Styrian Vitamin D Hypertension Trial

Inclusion Criteria: * 25-hydroxyvitamin D levels below 30 ng/ml (75 nmol/L) * Arterial hypertension defined according to recent guidelines as an average office blood pressure on at least two occasions of systolic ≥ 140 and/or diastolic ≥ 90 mmHg or a mean 24-hour ABP of systolic ≥ 125 and/or diastolic ≥ 80, or a home blood pressure of systolic ≥ 130 and/or diastolic ≥ 85 or ongoing antihypertensive treatment which was initiated due to arterial hypertension * Age of ≥ 18 years * Written informed consent. Exclusion Criteria: * Hypercalcemia defined a serum calcium \>2.65 mmol/L * Pregnancy or lactating women * Drug intake as part of another clinical study * Acute coronary syndrome or cerebrovascular events in the previous 2 weeks * Glomerular filtration rate (GFR) according to the MDRD formula \< 15 ml/min/1.73m² * Systolic 24-hour ABP \> 160 mm Hg or \< 120 mm Hg * Diastolic 24-hour ABP \> 100 mm Hg * Change of antihypertensive treatment (drugs and/or lifestyle) in the previous 4 weeks or planned changes of antihypertensive treatment during the study * Any disease with an estimated life expectancy below 1 year * Any clinically significant acute disease requiring drug treatment * Chemotherapy or radiation therapy during the study * Regular intake of more than 880 International Units (IU) vitamin D per day in the last four weeks before study entry or during the study