Do multivitamins work?

Find out whether you should take multivitamins and vitamin supplements.

By Joe Schwarcz

Do multivitamins work: Are there health benefits to taking vitamins?
Vitamins are certainly essential components of the diet and prevent the classic vitamin-deficiency diseases like rickets and scurvy. But some vitamins also have antioxidants properties, which brings up the question of their possible additional benefits.

So should we be taking vitamin supplements?

A pretty simple question to answer, one might think. After all, there have been literally thousands of studies on how vitamin and mineral intakes relate to health. More than 100 million people in North America believe the question has been answered and take a variety of daily supplements to protect themselves against disease, spending some $25 billion in the process. But could they be on the wrong track?

The role of supplements
There are several ways to investigate the potential role of supplements. Surveys can identify those people who take supplements and make correlations to their health status. Alternatively, researchers can measure blood levels of specific antioxidants and relate the finding to disease patterns. Or they can carry out intervention studies in which results are evaluated after subjects take either the substance being tested or a placebo over an extended period. Finally, a "meta-analysis" can be undertaken in which the results of various high-quality studies are pooled to reveal information that is not apparent from looking at single studies.

A typical survey-type, or "observational," study involved over 83,000 healthy American physicians who filled out questionnaires about supplement intake and dietary habits. Roughly 30 percent of the doctors regularly took vitamin supplements. After about six years, 1,000 or so had died of some form of cardiovascular disease. Were the deceased more or less likely to have been taking antioxidant supplements? As it turned out, there was no relationship between supplement intake and cardiovascular death.

Of course, it is possible that physicians are more health conscious that others and pay more attention to their diet, so that they already had a sufficient intake of antioxidants. Some studies have even shown a negative supplement effect. Analysis of data collected from some 70,000 postmenopausal nurses showed that over an 18-year period, those who consumed the most vitamin A from food or from supplements had the greatest risk of bone fractures. On the other hand, low vitamin E intake during pregnancy has shown to increase the risk of childhood asthma, and women who take vitamin supplements during pregnancy appear to have a reduced risk of having infants who develop brain tumours.

Vitamin C
How about studies of blood levels of vitamins? English researchers in one case found that among 20,000 people, those who had the highest level of vitamin C in the blood lived the longest. But was this because of the vitamin C, or was the vitamin C just acting as a marker for increased fruit and vegetable intake? Low levels of folic acid have been linked with breast cancer, heart disease and, most significantly, with giving birth to babies with neural tube defects. Still, such studies do not show cause and effect. You can never be certain that the observations are not due to some other dietary factor that happens to parallel folic acid in its presence. That's why intervention studies are the most meaningful. And in the case of folic acid in pregnant women, they certainly back up the observational studies. Supplementing the diet with 400 micrograms of folic acid daily significantly reduces the risk of neural tube defect.

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Excerpted from An Apple a Day: The Myths, Misconceptions and Outright Exaggerations about Diet, Nutrition and the Foods We Eat. Published by HarperCollins Publishers Ltd. Copyright 2007 by Dr. Joe Schwarcz. All rights reserved. Reprinted by permission of HarperCollins Publishers Ltd.

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