Association of the composite dietary antioxidant index with advanced cardiovascular–kidney–metabolic syndrome in U.S. adults

This study aimed to examine the association between the composite dietary antioxidant index (CDAI) and advanced cardiovascular–kidney–metabolic syndrome (CKM) and characterize its dose–response shape. This cross-sectional study included 23,968 National Health and Nutrition Examination Survey participants aged ≥20 years (2001–2018). Advanced CKM was stages 3 and 4 combined, per the 2023 American Heart Association framework. The CDAI was the sum of sex-specific z-scores for 6 dietary antioxidants (vitamins A, C, and E, carotenoids, zinc, and selenium) from a single 24-hour recall, analyzed in quartiles (Q1–Q4). Multivariable logistic regression assessed the association, and restricted cubic splines tested nonlinearity. Multiple imputation, propensity score matching, survey-weighted models, and subgroup analyses evaluated robustness. Crude prevalence of advanced CKM fell from 33.6% (Q1) to 20.8% (Q4). After full adjustment, odds ratios (ORs) vs Q1 were 0.87 (95% confidence interval 0.78–0.97) for Q2, 0.79 (0.70–0.89) for Q3, and 0.83 (0.72–0.95) for Q4 ( P for trend = .002). Splines showed an L-shaped association with a nadir at a CDAI of approximately 0.36; below this threshold each 1-unit increase was associated with marginally lower odds (OR 0.96, 95% confidence interval 0.92–1.00, P  = .048), whereas above it the association plateaued. The associations were consistent across age, sex, smoking, alcohol intake, poverty income ratio, and physical activity strata (all P for interaction > .05). After multiple imputation the Q4 OR was 0.77 (0.69–0.85); propensity score–matched and survey-weighted estimates were directionally consistent, with a significant trend in each ( P for trend = .045, .039). A higher food-derived CDAI was independently associated with a lower prevalence of advanced CKM, with the inverse association confined to the low-to-moderate intake range. These findings are consistent with dietary guidance emphasizing whole foods rich in diverse antioxidants, although the cross-sectional design precludes causal inference.