25-Hydroxyvitamin D in Obese Youth Across the Spectrum of Glucose Tolerance From Normal to Prediabetes to Type 2 Diabetes

OBJECTIVE To 1) determine if plasma 25-hydroxyvitamin D (25[OH]D) concentrations differ among obese youth with normal glucose tolerance (NGT) versus prediabetes versus type 2 diabetes and 2) assess the relationships between 25(OH)D and in vivo insulin sensitivity and beta-cell function in this cohort. RESEARCH DESIGN AND METHODS Plasma 25(OH)D concentrations were examined in banked specimens in 9- to 20-year-old obese youth (n = 175; male 42.3%, black 46.3%) (NGT, n = 105; impaired glucose tolerance [IGT], n = 43; type 2 diabetes, n = 27) who had in vivo insulin sensitivity and secretion measured by hyperinsulinemic-euglycemic and hyperglycemic clamp techniques and had an assessment of total body composition and abdominal adiposity. RESULTS The mean age and BMI of the subjects were 14.3 +/- 2.1 years and 35.7 +/- 5.6 kg/m(2), respectively. BMI, plasma 25(OH)D, and the proportion of vitamin D-deficient and -insufficient children did not differ across the three groups. Furthermore, there was no association between 25(OH)D and in vivo insulin sensitivity or beta-cell function relative to insulin sensitivity (disposition index) in all groups combined or in each group separately. CONCLUSIONS Our data in obese youth show 1) no differences in plasma 25(OH)D concentrations across the glucose tolerance groups and 2) no relationship between 25(OH)D and in vivo insulin sensitivity and beta-cell function relative to insulin sensitivity in any of the groups. It remains uncertain if enhancement of the vitamin D status could improve pathophysiological mechanisms of prediabetes and type 2 diabetes in obese youth.