I heard that pyrocalciferol and isopyrocalciferol can only be formed above 100°C/212°F, yet some images in the web depict them as forming in vertebrate skin. So, I wonder if pyrocalciferol and isopyrocalciferol do form in vertebrate skin. If they do, is there something catalyzing the thermal transformation of previtamin D or is it also a result of UV irradiation?

  • $\begingroup$ Could you add links to references of both claims? $\endgroup$
    – BagiM
    Commented Dec 15, 2019 at 6:49
  • $\begingroup$ An example of the former is ScienceDirect, which claims that "By increasing the temperature to 100-200°C, a new electrocyclization takes place, resulting in formation of pyrocalciferol (7) and isopyrocalciferol (8).". Example for the latter is the second image in the chemistry section of the "About Vitamin D" web site, which shows both pyrocalciferol and isopyrocalciferol (albeit with the names and compounds reversed) forming in skin. $\endgroup$
    – JMRD
    Commented Dec 15, 2019 at 14:37
  • $\begingroup$ ScienceDirect is a website which hosts over 900000 articles. Adding a link to specific article would be much better. You can read here on how edit your question to add links. I am not versed in skin chemistry, but people here could help you better if thay can read and evaluate your sources directly. When I write "About Vitamin D" in search engine I get numerous result sites without any way of knowing which is the one you have. Again adding a specific link would be much better. $\endgroup$
    – BagiM
    Commented Dec 16, 2019 at 6:32
  • $\begingroup$ For first, 'sciencedirect.com/topics/chemistry/provitamin', then use search in page tool, with pyrocalciferol inputted. For second, 'vitamind.ucr.edu/about', then go to chemistry section. $\endgroup$
    – JMRD
    Commented Dec 16, 2019 at 14:35


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