FIGURE 1. Vitamin D (VD) synthesis and its effects.
VD is obtained through the skin production or by alimentary consumption.
7-dehydrocholesterol, which can be transformed to
cholesterol,A converts to previtamin
D3B,C through ultraviolet B radiation. Via spontaneous
isomeration,D precholecalciferol changes to
cholecalciferol.E VD can be obtained from food, both
of animal (cholecalciferol) and plant origin
(ergocalciferol).E Cholecalciferol is metabolized in
the liver to 25-hydroxyvitamin D.F,G The active form
of VD, 1,25-dihydroxyvitamin D, is obtained in the kidneys by the enzyme
25-Hydroxyvitamin D-1α-hydroxylase (which, in turn, is regulated by
stimuli).C Calcitriol has diverse effects on different
tissues.C
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