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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.
While some studies have found that vitamin D 3 raises 25(OH)D blood levels faster and remains active in the body longer, [43] [44] others contend that vitamin D 2 sources are equally bioavailable and effective for raising and sustaining 25(OH)D. [45] [46] If digestive disorders compromise absorption, then intramuscular injection of up to ...
In medical practice, a blood test for 25-hydroxy-vitamin D, 25(OH)D, is used to determine an individual's vitamin D status. [11] 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 ...
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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These two forms of vitamin D are metabolized in the liver and stored as 25-hydroxyvitamin D. [4] Before biological use, the storage form must be converted into an active form. One common active form is 1,25-dihydroxyvitamin D. [4] The term vitamin D in this article means cholecalciferol, ergocalciferol, 25-hydroxyvitamin D, and the active forms ...
Calcitriol is a hormone and the active form of vitamin D, normally made in the kidney. [8] [9] [10] It is also known as 1,25-dihydroxycholecalciferol.It binds to and activates the vitamin D receptor in the nucleus of the cell, which then increases the expression of many genes. [11]
It requires two hydroxylations to become active: the first in the liver by CYP2R1 to form 25-hydroxyergocalciferol (ercalcidiol or 25-OH D 2 [20]), and the second in the kidney by CYP27B1, to form the active 1,25-dihydroxyergocalciferol (ercalcitriol or 1,25-(OH) 2 D 2), which activates the vitamin D receptor. [21]