Association between subjective well-being and low muscle mass among Chinese older adults: a nationwide cross-sectional study.

BACKGROUND: Mental health represents a significant global health issue, with emerging evidence suggesting a link between psychological well-being and physical health outcomes, including muscle health. Subjective well-being, a key component of mental health, may influence muscle mass through lifestyle factors (e.g., nutrition, sleep) and physiological mechanisms (e.g., neuroendocrine function, inflammation). However, its specific association with low muscle mass among older Chinese adults remains unclear. METHODS: This cross-sectional study utilized data from 11,345 participants in the 2018 wave of the Chinese Longitudinal Healthy Longevity Survey. Subjective well-being was assessed using a validated and applied eight-item scale, comprising one life satisfaction item, four positive emotion items, and three negative emotion items. Low muscle mass was defined using anthropometric indicators with sex-specific thresholds for appendicular skeletal muscle mass/height². Logistic regression was employed to examine the associations between SWB and LMM, adjusting for demographic, socioeconomic, behavioral, and health-related covariates. To explore the potential nonlinear association, spline smoothing analysis and threshold effect analysis were employed. Subsequently, to ensure the robustness of the findings, several sensitivity analyses were conducted. RESULTS: After adjusting for confounding factors, participants with better subjective well-being exhibited a reduced likelihood of low muscle mass [OR = 0.82, 95% confidence interval (CI) 0.73-0.92, P value < 0.001]. Notably, this inverse association displayed nonlinear characteristics (P for non-linear = 0.015), with an inflection point at a subjective well-being score of 28.00. Below this threshold, no significant association was detected (OR = 1.02, 95% CI 0.98-1.06), while each unit increase above 28.00 was associated with a 4% decrease in the likelihood of low muscle mass (OR = 0.96, 95% CI 0.94-0.98). The results remained consistent across sensitivity analyses. CONCLUSION: Our findings suggest that subjective well-being is a nonlinear modifiable determinant of low muscle mass in older adults. These results indicate that interventions aimed at enhancing subjective well-being may complement conventional strategies for regulating muscle homeostasis.