Association between Life's Crucial 9 and sarcopenia: The mediating role of testosterone partially

Sarcopenia, an age-related decline in skeletal muscle mass and function, is influenced by modifiable lifestyle factors. Life's Crucial 9 (LC9), a composite cardiovascular health metric, may mitigate sarcopenia risk, potentially mediated by testosterone. However, population-level evidence and mechanistic insights remain limited. This cross-sectional study analyzed 5726 adults from the 2011 to 2016 the National Health and Nutrition Examination Survey. Sarcopenia was diagnosed using sex-specific thresholds for appendicular skeletal muscle mass index. LC9 scores (0-100) were calculated across 9 domains. Multivariable logistic regression evaluated LC9-sarcopenia associations, while mediation and restricted cubic spline analyses assessed testosterone's role and nonlinear relationships. Higher LC9 scores were inversely associated with sarcopenia prevalence (fully adjusted odds ratio per unit increase: 0.96, 95% confidence interval: 0.95-0.97). Participants with ideal LC9 adherence had 82% lower risk (odds ratio: 0.18, 95% confidence interval: 0.10-0.32) versus low adherence. The association was partially mediated by testosterone, which accounted for a significant 9.85% of the total effect. A nonlinear threshold effect emerged, with risk reduction accelerating at LC9 scores > 73.3. Subgroup analyses confirmed consistent associations across demographics and comorbidities. Our findings suggest that adherence to LC9 is associated with a lower risk of sarcopenia, partially mediated through testosterone homeostasis. Early improvement in LC9 metrics, especially in individuals with poor baseline cardiovascular health, may help mitigate age-related muscle decline, highlighting the potential value of integrated lifestyle interventions. Further longitudinal studies are needed to confirm causality and elucidate the long-term relationship between LC9 optimization and sarcopenia prevention.