Coexisting low bone mass and low muscle phenotype in relation to falls and depressive symptoms among Korean adults: a nationally representative cross-sectional study

Coexisting low bone mass and impaired muscle health may identify adults vulnerable to falls and depressive symptoms, but population-based evidence from Asian adults is limited. This study examined associations of a combined bone–muscle phenotype and its individual components with these outcomes. This cross-sectional study used data from the 2024 Korea National Health and Nutrition Examination Survey for adults aged ≥ 40 years. Participants were classified into four mutually exclusive groups: neither deficit, low bone mass alone, a low muscle phenotype alone, or both deficits. Low bone mass was defined as the lowest dual-energy X-ray absorptiometry (DXA) T-score ≤ − 1.0 at the total femur, femoral neck, or lumbar spine. The low muscle phenotype was defined as low bioelectrical impedance-derived appendicular skeletal muscle mass index (ASMI) or low handgrip strength, using the Asian Working Group for Sarcopenia 2019 cut-points. Presence required at least one observed low component, whereas absence required both components to be measured and normal; indeterminate cases were excluded. Outcomes were self-reported falls in the past year and Patient Health Questionnaire-9 (PHQ-9) scores for depressive symptoms. Survey-weighted logistic and linear regression incorporated the complex sampling design and prespecified covariates. Among 3,141 adults, the combined phenotype was associated with higher odds of past-year falls (adjusted odds ratio 2.07, 95% confidence interval [CI] 1.30–3.29) and a 0.72-point higher PHQ-9 score (95% CI 0.29–1.15) than participants with neither deficit. Neither deficit alone was statistically associated with either outcome. In mutually adjusted component analyses, low ASMI was associated with falls (adjusted odds ratio 1.54, 95% CI 1.05–2.24), whereas low handgrip strength was associated with a 0.78-point higher PHQ-9 score (95% CI 0.08–1.49). In sensitivity analyses, the combined phenotype remained statistically associated with both outcomes among participants for whom both muscle components were measured; under the DXA-derived definition, it remained associated with higher PHQ-9 scores, whereas the association with falls did not reach statistical significance. These findings highlight the value of considering bone and muscle health jointly when characterizing physical and psychological vulnerability in adults. The distinct associations of muscle mass and muscle strength suggest that these components provide complementary rather than interchangeable information.