For decades, researchers have puzzled over why rich northern countries have cancer rates many times higher than those in developing countries ? and many have laid the blame on dangerous pollutants spewed out by industry.

But research into vitamin D is suggesting both a plausible answer to this medical puzzle and a heretical notion: that cancers and other disorders in rich countries aren't caused mainly by pollutants but by a vitamin deficiency known to be less acute or even non-existent in poor nations.

Those trying to brand contaminants as the key factor behind cancer in the West are "looking for a bogeyman that doesn't exist," argues Reinhold Vieth, professor at the Department of Nutritional Sciences at the University of Toronto and one of the world's top vitamin D experts. Instead, he says, the critical factor "is more likely a lack of vitamin D."

What's more, researchers are linking low vitamin D status to a host of other serious ailments, including multiple sclerosis, juvenile diabetes, influenza, osteoporosis and bone fractures among the elderly.

The main way humans achieve healthy levels of vitamin D is not through diet but through sun exposure. (Eliseo Fernandez/Reuters)

Not everyone is willing to jump on the vitamin D bandwagon just yet. Smoking and some pollutants, such as benzene and asbestos, irrefutably cause many cancers.

But perhaps the biggest bombshell about vitamin D's effects is about to go off. In June, U.S. researchers will announce the first direct link between cancer prevention and the sunshine vitamin. Their results are nothing short of astounding.

A four-year clinical trial involving 1,200 women found those taking the vitamin had about a 60-per-cent reduction in cancer incidence, compared with those who didn't take it, a drop so large ? twice the impact on cancer attributed to smoking ? it almost looks like a typographical error.

And in an era of pricey medical advances, the reduction seems even more remarkable because it was achieved with an over-the-counter supplement costing pennies a day.

One of the researchers who made the discovery, professor of medicine Robert Heaney of Creighton University in Nebraska, says vitamin D deficiency is showing up in so many illnesses besides cancer that nearly all disease figures in Canada and the U.S. will need to be re-evaluated. "We don't really know what the status of chronic disease is in the North American population," he said, "until we normalize vitamin D status."

Sunshine vitamin

For decades, vitamin D has been the Rodney Dangerfield of the supplement world. It's the vitamin most Canadians never give a second thought to because it was assumed the only thing it did was prevent childhood rickets, a debilitating bone disease. But the days of no respect could be numbered. If vitamin D deficiency becomes accepted as the major cause of cancer and other serious illnesses, it will ignite the medical equivalent of a five-alarm blaze on the Canadian health front.

For many reasons, Canadians are among the people most at risk of not having enough vitamin D. This is due to a quirk of geography, to modern lifestyles and to the country's health authorities, who have unwittingly, if with the best of intentions, played a role in creating the vitamin deficiency.

Authorities are implicated because the main way humans achieve healthy levels of vitamin D isn't through diet but through sun exposure. People make vitamin D whenever naked skin is exposed to bright sunshine. By an unfortunate coincidence, the strong sunshine able to produce vitamin D is the same ultraviolet B light that can also causes sunburns and, eventually, skin cancer.

Only brief full-body exposures to bright summer sunshine ? of 10 or 15 minutes a day ? are needed to make high amounts of the vitamin. But most authorities, including Health Canada, have urged a total avoidance of strong sunlight or, alternatively, heavy use of sunscreen. Both recommendations will block almost all vitamin D synthesis.

Those studying the vitamin say the hide-from-sunlight advice has amounted to the health equivalent of a foolish poker trade. Anyone practicing sun avoidance has traded the benefit of a reduced risk of skin cancer ? which is easy to detect and treat and seldom fatal ? for an increased risk of the scary, high-body-count cancers, such as breast, prostate and colon, that appear linked to vitamin D shortages.

The sun advice has been misguided information "of just breathtaking proportions," said John Cannell, head of the Vitamin D Council, a non-profit, California-based organization.

"Fifteen hundred Americans die every year from [skin cancers]. Fifteen hundred Americans die every day from the serious cancers."

Health Canada denies its advice might be dangerous. In an e-mailed statement, it said that most people don't apply sunscreen thoroughly, leaving some skin exposed, and that people spend enough time outside without skin protection to make adequate amounts of vitamin D.

However, the Canadian Cancer Society last year quietly tweaked its recommendation to recognize that limited amounts of sun exposure are essential for vitamin D levels.

Avoiding most bright sunlight wouldn't be so serious if it weren't for a second factor: The main determinant of whether sunshine is strong enough to make vitamin D is latitude. Living in the north is bad, the south is better, and near the equator is best of all.

Canadians have drawn the short straw on the world's latitude lottery: From October to March, sunlight is too feeble for vitamin D production. During this time, our bodies draw down stores built by summer sunshine, and whatever is acquired from supplements or diet.

Government regulations require foods such as milk and margarine to have small amounts of added vitamin D to prevent rickets.

Other foods, such as salmon, naturally contain some, as does the cod liver oil once commonly given to children in the days before milk fortification. But the amounts from food are minuscule compared to what is needed for cancer prevention and what humans naturally can make in their skin.

Vitamin D levels in Canada are also being compromised by a lifestyle change. Unlike previous generations that farmed or otherwise worked outside, most people now spend little time outdoors.

One survey published in 2001 estimated office- and homebound Canadians and Americans spend 93 per cent of waking time in buildings or cars, both of which block ultraviolet light.

Consequently, by mid-winter most Canadians have depleted vitamin D status. "We're all a bit abnormal in terms of our vitamin D," said Dr. Vieth, who has tested scores of Canadians, something done with a simple blood test.

How much is enough?

Just how much vitamin D is required for optimum health is the subject of intense scientific inquiry.

Dr. Vieth has approached the matter by asking: What vitamin D level would humans have if they were still living outside, in the wild, near the equator, with its attendant year-round bright sunshine? "Picture the natural human as a nudist in environments south of Florida," he says.

He estimates humans in a state of nature probably had about 125 to 150 nanomoles/litre of vitamin D in their blood all year long ? levels now achieved for only a few months a year by the minority of adult Canadians who spend a lot of time in the sun, such as lifeguards or farmers.

For the rest of the population, vitamin D levels tend to be lower, and crash in winter. In testing office workers in Toronto in winter, Dr. Vieth found the average was only about 40 nanomoles/L, or about one-quarter to one-third of what humans would have in the wild.

The avalanche of surprising research on the beneficial effects of vitamin D could affect dietary recommendations as well. Health Canada says that, in light of the findings, it intends to study whether recommended dietary levels need to be revised, although the review is likely to be years away.

A joint Canadian-U.S. health panel last studied vitamin D levels in 1997, concluding the relatively low amounts in people's blood were normal. At the time, there was speculation vitamin D had an anti-cancer effect, but more conclusive evidence has only emerged since.

"There needs to be a comprehensive review undertaken and that is planned," says Mary Bush, director general of Health Canada's office of nutrition policy and promotion.

But Ms. Bush said the government doesn't want to move hastily, out of concern that there may be unknown risks associated with taking more of the vitamin.

Those who worry about low vitamin D, however, say this stand is too conservative ? that the government's caution may itself be a health hazard.

To achieve the vitamin D doses used for cancer prevention through foods, people would need to drink about three litres of milk a day, which is unrealistic.

If health authorities accept the new research, they would have to order a substantial increase in food fortification or supplement-taking to affect disease trends. As it is, the 400 IU dosage included in most multivitamins is too low to be an effective cancer fighter.

Dr. Vieth said any new recommendations will also have to reflect the racial and cultural factors connected to vitamin D. Blacks, South Asians and women who wear veils are at far higher risks of vitamin D deficiencies than are whites.

Although humans carry a lot of cultural baggage on the subject of skin hue, colour is the way nature dealt with the vagaries of high or low vitamin D production by latitude.

Those with very dark skins, whose ancestors originated in tropical, light-rich environments, have pigmentation that filters out more of the sunshine responsible for vitamin D; in northern latitudes, they need more sun exposure ? often 10 times as much ? to produce the same amount of the vitamin as whites.

Dr. Vieth says it is urgent to provide information about the need for extra vitamin D in Canada's growing non-white population to avoid a future of high illness rates in this group.

Researchers suspect vitamin D plays such a crucial role in diseases as unrelated as cancer and osteoporosis because the chemical originated in the early days of animal evolution as a way for cells to signal that they were being exposed to daylight.

Even though living things have evolved since then, almost all cells, even those deep in our bodies, have kept this primitive light-signalling system.

In the body, vitamin D is converted into a steroid hormone, and genes responding to it play a crucial role in fixing damaged cells and maintaining good cell health. "There is no better anti-cancer agent than activated vitamin D. I mean, it does everything you'd want," said Dr. Cannell of the Vitamin D Council.

Some may view the sunshine-vitamin story as too good to be true, particularly given that the number of previous claims of vitamin cure-alls that subsequently flopped. "The floor of modern medicine is littered with the claims of vitamins that didn't turn out," Dr. Cannell allowed.

But the big difference is that vitamin D, unlike other vitamins, is turned into a hormone, making it far more biologically active. As well, it is "operating independently in hundreds of tissues in your body," Dr. Cannell said.

Referring to Linus Pauling, the famous U.S. advocate of vitamin C use as a cure for many illnesses, he said: "Basically, Linus Pauling was right, but he was off by one letter."