Urbanisation cutting off sunlight

Urbanisation is cutting off people from adequate sunlight — which helps the skin produce vitamin D and facilitates calcium absorption by the body, a new study has claimed.

As people move more often and become more urbanised, skin colour — an adaptation that took hundreds of thousands of years to develop in humans — may lose some of its evolutionary advantage, according to Nina Jablonski, a Penn State anthropologist.
In addition to moving regularly, most people now live in cities with limited exposure to the sun. Nearly 60 per cent of the people in the world live in cities now, said Jablonski.

Most people who live in cities also work indoors, further reducing their ability to make enough vitamin D in their skin.

Health problems are compounded when people do not receive enough sunlight, or when they have a mismatch between their skin pigmentation and ultraviolet radiation.

“This can lead to a vitamin D catastrophe for many people,” Jablonski said.
About 2 million years ago, permanent dark skin colour imparted by the pigment - melanin - began to evolve in humans to regulate the body’s reaction to ultraviolet rays from the sun, said  Jablonski.

Melanin helped humans maintain the delicate balance between too much sunlight and not enough sunlight. The pigment allowed enough ultraviolet radiation to produce vitamin D, a vitamin that helps the body absorb calcium, while protecting the skin from the intense ultraviolet radiation in the equator. Too much sunlight can cause the destruction of folate, which is also critical to cell division. As people moved away from the equator to places where the sun’s rays are not nearly as intense, they lost pigmentation, said Jablonski.