Background: Clinical reference ranges are often used to assess nutritional status, but whether having lower or higher than the current clinical reference range for micronutrients, inflammation, and oxidative stress is related to metabolic syndrome (MetS) is not known. Our objectives are to estimate the odds of having MetS outside of established clinical references, and to identify any effect modifications by sex have for these relationships.
Methods: Data from the 2005 to 2006 National Health and Nutrition Examination Survey were used (≥20 years; N = 2049) with MetS defined utilizing the harmonized criteria from the Joint Interim Statement. The odds of having MetS in individuals with lower or higher than the clinical reference range for the serum concentrations of micronutrient antioxidants, inflammation, and oxidative stress were estimated following adjustments for age, sex, ethnicity, education, income, smoking, alcohol intake, recreational physical activity, and BMI.
Results: Having lower than the clinical reference range for carotenoids and vitamin C [odds ratios (95% confidence interval): 1.37 (1.05-1.78) and 1.39 (1.01-1.90), respectively] was associated with significantly greater odds of MetS. By contrast, having higher than the clinical reference range for vitamins A and E, uric acid, and γ-glutamyl transferase (GGT) [2.10 (1.50-2.92), 2.36 (1.78-3.13), 2.65 (1.54-4.57), and 2.08 (1.61-2.69), respectively] was associated with higher odds of MetS, whereas higher levels of vitamins B12 were protective [0.64 (0.42-0.98]. Sex moderated these relationships for carotenoids, vitamin A, C, E, uric acid, C-reactive protein, and GGT.
Conclusions: Lower carotenoids and vitamin C and higher vitamins A and E, uric acid, and oxidative stress were associated with a greater likelihood of MetS, whereas higher vitamin B12 was protective. Further research is necessary to replicate these findings in a prospective setting to confirm the importance of the overall and sex-specific findings.
Keywords: carotenoids; inflammation; micronutrients; oxidative stress; serum biomarkers; vitamins.