Alpalhão, MiguelFilipe, Paulo2021-02-192021-02-192020Photodermatol Photoimmunol Photomed. 2020 Sep;36(5):412-4130905-4383http://hdl.handle.net/10451/46438© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons LtdVitamin D is a fat-soluble hormone that plays a significant role in calcium-phosphate metabolism, in addition to intervening in cell metabolic activity, immune regulation, among other functions. Vitamin D is synthesized in skin epithelium under ultraviolet B (UVB) radiation. It then undergoes two successive hydroxylations in the 25- and 1- carbons, in the liver and in the kidney, respectively, to yield the active form, calcitriol. A minor portion of vitamin D is obtained from alimentary sources.engjournal article10.1111/phpp.125791600-0781