Independent and combined associations of activities of daily living and appendicular skeletal muscle mass with depressive symptoms: A population-based study.

BACKGROUND: The aging of populations worldwide has brought depressive symptoms in adults in the second half of life to the forefront of public health concerns. Although limitations in activities of daily living (ADL) and diminished appendicular skeletal muscle mass (ASM) each correlate with physical and psychological well-being in later adulthood, the degree to which they exert independent contributions, exhibit non-linear patterns, and operate through mediating pathways in relation to depressive symptoms has not been fully characterized. METHODS: The study sample was drawn from the 2015 CHARLS national survey, yielding an analytic cohort of 16,787 adults at least 45 years of age. Depressive symptomatology was operationalized with the CESD-10 instrument. Scores for ADL (comprising BADL and IADL subscales) and ASM were derived through validated measurement approaches. Analyses were performed using multivariable logistic models, with non-linearity probed via restricted cubic splines and piecewise regression; mediation was examined under a counterfactual framework. RESULTS: Across the cohort, 38.4% met the threshold for depressive symptoms. With all covariates held constant, the odds of depressive symptomatology rose by 10% for each additional point on the ADL scale (OR = 1.10; 95% CI: 1.09-1.12). A non-linear relationship was identified, with an inflection at an ADL score of 20.7. Relative to the low ASM tertile, individuals in the high tertile showed 26% diminished odds (OR = 0.74; 95% CI: 0.64-0.86). CONCLUSION: Greater ADL impairment was independently associated with elevated odds of depressive symptoms, whereas higher ASM showed an inverse relationship. Preserving day-to-day functional capacity and skeletal muscle mass may contribute to a lower burden of depressive symptoms and support healthy aging trajectories.