SCIENCE / MEDICINE : Shades of Opinion in the Debate Over Skin Cancer : Research: A San Diego epidemiologist sees the need for rays in production of Vitamin D. Others say more study is necessary to determine the risks and benefits of sunlight.

Slowly but steadily, the evils of sunbathing have been etched into American consciousness. Stay out of the sun, most everyone has been warned by physicians at one time or another, to minimize the risk of skin cancer, not to mention an onslaught of wrinkles. If sun worshiping is still a must, so is sunscreen, most doctors say.

Now, some researchers are crying “overkill.” Getting a little sun, they claim, isn’t a bad idea. Minimal sun exposure may actually decrease the risks of colon, rectal and breast cancers, partly by triggering adequate production of Vitamin D, especially in the elderly, suggests Cedric Garland, a San Diego epidemiologist and associate professor of community and family medicine at the UC San Diego School of Medicine.

He is not promoting a return to the old bake-at-the-beach mentality. But 10 or 15 minutes a day of sunlight exposure may actually be healthy for some people, contends Garland, who earlier this year presented his research findings in New Orleans at the annual meeting of the American Assn. for the Advancement of Science.

Dermatology and cancer specialists emphasize that the work of Garland and others should be viewed with caution and that further work needs to be done to determine the relative risks and benefits of sunlight.

Colon and rectal cancer will kill 61,000 people this year, while breast cancer will claim another 44,000 lives, according to American Cancer Society estimates. Another 8,800 people will die of skin cancer in 1990, most of them from the most deadly form, called melanoma.

Garland began rethinking traditional sun exposure advice about a decade ago, when he and his brother, Frank Garland, head of the epidemiology program of the U.S. Naval Health Research Center in San Diego, examined a U.S. map showing county-by-county death rates from different types of cancers. The brothers became intrigued by the low colon cancer rates in the Southwest and the high rates in the Northeast, wondering if the amount of sunlight and the Vitamin D it helps produce might play a role.

Next, the Garlands, working with other researchers, analyzed the diets of nearly 2,000 men and found that the risk of colon cancer was correlated with low levels of dietary Vitamin D. In another study, published late last year in The Lancet, Garland and his colleagues thawed blood samples collected years earlier from colon cancer patients, comparing them to samples drawn from healthy subjects. Vitamin D levels were lower in the cancer patients than in controls, said Garland, who concludes that maintaining high levels of Vitamin D might reduce colon and rectal cancer risk by as much as 80%.

An unpublished study by the Garlands and UC San Diego epidemiologist Edward D. Gorham found that breast cancer death rates in the darkest republics of the Soviet Union are three times those in republics with more sunshine. He found that breast cancer death rates in northern parts of the United States are about 1.5 times higher than the death rates in the sunnier southern parts of the country.

Any protective effect of Vitamin D probably works in more than one way, Garland said. “It may maintain tight junctions between cells in the bowel’s lining, for instance, thus . . . preventing the evolution of early cancers.”

The Garlands are not the only ones doing research in this area.

In a University of Utah study, dietary calcium was termed a “mitigating factor” in colon cancer after researcher Martha Slattery followed 231 patients eventually diagnosed with colon cancer and 391 patients who remained cancer-free. Vitamin D helps regulate the amount of calcium absorbed by the body.

She compared the dietary habits of the groups two years before the cancer diagnosis and found that dietary calcium decreased the risk of colon cancer in low-risk people. It may do so, Slattery speculates, by decreasing the exposure of the bowel’s lining to irritating fatty acids and bile acids. Her research was published in 1988 in the American Journal of Epidemiology.

In another study, researchers found that chronic sunscreen use decreases concentrations of circulating Vitamin D. The researchers, whose study was published in late 1988 in the Archives of Dermatology, compared 20 long-term sunscreen users with 20 control subjects who were about the same age and who were accustomed to about the same sunlight exposure.

Based on this body of research, Cedric Garland offers several pieces of advice:

* Spend just a few minutes in the sun every day, especially if you are 65 or older. But the advice doesn’t hold for very fair-skinned people or those with a history of serious skin disorders, Garland added.

* Minimize sun exposure otherwise. Skip sunscreen, Garland advises, although other experts strongly disagree with him.

“Sunscreen interferes with the production of Vitamin D in the skin and reduces circulating Vitamin D levels by half,” said Garland. And he is not convinced that sunscreen prevents melanoma.

The sunscreen industry thinks differently. “What we know is sunscreen blocks the sun and sunlight contributes to melanoma,” said Jerry McEwen, vice president of science for the Cosmetic, Toiletry and Fragrance Assn., a Washington-based trade group.

* If you do use sunscreen, be sure to eat sufficient amounts of Vitamin D-containing foods, Garland suggested. Milk and fish such as tuna are good choices, he added.

How much Vitamin D is enough? About 400 International Units (IUs) a day, Garland suggested. That is the current recommended dietary allowance (RDA) for children and double the RDA for adults. (A cup of milk, for instance, supplies about 100 IUs of Vitamin D.) “And we may have reason to take that up to 1,000 IUs (based on research in progress),” Garland added.

Not everyone agrees with Garland’s advice. Dr. Clark Heath, vice president for epidemiology and statistics for the American Cancer Society, calls Garland’s advice and ideas “interesting but unproven,” adding that “further research may or may not bear them out.” What is known, Heath said, is that “excessive sunlight is clearly linked with all forms of skin cancer.”

In a consensus statement issued in 1988, the American Academy of Dermatology called for “further documentation of the impact sunscreen use has on elderly patients at risk of Vitamin D deficiency,” according to a spokesman for the academy. “We stand by our advice to use sunscreen with a sun protection factor of 15 or greater,” he added.

But some physicians have adopted a middle-of-the-road stance, pending further studies. “We don’t yet know what role 10 minutes a day plays in (the development of) skin cancer, but it would probably be safe,” said Dr. Jeff Ashley, USC associate clinical professor of medicine and a Burbank dermatologist, who cautions his patients never to sunburn.

“If you are taking sun-avoidance advice seriously,” Ashley also tells his patients, “you need to pay attention to Vitamin D. Drink three or four glasses of milk a day, or take a Vitamin D supplement. Take it with calcium. The metabolism of the two are so closely linked that those people not getting enough Vitamin D may not be getting enough calcium either.”