Effect of a Vitamin D Analogue vs Placebo on p-NT-proBNP in Patients With Type 1 DM and Diabetic Nephropathy

Inclusion Criteria: * 18-75 years of age * Type 1 diabetes mellitus * Diabetic nephropathy (defined by persistent albuminuria, \> 300 mg/24 hr or 200µg/min in 2 of 3 consecutive samples, presence of diabetic retinopathy and absence of clinical or laboratory evidence of other kidney or renal tract disease * Chronic kidney disease stage 3 and 4 * S-Parathyroid hormone (s-PTH)\> 35pg/ml * Stabile RAAS-blocking and diuretic treatment Exclusion Criteria: * Other kidney disease than diabetic nephropathy * Myocardial infarction within the last three months prior to visit 1 * Coronary artery revascularization within the last three months prior to visit 1 * Transitional cerebral ischemia (TCI) or apoplexia within the last three months prior to visit 1 * Cardiac Failure (NYHA Class III or IV) * Kidney Failure (GFR \<15ml/min), dialysis, kidney transplantation) * Liver disease with serum alanine aminotransferase (ALT\>3 x the normal value * Alcohol/drug abuse * Hypercalcemia (serum ionized calcium \>1.35 mmol /L) * Medication with phosphate and/or vitamin D-containing medications, which can not be paused during the study * Clinical signs of vitamin D toxicity * Pregnant or nursing women * Fertile women not using chemical or mechanical (IUD) contraceptive methods * Current disulfiram treatment * Allergy to the study drug * Patient unable to understand the informed consent * Any other condition or therapy which, in the opinion of the investigator, makes the patient not suited for participation.