Plasma concentrations of vitamin D metabolites during puberty of diabetic children.

Plasma concentrations of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D and vitamin D binding protein were determined in 87 serum samples from 46 Type 1 (insulin-dependent) diabetic children and adolescents at the various stages of puberty. The results were compared with data similarly obtained from healthy pubertal children. The diabetic patients had lower mean 1,25-dihydroxyvitamin D concentrations (p less than 0.05) and higher molar ratios of 24,25-dihydroxyvitamin D to 25-hydroxyvitamin D (p less than 0.05) than their healthy counter parts. In contrast to the reference group, the diabetic patients failed to attain the increase in 1,25-dihydroxyvitamin D normally seen during the pubertal stages of maximal growth velocity. The mean plasma levels of vitamin-D binding protein did not differ between the two groups, and a calculated 'free' 1,25-dihydroxyvitamin D value followed a pattern similar to that of total 1,25-dihydroxyvitamin D throughout puberty for both groups. The results suggest that the regulatory mechanisms of the vitamin D endocrine system are altered in diabetic children at puberty, resulting in a relative decrease in 1,25-dihydroxyvitamin D plasma concentration and increased 24,25-dihydroxyvitamin D levels.