Vitamin D is synthesized in human skin after the photoisomerization of 7-dehydrocolesterol to pre-vitamin D3 under the influence of UV B radiation (wavelength, 280–315 nm) ( Fig. Therefore, vitamin D is now viewed from a controller of calcium homeostasis (calciotropic) to an hormone with pleiotropic actions. This vigorous increase of interest in vitamin D is powered by the spectacular insights into the pivotal regulatory role of vitamin D with regard to pleiotropic functions, by the data on worldwide trend to nutritional vitamin insufficiency ( 2) and by new knowledge on intracrine and paracrine actions of vitamin D metabolites ( 3).ĭespite the fact that vitamin D is still called and known as a vitamin, it actually comprises a group of very closely interrelated hormonal compounds also related to the other main calciotropic hormone, the parathyroid hormone. Not surprisingly, TIME magazine nominated vitamin D as one of the “top medical breakthroughs” in the December issue of 2007. Many arguments are favouring a renewed interest in vitamin D physiology, with a consequent increase in the number of scientific publications and media reports ( 1).
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