الفهرس 
Introduction
Aim of the workOnly 14 pages are availabe for public view
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Abstract
Vitamin D is a fat soluble vitamin that occurs naturally in only a few foods and that is also manufactured in the skin when a precursor interacts with the short ultraviolet rays.
Two forms of vitamin D exist: vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol) Vitamin D3 (cholecalciferol) is derived from cutaneous synthesis and animal sources. Vitamin D2 (ergocalciferol) is derived from plant sources and yeast.
Vitamin D may be acquired from three main sources: food, sun exposure, or dietary supplements. However, dietary intake can provide only 20% of the body’s daily requirements of vitamin D.
Vitamin D is metabolized to 25 hydroxy vitamin D (25(OH) D) in the liver and subsequently to 1 α 25-dihydroxy vitamin D (1α 25 (OH) 2D) in the kidney.
The (1 α 25 (OH) 2D) is considerd as the active form of vitamin D and it exerts a wide variety of biological actions in the body.
Vitamin D metabolism through the endocrine pathway exerts a significant effect on bone metabolism and the associated calcium and phosphorus balance. Vitamin D metabolism through the autocrine pathway exerts a profound effect on many other body systems.
The mechanism of action of the active form of 1,25(OH)2D is similar to that of other steroid hormones and is mediated by binding to VDR.
Vitamin D receptors (VDR) are found in most tissues, not just those participating in the classic actions of vitamin D such as bone, gut, and kidney. These non-classic tissues are, therefore, potential targets for the active metabolite of vitamin D. Furthermore, several tissues, including the brain and the placenta, also contain the 25- (OH)D3-1α-hydroxylase enzyme capable of producing 1, 25 (OH)2D from the circulating form of vitamin D.
The risk of vitamin D deficiency is higher in dark skinned populations, children who live at higher latitudes, exclusively breastfed infants and children, infants born to vitamin D deficient mothers, and premature infants and may also be affected by cultural practices (including nature of clothing and use of sunscreen).
Vitamin D is essential for promoting calcium absorption in the gut and maintaining adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and prevent hypocalcemic tetany. It is also needed for bone health and optimal over all health and disease prevention.
In addition to the traditional known metabolic activities, vitamin D has been shown to modulate the immune system, and its deficiency has been linked to the development of several autoimmune disorders including type 1 diabetes and multiple sclerosis, food allergy and asthma.
There is accumulating evidence that vitamin D is a nonclassical risk factor for cardiovascular diseases. The active vitamin D metabolite, 1,25-dihydroxyvitamin D, down-regulates several negative and up-regulates various protective pathways in the heart and vasculature .First randomized trials demonstrate that vitamin D supplementation leads to vasodilatation and suppresses cardiovascular risk markers such as triglycerides and the inflammation marker tumor necrosis factor-α.
There is now clear evidence that vitamin D is a plausible biological risk factor for neuropsychiatric disorders and that vitamin D acts as a neurosteroid with direct effects on brain development.
There is scientific evidence suggesting that increased exposure to sunlight, which increases vitamin D3 synthesis and a person’s vitamin D status, can influence the risk for an outcome of many deadly cancers. The recent observation indicat that the use of vitamin D3 along with adequate calcium supplementation markedly reduces the risk for developing cancer.
Vitamin D deficiency can cause growth retardation and skeletal deformities and may increase the risk of hip fracture later in life. It can play a role in increasing the risk of many chronic illnesses, including common cancers, autoimmune diseases (type 1 diabetes and multiple sclerosis) infectious diseases, and cardiovascular disease.
The only way to determine whether a person is vitamin D deficient or sufficient is to measure their circulating level of 25(OH)D. There are a variety of assays used to measure 25(OH)D. Several laboratories have now use LC-MS method,which measures both 25(OH)D2 and 25(OH)D3 quantitatively. The total 25(OH)D, i.e., 25(OH)D2 plus 25(OH)D3, is what physicians need to be aware of for their patients. A level 30 ng/mL is now considered to be the preferred healthful level that all children and adults should maintain throughout the year.
The American Academy of pediatrics recommendations are based on evidence from more recent clinical trials and the history of safe use of 400 IU/day of vitamin D in pediatrics and adolescents populations. The American academy of pediatrics recommends that exclusively and partially breastfed infants receive supplements of 400 IU/day of vitamin D shortly after birth and continue to receive these supplements until they are weaned and continue ≥ 1000 IU/day of vitamine D fortified formula or whole milk.
There is clear evidence that a blood level of 30-50 ng/mL is necessary for optimal health. In the absence of adequate sun exposure, 1,000 IU vitamin D daily for children and adults is required to achieve these levels.
Vitamin D deficiency can be managed by either oral or intramuscular provision of vitamin D, together with adequate elemental calcium to prevent hypocalcemia that may be associated with remineralization of the bone matrix (“hungry bone syndrome”).
Vitamin D excess (Hypervitaminosis) is secondary to excessive intake of vitamin D. It may occur with long-term high intake or with a substantial, acute ingestion. Most cases are secondary to misuse of prescribed vitamin D supplement. The signs and symptoms of vitamin D intoxication are secondary to hypercalcemia.
Gastrointestinal manifestations, possible cardiac finding and hyper- tension also CNS and renal function is also affected. Deaths are usually associated with arrhythmias or dehydration.
Conclusion and recommendation:
• Vitamin D is essential at all ages particularly during infancy and childhood, adolescence, pregnancy and lactation and elder persons.
• Serum 25-hydroxycalciferol is the best detector of vitamin D status and should be applied in our labs.
• Requirements of vitamin D at all ages should be taken by all populations and supplements should be implemented.
• The role of sunrays in prevention of vitamin D deficiency and proper exposure for various age and ethnic groups should be encouraged.
• Researches about our population vitamin D status should be encouraged and it relation to our health problems should be investigated in addition to the proper methods of supplementation.
• Health education about topics regarding sunrays exposure and vitamin D role for a healthy life is an important cost-effective topic that should be conducted to all populations.