Vitamin D Synthesis Process

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Vitamin D exists in two forms. These forms are Vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). Vitamin D3 production occurs in the skin when exposed to ultraviolet sunlight. Such exposure to ultraviolet light initiates conversion of 7-dehydrocholesterol to Provitamin D3, a precursor of Vitamin D3, and consequently to Vitamin D3. Moreover, it can be obtained from animal sources including fish’s liver oil and flesh of fatty fish. On the other hand, Vitamin D2 (ergocalciferol) is primarily obtained from plant sources such as mushrooms and yeast. However, vitamin D from these sources is biologically inert and requires activation to attain its desirable physiological function (Holick, 2007) .
Activation of inactive Vitamin D requires two hydroxylation processes. The first hydroxylation process occurs in the liver. During this process, the inactive vitamin D is hydroxylated at carbon 25 (C-25) by 25 hydroxylases (25OHase). This hydroxylation process results in the chemical conversion of Vitamin D to 25 hydroxyvitamin D (25(OH) D), which is the primary form of vitamin D in the circulation system. This property of 25 hydroxyvitamin D makes it
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This transporting carrier protein is called vitamin D-binding protein (DBP).
The primary function of vitamin D is to maintain calcium and phosphorus homeostasis through three different mechanisms. One of these mechanisms involves increasing intestinal calcium absorption. The homeostatic state is also achieved by moving calcium and phosphorus from a skeletal body part to the blood in order to ensure an optimal blood level. Finally, decreasing renal calcium and phosphorus excretion is also crucial to reach a homeostatic balance of the body. Other functions of vitamin D include cell differentiation, immune system regulation, insulin secretion, and blood pressure control (Holick,

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