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Vitamin D and Type 2 Diabetes Study

Observational studies have shown an association between low vitamin D levels and the risk of type 2 diabetes. It is hypothesized that vitamin D may influence diabetes risk through its effect on the function of beta-cells in the pancrease (which produce insulin). However, it is not known whether taking a vitamin D supplement can lower the risk of diabetes. The aim of this study was to investigate whether taking 4000 IU per day of vitamin D3 could lower the incidence of type 2 diabetes in people at high risk for the disorder.

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Eligible Participants

Eligible participants for this study met the following criteria:

  • Adults 30 years of age or older
  • Having prediabetes (“borderline” diabetes) as defined by the 2010 American Diabetes Association guidelines

Study Design

This was a multi-site trial involving 22 academic medical centers in the United States. A total of 2,423 participants with prediabetes were randomly assigned to take either 4000 IU of vitamin D3 or a placebo daily for 4 years. In order to qualify for the study, participants had to meet at least two of the three glycemic criteria for prediabetes: fasting blood sugar between 100-125 mg/dL, 2-hour glucose between 140-199 mg/dL, and Hemoglobin A1c (HbA1c) between 5.7 and 6.4%. Every 3-6 months, participants completed clinic visits that were designed to encourage adherence to the trial regimen and assess for any occurrence of diabetes.

Conclusions

The results of the study showed that people at high risk for diabetes, not selected for vitamin D insufficiency, who took a daily vitamin D3 supplement did not have a significantly lower risk of type 2 diabetes than those taking a placebo. As response to a nutritional intervention depends on nutritional status at baseline, the high percentage of participants with adequate levels of vitamin D may have limited the ability of the trial to detect a significant effect.

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