TORONTO (CP) _ It's definitely a bit of a conundrum: sunlight is the best source of vitamin D, and vitamin D appears to have all kinds of health benefits. But too much sun can cause skin cancer, including the most deadly form, malignant melanoma.

So what should Canadians do?

That's what a group of doctors and researchers from across North America are trying to figure out as they gather in Toronto this week to assess the risks and benefits of ultraviolet radiation and the vitamin produced from exposure to the sun.

People have been confused by conflicting messages about sun exposure, conceded Heather Logan of the Canadian Cancer Society, which organized the conference.

``There's been mounting scientific evidence to suggest that being in the sun unprotected _ that is, not using sunscreen _ may reduce your risk of some big cancers, like breast, prostate, colorectal and non-Hodgkin's lymphoma,'' said Logan, director of cancer control policy.

``But we know, based on a solid body of evidence, that exposure to ultraviolet radiation can increase your risk of skin cancer, premature aging and cataracts. It's not an easy situation to deal with, and what we don't want people to do is to end up outside unprotected _ to trade cancers for cancers.''

What is known is that exposing the hands and face (without sunscreen) to sunlight for just five to 10 minutes a week, even on sunny days in winter, will boost vitamin D levels, she said.

In summer, when UV levels are high, just 20 seconds of sun exposure allows the body to manufacture 400 international units (IUs) of vitamin D, the current recommended daily allowance in Canada and the United States for many age groups, said Dr. Edward Giovannucci, a professor of epidemiology and nutrition at the Harvard School of Public Health.

But Giovannucci was among several experts at Wednesday's sessions who suggested the recommended daily amounts of vitamin D are likely woefully insufficient for optimizing health.

Animal and laboratory studies have shown that vitamin D protects against cells replicating too rapidly _ uncontrolled cell growth is the hallmark of cancer _ and from spreading to other parts of the body, he said. Vitamin D is also believed to affect the immune system, which may explain why rates of multiple sclerosis are higher in northern countries like Canada, especially among darker-complexioned people whose skin provides poor absorption of sunlight.

``Throughout human history, going back tens of thousands of years, we evolved primarily where there was a lot of sun, and then we moved up into more northern regions,'' Giovannucci said in an interview at the conference. ``There was always plenty of vitamin D around and cells needed to use this for many purposes.

``We generally make a lot less vitamin D from the sun than we used to, and there's not much vitamin D in foods,'' he said, noting that the nutrient is found naturally in cold-water fish like salmon and is added to milk.

``Cells are becoming relatively starved of the vitamin D ... and they can't really function 100 per cent properly. At least that's the hypothesis, that these lower levels of vitamin D may be increasing the risk of cancers and other conditions.''

So during winter months especially, Giovannucci said, people should take vitamin D supplements, specifically the type known as D3.

``Probably 1,000 IU is a real minimum and realistically we probably need to go up to 2,000 IUs, which is the upper limit before you worry about toxic or adverse affects.''

Reinhold Vieth, an internationally recognized expert on vitamin D, was unequivocal about current government and medical bodies' recommendations regarding daily doses, calling them ``absurd.''

For instance, the Canadian Pediatric Society suggests infants need 400 IUs a day _ while other official guidelines tell adults under 50 to take half that amount, despite the obvious difference in physical size, said Vieth, director of the Bone and Mineral Laboratory at Mount Sinai Hospital in Toronto.

``I think people who advocate avoidance of sun should likewise advocate 2,000 units of vitamin D a day, or more,'' said Vieth, who believes 400 units daily is adequate for children under five, but anyone over that age should boost that amount fivefold.

He said official guidelines that warn of possible hazardous toxicity from taking too much of the fat-soluble vitamin have been ``totally overblown,'' and research suggests that even 10,000 units a day would be safe for adults.

``The bigger hazard is being phobic of it and not taking it. The rules have to be changed.''

Logan said the Canadian Cancer Society hopes to have a position statement advising Canadians on sun exposure an vitamin D before National Sun Safety Awareness Week at the end of May.

Copyright © 2006 The Canadian Press

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