Supplementation with cholecalciferol does not improve glycaemic control in diabetic subjects with normal serum 25-hydroxyvitamin D levels

Eur J Nutr. 2009 Sep;48(6):349-54. doi: 10.1007/s00394-009-0020-3. Epub 2009 Apr 16.


Background: Studies have suggested that vitamin D may be important for both insulin sensitivity and insulin secretion, and that supplementation with vitamin D may subsequently prevent development of type 2 diabetes.

Aim of the study: The objective of the current study was to test the hypothesis that supplementation with vitamin D would improve glycaemic control in subjects with type 2 diabetes.

Methods: Thirty-six subjects with type 2 diabetes, treated with metformin and bed-time insulin, were randomised to supplementation with cholecalciferol (40,000 IU per week) versus placebo for 6 months. Thirty-two subjects participated throughout the entirety of the study. Fasting blood samples were drawn before and at the end of the 6 month study without the previous bed-time insulin injection. The insulin and metformin doses were not changed throughout the study.

Results: After 6 months, the fasting glucose, insulin, C-peptide, fructosamine, and HbA(1c) levels were not significantly different from baseline values. In addition, changes in these parameters (values at 6 months minus values at baseline) did not differ between the vitamin D and the placebo group.

Conclusions: We were not able to demonstrate that vitamin D supplementation had a significant effect on glucose metabolism in subjects with type 2 diabetes but without vitamin D deficiency. Further studies are needed in larger groups of subjects with type 2 diabetes or impaired glucose tolerance, who also exhibit low serum 25-hydroxyvitamin D levels.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Blood Glucose / analysis*
  • C-Peptide / blood
  • Calcifediol / blood*
  • Calcium / blood
  • Cholecalciferol / administration & dosage*
  • Diabetes Mellitus, Type 2 / blood*
  • Diabetes Mellitus, Type 2 / drug therapy
  • Dietary Supplements
  • Female
  • Fructosamine / blood
  • Glycated Hemoglobin A / analysis*
  • Humans
  • Insulin / blood
  • Insulin, Long-Acting / therapeutic use
  • Male
  • Metformin / therapeutic use
  • Middle Aged
  • Young Adult


  • Blood Glucose
  • C-Peptide
  • Glycated Hemoglobin A
  • Insulin
  • Insulin, Long-Acting
  • hemoglobin A1c protein, human
  • Cholecalciferol
  • Fructosamine
  • Metformin
  • Calcifediol
  • Calcium