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Vitamin D 3 was shown to result from the ultraviolet irradiation of 7-dehydrocholesterol. Although a chemical nomenclature for vitamin D forms was recommended in 1981, [12] alternative names remain commonly used. [3] Chemically, the various forms of vitamin D are secosteroids, meaning that one of the bonds in the steroid rings is broken. [13]
Ergocalciferol, also known as vitamin D 2 and nonspecifically calciferol, is a type of vitamin D found in food. It is used as a dietary supplement [3] to prevent and treat vitamin D deficiency [4] due to poor absorption by the intestines or liver disease. [5]
Alfacalcidol (or 1-hydroxycholecalciferol) is an analogue of vitamin D used for supplementation in humans and as a poultry feed additive. Alfacalcidol has a weaker impact on calcium metabolism [ 3 ] and parathyroid hormone levels [ 4 ] than calcitriol ; but significant effects on the immune system , including regulatory T cells . [ 5 ]
The natural, active form of vitamin D is calcitriol (1,25-dihydroxycholecalciferol). This molecule and other naturally occurring forms of vitamin D, including its precursors and metabolites, have been modified to synthesize pharmaceuticals with potentially greater, or selective, therapeutic actions. [1] [2] [3] [4]
The Institute of Medicine in 2010 recommended a maximum uptake of vitamin D of 4000 IU/d, finding that the dose for lowest observed adverse effect level is 40,000 IU daily for at least 12 weeks, [25] and that there was a single case of toxicity above 10 000 IU after more than seven years of daily intake; this case of toxicity occurred in ...
Calcifediol binds in the blood to vitamin D-binding protein (also known as gc-globulin) and is the main circulating vitamin D metabolite. [4] [5] Calcifediol has an elimination half-life of around 15 to 30 days. [4] [9] Calcifediol is further hydroxylated at the 1-alpha-position in the kidneys to form 1,25-(OH) 2 D 3, calcitriol.
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Calcitriol was identified as the active form of vitamin D in 1971 and the drug was approved for medical use in the United States in 1978. [7] It is available as a generic medication . [ 12 ] In 2022, it was the 254th most commonly prescribed medication in the United States, with more than 1 million prescriptions.