Association between RCII/eGDR ratio and cardiovascular disease in Chinese middle-aged and older adults: evidence from the CHARLS cohort

Aims Cardiovascular diseases (CVD) are the leading global causes of death and disability. The residual cholesterol inflammation index (RCII) and estimated glucose disposal rate (eGDR) reflect inflammatory-metabolic risk and insulin resistance, respectively. However, their combined predictive capacity remains unclear. This study examined the associations between the RCII/eGDR ratio and risks of CVD, stroke, and heart disease. Materials and methods This study included 6,981 baseline CVD-free adults aged ≥ 45 years from the CHARLS cohort. Cox proportional hazards regression, with progressive adjustment for confounders, and restricted cubic spline (RCS) models were used to assess associations between the RCII/eGDR ratio and risks of CVD, stroke, and heart disease. Results After a median 9-year follow-up, incident CVD, stroke, and heart disease occurred in 23.7%, 8.3%, and 18% of participants, respectively. In fully adjusted models, each 1-unit increase in RCII/eGDR was associated with a 4% higher CVD risk (HR = 1.04, 95% CI: 1.01–1.06) and a 7% higher stroke risk (HR = 1.07, 95% CI: 1.04–1.10), but was not significantly associated with heart disease (HR = 1.02, 95% CI: 0.99–1.06; P = 0.163). Quartile-based analyses showed graded higher risks across ascending RCII/eGDR quartiles. Relative to Q1, Q3 and Q4 exhibited significantly elevated CVD (Q3: HR = 1.40, 95% CI: 1.21–1.61; Q4: HR = 1.56, 95% CI: 1.35–1.79), stroke (Q3: HR = 1.74, 95% CI: 1.35–2.23; Q4: HR = 2.02, 95% CI: 1.58–2.59), and heart disease risks (Q3: HR = 1.34, 95% CI: 1.14–1.58; Q4: HR = 1.46, 95% CI: 1.24–1.71). RCS models confirmed nonlinear dose-response relationships for all three outcomes. Conclusions Elevated RCII/eGDR was associated with higher risks of CVD, stroke, and heart disease. As a convenient composite marker integrating metabolic and inflammatory status, it may offer potential value for cardiovascular risk stratification in Chinese middle-aged and older adults.