Shining a light on impulse to seek sun

Medical Matters

May 25, 2007|By Judy Foreman | Judy Foreman,Special to the Sun

Are people genetically programmed to seek the sun?

Personally, I've always thought so. And now a new study suggests that there may really be a genetic impulse to seek the sun, though there's plenty of evidence that excess exposure to sunlight can cause skin cancer.

In the study, published in the March 9 issue of CELL, Dr. David E. Fisher, director of the melanoma program at the Dana-Farber Cancer Institute, reported that the same biochemical process that leads to skin tanning also raises levels of a natural opiate, the "feel good" chemical, beta-endorphin.

Evolution might have favored this because, by making sunning pleasurable, the body increases production of melanin, the pigment that makes the skin tan. People who can tan have a much lower risk of skin cancer, including melanoma, than non-tanners.

The link between sun exposure and release of beta-endorphins "is an intriguing hypothesis worthy of pursuit," said Dr. Hensin Tsao, director of the Massachusetts General Hospital melanoma and pigmented lesion center. He said he'd like to see follow-up research examine whether enough beta-endorphins are released during tanning to make people want to spend more time in the sun.

There's another interesting tidbit in all this: The body makes vitamin D in response to sunlight. As our ancestors migrated away from the equator, their skins got lighter. Gene mutations that triggered lighter skin would have allowed people to make sufficient vitamin D, even as sunlight became weaker.

But the cautious take: You should protect your skin most of the time with sunscreen and clothing, especially if you have fair skin and do not tan.

Is virtual colonography - a screen for colon cancer - ready for prime time?

Almost. In fact, by the end of the year, the American Cancer Society, which is working on new guidelines, may include virtual colonography as one of the recommended ways to screen Americans over 50 for colon cancer.

In a virtual colonography, the colon is examined by a CT scan - a less invasive screening method than conventional colonoscopy, in which patients often have to be sedated so a viewing tube can be inserted into the rectum.

Most insurers do not pay for virtual colonography, which costs about $650. But data expected to be published later this year, as well as a study published in the journal Cancer late last month, are building momentum for greater acceptance.

With virtual colonography, if polyps greater than 5 millimeters are found, the patient must go on to have a regular colonoscopy so that a doctor can snip the polyps out.

A growing body of evidence suggests that polyps of less than 5 millimeters are not dangerous so long as you get a repeat scan in 10 years, said Dr. Michael Zalis, director of CT colonography at Massachusetts General Hospital in Boston.

Since most polyps are this tiny, virtual colonography means that roughly 85 percent of the time, people need no further testing.

Though some gastroenterologists have feared that if everybody switches to virtual exams, their incomes could go down, Dr. Perry Pickhardt, the lead author of the Cancer study and a radiologist at the University of Wisconsin, said this has not happened in his program.

Because the virtual exam is less anxiety-provoking, more people get screened, he said. And there are enough people who do need further testing that gastroenterologists' business has increased, he said.

Send your questions to foreman@baltsun.com.

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