Association Between Triglyceride-Glucose-Body Mass Index and Cardiometabolic Multimorbidity Risk in Middle-Aged and Older Chinese Adults

Objective: Cardiometabolic multimorbidity (CMM) typically evolves from a healthy state to an initial cardiometabolic disease (FCMD) and subsequently to CMM. The triglyceride-glucose-body mass index (TyG-BMI) is a composite surrogate marker of insulin resistance. However, its associations with incident cardiometabolic outcomes across different baseline CMD profiles remain insufficiently characterized. Using data from the China Health and Retirement Longitudinal Study (CHARLS), we examined the associations of TyG-BMI with incident first cardiometabolic disease (FCMD) among participants without CMD at baseline and incident CMM among those with one CMD at baseline. Methods: Participants were classified into two groups according to their baseline CMD status: the healthy-to-FCMD group and the FCMD-to-CMM group. Separate Cox proportional hazards models were fitted to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for each group. Dose–response relationships were evaluated using restricted cubic splines (RCS). Sensitivity analyses included a two-year landmark analysis and a complete-case analysis. Results: The healthy-to-FCMD group included 5707 participants (median follow-up: 9.0 years; 2599 incident FCMD cases), whereas the FCMD-to-CMM group included 2256 participants (median follow-up: 7.0 years; 1040 incident CMM cases). After adjustment for potential confounders, the HRs for the highest TyG-BMI quartile (Q4) compared with the lowest quartile (Q1) were 2.268 (95% CI: 2.022–2.544) for FCMD and 1.895 (95% CI: 1.574–2.282) for CMM. Each 1-standard deviation (SD) increase in TyG-BMI was associated with a 38.5% higher hazard of FCMD (HR = 1.385, 95% CI: 1.332–1.440) and a 31.5% higher hazard of CMM (HR = 1.315, 95% CI: 1.232–1.404). RCS analyses indicated positive associations between TyG-BMI and both outcomes, with no statistically significant evidence of nonlinearity within the observed range (p for nonlinearity = 0.963 and 0.150, respectively). The associations were generally consistent in sensitivity analyses. Conclusion: Higher TyG-BMI was associated with an increased hazard of incident FCMD among participants without CMD at baseline and incident CMM among those with one CMD at baseline. These findings provide complementary observational evidence on cardiometabolic risk across different baseline CMD profiles.