Emerging evidence suggests that vitamin D [25-hydroxyvitamin D; 25(OH)D] may play a role in the etiology of type 2 diabetes. Vitamin D levels are lower in those with type 2 diabetes and impaired glucose tolerance (IGT) compared with those with normal glucose tolerance (NGT). In addition, a few prospective studies have shown a significant inverse association of baseline serum 25(OH)D with incident diabetes. To date, however, the exact mechanisms through which vitamin D affects diabetes risk are not yet fully known, particularly whether vitamin D plays a role in insulin resistance (IR) and/or b-cell dysfunction, the main pathophysiological disorders underlying type 2 diabetes. So, the investigators plan to examine the prospective associations of baseline vitamin D [25-hydroxyvitamin D; 25(OH)D] with insulin resistance (IR), b-cell function, and glucose homeostasis in subjects at risk for type 2 diabetes.

Inclusion Criteria:

• one or more risk factors for diabetes, including:

  • obesity
  • hypertension
  • dislipidemia
  • a family history of diabetes

Exclusion Criteria:

• previous diagnosed diabetes
• vitamin D supplement.

Study participants, aged over 30 years, are recruited from Korea, between January 2006 and December 2011. Participants are at high risk for type 2 diabetes, as they are recruited on the basis of the presence of one or more risk factors for diabetes, including obesity, hypertension, dislipidemia, and a family history of diabetes. Participants are contacted every 6 month after the baseline visit to update contact information and collect data on major health events. Participants are invited to return to the clinic examination centers after 3 years for follow-up assessments.