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• How much is too much?
  Macleans.ca helps you sort through the confusion over the proper amount of nutrients to take

Convention says calcium is good for bones. But if you read recent research you might never take calcium supplements again. They may increase the risk of heart attack in healthy post-menopausal women, according to a report by scientists at the University of Auckland in January’s British Medical Journal. Incidentally, post-menopausal women are probably the group mostly taking calcium pills to prevent osteoporosis, which makes bones more breakable. Then, in March, the Harvard Health Letter announced that “high calcium may not prevent fractures.” Confused?

Consumers aren't the only ones. Turns out the incessant flow of contradictory studies released daily is stumping just about everybody, says Gerry Harrington of the Ottawa-based Nonprescription Drug Manufacturers Association, whose members include vitamin and mineral supplement makers. "Health Canada struggles with it. Manufacturers struggle with it. There are even individual scientists who struggle," he concedes. Harrington's warning: "Pay attention. Don't take anything for granted."

Across the spectrum, most nutrition experts agree that vitamin and mineral pills — even ones that hold tremendous potential and do provide benefits — can actually be harmful too. Most damage happens when they're consumed in excess — at doses 10 or more times higher than the recommended daily intake. Even multivitamins can contain very high doses of certain nutrients, as vitamins and minerals are collectively known. Nutrient supplements "can have very negative human consequences" if mishandled, says Bill Jeffery of the Centre for Science in the Public Interest in Ottawa.

The evidence is mounting: in January, the Mayo Clinic declared that certain nutrient pills such as beta carotene and vitamin E either had no effect or appeared to increase cancer incidence and mortality. The U.S. National Institutes of Health, in a 2006 study, concluded in part that the safety and quality of multivitamin and mineral supplements are inadequate, and uncovered "disturbing evidence of risk" associated with taking some nutrient supplements. And back in 2003, the U.K.'s Food Standards Agency studied 34 vitamins and minerals and found that one could cause cancer, six could induce "irreversible, harmful effects," and three could have "short-term harmful effects."

These cautions come at a time when vitamin and mineral supplement use is at a high — nearly half of Canadian adults have taken a multivitamin in the past month, according to Statistics Canada, and more than one in three children have too. That nutrient supplementation is so popular indicates that people are increasingly taking their health into their own hands. With five million Canadians now doctorless, who can blame them? Plus many don't eat as well as they'd like; vitamins seem to be a quick fix. With relentless media reports that this nutrient can prevent or cure that problem, it's no wonder the nutrient market in Canada is worth at least $400 million this year, says Harrington.

What's missing, however, may be prudence. Taking too many or too much of just one, such as vitamin C, can lead to an overdose that causes diarrhea; in more serious cases, excess vitamin A can induce liver damage. Moreover, some nutrients such as E and K shouldn't be taken in combination with particular medications, including the widely prescribed blood thinner warfarin. Even a history of smoking or kidney disease can put people at more risk for illness or death if they take some vitamins or minerals. Many people don't even talk with their doctor about the nutrients they're taking. Instead they self-prescribe. And then they miss the latest study that contradicts the one that got them started on vitamin supplements in the first place.

Of course, when a person suffers a real deficiency of vitamins or minerals, the use of supplements can produce remarkable results, says Susan Whiting, a member of Dietitians of Canada, and professor and head of nutrition at the University of Saskatchewan. It's universally agreed upon that pregnant women should consume folic acid to prevent birth defects such as spina bifida. And in sun-deprived locations such as Canada in the winter, the case for vitamin D supplementation seems to make sense. Some people in the health care community even declare the use of vitamins and minerals at high doses as the future of personalized medicine, which will see supplements used as drugs in a targeted way.