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Forms and structure of vitamin D

All forms of vitamin D are secosteroids, sharing a close structural and functional resemblance to steroids. The full implications of a “vitamin” acting as a steroid has yet to be fully appreciated by many in the research community. The overlap between steroids and secosteroids is key to understanding the Marshall PathogenesisA description for how chronic inflammatory diseases originate and develop.. It explains how this “vitamin” can exert short-term palliative effects and long-term harm. Patients on the MP are advised to avoid consuming vitamin D, because of its immunomodulatory effects.

Is vitamin D a steroid?

Summary of different forms

Name Source / How created Description and function Other names
7-dehydrocholesterolA cholesterol precursor manufactured by humans. When exposed to ultraviolet light converted into vitamin D3. Also known as previtamin-D3. a cholesterol precursor biologically inactive previtamin-D3
vitamin D2 created by plants and fungi ergocholecalciferol
vitamin D3 two sources: made in the skin when exposed to light; fish and meat cholecalciferol; activated 7-dehydrocholesterol
25-DThe vitamin D metabolite widely (and erroneously) considered best indicator of vitamin D "deficiency." Inactivates the Vitamin D Nuclear Receptor. Produced by hydroxylation of vitamin D3 in the liver. produced by hydroxylation of vitamin D3Form of vitamin D made in the skin when exposed to light. Also available in fish and meat. This secosteroid is sometimes converted into 25-D. Also known as cholecalciferol and activated 7-dehydrocholesterol. in the liver inactivates the vitamin D nuclear receptorA nuclear receptor located throughout the body that plays a key role in the innate immune response.; widely (and erroneously) considered best indicator of vitamin D “deficiency” 25-hydroxyvitamin D; calcidiol; calcifediol
1,25-DPrimary biologically active vitamin D hormone. Activates the vitamin D nuclear receptor. Produced by hydroxylation of 25-D. Also known as 1,25-dihydroxycholecalciferol, 1,25-hydroxyvitamin D and calcitirol. 25-D is further hydroxylated in the kidneys and infected macrophages by the enzyme 1-alpha-hydroxylase primary biologically active vitamin D hormone; activates the vitamin D nuclear receptor 1,25-dihydroxycholecalciferol; 1,25-dihydroxyvitamin DPrimary biologically active vitamin D hormone. Activates the vitamin D nuclear receptor. Produced by hydroxylation of 25-D. Also known as 1,25-dihydroxycholecalciferol, 1,25-hydroxyvitamin D and calcitirol.; calcitirol
“Backbone” of a secosteroid versus that of a traditional steroid. Secosteroids share structural and functional similarities with steroids.

Vitamin D is a secosteroid

All forms of vitamin D belong to a family of lipids called secosteroids. Secosteroids are very similar in structure to steroids except that two of the B-ring carbon atoms of the typical four steroid rings are not joined, whereas in steroids they are.

The levels of each of the vitamin D metabolites are affected by a complex network of feedback mechanisms involving multiple enzymes and receptors, indicating vitamin D is regulated more like a steroid than a nutrient.

In the published literature, researchers sometimes distinguish between “steroid” and “secosteroid,” but not always.1) 2)

This failure to discriminate is less an indication of sloppy research and more a testament to how vitamin D behaves. The vitamins D act very much like steroids, binding nuclear receptorsIntracellular receptor proteins that bind to hydrophobic signal molecules (such as steroid and thyroid hormones) or intracellular metabolites and are thus activated to bind to specific DNA sequences which affect transcription. and modulating the immune response. Not only that, there's growing evidence that vitamin D causes adverse side effects like chronic disease over the long term as do anabolic steroids and corticosteroids.

Notes and comments

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References

1)
An endocytic pathway essential for renal uptake and activation of the steroid 25-(OH) vitamin D3.
Nykjaer A, Dragun D, Walther D, Vorum H, Jacobsen C, Herz J, Melsen F, Christensen EI, Willnow TE
Cell96p507-15(1999 Feb 19)
2)
Membrane receptors for vitamin D steroid hormones: potential new drug targets.
Farach-Carson MC, Nemere I
Curr Drug Targets4p67-76(2003 Jan)
home/pathogenesis/vitamind/forms.txt · Last modified: 06.21.2017 by sallieq
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