Vitamin D and Type 2 Diabetes Study (D2d Study)

The purpose of this study is to evaluate the effect of taking vitamin D supplements on the prevention of diabetes in people who are at high risk for diabetes. D2d is a multi-center trial, and will consist of a total of approximately 2,400 participants nationwide. Please feel free to check the study website for more information. 

Eligible Participants

Eligible participants for this study meet the following criteria:

  • Both men and women
  • 30 years of age or older
  • Have prediabetes (“borderline” diabetes)
  • Must be willing to be randomly assigned to take either a vitamin D supplement (4000 international units) or a placebo for roughly 4 years

Study Design

Participation in the study will require up to 13 scheduled visits to the Clinical Translational Unit (CTRU) at Stanford Hospital & Clinics, which will include blood draws at certain time points.

Depending on study involvement, participants may receive up to $320 in compensation over 4 years.

How to Participate

We have completed the recruitment and are completing the final phase of the study. If you have questions, please contact the study coordinator, Melanie Rosenberg, at or 650-485-3910.

Stanford Prevention Research Center

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