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The conversion of vitamin D, especially cholecalciferol, to 25(OH)D (calcifediol) is one of the key steps in the vitamin D hormonal system. The CYP2R1 enzymatic activity achieving this process was previously thought to be constitutively expressed and stable, so that serum 25(OH)D was a measure of the supply of vitamin D. [9]
Shortly thereafter, the conversion of vitamin D to calcifediol and then to calcitriol, the biologically active form, was confirmed. [236] The photosynthesis of vitamin D 3 in skin via previtamin D 3 and its subsequent metabolism was described in 1980. [237]
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.
7-Dehydrocholesterol (7-DHC) is a zoosterol that functions in the serum as a cholesterol precursor, and is photochemically converted to vitamin D 3 in the skin, therefore functioning as provitamin-D 3. The presence of this compound in human skin enables humans to manufacture vitamin D 3 (cholecalciferol).
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Cholecalciferol is a form of vitamin D which is naturally synthesized in skin and functions as a pro-hormone, being converted to calcitriol. This is important for maintaining calcium levels and promoting bone health and development. [4] As a medication, cholecalciferol may be taken as a dietary supplement to prevent or to treat vitamin D ...
Ergosterol is a biological precursor of vitamin D 2, the chemical name of which is ergocalciferol. Exposure of white button mushrooms to UV-C irradiation produces time-dependent increases in vitamin D2 concentrations in the mushrooms.
Previtamin D 3 is an intermediate in the production of cholecalciferol (vitamin D 3). It is formed by the action of UV light, most specifically UVB light of wavelengths between 295 and 300 nm, acting on 7-dehydrocholesterol in the epidermal layers of the skin. [1] [2] [3] The B ring of the steroid nucleus structure is broken open, making a ...