Photochemistry and Photobiology of Vitamin D

Authored by: Michael F. Holick

Handbook Ofphotomedicine

Print publication date:  October  2013
Online publication date:  October  2013

Print ISBN: 9781439884690
eBook ISBN: 9781439884706
Adobe ISBN:


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Vitamin D is one of the oldest hormones, if not the oldest, which has existed in life forms for more than 500 million years (Holick 1989). Emiliania huxleyi is phytoplankton that has existed unchanged in the Sargasso Sea for more than 500 million years. When this organism was cultured and then exposed to ultraviolet (UV) radiation, the ergosterol (previtamin D2) in this organism was converted to previtamin D2 (Holick 2003). Similarly, Skeletonema menzelii, a phytoplankton species that contains calcium carbonate for its cytoskeleton, when exposed to UV radiation, also converted its ergosterol to previtamin D2. Previtamin D2, in turn, isomerized to vitamin D2. Remarkably, the amount of ergosterol present in E. huxleyi was 1 μg/g weight. An evaluation of plankton net tows from the Atlantic Ocean revealed a wide variety of provitamin Ds, including ergosterol and 7-dehydrocho-lesterol, which were present in the collection of organisms that included phytoplankton and zooplankton (Holick 1989, 2003).

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