No protective effect of calcitriol on beta-cell function in recent-onset type 1 diabetes: the IMDIAB XIII trial.

Objective: We investigated whether supplementation of the active form of vitamin D (calcitriol) in recent-onset type 1 diabetes can protect beta-cell function evaluated by C-peptide and improve glycemic control assessed by A1C and insulin requirement.
Research Design and Methods: Thirty-four subjects (aged 11-35 years, median 18 years) with recent-onset type 1 diabetes and high basal C-peptide >0.25 nmol/l were randomized in a double-blind trial to 0.25 microg/day calcitriol or placebo and followed-up for 2 years.
Results: At 6, 12, and 24 months follow-up, A1C and insulin requirement in the calcitriol group did not differ from the placebo group. C-peptide dropped significantly (P < 0.001) but similarly in both groups, with no significant differences at each time point.
Conclusions: At the doses used, calcitriol is ineffective in protecting beta-cell function in subjects (including children) with recent-onset type 1 diabetes and high C-peptide at diagnosis.