The purpose of this study is to evaluate if treatment with vitamin D increase beta cell function and insulin sensitivity in subjects with pre-diabetes or newly diagnosed diabetes mellitus type 2.

Inclusion Criteria:

• Meeting criteria for IFG, IGT, IFG+IGT or diabetes mellitus at OGTT.
• BMI ≤ 32 kg/m2.
• HbA1c ≤ 7.0 % (MonoS) or ≤ 63 mmol/mol (IFCC).
• Fasting plasma glucose < 9 mmol/l
• S-25-OH-vitamin D3 < 75 nmol/l.

Exclusion Criteria:

• Treatment with any vitamin D preparation.

• Regular sun-bathing in solarium.

• Hypercalcemia at screening, defined as free s-calcium > 1.35 mmol/l.

• Hyperphosphatemia at screening, defined as s-phosphate > 1.5 mmol/l.

• Sarcoidosis or other granulomatous disease.

• Treatment with phenytoin, barbiturates, rifampicin, isoniazid, cardiac glycosides, orlistat or colestyramin.

• Impaired hepatic function.

• Impaired renal function

• Cardiac disease defined as:

  • Unstable angina pectoris
  • Myocardial infarction within the last 6 months
  • Congestive heart failure NYHA class III and IV

• Cerebral stroke within the last 6 months.

• Anti-diabetic medication of any kind.

• Females of childbearing potential who are pregnant, breast-feeding or intend to become pregnant or are not using adequate contraceptive methods.