1. Introduction
Vitamin D exists in two forms: D2 (ergocalciferol) and D3
(cholecalciferol). Vitamin D3, “the sunshine vitamin,” is synthetized
in the human epidermis via ultraviolet irradiation, or
it may be consumed in the form of oily fish or supplements.
Vitamin D2 is found in plants, as a product of irradiation
of ergosterol [1]. The vitamin is converted in the liver and
kidney to calcidiol and calcitriol, respectively, and acts on
specific target tissues via vitamin D receptors. Calcitriol, the
active form of vitamin D, binds to vitamin D receptors in the
intestines, bones, and kidneys to increase calcium absorption
from the intestines, promote calcium deposition in bones,
and decrease parathyroid hormone concentrations (PTH).
Its extraosseous effects are less known. Vitamin D receptors
were found in other tissues, as well, including the brain,
cardiomyocytes, vascular smooth muscle cells, endothelial
1. IntroductionVitamin D exists in two forms: D2 (ergocalciferol) and D3(cholecalciferol). Vitamin D3, “the sunshine vitamin,” is synthetizedin the human epidermis via ultraviolet irradiation, orit may be consumed in the form of oily fish or supplements.Vitamin D2 is found in plants, as a product of irradiationof ergosterol [1]. The vitamin is converted in the liver andkidney to calcidiol and calcitriol, respectively, and acts onspecific target tissues via vitamin D receptors. Calcitriol, theactive form of vitamin D, binds to vitamin D receptors in theintestines, bones, and kidneys to increase calcium absorptionfrom the intestines, promote calcium deposition in bones,and decrease parathyroid hormone concentrations (PTH).Its extraosseous effects are less known. Vitamin D receptorswere found in other tissues, as well, including the brain,cardiomyocytes, vascular smooth muscle cells, endothelial
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