Sustained serum 25-hydroxyvitamin D concentrations for one year with cholecalciferol supplementation improves glycaemic control and slows the decline of residual β cell function in children with type 1 diabetes

Introduction
Studies using vitamin D for preservation of residual b-cell function (RBCF) and improvement of glycaemic control in type 1 diabetes (T1D) have shown inconsistent results. The possible causes of the discrepancies in the results are related to the dosage, type, and duration of vitamin D supplementation, C-peptide concentration at entry into the study, and the influence of glycaemic control on RBCF during supplementation.

Aim of the study
To evaluate the effect of cholecalciferol supplementation on RBCF and glycaemic control in children with T1D.

Material and methods
Forty-two children aged 6-12 years and within 1-2 years of diagnosis of T1D received cholecalciferol 3000 IU/day for one year (Group A). Thirty patients were recruited as controls (Group B). The mean changes in stimulated C-peptide levels, HbA1c, fasting blood glucose (FBG), mean blood glucose (MBG), and mean total daily insulin (TDI) dose from baseline to the study endpoint were calculated.

Results
Children in Group A showed lower mean FBG, MBG, HbA1c, and lesser TDI as compared to Group B at all follow-up visits. However, the differences in these parameters between the two groups reached statistical significance towards the study endpoint. Within group A, the decline in C-peptide levels from baseline to the endpoint was minor (–0.13 ±0.11, p-value = 0.16) as compared to a substantial decline in Group B (–0.41 ±0.07, p-value = 0.00). Comparison of the mean decrease in stimulated C-peptide levels from baseline to the endpoint between the two groups was also statistically significant (–0.13 ±0.11 vs. -0.41 ±0.07, p-value = 0.00). The mean decrease in FBG and MBG in Group A were greater, whereas the comparison of the mean decrease in HbA1c between the groups reached statistical significance at the study endpoint (p-value = 0.04). The decrease in the TDI was, however, similar in the two groups (p-value = 0.10).

Conclusions
Sustained serum 25-(OH)D concentrations with cholecalciferol supplementation for one year improves metabolic control and slows the decline of RBCF in children with T1D. Larger studies with longer duration and cholecalciferol dosage stratification are suggested.