Effects of correction of vitamin D insufficiency on serum osteocalcin and glucose metabolism in obese children

Objectives Osteocalcin (OCN) and vitamin D insufficiency (VDI) have been shown to be associated with abnormal glucose metabolism (GluMet). Whether correction of VDI affects serum OCN is unknown. This study evaluated the effects of correction of VDI on OCN and GluMet, and determined the associations of OCN with 25-hydroxyvitamin D (25-OHD) and GluMet. Design, patients and measurements This study involved 230 obese children in a cross-sectional part and 72 participants in a prospective part in which children with VDI were treated with vitamin D2 at a dose of 20 000 IU daily for 28 days. All 230 children underwent an oral glucose tolerance test and had their serum total and undercarboxylated OCNs and 25-OHD measured. Forty of 72 children were reassessed for the GluMet and serum total and undercarboxylated OCNs and 25-OHD after the vitamin D2 treatment. Results In the prospective part, correction of VDI by raising mean (SD) 25-OHD of 51·5 (12·3) to 141·8 (40·8) nmol/l resulted in an improvement of their GluMet and increase in their whole-body insulin sensitivity index with no changes in their OCN measures. In the cross-sectional part, after adjustments for age, sex and puberty, the total (β = 0·322) and undercarboxylated OCNs (β = 0·315) were positively associated with insulinogenic index, which is an index of insulin secretion (P = 0·034 and 0·037, respectively) in the group of prediabetic and diabetic children. Conclusions Correction of VDI increased insulin sensitivity and improved GluMet, but had no effect on serum OCN measures. OCN was associated with increased insulin secretion in children with abnormal GluMet.