Mahzad Irandoust
1 , Hashem Nayeri
1* , Hossein Irandoust
2 1 Department of Biochemistry, Falavarjan Branch, Islamic Azad University, Isfahan, Iran.
2 Agricultural Research, Education and Natural Resources Research Center, Agricultural Research, Education and Extension Organization, Isfahan, Iran.
Abstract
Vitamin D is a group of fat-soluble hormone precursor that enters the body through food and nutritional supplements. Vitamin
D has two important forms which are vitamin D2
(ergocalciferol) and vitamin D3
(cholecalciferol). This vitamin is activated in the
body through two hydroxylation reactions and produces calcitriol (1,25-dihydroxycholecalciferol), which is its active form. The
metabolites and other analogues of these substances also refer to vitamin D. Vitamin D plays a significant physiological and essential
role in maintaining the levels of extracellular calcium ions. The most important role of extracellular calcium is its contribution to
muscle contractions. Around 10% to 20% of vitamin D is supplied by the foods. Vitamin D sources include salmon, cod liver oil,
wild mushroom, milk, and meat and also egg yolk. However, 80% of vitamin D comes from sunlight. Vitamin D has an important
role in the process of bone metabolism, regulation of proliferation and cellular differentiation, as well as the regulation of immune
responses. The purpose of this review article is to study the importance of vitamin D and its use in the body as well as examining the
vitamin D levels in different continents.