Cancer prevention trial (SELECT) comes to a halt

Marc B. Garnick, M.D., puts the latest findings on selenium and vitamin E into perspective

For men everywhere, the news was disappointing. At the end of October 2008, the National Cancer Institute (NCI) announced that a study designed to test whether selenium and vitamin E, taken alone or in combination, could lower the risk of prostate cancer was ending early; researchers had grown concerned that taking the supplements might do more harm than good. It wasn’t the conclusion we were expecting.

Based on earlier data, researchers had had high hopes for selenium and vitamin E as cancer fighters. Though a study of selenium and skin cancer first reported in 1996 found that the supplement offered no protection against skin cancer, researchers discovered that the incidence of prostate cancer was 63% lower among men who had taken selenium for about six-and-a-half years than among men who had taken a placebo. A 2002 follow-up report showed that among men who took selenium for more than seven-and-a-half years, the incidence was 52% lower.

In that same vein, a 1998 study of supplements and lung cancer in 29,133 male smokers in Finland reported 32% fewer cases of prostate cancer and 40% fewer prostate cancer–related deaths among men who took vitamin E than among men who took a placebo. Some men in that trial also took beta carotene supplements, but neither substance did anything to prevent lung cancer, and beta carotene did not affect prostate cancer rates. (To read these studies on your own, see “Early selenium and vitamin E studies.”)

Neither of those studies, however, was specifically designed to measure changes in prostate cancer risk. Many variables, such as the age of participants and their family history, could have skewed the results. So in 2001, researchers launched SELECT, short for the Selenium and Vitamin E Cancer Prevention Trial, enrolling more than 35,000 male volunteers. Participants were randomly assigned to take one of these combinations daily:

• 200 micrograms (mcg) of selenium and 400 international units (IU) of vitamin E
• 200 mcg of selenium and a placebo
• 400 IU of vitamin E and a placebo
• Two placebos

The placebos looked exactly like the supplements. Neither the participants nor the researchers knew who received which combination.

The trial had been expected to run until 2011. But in reviewing an average of five years’ worth of data, the independent Data and Safety Monitoring Committee found that the supplements, taken alone or together, did not prevent prostate cancer.

Two worrisome — though not statistically significant — trends also emerged: there were slightly more cases of prostate cancer in men taking only vitamin E and slightly more cases of diabetes in men taking only selenium. True, these findings could be due purely to chance. But noting the lack of any benefit and the potential risks associated with the supplements in this trial, researchers appropriately brought SELECT to a close.

Patients have asked me if they should stop taking multivitamins because they contain selenium and vitamin E. A typical multivitamin contains about 50 mcg of selenium and 200 IU (or less) of vitamin E, much less than was prescribed for SELECT participants. Still, there is no evidence that multivitamins prevent heart disease, cancer, or other illnesses. If you are taking a multivitamin, you might drop it in favor of simply taking vitamin D, the only component that you’re not likely to get enough of from foods.

The results of SELECT serve as a reminder that vitamins, nutritional supplements, and so-called natural remedies need to be thoroughly studied before people use them to prevent disease. Some may indeed prove efficacious in time, but until then, savvy consumers should save their money and work to lower their cancer risk by making some tried-and-true lifestyle changes.

First, lose weight if you are overweight. Men who are obese have a higher risk of developing prostate cancer, especially the more aggressive type. Losing weight can bring that risk way down. One study showed that, compared with men who held their weight steady, men who lost more than 11 pounds enjoyed a 42% lower risk of being diagnosed with high-grade prostate cancer.

Next, look at your diet. Consuming certain foods, such as red, fatty, and processed meats and an excessive amount of dairy products, may increase your risk of prostate cancer. Foods that may decrease risk include fish, especially fatty fish like salmon and sardines, leafy green vegetables, broccoli, and tomatoes. Why tomatoes? Some evidence suggests that men who eat more tomatoes, which are rich in lycopene along with oils to aid absorption, have a lower risk of prostate cancer. It remains unclear whether lycopene, some other nutrient, or a combination of nutrients underlies the protective effect of tomatoes. Clinical trials sponsored by the NCI will assess the value of lycopene and other agents, such as soy and green tea extract.

Even if these steps do little to influence your prostate cancer risk, they’ll likely improve your health in other ways. And given that most men with prostate cancer now die with their disease, not from it, watching your weight, sticking with a heart-healthy diet, and exercising regularly are your best bets.

For more information about SELECT, visit www.cancer.gov.

Related content: Disappointing results for Vitamin E and selenium supplements

Originally published March 2009; last reviewed February 24, 2011.