The effect of administration of vitamin D is tested on the long-term control of blood sugar (as measured by HbA1-c levels in blood) and mean blood pressure (as measured by 24 hour blood pressure profiles)in patients with stable type 2 diabetes mellitus

Inclusion criteria

• Men and women, ages ≥18 years
• Official diagnostic criteria for type 2 diabetes fulfilled in patients on any type of oral or parenteral glucose-lowering treatment
• Independent living at home
• On stable regimen of BP meds (if any) with BP well controlled and/or K supplement (if any) for 2 months and which is deemed unlikely to change during the study
• Stable glucose control for 2 months by any approved method including insulin

Exclusion criteria

• Patients with type 1 diabetes (or insulin-requiring diabetes of unclear type)
• Patients on hemodialysis, with hyperparathyroidism or active cancer disease
• Patients with known metabolic bone disease
• Laboratory evidence of kidney (eGFR < 60 ml/min) or liver disease
• Dietary calcium intake exceeding 1500mg/d (as estimated by dietary history)
• 25(OH) vitamin D levels at baseline > 70 nmol/L
• Calciuria (> 8 mmol/24 hours as measured by 24 hour urine collections)
• Hypo- and hypercalcemias and hypo- and hyperphosphatemias of any cause
• Medications that affect vitamin D metabolism (e.g. antiepileptic drugs, calcimimetics, 1-34 PTH (Forsteo) vitamin D therapy over and above 400U daily 6 months prior to enrollment and during the study)
• Foreseeable need for adaptation of either glucose- or blood pressure lowering during the next 6 months as decided by the family physician or the treating diabetologist - see above
• History of binge eating or wt gain or loss exceeding 6 kg in past 18 months
• Patients on any type of inhibitors of plasma coagulation (i.e. coumarine, heparins)