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I am aware of the affect on vitamin D production by melanin (in sunlight) but I can not find any information regarding a reverse connection.

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Darker skin, as opposed to common belief, probably did not develop as cancer protection. Cancer is usually something that attacks the body in a subsequent life. Even pale individuals under the sun are likely to survive far beyond their reproductive era before they are wiped off by skin cancer.

Instead, it is believed that folic acid manufacturing is the highest selection pressure causing darker skin. Folic acid (vitamin B9) which is used all over the flesh, especially during pregnancy and childhood, will decompose in sunlight.

So the skin tone tries to discover the ideal equilibrium between vitamin D and minimal folic acid breakdown.

As a consequence, if you genuinely have enough vitamin D in your diet, there is no need for lighter skin (and further proof for the vitamin-d hypothesis). That is why the Inuit have lighter skin than expected for their extreme location: the intake of vitamin D is large, so the folic acid part of the equation "wins" and pale skin is not preferable. This is why Inuit individuals do not need so much sun.

Source:

scienceline.org/2007/06/ask-dricoll-inuiteskimos/

pnas.org/content/107/Supplement_2/8962

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  • $\begingroup$ This is not true. Skin color is highly correlated with UV-radiation, with the highest pigmentation present in areas where the radiation is the highest. This is said in both references, we also know that the skin cancer rates are much lower in people with high pigmentation. Melanin is a very effective protection for your skin. Folic acid is not mentioned in your sources, so please edit them. $\endgroup$ – Chris Jul 7 at 14:39
  • $\begingroup$ @Chris I don't claim to be expert in this area (hence the question) but nowhere did I claimed the absence of correlation of skin color and UV, quite the contrary. Also, nowhere did I dispute, "skin cancer rates are much lower in people with high pigmentation." or "Melanin is a very effective protection for your skin. (regarding cancer)." $\endgroup$ – tejasvi88 Jul 8 at 4:02
  • $\begingroup$ @Chris Ctrl+F yields following two paragraphs from each source: $\endgroup$ – tejasvi88 Jul 8 at 4:03
  • $\begingroup$ @Chris "The possibility that photolysis of folate by sunlight was a determining factor in the evolution of dark pigmentation was first explored (24) before the full importance of folate in DNA biosynthesis, repair, DNA methylation, amino acid metabolism, and melanin production was recognized. In 2000, we advanced the theory that dark skin pigmentation in humans had evolved primarily to prevent reduction of fertility due to the photolysis of folate present in cutaneous blood vessels (7). We ..." $\endgroup$ – tejasvi88 Jul 8 at 4:06
  • $\begingroup$ @Chris "Ultraviolet, or UV rays, from the sun are responsible for activating the melanin. As melanin levels rise and our body’s natural pigment darkens, protection against the sun’s rays increases. Too much UV exposure can deplete vitamin B folate –used by the cells to create DNA. On a smaller scale, the rays can also cause painful sunburns, with too much exposure leading to cancer." $\endgroup$ – tejasvi88 Jul 8 at 4:06

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