Skin color, sunshine, vitamin D deficiency and health

Vitamin D deficiency due to lack of exposure to sunlight is implicated in numerous diseases 

Scientists claim human skin color is directly linked to our survival as a species. As we lost our fur during evolution, our skin was exposed to the strong equatorial sun. Therefore, we developed the skin pigment melanin, which gives our skin color, to protect us from the sun.

Over the course of evolution, scientists argue, skin color was also influenced by our need for vitamin D, which is produced in high levels by our skin when it is exposed to ultraviolet light from the sun.

A basic function of vitamin D is that it helps our intestines absorb calcium, which is a critical nutrient in our bones.

Vitamin D deficiency in children causes rickets, which results in skeletal deformities.  Vitamin D deficiency in adults, can lead to osteomalacia, which results in muscular weakness in addition to weak bones. Limited sun exposure is the primary cause of vitamin D deficiency.

As some of our ancestors migrated to areas away from the equator, with lower ultraviolet radiation, their darker pigmentation became a problem and they had to evolve lighter pigmentation to absorb adequate ultraviolet light in less sunny climates.

Because darker skin has larger concentrations of melanin which protects against overexposure to ultraviolet light, it therefore protects against skin cancers. In general, the more melanin there is in the skin the more solar radiation can be absorbed. Light-skinned people have about a tenfold greater risk of dying from skin cancer, compared to dark-skinned people, under equal sunlight exposure.

But while dark skin offers better protection from intense ultraviolet light and cancer, it may result in low absorption of vitamin D. This has led to concern that darker skinned people living at relatively high latitude, such as African Americans, may be more susceptible to vitamin D deficiency.

For example, a person from Africa who is very darkly pigmented would have to be out in the sun at least 10 to 15 times longer to produce the same amount of vitamin D as a lightly-pigmented person from Europe.

Since heavily pigmented skin reduces a person’s ability to produce vitamin D in the skin, all being equal, darker skinned people, especially those living away from the tropics, are more likely to be deficient in vitamin D.

Recent research suggest that vitamin D deficiency is associated with a host of health problems: such as asthma, upper respiratory infections in children, and osteoporosis, hypertension (high blood pressure), type 1 diabetes, cancer, especially colorectal cancer, and several autoimmune diseases, including: multiple sclerosis, lupus, rheumatoid arthritis, and chronic lymphocytic leukemia, and immune deficiency diseases such as Crohn's disease.

Lupus, for example, is of great concern because it occurs more frequently and with greater severity among people of non-European descent and it tends to be most prevalent among people of Afro-Caribbean descent.

One would expect that Caribbean immigrants in North America and Western Europe are far less exposed to sunlight than they were in the Caribbean and therefore are more susceptible to vitamin D deficiency.

But nowadays, most people spend most of their days indoors, away from sunlight, which has implications for the people in the Caribbean as well. Moreover, widespread use of skin lighteners among Caribbean populations suggests preference for lighter skin which would drive some people to avoid sunlight.

Anecdotal evidence suggest that many of the ailments that plague Caribbean people,  especially autoimmune diseases and cancers, may be related to vitamin D deficiency which in turn is likely related to their decreasing exposure to sunlight.

Note: The current wisdom is that once Lupus is present, sunlight should be avoided, because sunlight exacerbates the disease. 

 

Sources: WebMDMayo ClinicThe Tanning GuruLinus Pauling InstituteCNN Light Years BlogAmerican AutoimmuneWikipedia

Editor's note: This article was first published  on May 6, 2013. From time to time we will re-post articles of great importance. We will use "Caribbean-events replay" to acknowledge that the article is a re-post of our previous publication.

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