ATLANTA — Your parents may still tell you to take your vitamins, but a cancer doctor might hesitate.

A recent study that found calcium and vitamin D supplements don't reduce the odds of developing breast cancer is the latest to deflate the cancer-prevention claims of some vitamin proponents.

A federal science panel last month had 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.

"There is no vitamin or mineral supplement proven to reduce the risk of cancer," said Eric Jacobs, a senior epidemiologist and vitamin specialist with the American Cancer Society.

However, many doctors continue to recommend daily multivitamins for general health. And some experts say certain supplements may yet prove to be a help in the fight against cancer — once scientists can work out the right amounts and better ways to study their effects.

"I do think there is a fundamental issue of finding the optimal dose of essential nutrients," said Dr. Walter Willett, a professor of epidemiology and nutrition at the Harvard School of Public Health.

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.

Studies also have found that beta-carotene has no impact on the incidence of lung cancer in non-smokers, or prostate or breast cancer. And research has found vitamin B2 and niacin had no impact on the occurrence of cancers, and selenium did not decrease skin cancer in people with a history of that disease.

More recently, a study published in April in the Journal of the National Cancer Institute concluded that a low-dose vitamin A derivative did not prevent head and neck tumors. Earlier research had suggested that higher doses of the derivative cut occurrence of subsequent tumors. But those higher doses caused severe cracking of the lips, eyelid inflammation and other problems, researchers said.