"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 fact without sunscreen to sunlight for just 5 to 10 minutes a week, even on sunny days in winter, will boost vitamin D levels.

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."