Skeletal muscle mass index is independently associated with all-cause mortality in men: The Nagahama study

We aimed to determine if skeletal muscle mass is a predictor of all-cause mortality and if muscle mass plays a role in the association between body mass index (BMI) and all-cause mortality in community residents.

The study population consists of 3582 elderly (age ≥65 years) adults. The skeletal muscle mass index (SMI) was measured between 2013 and 2016. Men with SMI <7.0 kg/m² and women with SMI <5.7 kg/m² were considered to have low SMI. All-cause mortality was determined by reviewing residential registry records (follow-up duration: 2564 ± 373 days).

The mortality rate of the low SMI group was significantly higher than that of the normal SMI group in men (191.3 vs. 93.0 per 10 000 person-years, P < 0.001), but not in women (P = 0.191). In Cox proportional hazard analysis adjusted for possible covariates, the group differences remained significant (hazard ratio = 1.82, P = 0.011). The results were similar when individuals who died within 1 year of follow-up were excluded from the analysis (P = 0.015). Cubic splines revealed that SMI <6.9 kg/m² is a risk factor of all-cause mortality in men. BMI was found to be significantly associated with all-cause mortality in men (P = 0.010), but not in women (P = 0.288); however, the association disappeared after adjustment for SMI (P = 0.163).

SMI <6.9 kg/m² is a risk factor of all-cause mortality in men but not in women. SMI underlies the relationship between BMI and all-cause mortality. Geriatr Gerontol Int 2022; 22: 956-960.