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In recent weeks, an advertisement has been running prominently in The Globe and Mail that makes some eye-popping claims, among them that vitamin D deficiency is causing widespread illness and premature deaths, costing the health system $20-billion a year.

The solution, according to the Pure North S'Energy Foundation, is to dramatically increase Canadians' intake of vitamin D from the current recommendation of 600 to 800 international units daily to 6,000 to 9,000 IUs a day.

Canadians can find "true happiness for pennies a day" by purchasing and consuming large quantities of vitamin D supplements, says one of the ads.

Perhaps the most surprising part of this story is that the ads are not sponsored by a vitamin-maker, but by a foundation that does not appear to stand to gain financially from supplement sales.

Rather, it seems to be a quixotic campaign by wealthy Calgary entrepreneur Allan Markin, who claims to have invested $200-million in Pure North. Mr. Markin, a chemical engineer, credits taking 12,000 IUs of vitamin D daily for his own good health.

There is no question that vitamin D is an essential nutrient and important for bone health. There is also no doubt that its deficiency can have serious consequences, including rickets.

But the claims that it's a miracle drug that can prevent a wide range of illnesses – 13 types of cancer, diabetes, heart disease, kidney disease, multiple sclerosis, chronic obstructive pulmonary disease, asthma, arthritis, premenstrual syndrome and gum disease, according to a brief scan of published medical literature – have to be kept in context.

What this observational research shows is that people with adequate vitamin D levels have lower rates of a wide range of chronic illnesses. Stated simply, healthy people tend to be healthy.

Not long ago, scientists were pretty excited about vitamin D's potential, particularly when studies suggested that supplementation could cut mortality by about 7 per cent. But that enthusiasm has waned with disappointing clinical trials. In fact, there is increasing evidence that too much vitamin D can be as harmful as too little.

Our principal source of vitamin D is sunshine. About 10 minutes a day of exposure (a little more for people who are dark-skinned or obese) produces as much as the body needs, according to U.S. Institute of Medicine guidelines. Vitamin D can also be consumed in food. In Canada, milk is fortified with vitamin D, and so are some juices. Newborns are routinely given drops because breast milk is a poor source.

In northern climes like Canada, vitamin D levels can be low, particularly in winter. But definitions of adequacy, insufficiency and deficiency vary around the world.

This does not mean we should be measuring everyone's vitamin D levels, something that is in vogue in some circles. The U.S. Preventive Services Task Force, in its review, said there is no evidence to justify screening, except in a small number of high-risk patients with bone-related diseases. At roughly $100 a test, the main harm would be to the wallet.

Health Canada nutritional guidelines suggest that 600 to 800 IUs of vitamin D is sufficient. In Canada, supplements cannot contain more than 1,000 IUs of vitamin D (the U.S. limit is 7,000 IUs), but nothing stops people from taking as many as they like. The principal risk of too much is kidney stones.

True North's campaign takes issue with the recommended daily allowance, claiming that it was established based on a mathematical error made by the IOM. That debate can be left to statisticians.

The more eyebrow-raising claims merit closer scrutiny, however. They derive principally from a 2010 paper by William Grant, a physicist who works for the Sunlight, Nutrition and Health Research Center in San Francisco.

Dr. Grant argued that insufficient vitamin D levels are responsible for 37,000 premature deaths in Canada every year – about one in six deaths. He calculated that resulting chronic illnesses cost the health system between $8-billion and $20-billion a year.

These are preposterous claims based on the dubious premise that by hiking the amount of vitamin D in our blood, a broad range of illness would disappear.

The fundamental error here is confusing correlation and causation. Yes, people with adequate vitamin D levels have less disease. But it does not follow that pumping everyone full of supplements will make them healthier. Enthusiasm for this panacea simply doesn't match the scientific evidence.

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