Vitamin D and Type 2 Diabetes Study

The goal of the Vitamin D and type 2 diabetes (D2d) study is to determine if vitamin D supplementation works to delay the onset of type 2 diabetes in people at risk for the disease and to gain a better understand how vitamin D affects glucose (sugar) metabolism. Researchers at US sites will enroll people with pre-diabetes (people who have higher than normal blood glucose level but not high enough to meet the diagnosis of diabetes). The study will enroll participants over approximately 2 years and participants will be followed for approximately 3 years. Participants will receive either Vitamin D or a placebo by chance. Participants will take 1 pill a day for the duration of the study.

Inclusion criteria

• Pre-diabetes ("at increased risk for diabetes") defined by meeting 2-out-of-3 of the following glycemic criteria at the baseline visit:

• Fasting plasma glucose (FPG) 100-125 mg/dL
• 2-hour plasma glucose (2hPG) 140-199 mg/dL
• Hemoglobin A1c (HbA1c) 5.7-6.4%
• Age ≥ 30 years .(≥25 years for people of the following races: American-Indian, Alaska Native, Native Hawaiian or Other Pacific Islander).
• Body Mass Index ≥ 24.0 (22.5 for Asians) and ≤ 42.0 kg/m2
• Provision of signed and dated written informed consent prior to any study procedures.

Major Exclusion Criteria:

• Diabetes based on either of the following criteria:

• History (past 1 year) of hypoglycemic pharmacotherapy (oral or injectable medication approved by the FDA for type 2 diabetes), used for any condition (e.g. pre-diabetes, diabetes, polycystic ovarian syndrome.
• Meeting the diagnosis criteria for diabetes
• History (past 3 years) of hyperparathyroidism, nephrolithiasis or hypercalcemia.
• Pregnancy (past 1 year by report or positive pregnancy test at screening), intent to become pregnant in the next 4 years or unprotected intercourse. History of gestational diabetes is not an exclusion criterion.
• Currently breastfeeding.