Americans want to believe in vitamin and mineral pills: We spent an estimated $10 billion on them in 2008, according to the Nutrition Business Journal.
But recent studies undertaken to assess their benefits have delivered a flurry of disappointing results. The supplements failed to prevent Alzheimer's disease, cancer, heart attacks, strokes, type 2 diabetes, and premature death.
"We have yet to see well-conducted research that categorically supports the use of vitamin and mineral supplements," says Linda Van Horn, Ph.D., a professor of preventive medicine at Northwestern University's Feinberg School of Medicine in Chicago. "Most studies show no benefit, or actual harm."
The power of food
While some people may need supplements at certain stages of their lives, nutritional deficiencies are uncommon in the U.S. "Almost all of us get or can get the vitamins and minerals we need from our diet," says Paul M. Coates, Ph.D., director of the Office of Dietary Supplements at the National Institutes of Health (NIH).
Major health organizations for cancer, diabetes, and heart disease all advise against supplements in favor of a healthful diet rich in fruits, vegetables, whole grains, and legumes. Unlike pills, those foods contain fiber plus thousands of health-protective substances that seem to work together more powerfully than any single ingredient can work alone. "That's why it's dangerous to say, 'I know I don't eat well, but if I pop my vitamins, I'm covered,' " says Karen Collins, R.D., nutrition adviser to the American Institute for Cancer Research. "We now know that you're not covered."
Too much can harm
Another concern is that some vitamin pills can be toxic if taken in high doses for a long time. Studies show that beta-carotene pills, for example, can increase the risk of lung cancer in smokers, and a 2008 review suggests that the pills, plus supplemental doses of the vitamins A and E, may increase the risk of premature death. In addition, a government survey found that more than 11 percent of adults take at least 400 international units of vitamin E a day, a dose that has been linked to heart failure, strokes, and an increased risk of death.
People are also apt to combine vitamin tablets and fortified foods, which can cause problems. For instance, too much folic acid—added to wheat products in this country—can mask vitamin B12 deficiency. Untreated, that can lead to irreversible nerve damage. In addition, high doses of folic acid may be associated with an increased risk of precancerous colon polyps, according to a trial of some 1,000 people at risk for them. "We're getting several alarming signals that more may not be better," says Susan T. Mayne, Ph.D., a professor of epidemiology at the Yale School of Public Health.
Yet despite the unfavorable results, vitamin and mineral pills are widely used to fend off diseases. Read on to find our review of the latest evidence on their effects.
This story first appeared in the February 2010 issue of Consumer Reports on Health