[T@T]

Interesting article on skin color. It's bone deep!

By about 1.2 million years ago, humans ancestors had lost their fur and were able to sweat more efficiently to avoid overheating.
Without fur, however, our skin was exposed to the strong equatorial sun. The skin pigment melanin, which is responsible for most of the color of our skin. Melanin is a terrific sunscreen, and darkly pigmented skin became a substitute for fur.

But as our ancestors migrated away from the Earth’s equator, which has lots of UV exposure, it became less and less beneficial for those populations to have so much pigmentation as protection from the sun. Why? For answers, we must look at vitamin D.

“Vitamin D is produced at high levels in the skin when it is exposed to ultraviolet light from the sun,” says Dr. Michael Holick, a professor of medicine, physiology and biophysics at Boston University Medical Center. He is a leader in vitamin D nutrition, and among countless other works, published the book “The Vitamin D Solution.”
According to Holick, back in the 1930s to 1950s, it was thought that the main reason for skin pigmentation was to prevent having too much vitamin D being produced in the skin. Too much vitamin D leads to vitamin D intoxication, which can result in death. However, in the early 1980s, Holick and his colleagues published a paper that disproved that theory.
“It turns out that Mother Nature was quite clever, in that any excessive exposure to sunlight destroys any excess vitamin D produced in the skin,” Holick explained.

Vitamin D is produced in skin that’s exposed to the sun, and it’s involved in helping the intestines absorb calcium, which is a critical nutrient in our bones. However, heavily pigmented skin reduces a person’s ability to produce vitamin D in the skin “probably by 90-95%,” according to Holick, meaning they were more likely to be deficient in the vitamin.
As our ancestors migrated to areas away from the equator, with lower UV radiation, pigmentation became a problem. For example, Holick explained, a person from Africa who is very darkly pigmented has a sun protection factor of around 30. That person 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.
Vitamin D is critical for healthy bones, which have always been essential to human survival. Not only are healthy bones important to movement and holding our bodies upright, but they are essential for reproduction. A pregnant mother who is vitamin D deficient can have a baby born with infantile rickets syndrome, a disease that leads to severe bone abnormalities. If the mother remains vitamin D deficient, she is also calcium-deficient. If breast milk is the main food source for the infant, the infant will not receive enough calcium to build healthy bones.

http://lightyears.blogs.cnn.com/2013...eep/?hpt=hp_c4