الفهرس 
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Abstract
Vitamin D or calciferol is a generic term and refers to a group of lipid soluble compounds with a four-ringed cholesterol backbone. In addition to its skeletal effects and control of calcium hemostasis, 1,25-Dihydroxy vitamin D3 showed potent antiproliferative and immunomodulatory properties, there has been appealing evidence on the“nonclassic” role of vitamin D in many autoimmune diseases including rheumatoid arthritis, scleroderma, psoriasis, multiple sclerosis, and also metabolic syndrome and Type 1 Diabetes Mellitus.
Vitamin D deficiency increases the risk of diabetes development and supplementation showed protective effects, many studies looked at the protective effect of vitamin D on diabetes progression and control.
Much evidence suggested that vitamin D is involved in several mechanisms in addition to bone metabolism, and its role in abnormal glucose metabolism as well as in type 2 diabetes has been demonstrated A recent review indicates that vitamin D deficiency may predispose to glucose intolerance, altered insulin secretion and type 2 diabetes either through a direct action via vitamin D receptor (VDR) activation or indirectly via calcemic hormones and also via inflammation.
It is recognized that VDR, the receptor of the steroid hormone 1,25(OH)2D3, is widely distributed in more than 38 tissues where it
Summary
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clearly controls vital genes related to bone metabolism, oxidative damage, chronic diseases and inflammation.
VDR is expressed by macrophages and dendritic cells, which suggests that vitamin D plays an important role in the modulation of inflammatory response.
Low serum 25-hydroxyvitamin D, a measure of vitamin D status, is associated with an increased risk of metabolic syndrome
Adiposity is an important determinant of serum 25-hydroxyvitamin D and may be primarily responsible for the association between low vitamin D status and various disease outcomes, including the metabolic syndrome. Observations in both morbidly obese individuals and healthy people support a general association between adiposity and vitamin D status. The association between increased body fat and low serum 25-hydroxyvitamin D concentrations was recognized in humans and animal models more than 30 years ago, A number of studies have demonstrated associations between vitamin D levels and various PCOS symptoms, including insulin resistance, infertility and hirsutism.
Vitamin D is thought to influence the development of PCOS through gene transcription and hormonal modulation influences insulin metabolism and fertility regulation.