Hello fellows!

while reading some cientific review on endocrine disrupters i came across some intresting informations about the vitamin d3 metabolism.

you guys can find the whole paper here:
http://www.oecd.org/officialdocument...doclanguage=en

and this is the info i would like to share:

"Vitamin D is an ancient molecule that is found in animals, plants, and zooplankton. While vitamin D is ubiquitous among organisms, VDR is only found in vertebrates.570 VDR and vitamin D signaling
likely originated with stem vertebrates, as a functional VDR has been identified in the sea lamprey
(Petromyzon marinus), a basal vertebrate lacking a calcified skeleton.571; 572 Comparisons of vertebrate
VDR protein sequences demonstrate a high degree of conservation across species, suggesting that the
vitamin D endocrine axis may be highly conserved throughout vertebrate evolution.573 In humans and
rodents, 36 tissues express VDR, including tissues that are not associated with the classic vitamin D
effects of calcium mobilization and ion homeostasis.569 In fact, recent investigation of VDR function
suggests that VDR signaling has additional non-calcemic roles, including roles in immune system
function, cell proliferation, and neurodevelopment"

"Synthesis
225. All vertebrates possess the vitamin D endocrine axis.574 Aquatic vertebrates obtain vitamin D
solely from the diet, while terrestrial vertebrates can obtain vitamin D from both the diet and from the
photolytic conversion of 7-dehydrocholesterol to pre-vitamin D3 in the skin. 7-dehydrocholesterol is
present in large quantities in the skin of higher vertebrates and is a precursor molecule in the cholesterol
biosynthesis pathway.569; 575 7-dehydrocholesterol absorbs UVB light in the 290315 nm wavelength,
which breaks the bond between carbons 9 and 10, creating pre-vitamin D3. Pre-vitamin D3 is
thermodynamically unstable and rapidly isomerizes to vitamin D3. 568; 576 This photochemical reaction
does not involve any enzymes and is related to the amount of UVB exposure an individual receives.
Factors such as latitude, sunscreen use, ethnicity, age, and nutritional status can affect vitamin D3
production in the skin.577 Vitamin D3 is not biologically active and must be metabolized to its active form
through two hydroxylation reactions.
226. The first hydroxylation reaction takes place in the liver. Vitamin D3 is transported from the skin
bound to transport proteins in the bloodstream. Most vitamin D3 is bound to vitamin D binding protein
(VDBP), but some is also bound to albumin.568; 578 Once in the liver, the P450 enzyme 25-hydroxylase
(CYP2R1) adds a hydroxyl group to carbon 25, creating 25-hydroxyvitamin D3. Several P450 enzymes
have been shown to hydroxylate vitamin D on carbon 25, but only CYP2R1 is highly expressed in the
liver, and mutations in CYP2R1 are linked to low vitamin D levels and rickets. 568; 579-581 Mutations in
other candidate P450s do not alter 25-hydroxyvitamin D3 levels. This hydroxylation step is not well
regulated and is dependent on vitamin D3 substrate availability. Because this reaction reflects the vitamin
D3 status of an individual, measuring serum levels of 25-hydroxyvitamin D3 is a common method of
determining the vitamin D status of patients.56

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the last part of the text was in a bad formatation so i coudnt copy so a pic will do

i hope you guys find the information usefull