Skin Color and Vitamin D

Nina Jablonski, a professor of anthropology at Penn State University, has made a career of researching the origins of the evolution of skin color among human beings. Her findings have illuminated our view of racial identity, but they have also expanded our understanding of the role of vitamin D in human health. Dr. Jablonski says skin color regulates how much sunlight we admit into our bodies to make vitamin D, which is critical for bone health, successful pregnancies and strong immune systems.

In ancient times, she has found, skin color correlated with the amount of sunlight in the regions where people lived. People living in the tropics had darker skin, and those in more temperate zones had lighter skin. For thousands of years human beings spend most of their time in the out-of-doors, and they remained in the geographical areas in which they were born.

Two things changed over time. First, people began to migrate to new areas of the world.

“You’ve got people from England moving to Australia; people from West Africa moving to Finland. You have this dramatic movement of people to environments to which they are poorly adapted from a solar perspective.”

Second, as the world changed, people began to spend more time inside, away from sunlight.

In terms of health, both these trends have had the strongest effect on dark-skinned people. Light-skinned people are able to adapt in sunnier climates, applying sunscreen to ward off skin cancer (and the destruction of folate) while still getting enough of the ultraviolet B radiation necessary to produce vitamin D. She adds:

“If you’re a darkly pigmented person living in a far northern place or living in a city and not getting much sun exposure, though, then we are not addressing the problem of likely vitamin D deficiency.”

Lisa Bodnar who holds a doctorate in nutrition and does research at University of Pittsburgh’s Graduate School of Public Health, has found that pregnant women with vitamin D deficiencies are more likely to suffer from preeclampsia and have premature babies. She says nearly half of African-American mothers have vitamin D deficiencies, compared with ten percent of Caucasian mothers.

A study in Capetown, South Africa, has also shown that, among darker-skinned South Africans, the more time they spend indoors, the lower their level of vitamin D and the weaker their immune systems. Fortunately, vitamin D supplements can reverse this situation.