Document Type : Research Article
Abstract
Vitamin D is also known as calciferol because of its role in calcium metabolism and antirachitic factor because it prevents rickets. It is a modified steroid, synthesised in the skin under the influence of sunlight and is necessary for metabolism of calcium and phosphorus. Its RDA is 400 IU or 10 mg, it binds to the receptor of target cells and regulate through gene expression. Vitamin D undergoes hydroxylation in the liver to form 25 hydroxy vitamin D [25(OH) vitamin D]. The two main forms are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). The main source of vitamin D in humans is in the form of vitamin D3, which is derived from synthesis in the skin via exposure of 7- dehydrocholesterol, concentrated in the stratum basale and stratum spinosum, to ultraviolet B (UV-B) radiation. Vitamin D2 is obtained from the diet, and is derived from ultraviolet irradiation of ergosterol, found in fungi. Both metabolites are transported in the blood bound to vitamin D binding protein (DBP). These inactive vitamin D metabolites must undergo a two-step hydroxylation process to become biologically active. Initially, vitamin D2 and D3 undergo hydroxylation in the maternal liver, via the action of vitamin D 25-hydroxylase enzyme (CYP27A1), to form the inactive steroid precursor 25-hydroxyvitamin D (25[OH]D). 25[OH]D is the major circulating and stored form of vitamin D. In this present review we have focused on need of vitamin D beyond bone.
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