Their study found that people who get lots of this vitamin in their food have only about half as much bladder cancer as those who take in relatively little. While intriguing, researchers say much more research is needed before they can recommend more than eating plenty of vitamin-rich fruits and vegetables.
Experts once had high hopes that vitamin E would prove to be an important safeguard against heart attacks. But that idea eventually faded as repeated studies failed to show any protective effect.
Now, some think the vitamin may protect against cancer perhaps by warding off the damaging effects of oxygen. The strongest evidence of this so far has been against prostate cancer, and a large federally sponsored experiment is under way to help prove this.
The new study offers a strong hint that dietary vitamin E may also protect against bladder cancer, which kills about 12,500 Americans annually.
The study was based on questionnaires of the eating habits of about 1,000 Houston residents. Those whose vitamin E intake was in the top 25 percent had just half as much bladder cancer as those in the lowest quarter. The actual difference in the amount of vitamin-rich food the two extremes ate was small, however, the equivalent of a single daily serving of spinach or a handful of almonds.
The research was funded largely by the state of Texas. It was presented by John Radcliffe, a nutrition researcher from Texas Woman's University, at a meeting of the American Association for Cancer Research in Orlando.
The reduction was roughly the same, regardless of whether people got their vitamin E from food alone or in combination with vitamin pills.
The team looked at the two most common forms of vitamin E, called alpha- and gamma-tocopherol, and found that only the alpha variety was linked with lower bladder cancer risk. Good sources of this include almonds, spinach, mustard greens, peppers, sunflower seeds and a variety of oils, including olive, cotton seed and canola.
Experts say it is too soon to make any firm recommendations about vitamin E intake for cancer prevention beyond the usual advice to eat plenty of vegetables and other plant-based foods.
"People need not be afraid to incorporate nuts and seeds into their diets," Radcliffe said. "For a long time, dietitians would not recommend them because they are high in fat. But half an ounce to an ounce of nuts and seeds daily would not shoot up someone's calorie levels appreciably."
Researchers would like to tease out which elements of the diet are especially healthful. Many studies have shown that people who eat lots of fruits and vegetables have lower risk of cancer. However, these foods contain more than 100 potentially helpful vitamins, minerals and other substances, and no one knows exactly which components do this.
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 or 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.