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When it comes to knowing how much vitamin D to take, Canadians can be forgiven for being confused.

The Canadian Paediatric Society, the Canadian Cancer Society and Health Canada all say people need the sunshine vitamin, but that's where the agreement ends. The pediatric society, for instance, recently said pregnant women should consider taking 10 times more vitamin D than the government recommends. The cancer society is advocating a dosage for all adults that is five times higher than the government guideline.

It is nearly unprecedented for respected public health groups to brazenly sidestep a Health Canada nutrition recommendation by issuing advice at odds with the government's.

Health Canada even tried to persuade the pediatric organization not to issue its recommendation for more vitamin D, but the group representing children's doctors found the evidence for taking more of the vitamin so compelling, and the government's position so lacking in scientific support, it ignored the agency.

“We found actually nothing to support their position in the [scientific] literature,” said John Godel, who helped develop the pediatric society recommendation.

Following the advice from the two societies involves taking far more vitamin D than is commonly available in multivitamins or food sources, and many Canadians, responding to the recommendations, have swooped down on drugstores to stock up on supplements.

But the contradictory advice – and the research suggesting the vitamin has anti-cancer and other health benefits – has made figuring out the right daily dose a pressing question. And the unusual debate over D isn't likely to end any time soon.

Health Canada has a policy of harmonizing Canadian nutrition standards with those in the United States, and, in an e-mailed statement to The Globe and Mail, said it is committed to a joint review process with the Americans on vitamin D supplement levels. Because of its desire to have North American standards, Health Canada isn't budging from its current recommendation.

But some critics believe the government's position is dated because it was developed 10 years ago, before the recent flurry of research suggesting vitamin D insufficiency may play a part in causing cancer, multiple sclerosis, diabetes and a number of other serious diseases. Dr. Godel said he has no doubt, based on an extensive review of the scientific research on the nutrient, that Health Canada's advice is out of date.

Health Canada, for its part, has issued a news release dismissing the recommendations made by the two organizations as “premature.”

The vitamin D recommendation made by Health Canada, which most adults can reach by drinking two glasses of milk a day, is based mainly on the nutrient's well-known role in promoting good bone health.

In the e-mailed statement to The Globe, Health Canada says it wants to study whether a standard for the vitamin is needed and is talking to the U.S. Department of Health about a formal review.

The two governments won't be conducting a review themselves, but will farm the work out to the Washington-based Food and Nutrition Board, a non-profit research organization that is part of the Institute of Medicine.

Although Health Canada wants to start a review, it hasn't yet contacted the Food and Nutrition Board to formally request such a study. Any review would cost an estimated $1-million, an amount the non-profit would have to get from the two governments before proceeding.

Health Canada said, “Conducting a rigorous evidence-based review of all available data on a given nutrient would likely take a year or two, even if fast-tracked.”

According to Health Canada, the advantages of collaborating with the United States in determining nutrient recommendations are “the ability to access an expanded pool of scientific expertise, and the harmonization of the science base that underlies nutrition policy.”

The Canadian Cancer Society wasn't approached by Health Canada to alter its call on vitamin D, a spokesperson said.

The society made its recommendation in June after the publication in the United States of a research paper indicating supplemented vitamin D levels substantially above what is recommended by Health Canada cut the risk of cancer in an experiment by 60 per cent.

However, there is controversy over the cancer society's announcement.

Richard Schabas, a former chief medical officer of health in Ontario, said the society jumped the gun and should have waited for more research to confirm the U.S. findings, which he said are open to dispute. “I don't think the evidence justified a public health recommendation of that kind at this time,” he said.

The Canadian debate over vitamin D requirements is all the more unusual because nothing similar has happened in the United States, where public health groups similar to the cancer and pediatric societies haven't made high-profile calls to take more of it.

However, Canadians are more at risk than Americans of having low levels of vitamin D because of the country's northern geography.

Vitamin D is known as the sunshine vitamin because people make most of what they need themselves, when skin is exposed to strong sunshine. In most areas of Southern Canada, people produce no vitamin D through sun exposure from just about now until March.