Nonlinear association between the composite dietary antioxidant index and kidney stone disease: Mediation by systemic immune-inflammatory status in a cross-sectional study.

ObjectiveOxidative stress and inflammation have been implicated in kidney stone disease. The Composite Dietary Antioxidant Index (CDAI) reflects the combined intake of multiple dietary antioxidants, but its association with kidney stones and the potential statistical contribution of immune-inflammatory markers remain unclear. This study aimed to examine the association between CDAI and kidney stones and to explore the potential statistical contribution of systemic immune-inflammatory markers to this association.MethodsThis was a retrospective cross-sectional study of adults aged ≥18 years. We analyzed data from 26,485 participants in the National Health and Nutrition Examination Survey (NHANES) 2007-2018. Survey-weighted logistic regression was used to examine the association between CDAI and self-reported history of kidney stones. Restricted cubic spline analyses were performed to assess nonlinear associations, and subgroup, sensitivity, and exploratory mediation analyses were conducted.ResultsAfter full adjustment for potential confounders, higher CDAI was inversely associated with kidney stones (OR = 0.97, 95% CI: 0.96-0.99). When CDAI was categorized into quartiles (Q1-Q4), participants in the highest CDAI quartile had 22% lower odds of kidney stones compared with Q1 (OR = 0.78, 95% CI: 0.66, 0.93). Restricted cubic spline analysis suggested a nonlinear inverse association that tended to plateau at higher CDAI levels. Furthermore, exploratory mediation analyses suggested statistical indirect associations through the systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), and neutrophil-to-lymphocyte ratio (NLR), with indirect association proportions of 3.11%, 5.27%, and 3.14%, respectively. The advanced lung inflammation index (ALI) showed no significant indirect association.ConclusionsIn this nationally representative cross-sectional study, higher CDAI was inversely associated with kidney stones. Exploratory mediation analyses suggested statistical indirect associations through immune-inflammatory markers. These findings should be interpreted as hypothesis-generating and require confirmation in prospective studies.