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A part from skeletal diseases, vitamin D deficiency is considered a risk factor for cardiovascular events and mortality. [1][2][3][4][5][6] Nevertheless, it remains unclear whether low 25-hydroxyvitamin D (25[OH]D) concentrations are a significant causal risk factor or are simply related to adverse outcomes because of reverse causation and confounding factors, such as obesity, reduced mobility with low sunlight exposure, poor nutrition, or inflammation. [1][2][3][4][5][6] Because high blood pressure (BP) has emerged as the leading risk factor for the global disease burden, it is important to evaluate whether vitamin D has a beneficial effect on lowering BP to clarify the potential role of vitamin D for public health. 7 Large observational studies and meta-analyses have shown that low 25(OH)D concentrations are a significant risk marker for arterial hypertension. 8,9 Molecular effects of vitamin D receptor activation, such as suppression of the renin-angiotensin-aldosterone system (RAAS), nephroprotective actions, or improvements in endothelial/vascular function, suggest Abstract-Vitamin D deficiency is a risk factor for arterial hypertension, but randomized controlled trials showed mixed effects of vitamin D supplementation on blood pressure (BP). We aimed to evaluate whether vitamin D supplementation affects 24-hour systolic ambulatory BP monitoring values and cardiovascular risk factors. The Styrian Vitamin D Hypertension Trial is a single-center, double-blind, placebo-controlled study conducted from June 2011 to August 2014 at the endocrine outpatient clinic of the Medical University of Graz, Austria. We enrolled 200 study participants with arterial hypertension and 25-hydroxyvitamin D levels below 30 ng/mL. Study participants were randomized to receive either 2800 IU of vitamin D3 per day as oily drops (n=100) or placebo (n=100) for 8 weeks. Primary outcome measure was 24-hour systolic BP. Secondary outcome measures were 24-hour diastolic BP, N-terminal-pro-B-type natriuretic peptide, QTc interval, renin, aldosterone, 24-hour urinary albumin excretion, homeostasis model assessment-insulin resistance, triglycerides, highdensity lipoprotein cholesterol, and pulse wave velocity. Methods Study DesignThe Styrian Vitamin D Hypertension Trial was sponsored by the Medical University of Graz, Austria, and is a single-center, double-blind, placebo-controlled, parallel-group study conducted at the Medical University of Graz, Austria. The publication of this trial adheres to the Consolidated Standards of Reporting Trials (CONSORT) 2010 statement. 29 The trial was initially registered at http://www.clinicaltrialsregister.eu (EudraCT number, 2009-018125-70) and was additionally registered at clinicaltrials.gov (ClinicalTrials.gov Identifier NCT02136771). ParticipantsEligible study participants were adults aged ≥18 years with arterial hypertension and a 25(OH)D serum concentration below 30 ng/mL (multiply by 2.496 to convert ng/mL to nmol/L). Arterial hypertension was classified in patients with an office BP of systol...

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Vitamin D deficiency is mainly a consequence of insufficient sunlight induced vitamin D production in the skin and has been associated with various chronic diseases including type 2 diabetes. Experimental data have shown that vitamin D is important for glucose induced insulin secretion, improves insulin resistance, and exerts anti-inflammatory actions. Epidemiological studies have largely documented that a poor vitamin D status is associated with higher risk of insulin resistance and type 2 diabetes. The majority of randomized controlled trials (RCTs) in healthy or prediabetic individuals have, however, failed to demonstrate relevant vitamin D effects on insulin resistance or diabetes incidence. In patients with type 2 diabetes, a few RCTs reported some moderate effects of vitamin D on glycemic control and insulin resistance. While these findings warrant further in-depth studies, the current evidence is insufficient to recommend vitamin D supplementation for the prevention or treatment of type 2 diabetes.