title: Immediate pigment darkening: its evolutionary roles may include protection against folate photosensitization.
abstract: The evolution of dark human skin colors in tropical areas is possibly related to photoprotection of folates. However, natural folates absorb mainly UVB radiation, and too little UVB can penetrate down to folates in dermal vessels to cause serious damage. However, endogenous photosensitizers, like riboflavin and uroporphyrin, absorbing UVA and visible light, can cause photosensitization of folates. Immediate pigment darkening (IPD), generated by UVA, has an absorption spectrum covering those of the endogenous photosensitizers. IPD is most prominent for darker skin types, which were typical for populations living under tropical solar fluences. We here propose that the biological role of IPD is protection of folates against photodegradation, which would be of large evolutionary importance for early hominids.
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Oslo University Hospital, Montebello 0310 Oslo, Norway.
authors.forename: Johan
authors.initials: J
authors.lastname: Moan
authors.forename: Kristian Pagh
authors.initials: KP
authors.lastname: Nielsen
authors.forename: Asta
authors.initials: A
authors.lastname: Juzeniene
mesh_terms: D000818:Animals; D005075:Biological Evolution; D020405:Dermis / Q000378:metabolism / Q000528:radiation effects; D005492:Folic Acid / Q000378:metabolism; D005542:Forearm; D015186:Hominidae; D006801:Humans; D007980:Levodopa / Q000378:metabolism; D008027:Light; D010782:Photolysis / Q000528:radiation effects; D012256:Riboflavin / Q000378:metabolism; D012867:Skin / Q000378:metabolism / Q000528:radiation effects*; D012880:Skin Pigmentation / Q000528:radiation effects*; D013053:Spectrophotometry / Q000379:methods; D013472:Sunlight; D013763:Tetrahydrofolates / Q000378:metabolism; D014329:Tropical Climate; D014466:Ultraviolet Rays; D014578:Uroporphyrins / Q000378:metabolism
chemical_list: D013763:Tetrahydrofolates; D014578:Uroporphyrins; D007980:Levodopa; D005492:Folic Acid; D012256:Riboflavin; C005984:5-methyltetrahydrofolate