Sarcopenia index as a prognostic indicator of mortality rates in community-dwelling centenarians: a prospective cohort study.

BACKGROUND: With global population aging rapidly, centenarians underscore the urgency of understanding their health trajectory and mortality determinants. Identifying reliable and accessible prognostic indicators of mortality rates, and exploring the influence of muscle health on healthy longevity, remain critical unmet needs. Traditional sarcopenia assessment tools including dual-energy X-ray absorptiometry (DXA) are costly and poorly accessible in the primary care. Sarcopenia index (SI), calculated from routine blood biochemical indicators, emerges as a promising low-cost alternative. This study aimed to evaluate prognostic value of SI for mortality rates in centenarians. METHODS: This prospective cohort study enrolled a total of 1002 community-dwelling centenarians from Hainan, China. Baseline data were collected through epidemiological survey and face-to-face interviews. SI was calculated as follows: serum creatinine (mg/dL)/cystatin C (mg/L) × 100. RESULTS: In a multivariate Cox regression analysis, SI was an independent predictor, with each unit increase associated with a 3.7% reduction in mortality rates (p < 0.001). Time-dependent receiver operating characteristic curve demonstrated moderate discriminative ability of SI. It identified the optimal SI cutoff points of 59.3, 63.1 and 64.2 for one-year, three-year and five-year mortality rates, respectively. Restricted cubic spline (RCS) analysis revealed a nonlinear relationship between SI and mortality rates characterized by a sharp decline in risk with an increasing SI before reaching a plateau. CONCLUSIONS: SI exhibited moderate but stable predictive performance for mortality rates among centenarians. As an easy-to-obtain surrogate marker rather than a direct diagnostic indicator of sarcopenia, SI demonstrated practical value with higher accessibility for predicting mortality rates among centenarians.