Low appendicular skeletal muscle mass is associated with the risk of mortality among adults in the United States

Low skeletal muscle mass has been shown to be a predictor of mortality, but very few studies have focused on the association between appendicular skeletal muscle mass and mortality risk in a large sample. This study aimed to determine the associations of low appendicular skeletal muscle mass with all-cause and cause-specific mortality in an adult population in the United States. Data were retrieved from 21,938 participants aged 20-85 years from the National Health and Nutrition Examination Survey (NHANES) (1999-2006 and 2011-2018) and merged with the Public-use Linked Mortality File of 2018. The appendicular skeletal muscle mass index (kg/m²) was determined by the skeletal muscle mass in the arms and legs (in kg) and divided by the square of the height (in meters) ² (kg/m²). Sex-specific quintiles were then used to categorize the appendicular skeletal muscle mass index. The major outcome in this study was mortality from all causes, and the secondary outcome was mortality from heart disease or cancer. Cox proportional hazards models were used to calculate hazard ratios, and 95% confidence intervals for all-cause and competing risk regression analyses were performed to analyze heart disease mortality and cancer mortality. During a 10.9-year median follow-up, 1632 males and 1253 females died. Compared with those of the 5th quintile of the skeletal muscle index, the fully adjusted HRs (95% CIs) of all-cause mortality were 0.81 (0.72-0.92), 0.63 (0.52-0.76), 0.52 (0.43-0.63), and 0.65 (0.52-0.81) for the 1st, 2nd, 3rd, and 4th quintiles of the skeletal muscle index, respectively. A 20-percentile increase in the appendicular skeletal muscle index was associated with a lower risk of all-cause mortality (HR, 0.86; 95% CI, 0.81-0.91) (P < 0.001 for trend) and a lower risk of cancer mortality (HR, 0.87; 95% CI, 0.78-0.96) (P = 0.009 for trend). High appendicular skeletal muscle mass was associated with decreased all-cause mortality and cancer mortality in adults, and interventions aimed at maintaining appropriate appendicular skeletal muscle mass may help prevent premature death.