Supplementation with cholecalciferol does not improve glycaemic control in diabetic subjects with normal serum 25-hydroxyvitamin D levels
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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.
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.
After 6 months, the fasting glucose, insulin, C-peptide, fructosamine, and HbA1c 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.
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.
KeywordsDiabetes mellitus Glucose Placebo-controlled study Vitamin D
The present study was supported by a grant from the Norwegian Diabetes Association. The superb assistance by Annika Gustafsson and the other nurses at the Clinical Research Unit and by Inger Myrnes and Astrid Lindvall at the Department of Medical Biochemistry, University Hospital of North Norway, is gratefully acknowledged.
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