Vitamin D 20,000 IU per Week for Five Years Does Not Prevent Progression From Prediabetes to Diabetes

J Clin Endocrinol Metab. 2016 Apr;101(4):1647-55. doi: 10.1210/jc.2015-4013. Epub 2016 Feb 1.


Context: Vitamin D deficiency is associated with insulin resistance and risk of future diabetes.

Objective: The objective of the study was to test whether supplementation with vitamin D to subjects with prediabetes will prevent progression to type 2 diabetes mellitus (T2DM).

Design: This was a randomized controlled trial performed in 2008 through 2015.

Setting: The study was conducted at the clinical research unit at a teaching hospital.

Patients: Five hundred eleven subjects (mean age 62 y, 314 males) with prediabetes diagnosed with an oral glucose tolerance test as part of the Tromsø Study 2007–2008 were included. A total of 256 were randomized to vitamin D and 255 to placebo. Twenty-nine subjects in the vitamin D and 24 in the placebo group withdrew because of adverse events.

Interventions: Interventions included vitamin D (cholecalciferol) 20 000 IU/wk vs placebo for 5 years. Annual oral glucose tolerance tests were performed.

Main outcome measure: Progression to T2DM was the main outcome measure. Secondary outcomes were change in glucose levels, insulin resistance, serum lipids, and blood pressure.

Results: The mean baseline serum 25-hydroxyvitamin D level was 60 nmol/L (24 ng/mL). One hundred three in the vitamin D and 112 in the placebo group developed T2DM (hazard risk 0.90; 95% confidence interval 0.69–1.18, Cox regression, P = .45, intention to treat analysis). No consistent significant effects on the other outcomes were seen. Subgroup analyses in subjects with low baseline 25-hydroxyvitamin D yielded similar results. No serious side effects related to the intervention were recorded.

Conclusions: In subjects without vitamin D deficiency, vitamin D supplementation is unlikely to prevent progression from prediabetes to diabetes. Very large studies with inclusion of vitamin D-deficient subjects will probably be needed to show such a putative effect. This study tested if supplementation with vitamin D to subjects with prediabetes will prevent progression to type 2 diabetes (T2DM).

Trial registration: NCT00685594.

Publication types

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

MeSH terms

  • Blood Glucose / metabolism
  • Diabetes Mellitus, Type 2 / etiology*
  • Diabetes Mellitus, Type 2 / metabolism
  • Diabetes Mellitus, Type 2 / prevention & control
  • Dietary Supplements
  • Female
  • Glucose Tolerance Test
  • Glycated Hemoglobin / metabolism
  • Humans
  • Insulin Resistance
  • Male
  • Middle Aged
  • Prediabetic State / complications*
  • Vitamin D / administration & dosage
  • Vitamin D / analogs & derivatives*
  • Vitamin D Deficiency / physiopathology*
  • Vitamins / administration & dosage


  • Blood Glucose
  • Glycated Hemoglobin A
  • Vitamins
  • hemoglobin A1c protein, human
  • Vitamin D
  • 25-hydroxyvitamin D

Associated data