Association Between Skeletal Muscle-Fat Distribution Metabolic Index and Cardiovascular Disease: A Cohort Study

Background: Cardiovascular disease (CVD) remains the leading cause of mortality globally. The associations between composite indices integrating body composition and lipid-related metabolic characteristics and CVD remain insufficiently investigated. We therefore constructed the skeletal muscle-fat distribution metabolic index (SMFDMI) and explored its association with CVD. Methods: Data were derived from the China Health and Retirement Longitudinal Study. The prospective analysis included 6785 participants aged ≥45 years followed from 2011 to 2020, while the cross-sectional analysis included 8279 participants. Cox and logistic regression models, restricted cubic splines, subgroup analyses, and sensitivity analyses were performed. Results: The cohort and cross-sectional analyses included participants with median ages of 58 and 59 years and male proportions of 47.19% and 46.42%, respectively. In Model 3, higher SMFDMI was associated with a lower risk of incident CVD, with a 25% lower risk in Q5 than in Q1 (HR = 0.75, 95% CI: 0.63–0.89). The cross-sectional analysis also showed an inverse association with prevalent CVD. Restricted cubic splines suggested an approximately N-shaped nonlinear relationship between SMFDMI and CVD risk. Subgroup analyses showed a stronger inverse association in males (Q5 vs. Q1: HR = 0.62, 95% CI: 0.48–0.81) and in those without chronic diseases. An alternative index yielded similar findings. Conclusions: Higher SMFDMI was associated with a lower risk of incident CVD in middle-aged and older Chinese adults. SMFDMI may provide additional insights into the relationship between muscle health and cardiovascular health during aging, with potential relevance to primary healthcare.