Low Muscle Mass, Sleep Quality, and Quality of Life Among Older Chinese Adults: A Cross-Sectional Study

Background: Low muscle mass (LMM), poor sleep quality, and reduced quality of life (QOL) are common concerns in older adults. This study examined their cross-sectional associations and explored the statistical indirect association involving sleep quality, with particular attention to sensitivity to body-size adjustment and alternative model specifications. Methods: We analyzed data from 9366 adults aged 65 years or older in the 2018 Chinese Longitudinal Healthy Longevity Survey. LMM was classified using anthropometrically predicted appendicular skeletal muscle mass, while sleep quality and overall QOL were assessed using single-item self-reports. Regression-based indirect associations were estimated with 5000 bootstrap resamples. Sensitivity analyses examined alternative measurements, body-size adjustment, depressive symptoms, model ordering, missing-data assumptions, and sampling weights. Results: Anthropometrically estimated LMM was associated with poorer sleep quality (B = −0.066, 95% CI: −0.110 to −0.022) and lower QOL (total association: B = −0.073, 95% CI: −0.108 to −0.039). Better sleep quality was associated with higher QOL (B = 0.163, 95% CI: 0.147 to 0.178). The indirect association was small (B = −0.011, 95% bootstrap CI: −0.018 to −0.003) and attenuated after continuous body mass index adjustment (B = −0.001, 95% bootstrap CI: −0.010 to 0.008). Adjustment for depressive symptoms further attenuated the estimated indirect association, while a reverse-order model also yielded a non-zero indirect association (B = −0.020). Residual-confounding sensitivity analyses indicated dependence on assumptions about unmeasured common causes. Conclusions: Anthropometrically estimated LMM was associated with poorer perceived sleep quality and overall QOL, but the estimated indirect association involving sleep quality was small and sensitive to body-size adjustment, psychological covariates, and model specification. These cross-sectional findings do not establish a muscle-specific association independent of overall body size or a causal sleep-mediated pathway. Longitudinal studies incorporating directly measured body composition and validated multidimensional sleep and QOL assessments are needed to clarify these relationships.