Association between phase angle and incidence of sarcopenia: a 6-year prospective cohort study

Phase angle (PhA), a parameter derived from bioelectrical impedance analysis (BIA), is a non-invasive indicator of cellular integrity and body cell mass. This study aimed to explore the longitudinal association between PhA and sarcopenia and to determine its predictive cut-off value among Chinese older adults. This was a 6-year prospective cohort study utilizing data from the West China Health and Aging Trend (WCHAT) Study. Baseline PhA was measured using bioelectrical impedance analysis (BIA) and analyzed both as continuous and categorical (quartiles, Q1-Q4) variables. Incident sarcopenia was diagnosed using the 2019 Asian Working Group for Sarcopenia (AWGS 2019) diagnostic criteria. Cox proportional hazards regression was employed to examine the association between PhA and the risk of sarcopenia. Receiver operating characteristic (ROC) curve was used to assess the cut-off value of PhA in predicting sarcopenia. This study included 1191 participants with a median age of 65 years (IQR, 63–69), and 62.7% were female. At baseline, PhA ranged from 3.3° to 7.8°. During a median follow-up of 5.0 years (IQR, 4–6 years), 204 (18.7%) participants developed sarcopenia. Higher PhA was associated with a lower risk of sarcopenia (HR: 0.51, 95% CI: 0.39–0.68). The hazard ratios for PhA Q2-Q4 were 0.53 (0.38–0.75), 0.49 (0.31–0.77), and 0.33 (0.21–0.53), respectively. ROC analysis demonstrated moderate predictive performance of PhA for sarcopenia in both sexes, with AUC values of 0.775 in men and 0.803 in women, and optimal cut-off points of 5.0° and 4.5°, respectively. Higher PhA is associated with decreased risk of sarcopenia and demonstrates modest predictive potential. These findings suggest that PhA could be a potential predictor for sarcopenia in Chinese older adults, though further validation in larger cohorts is needed.