Association of muscle mass, muscle quality, and function with mortality in community-dwelling older adults: Focus on segmental phase angle and extracellular to intracellular water ratio

Abstract

Background & aims: We investigated the prospective association between morphological muscle quality indicators-phase angle (PhA) and the extracellular to intracellular water (ECW/ICW) ratio-and all-cause mortality in community-dwelling older adults over a 12-year period by comparing them with traditional body composition and performing physical function tests.

Methods: This longitudinal study included a total of 868 older adults aged ≥65 years who underwent examinations from 2011 to 2019, and mortality data were monitored through to 2023 using the city's municipal database. Body composition was measured using multi-frequency bioelectrical impedance analysis (BIA) to assess whole-body and leg PhA, ECW/ICW resistance ratio (morphological muscle quality), appendicular lean muscle mass index (ALMI), leg SMI, and fat mass percentage (fat%) (body quantity). Physical function was evaluated using hand grip strength, a 5-m habitual walk (5-m walk), and a 5-repetition sit-to-stand test (chair stand). We performed Cox regression analysis to examine the prospective association of BIA and physical function variables with all-cause mortality and applied restricted cubic splines to reveal the dose-response relationship between them.

Results: The adjusted Cox model showed significant associations between lower leg PhA (hazard ratio [HR] 0.79, 95 % confidence interval [CI] 0.64-0.97), leg ECW/ICW resistance ratio (HR: 0.79, 95 % CI: 0.64-0.98), slower 5-m walk time (HR: 0.79, 95 % CI: 0.69-0.90), and longer chair stands time (HR: 0.87, 95 % CI: 0.76-0.999) and mortality (to allow for comparison, all variables were standardized into z-scores, where higher values consistently indicated better results). A dose-response relationship indicated a higher risk for individuals with values below the median in restricted cubic splines. No associations were found between ALMI, fat%, hand grip strength, and mortality.

Conclusion: Muscle quality, particularly leg PhA and ECW/ICW ratio, and physical function tests are key predictors of mortality in community-dwelling older adults.

Keywords: Bioelectrical impedance analysis; Bioimpedance; Dose–response relationship; ECW/ICW; Physical function; Skeletal muscle.