Association Between Frailty Status Transitions and Incident Pain Risk in Older Adults: A Prospective Cohort Study Across Three Countries

Objective: Frailty and pain frequently co-occur in older adults, yet evidence linking dynamic frailty transitions to incident pain across cultures is scarce. We examined associations of the Frailty Index (FI), frailty transitions, and cumulative frailty burden with incident pain in three countries. Methods: Adults aged ≥50 from CHARLS (China, n = 6,473), HRS (USA, n = 5,401), and ELSA (UK, n = 6,865) were included. A 28-item FI (covering chronic diseases, sensory impairment, physical functioning, depressive symptoms, and cognition) classified participants as robust (FI < 0.10), pre-frail (0.10 ≤ FI < 0.25), or frail (FI ≥ 0.25). Frailty transitions were assessed by comparing baseline and second-wave status (approximately 2 years apart). Pain was ascertained via a single self-reported item; participants free of pain at baseline were followed until incident pain, death, or last survey wave (up to 7–15 years). Cox proportional hazards models estimated HRs (95% CIs) with adjustment for demographics, socioeconomic factors, and health behaviors; missing covariate data were imputed using multiple imputation by chained equations(MICE). Kaplan–Meier(KM) curves visualized cumulative pain risk by transition group, and smoothed curves assessed non-linear FI–pain relationships. Results: Among 18,739 participants, baseline pre-frailty and frailty conferred ~2.7-fold and 9–13-fold excess pain risk, respectively. In transition analysis (n = 10,486), frailty progression elevated pain risk (CHARLS: HR 1.57; ELSA: HR 1.68; HRS: HR 1.11, NS). Pre-frail to frail worsening consistently increased risk (HR 1.59–1.74). Improvement reduced risk: pre-frail to robust (HR 0.66–0.70) and frail to less-frail (HR 0.63–0.76). KM curves showed early divergence and progressive separation across trajectories. Total FI tertiles demonstrated a significant dose–response gradient (highest tertile: HR 3.95–7.88; all P for trend < 0.0001), corroborated by smoothed curves showing a consistent positive FI–pain relationship across cohorts. Conclusion: Frailty transitions are bidirectionally associated with incident pain risk across China, the U.S., and England. Preventing frailty progression and promoting recovery may reduce pain burden in aging populations.