A truly sunny disposition

MILWAUKEE – It was a cool day, and a hazy sun had lured only a few of its worshippers to the beach.

Michael White was one of them. Although summer was nearly three weeks away, White was about as dark as a red-haired, light-skinned person can get.

It makes him feel good, the Milwaukee man says. And scientists think they might know why. A growing amount of research suggests that when skin is exposed to sunlight, a complex physiological response occurs, including the production of morphinelike substances.

If these so-called beta-endorphins get to the brain, it might explain why some people seem to be addicted to tanning.

“We never really had any firm data until recently,” said Stephen Snow, a professor of dermatology at the University of Wisconsin-Madison. “We know that 90 percent of people say it makes them look better, and 50 percent say it makes them feel better.”

In the past, that good feeling might have been explained simply by the improved appearance or the warmth of the light, not by a biological reaction that might be deeply rooted in our evolution.

But now researchers are focusing on a physiological mechanism in the skin that might have provided a reward for behavior that likely made sense in the formative years of our species.

“Ten thousand years ago, we couldn’t get vitamin D” from food or pills, Snow said. “The body concocted a mechanism to get it.”

In a study published in March in the journal Cell, researchers reported on how exposure to ultraviolet light activated a physiological response in the skin that included the production of beta-endorphins.

The researchers speculated that this response could explain sun-seeking behavior in people.

The question is, why would people evolve to produce endorphins when they were exposed to sunlight?

Since a primary way people get vitamin D is through ultraviolet light exposure, one possibility is that the response developed to encourage our ancestors to get adequate sunlight, said senior author David Fisher, director of the melanoma program at the Dana-Farber Cancer Institute in Boston.

“If you have insufficient UV exposure and it’s 50,000 years ago and you live in a cave, you might die of a vitamin D deficiency,” said Fisher, who also is a professor of pediatrics at Harvard Medical School.

Today, people are better off taking a vitamin D pill and avoiding the risk of skin cancer that comes from too much ultraviolet light exposure, he said.