Predictive value of creatinine muscle index reflecting muscle mass for cardiovascular disease among middle-aged and older adults

The creatinine muscle index (CMI, mg/day/1.73 m²) may be an accessible potential indicator for evaluating muscle mass. However, the correlation between CMI and muscle mass has not yet been validated, and its association with cardiovascular disease (CVD) is unclear. We aimed to assess the correlation between CMI and muscle mass and investigate the association of CMI with CVD. Participants aged 45–65 years without CVD from the 2011 China Health and Retirement Longitudinal Study were included and followed until 2020. CMI was calculated using serum creatinine and cystatin C-estimated glomerular filtration rate. Spearman’s correlation was used to assess the relationship between CMI and appendicular skeletal muscle mass (ASMM) estimated via a validated anthropometric prediction equation. Cox proportional hazards regression models and restricted cubic splines (RCS) were employed to analyze the association between CMI and CVD. Among the 5122 participants, 1100 participants developed CVD. CMI was correlated with ASMM in males ( r = 0.60, P < 0.001) and females ( r = 0.53, P < 0.001). After adjusting for multiple factors, higher CMI (tertile 3 versus 1) was associated with reduced risks of CVD in males (HR [95% CI]: 0.74 [0.57–0.95]) and females (HR [95% CI]: 0.79 [0.64–0.97]). RCS revealed a linear relationship between CMI and CVD (all P for non-linearity > 0.05). Subgroup analyses showed protective effects of higher CMI (tertile 3) against CVD in participants aged 45–65 years, married individuals, urban residents, and those without kidney disease. CMI may serve as a potential surrogate for muscle mass, and elevated CMI levels are independently associated with reduced CVD risk.