In this randomized, double-blind, placebo-controlled trial we plan to enrol 200 vitamin D deficient hypertensive patients. Our main objective is to evaluate whether vitamin D3 supplementation with 2,800 IU daily for 8 weeks has an effect on 24-hour systolic ambulatory blood pressure (ABP) compared to placebo. In addition, we also aim to evaluate whether vitamin D3 supplementation alters 24-hour diastolic ABP, pulse wave velocity, N-terminal-pro-brain natriuretic peptide (NT-pro-BNP), corrected QT interval (Bazett formula), renin, aldosterone, 24-hour urinary albumin excretion, HOMA-IR (HOmeostatic Model Assessment: Insulin Resistance), triglycerides and HDL-cholesterol.