Preservation of Residual Beta Cell Function with Vitamin D Supplementation in Type 1 Diabetes

Preservation of residual β-cell function (RBCF) at diagnosis of Type 1 diabetes (T1D) is important for major benefits in short and long term outcomes as endogenous insulin secretion is associated with better glycemic control, reduced risk of diabetes related complications and positive effects on physical development in children. Several immunotherapeutic interventions including nonspecific immunosuppression, epitope or antigen specific immunomodulation, cellular and β-cell trophic therapies have been tried for preservation of RBCF in T1D.Immunological interventions targeting the T cells that include therapies resulting in partial depletion or modulation of effector T cells (Teffs) and preservation or augmentation of regulatory T cells (Tregs) have shown the best potential. Recent evidence suggests that vitamin D is an effective agent for increasing the numbers as well as promoting the functions of Tregs in patients with T1D. A number of in vitro and in vivo studies have shown that vitamin D may prevent pancreatic β-cell destruction through its immunomodulatory effects when the blood concentrations are in the optimal ranges. However, clinical trials on patients with T1D have shown variable results. The authors conducted a case control interventional study on 30 children with T1D. After an oral cholecalciferol dose of 2000 IU per day for 6 months, a trend towards lesser decline of RBCF was seen. The percent decrease in stimulated C-peptide was also lower in the intervention group as compared to the control group. Three (20%) patients progressed to undetectable stimulated C-peptide over the study period as compared to 1 (6%) in the intervention group. The results were similar to the recently conducted similar studies but the effect size was lower. A number of limitations in the authors’ work as well as in the previous studies will need to be addressed in the future studies of vitamin D supplementation for preserving RBCF. These issues are related to dosage and type of vitamin D, C-peptide concentration at inclusion, glycemic control during supplementation, duration of supplementation, sunexposure quantification and assessment of epitope specific T cell frequencies. Depending upon the results of subsequent larger studies, vitamin D supplementation may emerge as an important arm of the combination therapies for preservation of RBCF.