Vitamin D, C-Reactive Protein, and Cardiometabolic Risk Clustering in Middle-Aged Adults: Results from the 2023 Korea National Health and Nutrition Examination Survey (KNHANES).

Background/Objectives: Cardiometabolic risk clustering (CMRC), the coexistence of multiple risk factors, markedly increases the risk of cardiovascular disease and diabetes. While obesity is central, the independent roles of vitamin D status and systemic inflammation remain unclear. This study examined determinants of CMRC in middle-aged Korean adults, focusing on vitamin D and C-reactive protein (CRP). Methods: Cross-sectional data were analyzed from 2062 adults aged 40-64 years in the 2023 Korea National Health and Nutrition Examination Survey. CMRC was defined as ≥3 of abdominal obesity, hypertension, diabetes, hypertriglyceridemia, and low high-density lipoprotein cholesterol. Serum 25-hydroxyvitamin D [25(OH)D], CRP, lifestyle behaviors, and covariates were assessed. Complex-sample logistic regression identified factors associated with CMRC. Results: CMRC prevalence was 16.5%. Older age (OR = 1.04, 95% CI: 1.02-1.06), current smoking (OR = 1.76, 95% CI: 1.26-2.45), elevated CRP (1-3 mg/L: OR = 1.40, 95% CI: 1.04-1.87; ≥3 mg/L: OR = 1.63, 95% CI: 1.00-2.66), and obesity (OR = 8.29, 95% CI: 6.12-11.21) increased CMRC risk. Protective factors included male sex (OR = 0.60, 95% CI: 0.45-0.81), sufficient vitamin D (≥20 ng/mL: OR = 0.76, 95% CI: 0.58-0.99), and meeting World Health Organization physical activity guidelines (OR = 0.71, 95% CI: 0.55-0.92). Conclusions: These survey-weighted associations may help identify at-risk mid-life adults at the population level and motivate longitudinal evaluation of vitamin D deficiency and inflammation in risk assessment and targeted prevention.