The Role of Vitamins in Determining Human Skin Color (mc)

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Apr 3, 2024

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The Role of Vitamins in Determining Human Skin Color Arguably, the most conspicuous human trait is skin color, which signals so much about an individual’s culture, region of origin, and, in some cases, diversity of genes. Anthropologists, both cultural and physical, have determined the continent of Africa to be the cradle of humanity, as the oldest evidence of human habitation is found there. During the time humans were living there exclusively, they were exposed to a massive daily dose of UV radiation; especially close to the Equator, (increasing distance from the Equator delivers less intense exposure). Humans adapted to this environment by producing eumelanin (a pigment) to absorb UV radiation before it could damage DNA in skin cells. An abundance of eumelanin produced a darker skin color, while a lesser amount produced results in lighter skin tone. Presumably, all people living in Africa at the time were pigmented with eumelanin to some extent, thus protected from the UV radiation. Between 40,000 and 100,000 years ago, some groups of people began migrating out of Africa through the Middle East into Asia and Europe. Some groups traveled east and settled Asia, and eventually Australia and the Americas. Other groups continued north into Europe, eventually reaching the high latitude regions. Since these people migrated on foot, and were not on a forced march, these migrations required generations to complete. Along the way, some people chose to settle down and stay, while others continued. At every point along the journey, people adapted to the environment they found. Moving farther north involved less exposure to UV radiation, which ultimately lead to less production of eumelanin, and eventually to the production of pheomelanin. This new pigment led to the production of light skin and hair color in people of the higher latitudes. Figure 1. Relationship between skin reflectance and latitude. (Source: Relethford, J.H. 1997. Hemispheric difference in human skin color)

1. Which of the following statements best describes the information presented in the graph above? a. people of the Scandinavian region tend to have light colored hair and pale skin b. people in the southern hemisphere have lower skin reflectance (i.e., absorbs more light) c. people endemic to regions near the Equator tend to have less reflective skin d. A, B and C are correct e. none of these are correct Dr. Nina Jablonski is an anthropologist at Penn State University, who was interested in the role of pigment change in groups of people around the world. The standard explanation for how eumelanin influences the change of skin color over time was skin cancer could develop without eumelanin and that would kill the individual. Thus, ensuring only people with pigmentation in the skin would live to have offspring, and those children would be pigmented. Jablonski reckoned this was not the proper explanation for the varying skin tones, as people have typically had their children and passed on genes before skin cancer could develop! Furthermore, if skin cancer was driving the pigmentation of human skin, everyone would have roughly the same dark skin tone. While attending a lecture, she learned about the importance of folate (a B vitamin found in green leafy vegetables) in producing normal sperm, and an uncomplicated pregnancy with subsequent normal brain development. Later work showed melanin (eumelanin and pheomelanin) protects folate circulating in the bloodstream; therefore, anyone with pigment protection will have a better chance to successfully reproduce, which puts the melanin gene (MC1R) into the next generation.

Figure 2. Levels of blood folate depend on exposure to UV radiation. Subjects ("patients") were exposed to UV radiation for 9 hrs every day for 3 months, while controls ("normals") were not exposed, and their blood levels of folate were measured. 2. Fill in the blanks based on the graph above; choose from these words for the three blanks (more, less, UV radiation, folate, vitamin D, pregnancy). Subjects exposed to UV radiation produced ______________________ __________________________, than is typical for sperm production and a successful _________________. 3. In the northern latitudes people have less eumelanin in the skin yet are still able to reproduce successfully. Why is this the case? a. UV radiation amount reaching Earth’s surface is reduced compared to the equatorial region b. more skin surface is likely to be covered by clothing at these latitudes c. during the summer months the sun shines 24 hours a day d. A and B are both correct The human relationship with UV radiation is complicated. UV radiation does provide a benefit to humans. As the skin absorbs it, a complicated process occurs that leads to the production of Vitamin D. This vitamin facilitates calcium ion absorption from the blood for storage in the bone or use in various physiological processes. When humans lived in low latitude regions, the Vitamin D production was not a problem as exposure to UV radiation was significant. However, as people with significant eumelanin moved north, the ability to produce Vitamin D declined, which lead to rickets and other diseases involving calcium deficiencies. In these people, a change in the MC1R gene lead to production of pheomelanin, which resulted in

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lighter skin that could make use of the limited amount of UV radiation available. A healthy body is a balancing act between the need to absorb and the need to avoid UV radiation. 4. Using the graph above, rank the three race/ethnicity groups in terms of Vitamin D production. a. 1 st is non-Hispanic whites, 2 nd is non-Hispanic blacks, 3 rd is Hispanics b. 1 st is Hispanics, 2 nd is non-Hispanic blacks, 3 rd is non-Hispanic whites c. 1 st is non-Hispanic whites, 2 nd is Hispanics, 3 rd is non-Hispanic blacks 5. Explain why the group with the least Vitamin D production is so low. a. coincidence b. crossing over of alleles c. greatest amount of eumelanin in the skin d. least amount of eumelanin in the skin Figure 3Levels of vitamin D in the blood of Americans. Serum total 25(OH)D, nmol/L means the amount of vitamin D in the blood.

6. Which of the three groups listed above is most likely to show a folate deficient? a. the non-Hispanic blacks because the eumelanin blocks UV radiation penetrating the skin b. Hispanics because their skin in usually albino c. the non-Hispanic whites because the lack of eumelanin means UV radiation can penetrate the skin more easily d. none of these are correct 7. The general tendency is to see lighter skin and hair as one goes north toward the higher latitudes. Native people living north of the Arctic Circle tend to have darker hair and skin than those living in the high latitude regions south of the Arctic Circle. How is it possible these natives can still maintain their eumelanin levels, while their more southernly neighbors are less pigmented? a. sufficient Vitamin C promotes strong bone growth b. natives north of the Artic Circle eat food from the sea which has a lot of Vitamin D. c. there is no evolutionary selection pressure to reduce eumelanin because Vitamin D is obtained via the diet instead of being made in the skin d. B and C only e. A, B and C

The Role of Vitamins in Determining Human Skin Color (mc)

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