Many have touted vitamin E for its antioxidant properties that can repair cell damage and, some hoped, prevent both heart disease and cancer. Clinical studies have undercut these hopes, though some have argued that those studies didn't follow their subjects long enough. Researchers in the Heart Outcomes Prevention Evaluation trial, which began in 1993, extended their research through 2003 to see if participants in that trial saw any benefit.

What the researchers wanted to know: Does long-term use of vitamin E prevent heart disease and cancer?

What they did: In an initial study, launched in 1993, researchers enrolled more than 9,500 patients, all of them at least 55 years old with a history of heart or vascular disease, stroke, or diabetes. Half then took a daily vitamin E supplement, and the other half took a placebo. The study ended in 1999, but the researchers asked the participants to continue, and about half of them agreed.

What they found: The number of people in each group who developed heart disease or cancer did not differ significantly, suggesting that vitamin E does not reduce the risk of either of these two diseases. Moreover, the rate of heart failure in participants who took vitamin E was about 13 percent higher, a small but meaningful difference. The researchers say that they don't have a good explanation for the relationship between vitamin E and heart failure.

What it means to you: This study adds to the evidence that vitamin E supplements are unlikely to prevent heart disease or cancer and should not be taken to achieve those goals. In an accompanying editorial, cancer researcher Greg Brown and cardiologist John Crowley say that the study "closes the door" on the idea of taking vitamin E to prevent heart disease or cancer; they advise against taking it for prevention, especially given that the risk of heart failure is slightly increased.

Caveats: Not all of the patients continued after the first trial, but the demographics of the second sample matched those of the first. The researchers say that dropouts probably did not skew their results.

Find out more: Even though vitamin E doesn't seem to prevent cancer or heart disease, some is needed for a healthy diet. For information on the vitamin and the controversy about its protective benefits, check out a nutrition fact sheet from the federal Office of Dietary Supplements.

Another good summary of vitamin E's benefits (or lack thereof) can be found in the University of California–Berkeley's Wellness Letter.

Read the article: HOPE and HOPE-TOO Trial Investigators, "Effects of Long-term Vitamin E Supplementation on Cardiovascular Events and Cancer." Journal of the American Medical Association. March 16, 2005, Vol. 293, No. 11, pp. 1338-1347.

Abstract online: http://jama.ama-assn.org