Association of the composite dietary antioxidant index with advanced cardiovascular-kidney-metabolic syndrome in U.S. adults: A cross-sectional study based on NHANES 2001-2018.

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.