Effect of Vitamin D Deficiency and Vitamin D Supplementation on Glucose Metabolism

Improved Insulin Sensitivity With Therapeutic Vitamin D Replacement in Pre-Diabetic Vitamin D Deficient Individuals

This study was intended to evaluate the effect of vitamin D supplementation on insulin sensitivity and pancreatic islet beta-cell function. Our hypothesis was that vitamin D supplementation to normal levels in patients with impaired fasting glucose will result in improved insulin sensitivity and improved beta cell function.

A modified frequently sampled intravenous glucose tolerance (mFSIGT) test was used. On day 0, baseline 22 time point mFSIGT was performed. Subjects were then treated with cholecalciferol (vitamin D3) supplementation - 10,000 IU/day - for 28 consecutive days. mFSIGT was then repeated measuring glucose, insulin and c-peptide at all time points. 25-OH vitamin D, PTH, and calcium were also measured at time point 0 pre and post vitamin D supplementation. Data was analyzed using the Bergman/Boston minimal model for insulin homeostasis with MinMod Millennium software.

Inclusion Criteria:

• Impaired fasting glucose
• Adult, age between 18 and 65
• Serum vitamin D level below 30 ng/mL

Exclusion Criteria:

• History of nephrolithiasis
• Any medications that can effect insulin sensitivity or beta cell function (i.e. antipsychotics, metformin)
• Pregnancy
• Liver disease
• Renal disease