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The name 25(OH)D refers to any combination of calcifediol (25-hydroxy-cholecalciferol), derived from vitamin D 3, and ercalcidiol (25-hydroxy-ergocalciferol), [1] derived from vitamin D 2. The first of these (also known as 25-hydroxy vitamin D3) is made by the body, or is sourced from certain animal foods or cholecalciferol supplements.
24,25-dihydroxyvitamin D 3 is formed from 25-hydroxyvitamin D 3 by the action of CYP24A1 (25-hydroxyvitamin D3-24-hydroxylase). CYP24A1 appears to be "a multicatalytic enzyme catalyzing most, if not all, of the reactions in the C-24/C-23 pathway of 25-OH-D 3 metabolism." [5]
[40] [61] [62] Ultraviolet light alone - sunlight or tanning beds - can raise serum 25(OH)D concentration to a bit higher than 100 nmol/L, but not to a level that causes hypervitaminosis D, the reasons being that there is a limiting amount of the precursor 7-dehydrocholesterol synthesized in the skin and a negative feedback in the kidney ...
The normal range for blood concentration of 25-hydroxyvitamin D in adults is 20 to 50 nanograms per milliliter (ng/mL). Blood levels necessary to cause adverse effects in adults are thought to be greater than about 150 ng/mL, leading the Endocrine Society to suggest an upper limit for safety of 100 ng/mL. [1]
CYP24A1 also is able to catalyze another pathway which starts with 23-hydroxylation of 1,25-(OH) 2 D 3 and culminates in 1,25-(OH) 2 D 3-26,23-lactone. [ 6 ] The side chains of the ergocalciferol (vitamin D 2 ) derivatives, 25-OH-D 2 and 1,25-(OH) 2 D 2 , are also hydroxylated by CYP24A1.
The liver is required to transform vitamin D into 25-hydroxyvitamin D. This is an inactive metabolite of vitamin D but is a necessary precursor (building block) to create the active form of vitamin D. [1] The kidneys are responsible for converting 25-hydroxyvitamin D to 1,25-hydroxyvitamin D. This is the active form of vitamin D in the body.
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 ...
Retrieved from "https://en.wikipedia.org/w/index.php?title=25-hydroxyvitamin_D&oldid=257668059"This page was last edited on 13 December 2008, at 10:34
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