Cholecalciferol supplementation improves suppressive capacity of regulatory T-cells in young patients with new-onset type 1 diabetes mellitus - A randomized clinical trial

- Suppressive capacity of Tregs decreases in the first year after T1D diagnosis in young patients.
- Cholecalciferol supplementation improves suppressive capacity of Tregs in T1D patients.
- Percentage of Tregs did not change after 12 months cholecalciferol supplementation in T1D.
- Cholecalciferol supplementation stabilized insulin requirements.

It is unknown if cholecalciferol is able to modify defects in regulatory T cells (Tregs) in type 1 diabetes (T1D). In this randomized, double-blind, placebo controlled trial 30 young patients with new-onset T1D were assigned to cholecalciferol (70 IU/kg bodyweight/day) or placebo for 12 months. Tregs were determined by FACS-analysis and functional tests were assessed with ex vivo suppression co-cultures at months 0, 3, 6 and 12. Suppressive capacity of Tregs increased (p < 0.001) with cholecalciferol from baseline (− 1.59 ± 25.6%) to 3 (30.5 ± 39.4%), 6 (44.6 ± 23.8%) and 12 months (37.2 ± 25.0%) and change of suppression capacity from baseline to 12 months was significantly higher (p < 0.05) with cholecalciferol (22.2 ± 47.2%) than placebo (− 16.6 ± 21.1%). Serum calcium and parathormone stayed within normal range.This is the first study, which showed that cholecalciferol improved suppressor function of Tregs in patients with T1D and vitamin D could serve as one possible agent in the development of immunomodulatory combination therapies for T1D.