Some wonder whether people who often eat fruits and vegetables have healthier living habits overall, so their diets might have little real importance. For now, the best scientists can do is recommend that people eat five more servings daily of a variety of vegetables and fruits.

The strongest evidence of vitamin E's cancer effects comes from a study several years ago on nearly 30,000 Finnish smokers. It unexpectedly found those who took alpha-tocopherol pills lowered their prostate cancer risk by one-third. The same study shocked researchers by showing that another once high-flying nutrient, beta carotene, appeared to actually increase their risk of lung cancer.

A National Cancer Institute study now under way is testing the effects of 400 milligrams of vitamin E and 200 micrograms of selenium daily on more than 32,000 men for seven years to see if they reduce prostate cancer.

Dr. David Alberts, head of cancer prevention at the University of Arizona, said studies like Radcliffe's "are extremely helpful in raising a hypothesis. It is very difficult to make a recommendation" that people take vitamin supplements without a carefully conducted experiment, like the ongoing prostate cancer study.

The recommended U.S. intake of vitamin E is 15 milligrams daily, which is roughly the amount in a multivitamin.