Role of composite dietary antioxidant index in staging and mortality risk of cardiovascular-kidney-metabolic syndrome: a study from NHANES 2001-2018

This study investigated the role of the Composite Dietary Antioxidant Index (CDAI) in cardiovascular-kidney-metabolic (CKM) syndrome staging and mortality using NHANES 2001–2018 data from 25,155 U.S. adults. Higher CDAI quartiles demonstrated progressively reduced odds of advanced CKM stages versus Stage 0 (Q4 vs. Q1 ORs: Stage 1: 0.71 (0.56–0.91); Stage 2: 0.58 (0.45–0.74); Stage 3: 0.30 (0.20–0.47); Stage 4: 0.46 (0.35–0.60); all P <  0.05). Weighted Quantile Sum regression identified a protective effect of the antioxidant mixture against advanced CKM (OR: 0.82 (0.76–0.88); P <  0.001), primarily driven by vitamins A (weight = 0.357), C (0.290), and selenium (0.212). In CKM patients, higher CDAI was associated with significantly lower all-cause (Q4 vs. Q1 HR: 0.63 (0.57–0.70)), cardiovascular (HR: 0.63 (0.51–0.78)), and non-cardiovascular mortality (HR: 0.63 (0.56–0.72); all P <  0.001). Nonlinear analyses revealed threshold effects for all-cause and non-CVD mortality at CDAI ≈ 0. These findings indicate that elevated CDAI is robustly associated with less severe CKM staging and reduced mortality, supporting dietary antioxidant optimization for CKM management and risk stratification.