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D2d Study

Title Vitamin D and Type 2 Diabetes (D2d) Study
Therapeutic Area Diabetes, Diabetes Mellitus
Principal Investigator Anastassios Pittas, MD MS
Min Age 30 Years
Gender Both
Contact Idy Tam, Kim Vo
More Information


A clinical trial to test whether taking vitamin D daily lowers the risk of diabetes in people who are at high risk for diabetes (e.g. overweight, older than 40 years, family history of diabetes, or had diabetes during pregnancy). Participants will take 1 pill a day (vitamin D or placebo) for the duration of the 4 year study. Participants will visit the study site for up to 13 scheduled visits during their participation. All participants receive education on diabetes prevention and are monitored twice a year for diabetes.

Study Details

Inclusion Criteria

  • Pre-diabetes defined by meeting 2-out-of-3 of the following glycemic criteria at the baseline visit:
    1. High fasting glucose level (100-125 mg/dL)
    2. High hemoglobin A1c (5.7-6.4%)
    3. High glucose level after a glucose tolerance test (140-199 mg/dL).
  • Age ≥ 30 years
  • Body Mass Index ≥ 24.0 (22.5 for Asians) and ≤ 42.0 kg/m2

    Exclusion Criteria

    • Diabetes based on either of the following criteria:
      1. On diabetes medication
      2. High glucose levels (as measured at the screening visit)
    • History of hyperparathyroidism, kidney stones or high blood calcium level.

    Study Requirements

    Details about the study can be found at Below is an overview.

    After the Screening visit (which lasts about 1 hour) and the Baseline visit (which lasts about 3 hours), qualified participants will visit the clinic in the morning about every 6 months for the 4 year long study. Participants will be required to fast (no food or drink except water) overnight for 8 hours before each visit.

    Study visits will include the following:

    • Answering questions about your health, diet and physical activity
    • Measurement of height, weight and blood pressure.
    • Blood draw and an Oral Glucose Tolerance Test (OGTT), which will last 3 hours.