Nonlinear association between remnant cholesterol inflammation index and incident stroke among middle-aged and older adults with hypertension: a CHARLS cohort study.

Background: The remnant cholesterol inflammation index (RCII) combines remnant cholesterol (RC) and high-sensitivity C-reactive protein (hs-CRP), two markers that may reflect residual lipid-related and inflammatory vascular burden. We examined whether baseline RCII was associated with incident stroke among hypertensive middle-aged and older adults and whether this association was nonlinear. Methods: We analyzed 3,823 stroke-free hypertensive participants aged 45 years or older from the China Health and Retirement Longitudinal Study (CHARLS). Participants were excluded if they lacked follow-up information, were younger than 45 years, had missing or biologically implausible RCII components, had hs-CRP > 10 mg/L, or had missing covariates. RCII was analyzed per 1-standard deviation (SD) increase and by quartiles. Cox proportional hazards models, restricted cubic splines, an exploratory two-piecewise Cox model, subgroup analyses, and sensitivity analyses were performed. Results: During a median follow-up of 9.08 years (interquartile range, 9.08-9.17), 526 incident strokes occurred (13.8%). In the fully adjusted model, the original-scale linear estimate was positive but not statistically significant (HR per 1-SD increase, 1.06; 95% CI, 0.99-1.14; Conclusions: Among hypertensive CHARLS participants, higher RCII categories were associated with incident stroke. The association was better characterized by categorical and nonlinear analyses than by a single original-scale linear estimate. RCII should be interpreted as an association marker, not as a validated predictive or clinical decision tool.