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.