Remnant cholesterol inflammatory index and its association with new-onset chronic diseases: evidence from two nationwide studies

BACKGROUND: Chronic diseases pose significant global health burdens, necessitating robust biomarkers for early detection. The remnant cholesterol inflammatory index (RCII), integrating lipid remnants and systemic inflammation, may predict chronic disease risk, but its longitudinal associations remain understudied across diverse populations. METHODS: We analyzed data from two prospective cohorts-the China Health and Retirement Longitudinal Study (CHARLS, N = 9,491) and the English Longitudinal Study of Ageing (ELSA, N = 6,054)-to evaluate associations between baseline RCII and new-onset chronic diseases. RCII was calculated as (remnant cholesterol × hsCRP)/10. Cox models estimated hazard ratios (HRs) for incident diseases, adjusting for sociodemographic, metabolic, and comorbidity covariates. RESULTS: In CHARLS, each unit increase in logarithm-transformed RCII (lnRCII) was associated with higher diabetes risk (HR = 1.09, 95% CI: 1.02-1.15). In ELSA, elevated lnRCII was associated with multiple outcomes, including diabetes (HR = 1.13, 95% CI: 1.01-1.27), stroke (HR = 1.26, 95% CI: 1.15-1.38), psychiatric disease (HR = 1.16, 95% CI: 1.03-1.30), asthma (HR = 1.27, 95% CI: 1.11-1.46), and COPD (HR = 1.36, 95% CI: 1.01-1.51). Associations for hypertension and heart disease were significant in unadjusted models but no longer significant after adjustment. CONCLUSION: RCII shows a consistent association with incident diabetes across both Chinese and UK cohorts, whereas its relationships with other chronic diseases were observed only in the UK cohort. These findings suggest that RCII may serve as a robust marker for diabetes risk and a broader indicator of multisystem vulnerability in certain populations, warranting cautious interpretation and further validation.