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 β-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 β-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 β-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.