In 2001, researchers from the National Cancer Institute (NCI) and the Southwest Oncology Group (SWOG) launched the massive SELECT study (short for Selenium and Vitamin E Cancer Prevention Trial) to find out whether taking selenium and vitamin E supplements could protect men from prostate cancer. In October 2008, researchers halted the trial after early analysis showed the supplements weren't working, and in fact, in some cases, may have been doing more harm than good.

More than 35,000 men over age 50 in the US, Puerto Rico, and Canada were enrolled in the trial. Each participant was randomly assigned to take either selenium, vitamin E, a combination of the two, or a placebo for the course of the study. After an average of 5 years, the analysis found no lower risk of prostate cancer in men taking the supplements, either alone or together.

Men who were taking only vitamin E actually had a slightly higher risk of developing prostate cancer. And men taking only selenium seemed to have a slightly higher risk of developing diabetes. This increased risk was not statistically significant in either case. That means the findings could be due to chance; they don't prove the supplements raise prostate cancer and diabetes risk. Still, researchers called the findings "concerning."

The men in the study were told to stop taking their study pills. The researchers plan to continue monitoring the participants for about 3 more years to see if there are long-term effects (good or bad) from taking the supplements.

In another large, long-term trial, called the Physicians' Health Study II, researchers from Brigham and Women's Hospital and Harvard Medical School studied whether taking vitamin E or vitamin C could reduce the risk of prostate cancer. Nearly 15,000 male doctors participated in the trial. After an average of 8 years, neither vitamin E nor vitamin C seemed to lower the risk of prostate cancer. However, taking the supplements also did not appear to cause any harm.

The results of both studies were published in the January 7, 2009 issue of the Journal of the American Medical Association.

So, what can you do to reduce your risk of prostate cancer? While it now seems unlikely that specific supplements will have a major effect on risk, other factors, such as maintaining a healthy weight and eating a healthy diet, may still play a role. Following the American Cancer Society’s guidelines for nutrition and physical activity may lower prostate cancer risk, and can clearly have other health benefits, including reducing the risk of some other cancers.

• Maintain a healthy weight. While being overweight or obese has not been strongly linked to prostate cancer risk, it does seem to raise the risk of getting more aggressive forms of prostate cancer, which could be harder to treat. 
• Get at least 30 minutes of moderate to vigorous physical activity, above usual activities, on 5 or more days of the week. The effect of exercise on overall prostate cancer risk is not clear, but some studies have suggested that getting more physical activity may reduce a man’s risk of advanced prostate cancer. 
• Try to eat at least 5 servings of vegetables (including legumes) and fruits each day. The more brightly colored the produce, the better – it's more likely to be packed with cancer-fighting, heart-healthy nutrients.
• Aim for at least 3 servings of whole grains each day. Eat oatmeal at breakfast, choose whole-wheat bread at lunch, or use brown rice at dinner instead of white.
• Cut back on red meats, especially high-fat or processed meats – they have been linked to an increased risk.

Tomatoes (raw, cooked, or in tomato products such as sauces or ketchup), pink grapefruit, and watermelon are rich in lycopenes, antioxidants that help prevent damage to DNA. Some studies have suggested lycopenes may help lower prostate cancer risk, although a more recent study found no link between blood levels of lycopene and risk of prostate cancer. Research in this area continues.

For more information, see "What are the risk factors for prostate cancer?" and "Can prostate cancer be prevented?"

"Effect of Selenium and Vitamin E on Risk of Prostate Cancer and Other Cancers." Published in the January 7, 2009 issue of the Journal of the American Medical Association. Corresponding Author: Scott M. Lippman, MD, Department of Thoracic and Head and Neck Medical Oncology, University of Texas M. D. Anderson Cancer Center, Houston, Texas.

"Vitamins E and C in the Prevention of Prostate and Total Cancer in Men: The Physicians' Health Study II Randomized Controlled Trial." Published in the January 7, 2009 issue of the Journal of the American Medical Association. Corresponding author: J. Michael Gaziano, MD, MPH, Brigham and Women's Hospital, Boston, Massachusetts.