.10– 1.44) to 1.71 (95% CI 1.31– 2.23) across the cohorts. Regarding dynamic changes, worsening frailty was associated with a significantly elevated risk; specifically, transitioning from pre-frail to frail was associated with HRs ranging from 1.45 (95% CI 1.08– 1.95) in SHARE to 2.06 (95% CI 1.42– 2.98) in MHAS. In contrast, improvement in frailty status was not associated with a significant reduction in arthritis risk in any cohort. Conclusion: The relationship between frailty and arthritis risk is markedly asymmetric. While frailty progression significantly elevates risk, restoring a robust state does not immediately reverse this vulnerability. This suggests that preventing decline is far more effective than attempting to reverse risk once damage has occurred.