The public has been whipsawed by good and bad news about vitamins, much of it from test-tube or animal studies and hyped manufacturer claims. Even when researchers compare people's diets and find that a vitamin seems to help, the benefit may not translate when that nutrient is obtained a different way, such as a pill.

"Antioxidants, which include vitamin C and vitamin E, have been shown as a group to have potential benefit," but have not been tested individually for a long enough time to know, said Howard Sesso of Harvard-affiliated Brigham and Women's Hospital in Boston.

The Physicians Health Study, which he helped lead, was designed to do that. It involved 14,641 male doctors, 50 or older, including 1,274 who had cancer when or before the study started in 1997. They were included so scientists could see whether the vitamins could prevent a second cancer.

Participants were put into four groups and given vitamin E, vitamin C, both, or dummy pills. The dose of E was 400 international units every other day; C was 500 milligrams daily.

After an average of eight years, there were 1,929 cases of cancer, including 1,013 cases of prostate cancer, which many had hoped vitamin E would prevent.

However, rates of prostate cancer and of total cancer were similar among all four groups.

The study was funded by the National Institutes of Health and several vitamin makers. Results were being reported Sunday at an American Association for Cancer Research conference in Washington.

"Well-conducted clinical trials such as this are rapidly closing the door on the hope that common vitamin supplements may protect against cancer," said Marji McCullough, nutrition chief at the American Cancer Society. "It's still possible that some benefit exists for subgroups that couldn't be measured, but the overall results are certainly discouraging.

"The American Cancer Society recommends getting these and other nutrients by eating a mostly plant-based diet with a variety of vegetables, fruits and whole grains. A bonus is that this type of diet helps to prevent obesity, which increases the risk of several cancers."

About 12 percent of Americans take supplements of C and E. The new study does not mean these vitamins have no value, just that they didn't prevent cancer in this group of doctors, who may be healthier than the general population, said Dr. Peter Shields, deputy director of Georgetown University's Lombardi Comprehensive Cancer Center.

The best bet, he said, is to do things that are known to prevent the disease - eat right, maintain a healthy weight, and exercise.