Skip to main content

The hype around vitamin D is intense, with new medical research almost weekly linking insufficiencies to everything from cancer to osteoporosis and childhood diabetes.

So the big question for the health-conscious is: how much to take?

Health Canada is currently studying the medical claims about vitamin D, and in the meantime says it's "premature" to jump on the supplement bandwagon. But many of the scientists investigating the nutrient, and presumably those most knowledgeable about it, are taking another approach. They're personally popping the vitamin, big time.

Story continues below advertisement

Bruce Hollis, a pediatrics professor at the Medical University of South Carolina in Charleston, has spent years studying whether more of the sunshine vitamin would help pregnant and breastfeeding women and their babies.

Dr. Hollis is so convinced about the possible health benefits that he has been taking 4,000 International Units daily, for years, but recently upped it to 6,000 IU, to raise his blood levels of the nutrient.

"I don't know of anybody who is studying this who isn't taking" the vitamin in robust amounts, Dr. Hollis says.

The quantities Dr. Hollis takes are well above what Health Canada recommends.

Based on research available in the mid-1990s, Health Canada pegged amounts at 200 IU to 600 IU a day, depending on age, and fixed 2,000 IU as a safe upper limit. Health Canada's review, being done in conjunction with the U.S. Dept. of Health, is expected to be released in the fall.

Several major health groups – including the Canadian Cancer Society and Osteoporosis Canada – aren't waiting for it. Much like the scientists, they're convinced people need to take more, and have issued advisories to that effect, although they're not calling for the big amounts some researchers are taking.

Recently, Dr. Hollis ran tests that found pregnant women on doses up to 4,000 IU a day have far lower rates of preterm births and lower rates of infection. The doses appear to be safe for both mother and baby.

Story continues below advertisement

"We haven't seen a single adverse event on those levels that would lead us to say there is any harm in doing it," Dr. Hollis says.

Other experts are just as keen on personally following the implications of their research.

Robert Heaney, a professor at Creighton University's school of medicine in Omaha, has been researching vitamin D's role in preventing osteoporosis and was a co-author of a peer-reviewed paper in 2007 that indicated the nutrient has the ability to sharply cut cancer incidence. "I personally take 3,000 [IU] a day," Dr. Heaney says.

"I've talked casually with virtually everyone [in the vitamin D research community] that I am in contact with and they're all taking vitamin D and they're taking it in doses greater than 1,000," Dr. Heaney says.

As an example, he cited a meeting a year ago of nine experts on the nutrient at the U.S. Centers for Disease Control, where he circulated a sheet and asked them to jot down how much they took. The amounts: 3,000 to 10,000 IU, with an average of 5,000 IU.

John White is a researcher at the department of physiology at McGill University who has been studying links between low levels of vitamin D and Crohn's disease, a painful gastrointestinal ailment.

Story continues below advertisement

His supplementation averages 2,000 IU a day, but he takes double that amount in the fall and winter when it isn't possible in Montreal to make the vitamin the natural way, by exposing skin to strong ultraviolet sunlight, and very little in the spring and summer.

Dr. White believes that, among vitamin D researchers, he's "at the liberal end of the conservative camp," as many scientists are taking far more.

To be sure, there are cautionary voices. Roger Bouillon, an authority on bone metabolism and professor of medicine at the Catholic University of Leuven in Belgium, says his colleagues are jumping the gun.

Dr. Bouillon seldom pops any vitamin D, never in summer and "occasionally in wintertime." He wouldn't recommend more than 800 IU a day, a level that, when combined with calcium, has been proven through drug-style trials efficacious for reducing fall and fracture risk

Most research linking vitamin D to other benefits, such as reductions in cancer, autoimmune diseases and heart conditions, is based on epidemiological studies or surveys that find those with more of the nutrient in their blood have better health outcomes.

Dr. Bouillon cautioned that these studies are speculative because they aren't backed by experiments using actual doses. Many formerly promising nutrients based on these kinds of studies have been found wanting or even dangerous when subjected to the rigours of drug-style clinical trials, he says.

Several major dosing studies of vitamin D are currently under way, but their results won't be available for years.

The higher doses the scientists take are safe, contends one prominent vitamin D expert. Cedric Garland, an epidemiologist and researcher at the Moores Cancer Center at the University of California, San Diego, was looking to see how much was too much and found "no toxicity below 10,000 IU after pretty extensively reviewing the [scientific] literature." That, coincidentally is about what people make when sunbathing.

Too much vitamin D, which is determined through a serum test, leads to kidney stones and excessive calcium in the blood.

Dr. Garland takes 2,000 IU a day, a level he says is suitable for men, but he believes women need more – possibly as much as 6,000 IU daily – to reach the blood levels of the nutrient associated with suppressing breast cancer.

"Because of the differential occurrence of breast cancer and its epidemic urgency … it's time for us to be moving to this higher dose in women," he says.

Report an error Licensing Options
About the Author
Investment Reporter

Martin Mittelstaedt has had a varied reporting career at the Globe and Mail, covering politics, the environment and business. He opened up the Globe's New York bureau for the Report on Business, and has also been on the banking and capital markets beats. He's written extensively on investing themes. More

Comments are closed

We have closed comments on this story for legal reasons. For more information on our commenting policies and how our community-based moderation works, please read our Community Guidelines and our Terms and Conditions.