Sustained moderate to high triglyceride-glucose index level is associated with a lower risk of sarcopenia in middle-aged and elderly adults: a nationally representative cohort study

BACKGROUND: Triglyceride-glucose (TyG) index, a novel surrogate marker for insulin resistance (IR), has shown emerging links to sarcopenia. Yet the comprehensive association between the TyG Index and sarcopenia risk remains inconsistent, especially regarding the role of longitudinal TyG exposure patterns. This study comprehensively examines the relationships of baseline TyG index, cumulative TyG index, and TyG index subgroups (defined by two time-point measurements) with incident sarcopenia in Chinese middle-aged and older adults. METHODS: We analyzed data from two China Health and Retirement Longitudinal Study (CHARLS) subcohorts: 6033 participants (aged ≥45) for baseline TyG index and sarcopenia; 5256 individuals for cumulative TyG and TyG index subgroup analyses. Sarcopenia was defined as low muscle mass along with either low muscle strength or physical performance. Hierarchical cluster analysis using TyG values measured in 2011 and 2015 was performed to identify distinct longitudinal TyG distribution patterns. Baseline TyG index was analyzed using multivariable-adjusted Cox proportional hazards models, whereas cumulative TyG index and TyG index subgroups were assessed with multivariable logistic regression. Restricted cubic spline (RCS) models were conducted to test for linear and nonlinear shapes of each association RESULTS: The mean age of participants was 57.16 (8.43) years, with 3207 females (51.8%) in the sample. During the 4-year observational period, 566 (9.38%) participants developed sarcopenia. Following adjustments for confounders, both the baseline index and the cumulative TyG index associated with sarcopenia exhibited significant nonlinear L-shapes, with inflection points observed at approximately 9.46 and 35.49, respectively. Three distinct subgroups: persistently low, moderate, and persistently high TyG groups were identified. Compared with the persistently low TyG index group, the moderate and persistently high TyG index groups showed gradually lower odds of sarcopenia, with multivariable-adjusted ORs of 0.526 (95% CI, 0.394-0.701) and 0.273 (95% CI, 0.184-0.406), respectively. Subgroup analyses demonstrated that the associations between TyG indices and sarcopenia were more significant in males, individuals with lower BMI, and rural residents, with specific population variations across different TyG measures. CONCLUSION: This longitudinal cohort study demonstrates that TyG indices exhibit L-shaped associations with sarcopenia status in Chinese adults aged ≥45 years, with identifiable thresholds. These findings suggest that the TyG index may serve as a biomarker indicative of a potential threshold for muscle health. Validation in multi-ethnic cohorts and mechanistic studies are warranted.