But for healthy adults, the jury is out. Whether a daily multivitamin provides any clinical benefit to the average healthy American depends on whom you ask.

"There's no evidence, no hard evidence that in the nutritionally replete, the person who consumes some fruits and vegetables every day, benefits," said Thomas Barringer, M.D., medical director of the center for cardiovascular health at Carolinas Medical Center in Charlotte, N.C. "I don't know why doctors recommend them. But it's very time-consuming trying to talk someone out of doing something that's pretty innocuous."

There are no randomized, double-blinded, controlled studies comparing a multivitamin with a placebo in healthy individuals to determine whether there's any tangible health benefit. Such a study would be costly and time-consuming. Experts on both sides of the issue agree on this point.

Where experts begin to disagree is whether the kind of evidence that currently exists on vitamins show any clinical benefit. The U.S. Preventive Services Task Force doesn't seem to think so.

In the July 1, 2003 issue of Annals of Internal Medicine, the task force said that "the best studies suggested no clear benefit of taking vitamins" and there was "insufficient scientific evidence to recommend vitamin supplements as a way to prevent cancer or heart disease." Their conclusions were based on a review of the literature.

The benefits of vitamin supplementation for the general population, said Janet Allen, Ph.D., R.N., vice chair of the task force, "remain uncertain."