View source for 7-Dehydrocholesterol

{{redirect|Provitamin D3|the inactive form of vitamin D<sub>3</sub> synthesized from 7-dehydrocholesterol|Cholecalciferol}}
{{chembox
| Verifiedfields = changed
| verifiedrevid = 477226494
| ImageFile = 7-Dehydrocholesterol.svg
| ImageClass = skin-invert-image
| ImageSize = 220
| ImageFile1 = 7-Dehydrocholesterol molecule ball.png
| ImageSize1 = 250
| ImageAlt1 = Ball-and-stick model of 7-dehydrocholesterol
| IUPACName = Cholesta-5,7-dien-3β-ol
| SystematicName = (1''R'',3a''R'',7''S'',9a''R'',9b''S'',11a''R'')-9a,11a-Dimethyl-1-[(2''R'')-6-methylheptan-2-yl]-2,3,3a,6,7,8,9,9a,9b,10,11,11a-dodecahydro-1''H''-cyclopenta[''a'']phenanthren-7-ol
| OtherNames = 
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 388534
| InChI = 1/C27H44O/c1-18(2)7-6-8-19(3)23-11-12-24-22-10-9-20-17-21(28)13-15-26(20,4)25(22)14-16-27(23,24)5/h9-10,18-19,21,23-25,28H,6-8,11-17H2,1-5H3/t19-,21+,23-,24+,25+,26+,27-/m1/s1
| InChIKey = UCTLRSWJYQTBFZ-DDPQNLDTBZ
| StdInChI_Ref = {{stdinchicite|changed|chemspider}}
| StdInChI = 1S/C27H44O/c1-18(2)7-6-8-19(3)23-11-12-24-22-10-9-20-17-21(28)13-15-26(20,4)25(22)14-16-27(23,24)5/h9-10,18-19,21,23-25,28H,6-8,11-17H2,1-5H3/t19-,21+,23-,24+,25+,26+,27-/m1/s1-dehydrocholesterol 
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = UCTLRSWJYQTBFZ-DDPQNLDTSA-N
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 434-16-2
| PubChem = 172
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = BK1IU07GKF
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 17759
| SMILES = O[C@@H]4C/C3=C/C=C1\[C@H](CC[C@]2([C@H]1CC[C@@H]2[C@H](C)CCCC(C)C)C)[C@@]3(C)CC4
| MeSHName = 7-dehydrocholesterol
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>27</sub>H<sub>44</sub>O
| MolarMass = 384.638
}}
}}

[[Image:Skinlayers.png|thumb|250px|right|The epidermal strata of the skin]] 

'''7-Dehydrocholesterol''' ('''7-DHC''') is a [[zoosterol]] that functions in the [[blood plasma|serum]] as a [[cholesterol]] precursor, and is [[photochemically]] converted to [[Cholecalciferol|vitamin D<sub>3</sub>]] in the [[skin]], therefore functioning as [[provitamin]]-D<sub>3</sub>. The presence of this compound in human skin enables humans to manufacture vitamin D<sub>3</sub> ([[cholecalciferol]]).  Upon exposure to [[ultraviolet]] UV-B rays in the sun light, 7-DHC is converted into vitamin D<sub>3</sub> via [[Previtamin D3|previtamin D<sub>3</sub>]] as an intermediate [[isomer]]. It is also found in the [[milk]] of several mammalian species.<ref>{{cite book | chapter = 7-dehydrocholesterol | title = The American Heritage Stedman's Medical Dictionary | publisher = Houghton Mifflin Company | date = 21 January 2007}}</ref><ref>{{cite web | title = 7-dehydrocholesterol | url = http://www.answers.com/topic/7-dehydrocholesterol | work = Answers.com | archive-url = https://web.archive.org/web/20121025151754/http://www.answers.com/topic/7-dehydrocholesterol | archive-date= 25 October 2012 }}</ref> [[Lanolin]], a waxy substance that is naturally secreted by wool-bearing mammals, contains 7-DHC which is converted into vitamin D by sunlight and then ingested during grooming as a nutrient. In insects 7-dehydrocholesterol is a precursor for the hormone [[ecdysone]], required for reaching adulthood.<ref>{{cite web | vauthors = Young E | author-link = Ed Yong | date = 2012 | title = Thanks to one gene, this fly needs a cactus to escape Neverland | url = http://blogs.discovermagazine.com/notrocketscience/2012/09/28/fly-cactus-neverland-gene/ | work = Not Exactly Rocket Science | access-date = 2012-09-28 | archive-date = 2012-09-30 | archive-url = https://web.archive.org/web/20120930065255/http://blogs.discovermagazine.com/notrocketscience/2012/09/28/fly-cactus-neverland-gene/ | url-status = dead }}</ref> 7-DHC was discovered by Nobel-laureate organic chemist [[Adolf Windaus]].

==Biosynthesis==
It is synthesized from [[lathosterol]] by the enzyme [[lathosterol oxidase]] (lathosterol 5-desaturase).  This is the next-to-last step of cholesterol biosynthesis.<ref name="pmid12812989">{{cite journal | vauthors = Krakowiak PA, Wassif CA, Kratz L, Cozma D, Kovárová M, Harris G, Grinberg A, Yang Y, Hunter AG, Tsokos M, Kelley RI, Porter FD | title = Lathosterolosis: an inborn error of human and murine cholesterol synthesis due to lathosterol 5-desaturase deficiency | journal = Human Molecular Genetics | volume = 12 | issue = 13 | pages = 1631–41 | date = July 2003 | pmid = 12812989 | doi = 10.1093/hmg/ddg172 | url = | doi-access = free }}</ref>  Defective synthesis results in the human inherited disorder [[lathosterolosis]] resembling [[Smith–Lemli–Opitz syndrome]].<ref name="pmid12812989"/>  Mice where this gene has been deleted lose the ability to increase vitamin D<sub>3</sub> in the blood following UV exposure of the skin.<ref name="pmid28330720">{{cite journal | vauthors = Makarova AM, Pasta S, Watson G, Shackleton C, Epstein EH | title = Attenuation of UVR-induced vitamin D3 synthesis in a mouse model deleted for keratinocyte lathosterol 5-desaturase | journal = The Journal of Steroid Biochemistry and Molecular Biology | volume = 171| pages = 187–194 | date = July 2017 | pmid = 28330720 | doi = 10.1016/j.jsbmb.2017.03.017 | s2cid = 206502190 | url = https://research.birmingham.ac.uk/portal/en/publications/attenuation-of-uvrinduced-vitamin-d3-synthesis-in-a-mouse-model-deleted-for-keratinocyte-lathosterol-5desaturase(11f96b2b-f9ff-4ea7-b10d-25547481754c).html}}</ref>

==Location ==
The skin consists of two primary layers: an inner layer, the [[dermis]], comprising largely [[connective tissue]], and an outer, thinner [[Epidermis (skin)|epidermis]]. The thickness of the epidermis ranges from 0.04&nbsp;mm to greater than 0.6&nbsp;mm.<ref>{{Cite journal |last1=Lintzeri |first1=D.A. |last2=Karimian |first2=N. |last3=Blume-Peytavi |first3=U. |last4=Kottner |first4=J. |date=2022 |title=Epidermal thickness in healthy humans: a systematic review and meta-analysis |journal=Journal of the European Academy of Dermatology and Venereology |language=en |volume=36 |issue=8 |pages=1191–1200 |doi=10.1111/jdv.18123 |issn=0926-9959|doi-access=free |pmid=35366353 }}</ref> The epidermis comprises five ''strata''; from outer to inner, they are the [[stratum corneum]], [[stratum lucidum]], [[stratum granulosum]], [[stratum spinosum]], and [[stratum basale]]. The highest concentrations of 7-dehydrocholesterol are found in the epidermal layer of skin—specifically in the stratum basale and stratum spinosum.<ref name="Norman_1998">{{cite journal | vauthors = Norman AW | title = Sunlight, season, skin pigmentation, vitamin D, and 25-hydroxyvitamin D: integral components of the vitamin D endocrine system | journal = The American Journal of Clinical Nutrition | volume = 67 | issue = 6 | pages = 1108–1110 | date = June 1998 | pmid = 9625080 | doi = 10.1093/ajcn/67.6.1108 | doi-access = free }}</ref> The production of pre-vitamin D<sub>3</sub> is, therefore, greatest in these two layers.

==Radiation==
Synthesis of pre-vitamin D<sub>3</sub> in the skin involves [[UVB radiation]], which effectively penetrates only the epidermal layers of skin. 7-Dehydrocholesterol absorbs UV light most effectively at [[wavelength]]s between 295 and 300 [[nanometer|nm]] and, thus, the production of vitamin D<sub>3</sub> will occur primarily at those wavelengths.<ref name="pmid6281884">{{cite journal | vauthors = MacLaughlin JA, Anderson RR, Holick MF | title = Spectral character of sunlight modulates photosynthesis of previtamin D3 and its photoisomers in human skin | journal = Science | volume = 216 | issue = 4549 | pages = 1001–3 | date = May 1982 | pmid = 6281884 | doi = 10.1126/science.6281884}}</ref> The two most important factors that govern the generation of pre-vitamin D<sub>3</sub> are the quantity (intensity) and quality (appropriate wavelength) of the UVB irradiation reaching the 7-dehydrocholesterol deep in the stratum basale and stratum spinosum.<ref name = "Norman_1998" /> Light-emitting diodes ([[LED]]s) can be used to produce the radiation.<ref name="pmid28904394">{{cite journal | vauthors = Kalajian TA, Aldoukhi A, Veronikis AJ, Persons K, Holick MF | title = Ultraviolet B Light Emitting Diodes (LEDs) Are More Efficient and Effective in Producing Vitamin D3 in Human Skin Compared to Natural Sunlight | journal = Scientific Reports | volume = 7 | issue = 1 | pages = 11489 | date = September 2017 | pmid = 28904394 | pmc = 5597604 | doi = 10.1038/s41598-017-11362-2}}</ref>

Another important consideration is the quantity of 7-dehydrocholesterol present in the skin. Under normal circumstances, ample quantities of 7-dehydrocholesterol (about 25&ndash;50 [[microgram|μg]]/cm<sup>2</sup> of skin) are available in the [[stratum spinosum]] and [[stratum basale]] of human skin to meet the body's vitamin D requirements. 7-DHC insufficiency has been proposed as an alternate cause for Vitamin D deficiency.<ref name=whackjob>{{cite journal | vauthors = Gokhale S, Bhaduri A | title = Provitamin D<sub>3</sub> modulation through prebiotics supplementation: simulation based assessment | journal = Scientific Reports | volume = 9 | issue = 1 | pages = 19267 | date = December 2019 | pmid = 31848400 | pmc = 6917722 | doi = 10.1038/s41598-019-55699-2 | doi-access = free | bibcode = 2019NatSR...919267G}}</ref>

== Sources ==
7-DHC can be produced by animals and plants via different pathways. It is not produced by fungi in significant amounts. It is made by some [[algae]], but the pathway is poorly understood.<ref>{{cite journal | vauthors = Jäpelt RB, Jakobsen J | title = Vitamin D in plants: a review of occurrence, analysis, and biosynthesis | journal = Frontiers in Plant Science | volume = 4 | pages = 136 | date = 2013 | pmid = 23717318 | pmc = 3651966 | doi = 10.3389/fpls.2013.00136 | doi-access = free| bibcode = 2013FrPS....4..136J }}</ref>

Industrially, 7-DHC generally comes from [[lanolin]], and is used to produce vitamin D3 by UV exposure.<ref name="Holick05">{{cite journal | vauthors = Holick MF | title = The vitamin D epidemic and its health consequences | journal = The Journal of Nutrition | volume = 135 | issue = 11 | pages = 2739S–2748S | date = November 2005 | pmid = 16251641 | doi = 10.1093/jn/135.11.2739S | quote = [Vitamin D3] is produced commercially by extracting 7-dehydrocholesterol from wool fat, followed by UVB irradiation and purification [...] [Vitamin D2] is commercially made by irradiating and then purifying the ergosterol extracted from yeast | doi-access = free }}</ref> [[Lichen]] ([[Cladonia rangiferina]]) is used to produce [[vegan]] D3.<ref>{{cite web |title=Vitamin D |url=https://www.vegansociety.com/resources/nutrition-and-health/nutrients/vitamin-d |website=The Vegan Society |language=en}}</ref><ref>{{cite journal |last1=Gangwar |first1=Gourvendra |title=Formulation of Lichen Based Pill a Natural Source of Vitamin D3 with a High Absorption Rate by Ambrosiya Neo-Medicine Pvt. Ltd |journal=International Journal of Biomedical Investigation |date=1 July 2023 |page=1 |url=https://openj.edwiserinternational.com/index.php/ijbi/article/download/102/101}}</ref>

7-DHC is used for vitamin D3 synthesis via [[lanosterol]] in land animals, via [[cycloartenol]] in plants, and in algae together with another provitamin D [[ergosterol]] for D2. In fungi solely ergosterol is used for synthesis of D2 via lanosterol.<ref>{{cite journal|last1=Göring |first1=Horst |title=Vitamin D in Nature: A Product of Synthesis and/or Degradation of Cell Membrane Components |url=https://www.researchgate.net/publication/328961025 |date=November 2018 |journal=Biokhimiya (Moscow) |volume=83 |issue=11 |pages=1350–1357 |doi=10.1134/S0006297918110056 |pmid=30482146 |s2cid=53437216 |access-date=December 2, 2023}}</ref>

==Interactive pathway map==
{{VitaminDSynthesis_WP1531|highlight=7-Dehydrocholesterol}}

== See also ==
* [[Vitamin D]]
* [[Smith–Lemli–Opitz syndrome]]
* [[7-Dehydrocholesterol reductase]]

== References ==
{{Reflist}}

{{Vitamin}}
{{Cholesterol metabolism intermediates}}
{{Vitamin D receptor modulators}}

{{DEFAULTSORT:Dehydrocholesterol, 7-}}
[[Category:Cholestanes]]
[[Category:Sterols]]
[[Category:Nutrition]]
[[Category:Vitamin D]]