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


OBJECTIVE
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.
Jorde
Rolf
R
Institute of Clinical Medicine, University of Tromsø, Tromsø, Norway. rolf.jorde@unn.no
Figenschau
Yngve
Y
D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000032:analysis*; D002096:C-Peptide / Q000097:blood; D002112:Calcifediol / Q000097:blood*; D002118:Calcium / Q000097:blood; D002762:Cholecalciferol / Q000008:administration & dosage*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000188:drug therapy; D019587:Dietary Supplements; D005260:Female; D019270:Fructosamine / Q000097:blood; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D007328:Insulin / Q000097:blood; D049528:Insulin, Long-Acting / Q000627:therapeutic use; D008297:Male; D008687:Metformin / Q000627:therapeutic use; D008875:Middle Aged; D055815:Young Adult
D001786:Blood Glucose; D002096:C-Peptide; D002112:Calcifediol; D002118:Calcium; D002762:Cholecalciferol; D019270:Fructosamine; D006442:Glycated Hemoglobin; D007328:Insulin; D049528:Insulin, Long-Acting; D008687:Metformin; C517652:hemoglobin A1c protein, human