Dose–response associations of the composite dietary antioxidant index and related nutrients with prevalent chronic kidney disease: NHANES 2003–2018

Oxidative stress is implicated in kidney dysfunction, but population-based evidence linking dietary antioxidant profiles to prevalent chronic kidney disease (CKD) remains limited. We examined associations of the composite dietary antioxidant index (CDAI) and selected antioxidant-related nutrients with prevalent CKD among U.S. adults aged ≥45 years. This cross-sectional analysis used 2003–2018 National Health and Nutrition Examination Survey (NHANES) data from adults with complete exposure, outcome, and covariate data and positive fasting subsample weights. CDAI summed standardized intakes of vitamins A, C, and E, selenium, zinc, and total carotenoids from the first 24-hour recall; niacin was examined separately. CKD was operationally defined as an estimated glomerular filtration rate < 60 mL/min/1.73 m 2 and/or a urinary albumin-to-creatinine ratio ≥ 30 mg/g based on a single examination. Primary analyses used WTSAF2YR/8 because Model 3 included fasting glucose. Survey-weighted logistic regression, restricted cubic splines, sequential dietary adjustment, residual-method energy adjustment, and age-expanded sensitivity analyses were performed. Among 8,676 participants, 2,058 had CKD. In Model 3, the odds ratio (OR) per 1-SD increase in CDAI was 0.816 (95% confidence interval [CI], 0.751–0.887). Vitamin E, selenium, zinc, and niacin were also inversely associated with CKD, whereas vitamin A, vitamin C, and total carotenoids were not. After simultaneous adjustment for total energy, protein, sodium, potassium, and phosphorus, the CDAI association was attenuated (OR, 0.973; 95% CI, 0.841–1.127), whereas vitamin E remained inversely associated (OR, 0.869; 95% CI, 0.768–0.982). Residual-method analyses produced a similar pattern for CDAI (OR, 0.913; 95% CI, 0.831–1.004) and vitamin E (OR, 0.869; 95% CI, 0.784–0.962). In an age-expanded analysis of 14,798 adults aged ≥20 years, the CDAI association differed between adults aged 20–44 and ≥45 years (P for interaction = 0.022). The sensitivity of the inverse CDAI–CKD association to adjustment for energy and correlated dietary factors suggests that CDAI may partly reflect broader dietary quality, food-source patterns, and nutritional status rather than an independent antioxidant-related effect. The comparatively stable vitamin E association is hypothesis-generating and does not establish an independent protective effect.