Association Between Composite Dietary Antioxidant Index and Metabolic Syndrome in Normal Weight Population: Evidence From NHANES

Objectives: Oxidative stress is one of the most important pathophysiological mechanisms of metabolic syndrome (MetS). There is limited research on the relationship between antioxidant diet and metabolically unhealthy individuals of normal weight (MUNW). We aimed to investigate the potential association between the Composite Dietary Antioxidant Index (CDAI) and MUNW to providing better dietary guidance. Methods: This study enrolled participants with a body mass index between 18.5∼24.9kg/m2 from the National Health and Nutrition Examination Survey (2007-2018). Exclusion criteria were: 1) aged < 20 years old; 2) pregnant woman; and 3) incomplete data. Participants who met at least three following criteria were identified as individuals with MetS: central obesity; elevated blood pressure (BP); elevated fasting blood glucose (FBG); elevated triglycerides (TG); and reduced high-density lipoprotein cholesterol (HDL-C). Participants were classified into four groups according to the interquartile of CDAI, which was calculated based on the standardized consumptions of vitamins A, C, and E, carotenoids, selenium, and zinc. The Logistic regression models were used to analyze the relationship of CDAI with Mets and its components. The restricted cubic splines were used to analyzed the potential non-linear relationships. Results: A total of 4,590 participants were included for analysis in this study. After fully adjustment, the odds ratios (ORs) (95% confidence intervals [CIs]) for MetS were 1.00 (reference), 0.80 (0.50-1.29), 0.85 (0.51-1.41), and 0.48 (0.26-0.87), for lowest to highest quintiles of CDAI, respectively (Ptrend = 0.026). Similar associations were observed for central obesity, elevated BP and elevated TG. The restricted cubic splines indicated an "L-shape" relationship between CDAI and MetS (Pnonlinearity<0.001). Similar "L-shape" association was observed between CDAI and elevated TG (Pnonlinearity = 0.013), while an "U-shape" association was observed between CDAI and reduced HDL-C (Pnonlinearity =0.047). No significantly relationships were observed between CDAI and elevated FBG in any of the models. Conclusions: CDAI was significantly negatively associated with MUNW in the United States. This association warrant replication using prospective studies. Funding Sources: Fujian Provincial Health Commission.