«Skin color and melanin
Melanin essentially has a protective function, since it defends the genome from the harmful action of ultraviolet rays. Close to the nucleus of the keratinocytes, it forms a sort of protective screen that acts as a filter, absorbing and rejecting part of the solar radiation.
To defend itself from solar radiation, the organism also initiates an auxiliary process that stimulates the proliferation of the stratum corneum, favoring the thickening of the epidermis.
The quantity and distribution of melanin in the skin also varies according to many parameters, linked to ethnicity, age (children's skin is less protected from solar radiation) and the body region (the most exposed areas are more pigmented but covered areas are also covered, such as the mammary areola or anogenital areas).
Habits and living conditions also affect the distribution of melanin. In this regard, latitude is undoubtedly one of the most interesting and influential aspects.
The individuals who populate the equatorial regions generally have darker skin than the Nordic populations who, on the contrary, have a particularly pale complexion. These differences are not accidental, but derive from the natural process of evolutionary selection, which chooses and maintains only those characteristics necessary for the preservation and improvement of the species.Millennium after millennium, natural selection has benefited dark-skinned individuals in tropical regions and pale-skinned individuals in northern regions.
In the tropics, the high presence of melanin is essential to protect the skin from damage from solar radiation (melanoma). Beyond this commonly known aspect, it seems that the most important region underlying the selection and differentiation process is linked to the ability of dark skin to prevent the destruction of folate, caused by strong exposure to ultraviolet rays. Folate, or vitamin B9, is extremely important during pregnancy, since its deficiency is accompanied by a high risk of alterations of the neural tube (an embryonic formation destined to form the canal that encloses the spinal cord). If the mother's diet is low in folate, the neural tube of the embryo can develop abnormally, giving rise to extremely serious diseases such as spina bifida. Folate is also essential for male fertility, as it participates in the process of spermatogenesis, which slows down in the absence of these vitamins, causing sterility.
In summary: UVA, which have a high penetration power, destroy the folates present in the blood, compromising the reproduction of the species. Dark skin prevents UV-induced destruction of folate and is therefore a beneficial feature for equatorial populations.
In the Nordic countries, where solar radiation is weak, the light color of the skin is essential to guarantee an adequate synthesis of vitamin D. This vitamin is essential for the intestinal absorption of calcium, therefore for the health of the skeletal system.
In the Nordic countries, solar radiation is less intense and, to ensure an "adequate synthesis of vitamin D, it is important that the skin is able to capture as many as possible.
QUESTION: Why do Arctic people, such as Eskimos, have rather dark skin? Probably because their diet is naturally rich in calcium (fish) and dark skin color (<vitamin D) is not a limiting factor for bone health.
QUESTION: Why do women of all populations generally have lighter skin (3-4%) than men? The calcium requirement of women is higher than that of men, especially during pregnancy and breastfeeding. We remind you that to favor the absorption of this mineral it is necessary that the skin is clear, since this characteristic guarantees a greater synthesis of vitamin D, with a consequent increase in the absorption and fixation of calcium in the bones.
CONTINUE: eye color "
