With the accelerated aging of China’s population, multimorbidity has become a major health challenge for middle-aged and older adults, placing higher demands on clinical care and health management systems. Obesity and insulin resistance are common pathophysiological foundations for multiple chronic diseases. However, there is a lack of large-scale prospective studies systematically evaluating the combined effects of the triglyceride-glucose (TyG) index, traditional obesity indices, and novel obesity indices on the risk of multimorbidity.

To investigate the impact and predictive value of the TyG index combined with traditional and novel obesity indices on the risk of multimorbidity, providing a scientific basis for early identification, risk stratification, and precision nursing interventions for chronic disease comorbidity.

Based on prospective cohort data from the China Health and Retirement Longitudinal Study (CHARLS) from 2011 to 2020, this study included 2 574 middle-aged and older participants aged 45 years or older without chronic diseases at baseline. Traditional and novel obesity indices were calculated, including body mass index (BMI), waist circumference (WC), waist-to-height ratio (WHtR), weight-adjusted waist index (WWI), a body shape index (ABSI), body roundness index (BRI), and Chinese visceral adiposity index (CVAI). Additionally, the TyG index and its derivatives combined with obesity indices (e.g., TyG-WC, TyG-BRI) were calculated. Cox proportional hazards regression models were used to analyze the associations between these indices and the risk of multimorbidity, while restricted cubic spline analysis was employed to examine dose-response relationships. Receiver operating characteristic (ROC) curves were used to evaluate the predictive performance of these indices.

The overall incidence of multimorbidity was 57.8%. After multivariate adjustment, all obesity indices and TyG-related indices were significantly positively associated with the risk of multimorbidity (P<0.05). Among these, WC showed the strongest association (hazard ratio ［HR］=1.39, 95% confidence interval ［CI］: 1.22-1.57), followed by BMI (HR=1.26, 95%CI: 1.10-1.43). The HRs for WHtR and BRI were both 1.35 (95%CI: 1.18-1.54), while the HRfor CVAI was 1.28 (95%CI: 1.12-1.45). The TyG index alone was significantly associated with the risk of multimorbidity (HR=1.21, 95%CI: 1.06-1.37), and its combination with obesity indices further enhanced the association: TyG-WC had an HRof 1.36 (95%CI: 1.20-1.54), TyG-BRI had an HRof 1.33 (95%CI: 1.17-1.52), and TyG-CVAI had an HRof 1.29 (95%CI: 1.13-1.46). Dose-response analysis revealed that most indices exhibited a nonlinear positive association with multimorbidity risk (all P for nonlinearity<0.05). ROC curve analysis showed that among traditional and novel obesity indices, WHtR and BRI had the best predictive performance (both AUC=0.560). Among TyG derivatives, TyG-BRI had the highest predictive performance (AUC=0.562), followed by TyG-WHtR (AUC=0.561) and TyG-WC (AUC=0.558).The DeLong test revealed that only TyG-WHtR exhibited a significantly higher AUC compared with TyG alone (P=0.038).

The combined use of the TyG index and obesity indices provides a more comprehensive assessment of multimorbidity risk in middle-aged and older adults. Compared with other obesity indexes, TyG-WHtR and TyG-BRI demonstrated superior performance in risk identification, supporting their utility as practical screening indicators in clinical nursing assessments and community health management.