Association Between Composite Dietary Antioxidant Index and Asthma-Chronic Obstructive Pulmonary Disease Overlap Syndrome: Evidence From a Large Cohort in the UK Biobank.

Research on the association of the composite dietary antioxidant index (CDAI) with asthma-chronic obstructive pulmonary disease overlap syndrome (ACOS) has not yet been reported. This study aimed to explore the association between CDAI and ACOS through a large-scale cohort study from the UK Biobank. The baseline population was divided into three groups based on the tertiles of CDAI. Three Cox proportional hazards models were constructed to explore the relationship between CDAI and ACOS. Restricted cubic splines (RCS) were constructed to explore the presence of nonlinear relationships, with inflection points calculated by a recursive algorithm. Kaplan-Meier methods were employed to investigate the cumulative risk of outcomes over time. Finally, subgroup analysis and sensitivity analysis were performed. After adjusting for all confounding factors, no significant association was found between CDAI and ACOS [1.01 (0.94, 1.09)]. Further RCS analysis revealed a nonlinear association, which may explain why the overall results were not statistically significant. The CDAI and ACOS exhibited an inverse association before and after the inflection point. The association was negative before and positive after the inflection point. Further stratified analysis revealed that the nonlinear association was only present in females, participants aged ≥ 60, and those with BMI < 30. No significant interactions were found in other subgroups. This large-scale cohort study revealed a nonlinear association between CDAI and ACOS, and further identified differences based on gender, age, and BMI.