Abstract
BACKGROUND: Previous studies have shown an association between low muscle mass (LMM) and all-cause mortality, but sex-specific patterns remain controversial. Moreover, the association between muscle mass changes and all-cause mortality has not been well established. This study aimed to examine the associations of muscle mass and its changes with all-cause mortality. METHODS: Data were derived from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) conducted between 2011 and 2014, with follow-up until 2019. A total of 7,051 participants were included (53.8% female; mean age 83.4 ± 11.0 years). Appendicular skeletal muscle mass (ASM) was estimated using anthropometry-based prediction equations incorporating age, sex, calf circumference, height, and weight. Skeletal muscle index (SMI) was calculated as ASM divided by height squared and categorized into quartiles. Muscle mass changes between 2011 and 2014 were classified into four groups according to sex-specific SMI cut-off values for LMM: persistent LMM, LMM to normal, normal to LMM, and persistent normal. Demographic characteristics, lifestyle factors, and health status indicators were adjusted as covariates. Cox proportional hazards models were used to examine the associations of estimated SMI and its changes with all-cause mortality. RESULTS: During 33,001 person-years of follow-up, 2,417 deaths occurred, including 1,054 (32.4%) among males and 1,363 (35.9%) among females. The association between SMI and all-cause mortality differed by sex, showing an L-shaped pattern in males and an inverse linear pattern in females. After sex stratification, low SMI was associated with a higher risk of all-cause mortality in females (P for interaction < 0.001). Compared with the highest SMI quartile (Q4), the hazard ratios (HRs; 95% confidence intervals [CIs]) for all-cause mortality in the lowest quartile (Q1) were 1.42 (1.13, 1.79) in males and 1.85 (1.45, 2.36) in females. Additionally, participants with persistent LMM had an increased risk of all-cause mortality compared with those with persistently normal muscle mass in both males (HR 1.42, 95%CI: 1.17, 1.74) and females (HR 1.31, 95%CI: 1.04, 1.65). CONCLUSIONS: Low muscle mass may serve as a sensitive indicator of all-cause mortality, and maintaining normal muscle mass may confer longevity-related health benefits. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12877-026-07008-6.