Vitamin D - Wikipedia. Vitamin D refers to a group of fat- soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, phosphate, and zinc and multiple other biological effects. In humans, the most important compounds in this group are vitamin D3 (also known as cholecalciferol) and vitamin D2 (ergocalciferol). The major natural source of the vitamin is synthesis of cholecalciferol in the skin from cholesterol through a chemical reaction that is dependent on sun exposure (specifically UVB radiation). The Dietary Reference Intake for vitamin D, made by the Institute of Medicine, assume all of a person's vitamin D is from oral intake, as recommendations about the amount of sun exposure required for optimal vitamin D levels are uncertain in view of the skin cancer risk. Vitamin D from the diet or skin synthesis is biologically inactive; enzymatic conversion (hydroxylation) in the liver and kidney is required for activation. As vitamin D can be synthesized in adequate amounts by most mammals exposed to sufficient sunlight, it is not an essential dietary factor, and so not technically a vitamin. These two vitamin D metabolites (called 2. D or 2. 5(OH)D) are measured in serum to determine a person's vitamin D status. Calcitriol also has other effects, including some on cell growth, neuromuscular and immune functions, and reduction of inflammation. Its discovery was due to effort to find the dietary substance lacking in rickets (the childhood form of osteomalacia). The two major forms are vitamin D2 or ergocalciferol, and vitamin D3 or cholecalciferol; vitamin D without a subscript refers to either D2 or D3 or both. These are known collectively as calciferol. In 1. 93. 5, the chemical structure of vitamin D3 was established and proven to result from the ultraviolet irradiation of 7- dehydrocholesterol. In the developed world, this is a rare disease. This condition is characterized by bow legs. In sunny countries such as Nigeria, South Africa, and Bangladesh, where the disease occurs among older toddlers and children, it has been attributed to low dietary calcium intakes, which are characteristic of cereal- based diets with limited access to dairy products. Characteristics of this disease are softening of the bones, leading to bending of the spine, bowing of the legs, proximal muscle weakness, bone fragility, and increased risk for fractures. Osteomalacia is usually present when 2. D levels are less than about 1. L. The threshold for vitamin D toxicity has not been established; however, according to some research, the tolerable upper intake level (UL) is 4,0. IU/day for ages 9–7. The FDA advised manufacturers of liquid vitamin D supplements that droppers accompanying these products should be clearly and accurately marked for 4. IU). In addition, for products intended for infants, the FDA recommends the dropper hold no more than 4. IU. One thousand micrograms per day in infants has produced toxicity within one month. If hypercalcemia is not treated, it results in excess deposits of calcium in soft tissues and organs such as the kidneys, liver, and heart, resulting in pain and organ damage. These may be followed by polyuria, polydipsia, weakness, insomnia, nervousness, pruritus and ultimately renal failure. Furthermore, proteinuria, urinary casts, azotemia, and metastatic calcification (especially in the kidneys) may develop. Kidney damage may be irreversible. Exposure to sunlight for extended periods of time does not normally cause vitamin D toxicity. The concentrations of vitamin D precursors produced in the skin reach an equilibrium, and any further vitamin D produced is degraded. Other countries often use nmol/l; ng x 2. A 2. 01. 4 review concluded that the most advantageous serum levels for 2. Fast facts on vitamin D. Here are some key points about vitamin D. More detail and supporting information is in the main article. Vitamin D's primary role is to.
OH)D for all outcomes appeared to be close to 7. The dietary reference intakes for vitamin D are chosen with a margin of safety and 'overshoot' the targeted serum value to ensure the specified levels of intake achieve the desired serum 2. OH)D levels in almost all persons. No contributions to serum 2. OH)D level are assumed from sun exposure and the recommendations are fully applicable to people with dark skin or negligible exposure to sunlight. Serum 2. 5(OH)D levels above 5. Research on vitamin D supplements, including large- scale clinical trials, is continuing. Use of vitamin D in children with normal vitamin D levels does not appear to improve bone density. As of August 2. 01. The greatest benefit with supplementation is seen in athletes who are deficient (2. OH)D serum levels < 3. OH)D serum levels < 2. Incremental decreases in risks are observed with rising serum 2. OH)D concentrations plateauing at 5. Reviews have described the evidence as being . However, lower vitamin D concentrations is also associated with poor nutrition and spending less time outdoors. Therefore, alternative explanations for the increase in cognitive impairment exist and hence a direct causal relationship between vitamin D levels and cognition could not be established. Many animals synthesize vitamin D3 from 7- dehydrocholesterol, and many fungi synthesize vitamin D2 from ergosterol. Click on genes, proteins and metabolites below to link to respective articles. Second, previtamin D3 spontaneously isomerizes to vitamin D3 (cholecalciferol) in an antarafacialsigmatropic . At room temperature, the transformation of previtamin D3 to vitamin D3 in an organic solvent takes about 1. The conversion of previtamin D3 to vitamin D3 in the skin is about 1. Dehydrocholesterol reacts with UVB light at wavelengths between 2. Exposure to light through windows is insufficient because glass almost completely blocks UVB light. The darker the skin, and the weaker the sunlight, the more minutes of exposure are needed. Vitamin D overdose is impossible from UV exposure; the skin reaches an equilibrium where the vitamin degrades as fast as it is created. Vitamin D is produced in the keratinocytes. Although primitive vertebrates in the ocean could absorb calcium from the ocean into their skeletons and eat plankton rich in vitamin D, land animals required another way to satisfy their vitamin D requirement for a calcified skeleton without relying on plants. Land vertebrates have been making their own vitamin D for more than 3. In birds and fur- bearing mammals, vitamin D is generated from the oily secretions of the skin deposited onto the feathers or fur and is obtained orally during grooming. Circulating calcifediol may then be converted into calcitriol, the biologically active form of vitamin D, in the kidneys. This reaction is catalyzed by the microsomal enzyme vitamin D 2. CYP2. R1 human gene, and expressed by hepatocytes. Several forms of vitamin D exist. The two major forms are vitamin D 2 or ergocalciferol, and vitamin D 3 or cholecalciferol; vitamin D without a subscript refers to. West Palm Beach Vitamin B12 MIC Ultra Burn Shots: The Palm Beach Wellness Center offers Vitamin B12 injections and B12 MIC Ultra Burn shots to help increase your. Can vitamin D help you lose weight, fight depression, or even avoid cancer? Could you be "D" deficient? BootsWebMD's slideshow covers the truth about vitamin D. Vitamin D information based on scientific evidence includes description, drug interactions, safety concerns, and effectiveness. The conversion of calcifediol to calcitriol is catalyzed by the enzyme 2. D3 1- alpha- hydroxylase, which is the product of the CYP2. B1 human gene. The activity of CYP2. B1 is increased by parathyroid hormone, and also by low calcium or phosphate. By binding to vitamin D- binding protein, calcitriol is transported throughout the body, including to the classical target organs of intestine, kidney and bone. When synthesized by monocyte- macrophages, calcitriol acts locally as a cytokine, modulating body defenses against microbial invaders by stimulating the innate immune system. Vitamin D deficiency can result in lower bone mineral density and an increased risk of reduced bone density (osteoporosis) or bone fracture because a lack of vitamin D alters mineral metabolism in the body. Vitamin D also affects the immune system, and VDRs are expressed in several white blood cells, including monocytes and activated T and B cells. British doctor Edward Mellanby noticed dogs that were fed cod liver oil did not develop rickets and concluded vitamin A, or a closely associated factor, could prevent the disease. In 1. 92. 2, Elmer Mc. Collum tested modified cod liver oil in which the vitamin A had been destroyed. He called it vitamin D because it was the fourth vitamin to be named. Alfred Fabian Hess stated: . A meeting took place with J. B. S. Haldane, J. D. Bernal, and Dorothy Crowfoot to discuss possible structures, which contributed to bringing a team together. X- ray crystallography demonstrated the sterol molecules were flat, not as proposed by the German team led by Windaus. In 1. 93. 2, Otto Rosenheim and Harold King published a paper putting forward structures for sterols and bile acids which found immediate acceptance. In the 1. 93. 0s, Windaus clarified further the chemical structure of vitamin D. A vitamin D deficiency is a known cause of rickets. Using $3. 00 of his own money, Steenbock patented his invention. His irradiation technique was used for foodstuffs, most memorably for milk. By the expiration of his patent in 1. US. In the liver, vitamin D was found to be converted to calcifediol. Calcifediol is then converted by the kidneys to calcitriol, the biologically active form of vitamin D. The vitamin D metabolites, calcifediol and calcitriol, were identified by competing teams led by Michael F. Holick in the laboratory of Hector De. Luca and by Tony Norman and colleagues. The recommended daily intake of vitamin D may not be sufficient if sunlight exposure is limited. This dose should be increased to 4,0. IU/day in some patients with very low vitamin D status or in case of comorbid conditions. For vitamin D labeling purposes 1. Daily Value was 4. IU (1. 0 . A table of the old and new adult Daily Values is provided at Reference Daily Intake. Food and supplement companies have until July 2. Upper intake levels. The recommendations were formed assuming the individual has no skin synthesis of vitamin D because of inadequate sun exposure. The reference intake for vitamin D refers to total intake from food, beverages and supplements, is intended for the North American population, and assumes that calcium requirements are being met. Proponents of this view, who include some members of the panel that drafted a now- superseded 1. D from the IOM, contend the IOM's warning about serum concentrations above 5.
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