Skin Pigmentation, Skin Cancer and Vitamin D Deficiency
By Parnian Derahvasht, Grade 11, Ghods Girls High School, 8th District, Tehran, Iran
Humans have been migrating throughout history. It is believed that the first Homo sapiens migrated out of Africa about 50 to 70,000 years ago, likely due to climate changes in Africa. [1]
As they left Africa to settle in other regions of the planet, they also interacted with other archaic human species such as the Neanderthals and Denisovans who were already living in those areas. [2]
Factors such as UV exposure, altitude and latitude, food sources, the overall climate, etc. vary from location to location and each species that inhabits those areas must have the biological qualities that are required for its survival and reproduction in that environment. Our ancestors did not have those qualities when they first migrated out of Africa and it took many generations to gain those traits and for natural selection to take part in this process although interbreeding with the Neanderthals and Denisovans did speed up the process and was advantageous for our survival in the new environment.
Our adaptive introgression inherited from Neanderthals has affected genes associated with body fat distribution, muscle contraction, brain size and functioning, keratin filaments, enamel thickness, sugar metabolism, as well as oocyte meiosis. Humans inhabiting in various locations on Earth adapted to those places and, as a result, the genes related to variation in skin pigmentation and hair morphology showed signs of positive selection. [3]
Melanin, which provides the skin with pigmentation, is also a filter for the ultraviolet radiation (UVR) that we are constantly exposed to. Long-term exposure to the sun’s UVRs can damage our DNA and lead to the development of skin cancer. In order to resolve this issue, we evolved to have particular amounts of melanin according to the environment we live in.
For example, in places with high latitude and low UVR, it is more favorable to have lighter skin. This is because of the fact that there is not much UVR to damage the DNA, so having skin that allows these rays to penetrate the skin to produce vitamin D is crucial for the individual’s well-being in that environment. It is a similar situation for darker skin populations that live in low latitudes (near the equator) where there is high UVR. It is best to have highly pigmented skin for a protection against the sun’s high levels of UV radiations.
The Fitzpatrick scale is a numeric chart for human skin color classification. It was developed in 1975 by Thomas B. Fitzpatrick, an American dermatologist, as a way to guess the response of different types of skin pigmentation to UV light.[4] In the Fitzpatrick scale, there are six major skin color categories:
Type I: Always burns, never tans (palest; freckles)
Type II: Usually burns, tans minimally (light colored but darker than fair)
Type III: Sometimes mild burn, tans uniformly (golden honey or olive)
Type IV: Burns minimally, always tans well (moderate brown)
Type V: Very rarely burns, tans very easily (dark brown)
Type VI: Never burns (deeply pigmented dark brown to darkest brown)
The potential of skin cancer varies between the categories, with the highest being in Type I, and the lowest chance being in Type VI. To put it simply: the lighter the skin the higher risk of developing skin cancer and burning. The darker the skin, the lower the risk of developing skin cancer and burning.
Although skin cancers can occur in any type of skin color, it is more likely to be seen in white populations as their skin is not well protected against the sun’s UV radiations. The most common type of skin cancer among white individuals is BCC (Basal Cell Carcinoma), followed by SCC (Squamous Cell Carcinoma). Both are non-melanoma skin cancers and can be cured if detected early. Lastly, the third most common kind of skin cancer is melanoma which can spread to other parts of the body and can be fatal.[5]
As said earlier, the human race has been migrating to new environments since our species first emerged. As human beings became more advanced, environmental factors became less of a reason for migration; instead, social and political factors such as wars, conflicts and government persecutions have been the main reasons for migration during these past centuries. Whatever the reason may be, not many people acknowledge the long-term health risks that come with migration to a completely different environment.
For years, there has been a skin cancer crisis in Australia. According to the website “World Cancer Research Fund International,” Australia had the highest overall rate of melanoma of skin in 2020, followed by New Zealand. [6] This could be because of a number of reasons including Australia experiencing high levels of UVR, resulting from the reduction in their ozone layer since the 1970s or the culture of tanning that has gained a lot of popularity over the decades. It is interesting to know that most of these cancer cases are in white Caucasian immigrants, and this is mainly because of the low levels of melanin that are produced in the skin, and thus having less protection against the sun’s UV rays than other races with darker skin tones.
On the other hand, some ethnic groups with darker skins, especially African Americans who live in North America are at greater risk of vitamin D deficiency.[7] Again, this could also be because of a number of reasons such as diet, health conditions that prevent the absorption of vitamin D and the overall increase in indoors time. A major amount of vitamin D that is produced by our body comes from the sun’s UVB rays, so it is obvious that skin types with high levels of melanin will have a hard time absorbing those UVB rays, thus producing insufficient amounts of vitamin D. The melanin in dark skin is twice as effective in blocking UVB compared to White skin. While the Black skin epidermis allows only 7.4% of UVB and 17.5% of UVA to penetrate the skin, 24% UVB and 55% UVA passes through white skin.[8]
If it has not become apparent by now, both of these cases (skin cancer and vitamin D deficiency) are more likely to be seen in immigrants from different countries and continents. Racial groups look different for a reason that has a lot to do with the race’s environment of origin; the relocation of those individuals might result in the health issues stated above.
As social and economic concerns are becoming more prominent every day, more people are choosing to emigrate to other countries; which means more people are going to be living in completely new environments that their biology has not adapted for.
To conclude, the best strategy for dealing with these issues is to take precautions. For light- skinned individuals living in tropical or subtropical areas, it is best to apply sunblock creams and avoid ‘tanning beds’ completely, because there is no such thing as “safe tanning.” People with darker skin living in polar and sub-polar zones should have a vitamin D rich diet along with other nutrients, and it might be better for them to be slightly more exposed to the sun than their light-skinned counterparts.
References:
[1] https://en.wikipedia.org/wiki/Early_human_migrations#:~:text=Around%201.8%20million%20years%20ago,around%201.9%20million%20years%20ago.
[2] https://en.wikipedia.org/wiki/Interbreeding_between_archaic_and_modern_humans#:~:text=Genes%20affecting%20keratin%20were%20found,cope%20with%20non-African%20environments
[3] Dolgova O, Lao O. Evolutionary and Medical Consequences of Archaic Introgression into Modern Human Genomes. Genes (Basel). 2018 Jul 18;9(7):358. doi: 10.3390/genes9070358. PMID: 30022013; PMCID: PMC6070777.
[4] https://en.wikipedia.org/wiki/Fitzpatrick_scale
[5] Bradford PT. Skin cancer in skin of color. Dermatol Nurs. 2009 Jul-Aug;21(4):170-7, 206; quiz 178. PMID: 19691228; PMCID: PMC2757062.
[6] https://www.wcrf.org/cancer-trends/skin-cancer-statistics/
[7] Harris SS. Vitamin D and African Americans. J Nutr. 2006 Apr;136(4):1126-9. doi: 10.1093/jn/136.4.1126. PMID: 16549493
[8] Brenner M, Hearing VJ. The protective role of melanin against UV damage in human skin. Photochem Photobiol. 2008 May-Jun;84(3):539-49. doi: 10.1111/j.1751-1097.2007.00226.x. PMID: 18435612; PMCID: PMC2671032.