Age-related changes in bioelectrical impedance analysis-derived phase angle (PhA) and the association between PhA and sarcopenic obesity in Chinese adults

There are limited studies on the phase angle (PhA) and sarcopenic obesity (SO) in the Chinese population. This study aimed to establish 50 kHz-PhA reference data for SO population, and to evaluate the correlation between 50 kHz-PhA and SO. A total of 10,312 participants including 5415 men and 4897 women were enrolled in this study, and their resistance and reactance at 50 kHz, and body composition parameters were measured a segmental multifrequency bioelectrical impedance analysis device (InBody 720). Participants were compared between the SO and non-SO groups. Then, age and fat parameters related changes in PhA were evaluated. Furthermore, Receiver Operating Characteristic (ROC) curves were used to identify the optimal PhA cutoff values for detecting SO in males and females. The results showed significant differences in PhA and body composition parameters between the SO group and the non-SO group in both sexes (P < .001), and the prevalence rates of SO increase with age in both sexes (P < .001). The PhA values decrease with age, with a significant decrease beginning at age 65 years for males and 66 years for females. The accumulation of excess adipose tissue was also found to be associated with decrease in 50 kHz-PhA value. Furthermore, PhA was negatively associated with SO, independent of age and sex. The area under the ROC curve (AUC) of PhA for SO was 0.790 (95% CI: 0.746-0.833, P < .001) in males and 0.763 (95% CI: 0.702-0.825, P < .001) in females. The optimal cutoff value was ≤ 5.55° (specificity 0.693, sensitivity 0.759) for males and ≤4.79° (specificity 0.687, sensitivity 0.738) for females. In conclusion, 50 kHz-PhA can be used as a predictor of SO, with cutoff values of ≤5.55° for males and ≤4.79° for females. This simple and practical method of using 50 kHz-PhA to predict SO could be valuable in clinical practice.