Serum 25-Hydroxyvitamin D Levels and Prediabetes Among Subjects Free of Diabetes

OBJECTIVE Animal studies suggest that low serum 25-hydroxyvitamin D (25[OH]D) may impair insulin synthesis and secretion and be involved in the pathogenesis of diabetes. Results in studies in humans have not been consistent, however. Prediabetes is a stage earlier in the hyperglycemia/diabetes continuum where individuals are at increased risk of developing diabetes and where prevention efforts have been shown to be effective in delaying or preventing the onset of diabetes. However, previous studies have not examined the association between low serum 25(OH)D levels and prediabetes. RESEARCH DESIGN AND METHODS We examined the 12,719 participants (52.5% women) in the third National Health and Nutrition Examination Survey aged >20 years who were free of diabetes. Serum 25(OH)D levels were categorized into quartiles (≤ 17.7, 17.8-24.5, 24.6-32.4, >32.4 ng/mL). Prediabetes was defined as a 2-h glucose concentration of 140-199 mg/dL, or a fasting glucose concentration of 110-125 mg/dL, or an A1C value of 5.7-6.4%. RESULTS Lower serum 25(OH)D levels were associated with prediabetes after adjusting for age, sex, race/ethnicity, season, geographic region, smoking, alcohol intake, BMI, outdoor physical activity, milk consumption, dietary vitamin D, blood pressure, serum cholesterol, C-reactive protein, and glomerular filtration rate. Compared with quartile 4 of 25(OH)D (referent), the odds ratio of prediabetes associated with quartile 1 was 1.47 (95% CI 1.16-1.85; P = 0.001 for trend). Subgroup analyses examining the relation between 25(OH)D and prediabetes by sex, BMI, and hypertension categories also showed a consistent positive association. CONCLUSIONS Lower serum 25(OH)D levels are associated with prediabetes in a representative sample of U.S. adults.