Prevalence, Trends, and Mortality of Low Muscle Mass and Its Association With Metabolic Diseases in the United States Population

Background
Low muscle mass is increasingly recognized to extend beyond aging and is closely linked to metabolic dysfunction. Its population-level burden, ethnic disparities, metabolic clustering and mortality impact in the United States remain incompletely characterized.
Methods
We analysed data from NHANES 1999–2016, including adults aged ≥ 18 years with dual energy X-ray absorptiometry (DEXA) measures. Low muscle mass was defined using established appendicular lean mass criteria adjusted for body size. Prevalence estimates were weighted to represent the US population. Temporal trends were assessed using Joinpoint regression, and mortality outcomes (all-cause, cardiovascular and cancer-related) were evaluated.
Results
Low muscle mass affected 8.35% (95% CI: 7.84% to 8.90% of US adults and remained stable over time (average annual percent change [AAPC]: −1.475, 95% CI: −3.853 to 0.961, p = 0.233). Mexican Americans had the highest prevalence (18.60%, 95% confidence interval [CI]: 15.64 to 21.98, p < 0.001), while non-Hispanic Blacks had the lowest (2.96%, 95% CI: 2.36 to 3.70, p < 0.001). Individuals with low muscle mass were older, had higher body mass index (BMI) and exhibited greater metabolic dysfunction, including hypertension (50.44%), diabetes (23.10%) and Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) (56.58%). Over a median follow-up of 166 months, low muscle mass was associated with increased all-cause mortality (adjusted hazard ratio: 1.43, 95% CI: 1.30 to 1.58, p < 0.001), though cardiovascular and cancer mortality associations attenuated after adjustment. The mortality risk was amplified when low muscle mass coexisted with diabetes, obesity, hypertension or hyperlipidaemia.
Conclusions
Low muscle mass affects nearly one in 12 US adults and is strongly intertwined with metabolic dysfunction. Our findings suggest that low muscle mass functions primarily as a marker of adverse metabolic health rather than an isolated predictor of mortality. Its coexistence with cardiometabolic disease confers substantially increased mortality risk, underscoring the need to identify, diagnose and manage low muscle mass within a metabolic disease framework rather than as an isolated muscle disorder.