Are Vitamin D Levels Affected by Dark Skin?

We talked earlier this year about sunscreen and the potential effect that it could have on vitamin D levels in the body. Naturally, my mind jumped from sunscreen to another relevant topic. If sunscreen could potentially lower how much vitamin D a person receives, how much of an effect would natural protection (melanin – I'll explain this more later) from the sun have?

I turned to good ole Google search and typed in a bunch of questions and topics. After much digging, I decided to compile the information that I found and create this blog post to address the question, how does dark skin impact the amount of vitamin D that a person absorbs into her body?

To give a bit of background, vitamin D deficiency is more prevalent in Black Americans than any other group of Americans. Although there is much debate as to what the optimal level of vitamin D is, some researchers and clinicians project that it could be somewhere around the 75-80 nmol/L level. Clinicians use the pre-hormone 25(OH)D as the primary measure for vitamin D status. It was found that the 25(OH)D levels in many Black Americans were much lower than the recommended amount (1).

For example, in the Third National Health and Nutrition Examination Survey (NHANES III), researchers found that 53%-76% of non-Hispanic Black Americans in the southern states had 25(OH)D levels lower than 50 nmol/L during the winter months, compared to only 8%-33% of non-Hispanic white Americans.

Taking it a step further, it was reported that from puberty onwards, the "median vitamin D intakes of Black Americans are below the recommended intakes in every age group" (1).

Since the low vitamin D levels are so widespread, there must be a reason behind it. Let’s start with the skin.

It Really is Skin Deep

Vitamin D synthesis begins its journey in the top layer of the skin, known as the epidermis. When sunlight reaches the epidermis, its type B ultraviolet (UVB) rays break down a compound in the skin called 7-dehydrocholesterol and convert it into pre-vitamin D3. Continuing the journey, the compound moves through to the liver and then to the kidneys where it becomes the biologically active form known as calcitriol. Calcitriol is the form that affects your blood calcium levels.

As I briefly mentioned earlier, melanin in the skin serves as natural protection to the sun. Melanin is the main determinant of the color of our skin and hair. People with dark skin have more melanin in their epidermis than people with light skin. Looking at vitamin D specifically, melanin absorbs some of the UV radiation that comes from the sun, dissipating the photons. It therefore competes with 7-dehydrocholesterol (one of the first intermediates in the path to vitamin D synthesis) in interacting with the UVB rays (2). This means that skin pigmentation impacts the effectiveness of vitamin D synthesis in the skin.

Dark Skin: Protection at the Cost of Production

According to research, the higher amount of melanin in dark skin interferes with the skin’s ability to create vitamin D from sunlight. It helps reduce how much UV radiation penetrates through the epidermis (2). One study found that the epidermis in black skin permitted only 7.4% of the UVB rays and 17.5% of UVA rays to pass through from the sun while the epidermis in white skin allowed 24% of UVB rays and 55% of UVA rays. Black skin essentially allowed about 3x less radiation in than light skin.

With all of this information combined, this means that darker-skinned people must spend more time out in the sun to produce the same amount of vitamin D as lighter-skinned people. This could mean at least three to five times longer exposure. Darker-skinned people, such as Black Americans and dark-skinned Asians, are more susceptible to developing vitamin D deficiency if they do not receive enough sunlight exposure and do not take vitamin D supplements. Further research is needed to decide if these lower vitamin D levels have significant health consequences for darker-skinned people (3).

Could the Tests Be Missing the Mark?

Currently, there is a blood test that medical professionals use in order to quantify the amount of vitamin D in a person’s body. The test measures a person’s total 25(OH)D level and generally consider levels below 20 ng/mL to be deficient. According to the guidelines, up to 90% of black Americans would be considered vitamin D deficient.

In one particular study of about 2100 adults, the average total level of vitamin D for Black Americans was a bit below 16 ng/mL while the average for white Americans was about 26 ng/mL (4). Interestingly, Black Americans typically have low levels of vitamin D in their blood, but they have about the same amount of the active form vitamin D as White Americans.

There is no one-size-fits-all for vitamin D recommendations. Researchers have found some genetic variations that could explain the differences in people’s levels of the vitamin D-binding protein. They found that most Black adults carried a gene variant linked to lower levels of the vitamin D-binding protein, while fewer than half of the white adults did. At the moment, there is no commercially available test that specifically measures bioavailable vitamin D (4). It would be beneficial if such a test was made so that we could more accurately record vitamin D in the body.

Lower Levels but Fewer Fractures

Another finding that has perplexed researchers is that blacks typically have lower levels of vitamin D in their blood than whites, yet they have lower incidence of falls and fractures. They are also reported to have greater bone mass. This stands at odds with existing research for other Americans because typically lower vitamin D levels correlated with more falls and fractures. Low levels of vitamin D in white Americans and Mexican Americans corresponded to increased risk of osteopenia and fractures, while it does not relate that way in Black Americans. Based on these results, the prevalence of vitamin D deficiency in the Black American community stands as a bit of a mystery. It seems therefore that optimum levels for vitamin D may vary for different ethnic and racial groups.

What Can We Say?

Overall, skin color affects the way in which vitamin D is absorbed into the body and how the body utilizes the nutrient. People who have darker skin require more time outside in the sun in order to reach sufficient levels of vitamin D. Given that people around the world are spending more time indoors due to the pandemic, it has been more difficult to get the vitamin D that they need. Since very few foods naturally contain a good source of vitamin D, people are not quite able to get enough of the nutrient through their diets (3). Therefore, one of the most accessible ways to get vitamin D is take vitamin D supplements.

Finding the right vitamin D supplement for you doesn’t have to be difficult. Take into consideration the ingredients, the size of the pill, the amount of active ingredient, and various other factors before you made your decision. The supplement should help you fulfill your health goals, bringing you closer to a healthier life step by step.

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Sources

1. Harris, S. S. (2006). Vitamin D and African Americans. The Journal of Nutrition, 136(4), 1126-1129. https://doi.org/10.1093/jn/136.4.1126

2. Brenner, M., & Hearing, V. J. (2008). The protective role of melanin against UV damage in human skin. Photochemistry and photobiology, 84(3), 539–549. https://doi.org/10.1111/j.1751-1097.2007.00226.x

3. Nair, R., & Maseeh, A. (2012). Vitamin D: The "sunshine" vitamin. Journal of pharmacology & pharmacotherapeutics, 3(2), 118–126. https://doi.org/10.4103/0976-500X.95506

4. Norton, A. (2013). Vitamin D Deficiency Might Be Overdiagnosed in Blacks, Study Suggests. Retrieved from https://www.medicinenet.com/script/main/art.asp?articlekey=175313

5. Brown, L. (2018). The vitamin D paradox in Black Americans. Retrieved from https://blogs.biomedcentral.com/bmcseriesblog/2018/05/15/vitamin-d-paradox-black-americans/