often receive calls and e-mails from "health professionals," who frequently recommend vitamin supplements for preventing cancer.

Unlike many consumers, they are not confusing important vitamins and minerals in foods with supplements. They're touting supplements because they're in the business of making money and often sell to vulnerable consumers.

But science continues to knock down supplement claims one after another.

A federal science panel recently concluded there is no evidence for recommending certain vitamin supplements for cancer prevention. Even the Council for Responsible Nutrition, a supplement trade association, won't say vitamins prevent cancer.

Also, a recent study found that calcium and vitamin D supplements don't reduce the odds of developing breast cancer.

"So far no study has shown any vitamin can prevent cancer, and if there's no proven benefit, people should not be taking vitamins to prevent cancer," said Dr. Vikram Chand, a Gundersen Lutheran cancer specialist. "Also megadoses of vitamins have been shown to be detrimental."

If people have a well-balanced diet, they don't need to take vitamin supplements, Chand said.

"I think people are looking for a quick fix with vitamin supplements," said Dr. Haleem Rasool, a Franciscan Skemp-Mayo cancer specialist. "A lot of money is spent on vitamins with no shown benefit. If you eat healthy, you don't need vitamins unless you have a deficiency."

Rasool said he doesn't take a multivitamin. But Chand said at least no studies have shown a multivitamin is harmful.

"If you're being sold vitamin supplements as a way to prevent cancer, ignore the sales pitch," Rasool said.

More than half of Americans are taking dietary supplements -- mostly multivitamins, according to the National Institutes of Health panel that critiqued supplemental vitamins.

Scientists once suspected vitamin E and beta carotene prevented lung cancer after a study showed people who took supplements appeared to have lower cancer incidence.

But a larger, more scientifically rigorous study found 50 milligrams a day of alpha-tocopherol, a form of vitamin E, had no effect on lung cancer incidence. And 20 milligrams of beta carotene, a precursor of vitamin A, actually increased lung cancer incidence in smokers by 18 percent. Health officials now warn smokers not to take beta carotene supplements.

Rasool would like to see patients take the money spent on vitamin supplements and use it to stop smoking or buy a fitness club membership.

"If we take better care of ourselves, we wouldn't think we need vitamin supplements," he said.

Both Rasool and Chand said they wouldn't dismiss vitamins completely, now and forever.

"Some day science could prove otherwise," Chand said. "That's why we need to continue the studies."