Disease-specific associations with low muscle mass in older adults: A nationwide cross-sectional study

Malnutrition is an important clinical condition, with skeletal muscle mass as a key indicator. Although associations between specific diseases and nutritional status have been reported, few studies have accounted for the overall burden of comorbidities. This study investigated the association between individual diseases and muscle mass in older adults, considering comorbidities.

This cross-sectional study used nationwide claims data from 2023. Individuals aged 65-99 years were included. Appendicular skeletal muscle mass index (ASMI) was estimated by a validated equation, with a low ASMI defined as <7.0 kg/m² for male and <5.4 kg/m² for female. Comorbidities were assessed using the Charlson Comorbidity Index (CCI). Multivariable Poisson regression with robust variance estimation was performed to examine the associations between low muscle mass and each CCI component, as well as total CCI scores, adjusting for age, sex, and the Barthel Index.

A total of 1,153,538 older adults were analyzed (mean age 79.0 ± 7.8 years; 53.3% female), of whom 66.7% had low muscle mass. In the multivariable Poisson regression analysis, several comorbidities were independently associated with low muscle mass, with the strongest associations observed for metastatic solid tumors (adjusted prevalence ratio [aPR] 1.115), any malignancy (aPR 1.093), and rheumatic disease (aPR 1.079). The association between CCI score and low muscle mass increased stepwise beginning at CCI ≥2.

This study identified variations in the strength of associations between comorbidities and low muscle mass in older adults, highlighting the value of incorporating comorbidity profiles into muscle mass assessment in clinical practice. Given the potential influence of body size, adiposity, and fluid status on estimated muscle mass, these findings should be interpreted with caution.