Cardiovascular Effects of Long-Term Vitamin D Supplementation: Summarised by Many but Studied by Few.

Vitamin D supplementation has been primarily studied for its effect on mineral metabolism and, therefore, bone resorption. Vitamin D is also known to play a role in the reninangiotensin-aldosterone system [1] and in inflammation [2] and is produced by vascular endothelial cells [3] . It is, therefore, a strong hypothesis that plasma vitamin D levels influence cardiovascular factors in terms of blood pressure, vascular function and cardiovascular risk. In this issue of Pulse , Veloudi et al. [4] provide a qualitative review of a selection of randomised controlled trials (RCTs) concerning the effect of vitamin D supplementation on blood pressure and measures of arterial stiffness. They also include a descriptive review of some studies concerning cardiovascular outcomes of low serum levels of vitamin D. The article presents a graphical representation of sample size and study duration of 36 studies investigating peripheral blood pressure and 9 studies investigating arterial stiffness. In so doing, the article highlights that very few of these studies show a beneficial effect of vitamin D supplementation. The graphical presentation of the data also allows a visual representation of the previous finding, demonstrated statistically, that there is no relationship between an increased dose of vitamin D supplement and beneficial cardiovascular effect [5] . The effect of vitamin D supplementation on cardiovascular factors is of great clinical interest, demonstrated by the number of studies identified in meta-analyses in recent years. This year alone, quantitative meta-analyses of arterial stiffness outcomes have been published by Upala et al. [6] and Rodríguez et al. [7] summarising 7 and 18 RCTs, respectively. A recent quantitative meta-analysis on peripheral blood pressure outcomes identified 46 independent vitamin D supplementation trials [5] . These quantitative studies, although not included in the review by Veloudi et al. [4] , support the same conclusion which Veloudi et al. [4] make from a qualitative review of RCTs, namely that vitamin D supplementation has no effect on arterial stiffness or blood pressure. However, Rodríguez et al. [7] surmise that larger, well-designed Received: October 28, 2016 Accepted: October 28, 2016 Published online: December 8, 2016