Bioimpedance analysis and physical functioning as mortality indicators among older sarcopenic people.

OBJECTIVES:To assess the prognostic significance of various characteristics and measurements of sarcopenia and physical functioning on all-cause mortality among home-dwelling older people with or at-risk of sarcopenia. DESIGN:Cross-sectional and longitudinal analyses. SETTING:Porvoo sarcopenia trial in open care. PARTICIPANTS:Community-dwelling people aged 75 and older (N = 428, of which 182 were re-examined at one year) with four years of follow-up. MEASUREMENTS:Body mass index (BMI), physical functioning (physical component of the RAND-36) and physical performance tests (Short Physical Performance Battery (SPPB)), hand grip strength, walking speed, Charlson Comorbity Index, bioimpedance-based surrogates for muscle mass: Single Frequency Skeletal Muscle Index (SF-SMI), and Calf Intracellular Resistance Skeletal Muscle Index (CRi-SMI). Date of death was retrieved from central registers. Survival analyses were performed using Life-Table analyses and Cox models. RESULTS:Most test variables (except BMI) were associated with four-year mortality in a dose-dependent fashion. After controlling for age, gender and co-morbidity, physical performance and functioning (both SPPB and RAND-36), muscle strength (hand grip strength) and CRi-SMI appeared to be independent mortality risk indicators (p < 0.001) whereas SF-SMI was not. When CRi-SMI values were grouped by gender-specific cut-off points, the probability of surviving for four years decreased by 66% among the older people with low CRi-SMI (HR = 0.34, 95%CI 0.15-0.78, p = 0.011). When low CRi-SMI was further controlled for SPPB, the prognostic significance remained significant (HR = 0.55, 95%CI 0.33-0.92, p = 0.021). After controlling for age, gender, comorbidity, and CRi-SMI, the physical component of the RAND-36 (p = 0.007), SPPB (p < 0,001) and hand grip strength (p = 0.009) remained significant mortality predictors. Twelve-month changes were similarly associated with all-cause mortality during the follow-up period. CONCLUSION:CRi-SMI, muscle strength, physical performance and physical functioning are each strong independent predictors of all-cause mortality among home-dwelling older people. Compared to these indicators, BMI seemed to be clearly inferior. Of two bioimpedance-based muscle indices, CRi SMI was better predictor of mortality than SF-SMI. In this regard, muscle mass, muscle strength and physical performance are all suitable targets for the prevention of sarcopenia-related over-mortality.