Intrinsic Capacity and Incident Hip Fracture Risk by Sarcopenia Status in Middle-Aged and Older Chinese Adults: A Prospective CHARLS Cohort Study

<title>Abstract</title> <p>Background Intrinsic capacity (IC), a core concept in the World Health Organization (WHO) framework of healthy ageing, reflects the overall functional reserve of middle-aged and older adults. Although lower IC has been linked to adverse health outcomes, its association with incident hip fracture, particularly across different sarcopenia states and in combination with sarcopenia status, remains unclear. This study aimed to investigate the association between IC and incident hip fracture, explore its heterogeneity according to sarcopenia status, and assess the joint effect of IC and sarcopenia status on hip fracture risk. Methods This prospective cohort study used data from the China Health and Retirement Longitudinal Study (CHARLS), 2011–2020, and included 2,047 participants aged 45 years or older without hip fracture at baseline. Cox proportional hazards models were used to examine the association between IC and incident hip fracture. Stratified analyses were conducted according to sarcopenia status, and a joint risk score combining IC level and sarcopenia status was constructed to assess their combined effect on hip fracture risk. Subgroup and interaction analyses were further performed to test the robustness of the associations. Results During 9 years of follow-up, 91 participants developed incident hip fracture, corresponding to a cumulative incidence of 4.45%. In the fully adjusted model, each 1-point increase in IC was associated with a 23% lower risk of incident hip fracture (hazard ratio [HR] = 0.77, 95% confidence interval [CI]: 0.68–0.88, P &lt; 0.001). Compared with the low-IC group, the moderate-IC and high-IC groups had 63% (HR = 0.37, 95% CI: 0.21–0.68, P = 0.001) and 69% (HR = 0.31, 95% CI: 0.18–0.53, P &lt; 0.001) lower risks of incident hip fracture, respectively, with a significant dose-response relationship (P for trend &lt; 0.001). Stratified analyses showed that this inverse association was mainly observed among participants with confirmed sarcopenia. In the fully adjusted model, each 1-point increase in IC was associated with a 22% lower risk of hip fracture in this subgroup (HR = 0.78, 95% CI: 0.62–0.99, P = 0.042). Joint risk score analyses showed a graded increase in hip fracture risk with increasing score. Compared with the reference group (score 0), the HRs were 2.35 (95% CI: 1.15–4.81, P = 0.019), 2.87 (95% CI: 1.45–5.65, P = 0.002), and 4.37 (95% CI: 2.08–9.18, P &lt; 0.001) for scores 2, 3, and 4, respectively. In subgroup analyses, the associations of IC and the joint risk score with incident hip fracture were generally consistent across strata, with no significant interactions observed. Conclusions Higher IC was significantly associated with a lower risk of incident hip fracture, and this association was more evident among individuals with confirmed sarcopenia. Declining IC and worsening sarcopenia status showed a joint adverse effect on hip fracture risk. These findings support the incorporation of IC into hip fracture risk assessment and suggest that early identification and integrated intervention based on functional reserve may be particularly important for middle-aged and older adults with or at high risk of sarcopenia.</p>