The patient group of hypomagnesesemic renal transplant recipients randomized to magnesium supplementation (number = 30). The assessments are a baseline fasting assessment of insulin resistance and an Oral Glucose Tolerance Test with derived indices of insulin secretion,which are repeated after 6 months.

The patient group of hypomagnesesemic renal transplantation recipients, randomized to no magnesium supplementation (number = 30). During 6 months, no magnesium supplementation is started, provided that the serum magnesium level remains > 1,2 milligram/deciliter. In case of cramps, intermittent supplementation is allowed, but will be recorded. The assessments are a baseline fasting assessment of insulin resistance and an Oral Glucose Tolerance Test with derived indices of insulin secretion,which are repeated after 6 months.

In the control group of normomagnesemic renal transplantation recipients (number = 10), only a baseline assessment will be performed. The assessments are a baseline fasting assessment of insulin resistance and an Oral Glucose Tolerance Test with derived indices of insulin secretion.

The supplementation starts with 450 mg of magnesium oxide daily, up to a maximum of 3 times 450 mg daily, while aiming at a serum magnesium level of > 1,9 mg/dl.

The primary outcome of the study is the evaluation of change in insulin resistance and insulin secretion after 6 months of supplementation (versus no supplementation). Insulin resistance is measured by 'Homeostatic Model Assessment' (HOMA) - modeling and the McAuley Index. Insulin secretion is assessed by 'Oral Glucose Tolerance test' (OGTT)- derived indices.

The secondary outcome is the evaluation of change in Hemoglobin A1c after 6 months of magnesium supplementation versus no supplementation.