Vitamin D was discovered due to its ability to cure rickets, but recently many other important functions for it in the human body have been discoverred, and it counteracts several other diseases, as diabetes and some forms of cancer. The nuclear vitamin D receptor has been found throughout the vertebrate phylum down to jawless fishes, but not in invertebrates. Its role in those organisms that are repsonsible for the main input to the aquatic food-web and to human nutrition, i.e. phytoplankton and zooplankton, is not understood.This chapter summa-rizes the discovery of vitamin D, and the chemistry and photochemistry of its precursors, transformations and metabolites. The physiological roles of 1,25-dihydroxyvitamin D are briefly described, as well as evolutionary aspects of the the signaling in animals based on this compound. The chapter is concluded with an overview of what is known about the occurrence and role of vitamin D in the plant kingdom, biogeographical aspects of vitamin D, and the relatively recent discovery of non-photochemical production of vitamin D.
vitamin D Provitamin D Previtamin D Lumisterol Tachysterol Absorption spectrum Action spectrum Rickets 25-hydroxyvitamin D 1