Independent associations of the TyG index and systemic immune-inflammation index with cardiovascular disease: evidence from NHANES 1999–2018

This study aimed to investigate the combined associations of the triglyceride-glucose (TyG) index and systemic immune-inflammation index (SII) with cardiovascular disease (CVD) and mortality in a large population-based survey, providing new perspectives for the CVD risk stratification. This study used cross-sectional data from NHANES (1999–2018) to assess the combined associations of the TyG index and SII with prevalent CVD, and linked National Death Index records for prospective follow-up on all-cause and cardiovascular mortality. Weighted multivariate logistic regression analysis, Cox proportional hazards models and restricted cubic spline (RCS) plots were applied to assess the associations between these indices and CVD prevalence and mortality. Potential multiplicative and additive interactions between TyG index and SII were also explored. A total of 19,168 participants (aged over 20 years) were included. The TyG index had a positive correlation with CVD prevalence (OR = 1.09, 95% CI 1.01–1.19, P = 0.047), while the SII showed no significant association with prevalent CVD (OR = 1.01, 95% CI 0.95–1.08, P = 0.705). The SII was significantly associated with all-cause mortality (HR = 1.11, 95% CI 1.10–1.12, P < 0.001) and cardiovascular mortality (HR = 1.10, 95% CI 1.07–1.12, P < 0.001), whereas the TyG index showed no significant association with all-cause or cardiovascular mortality. No significant multiplicative or additive synergistic interactions were observed between the two biomarkers. This study found that the TyG index and the SII were independent indicators for prevalent CVD and mortality, respectively. The TyG index had a positive correlation with CVD prevalence, and the SII showed a positive correlation with all-cause and cardiovascular mortality.