The purpose of the study is to evaluate the effects of Cholecalciferol (Vitamin D3) substitution on the posttransplant outcome (glomerular filtration rate as well as serum creatinine levels, number of acute rejection episodes, number of infections and C-reactive protein levels within the first year after transplantation) in vitamin D deficient kidney transplant recipients.

Apart from its classical actions in calcium homeostasis, vitamin D acts as a potent immunomodulatory agent. As such, vitamin D is thought to have beneficial effects in the transplant setting, especially in kidney transplant recipients considering the fact that approximately 40% of all kidney transplant recipients are vitamin D deficient.

Therefore, the objective is to conduct a randomized, double-blind, placebo-controlled study focusing on the impact of Cholecalciferol substitution in vitamin D deficient kidney transplant recipients on graft function (glomerular filtration rate as well as serum creatinine levels), incidence of acute rejection episodes, frequency and severity (CRP levels) of posttransplant infections within the first year after kidney transplantation.

Moreover, the impact of Vitamin D3 on renal osteodystrophy will be analyzed by means of bone mineral density. DXA measurements will be performed during the first four weeks after kidney transplantation, after 5, and after 12 months posttransplant.

Kidney transplant recipients found to have vitamin D deficiency (defined as 25-hydroxyvitamin D < 50 nmol/l) will be included and will be randomized to receive either oral Vitamin D3 therapy or placebo. Vitamin D3 will be administered at a daily dose of 6800IU over a time period of one year.

All in all, 200 subjects will be included in the VITA-D study.

Inclusion Criteria:

• age > 18
• deceased donor kidney transplant recipients
• only kidney transplant recipients
• vitamin D deficiency defined as 25 (OH)D < 50nmol/l

Exclusion Criteria:

• re-transplantation for the second time if the patient is highly immunized and therefore included in the aphaeresis program
• re-transplantation for the third or further time
• significant impaired intestinal resorption: malabsorption due to celiac sprue, systemic scleroderma; maldigestion due to chronic pancreatitis, pancreatic insufficiency, pancreas resection, mucoviscidosis, Zollinger-Ellison-syndrome
• history of inflammatory bowel disease: Crohn's disease, ulcerative colitis
• previous gastrectomy, small bowel or large bowel resection, intestinal bypass surgery
• severe liver disease: cirrhosis
• HIV positive