Vitamin E, Selenium Can Greatly Increase Prostate Cancer Risk

Alan Kristal, DrPH

Despite being quite popular, the dietary supplements vitamin E and selenium do not protect men from developing prostate cancer, and in fact greatly increase risk in certain patients if taken at doses higher than those recommended within the average diet, according to recently published results from the Selenium and Vitamin E Cancer Prevention Trial (SELECT).

In men with high levels of selenium at baseline, selenium supplements increased the risk of high-grade cancer by 91%, investigators found. Meanwhile, men with low selenium levels at baseline who took vitamin E supplements faced an increased total prostate cancer risk of 63% (P=.02) and an increased high-grade cancer risk of 111% (P=.008).

Led by the Fred Hutchinson Cancer Research Center, SELECT was a multi-center, randomized trial conducted by the SWOG cooperative group that began in 2001 and was stopped 5 years early in 2008 because no data supported the usefulness of selenium in the prevention of prostate cancer, and there was a suggestion that vitamin E increased risk, according to a press release issued by the institution. Participants stopped taking the supplements but were followed for 2 more years, after which those who had taken vitamin E supplements faced a statistically significant 17% increased risk of developing prostate cancer, according to the release.

Also confirmed was an earlier finding from the study: that selenium helps protect men from the harmful effects of vitamin E, the release stated.

In the study, 35,000 men took 400 IU per day of vitamin E and/or 200 mcg per day of selenium; alternatively, they took placebo. Of the participants, 1739 were diagnosed with prostate cancer (including 489 with highgrade disease), while 3117 were not.

Alan Kristal, DrPH, corresponding and first author of the study and a faculty member in the Public Health Sciences Division at Fred Hutchinson, summed up the study’s results in the press release.

“Many people think that dietary supplements are helpful or at the least innocuous. This is not true,” he said. “We know from several other studies that some high-dose dietary supplements— that is, supplements that provide far more than the daily recommended intakes of micronutrients—increase cancer risk. We knew this based on randomized, controlled, double-blinded studies for folate and beta carotene, and now we know it for vitamin E and selenium.”

“Men using these supplements should stop, period. Neither selenium nor vitamin E supplementation confers any known benefits—only risks,” he continued. “While there appear to be no risks from taking a standard multivitamin, the effects of high-dose single supplements are unpredictable, complex, and often harmful. Taking a broad view of the recent scientific studies, there is an emerging consistency about how we think about optimal intake of micronutrients. There are optimal levels, and these are often the levels obtained from a healthful diet, but either below or above the levels there are risks.”