Should You Be Worried About High Doses of Vitamin E and Selenium?

Taking high doses of selenium or vitamin E could raise a man’s risk of prostate cancer.

Starting in 2001, the SELECT trial gave roughly 35,500 men either selenium (200 micrograms a day of selenomethionine), vitamin E (400 IU a day of synthetic alpha-tocopherol), both, or a placebo. In 2008, researchers stopped the trial three years early because it was clear that the supplements were not preventing prostate cancer.

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In a new analysis, researchers compared 489 men in the study who were diagnosed with high-grade prostate cancer (a Gleason score of 7 to 10) during the trial to 3,117 men in the study without prostate cancer. The results:

■ Taking selenium roughly doubled the risk of high-grade prostate cancer among men who started the study with higher levels of selenium (measured in toenail samples), but not among men with lower levels.

■ Taking vitamin E roughly doubled the risk of high-grade prostate cancer among men who started the trial with lower selenium levels, but not among men with higher levels.

Among placebo takers, starting the trial with lower—or higher—selenium levels had no impact on the risk of prostate cancer.

What to do: Don’t take more than the Recommended Dietary Allowance for selenium (55 mcg) or vitamin E (22 IU). Scientists aren’t sure how to explain the results, which agree with other trials that found no lower—and possibly a higher—risk of cancer in people taking high doses of antioxidants.

Source: J. Natl. Cancer Inst. 2014. doi:10.1093/jnci/djt456 and doi:10.1093/jnci/dju005.

4 Replies to “Should You Be Worried About High Doses of Vitamin E and Selenium?”

  1. Another poorly designed study, using synthetic products to test nature’s powers to heal. Instead of or in addition to a (unnamed) placebo, some form of natural vitamin E could have been given. Now that would have been an interesting study! I suspect this one was funded by an entity with vested interests in pharmaceuticals.

    1. From Nutrition Action Heathletter: The study was funded by the U.S. National Institutes of Health, not a pharmaceutical company. Natural vitamin E supplements don’t prevent prostate cancer, either.

      Natural vitamin E failed to prevent prostate cancer in about 3,600 men in a Canadian study called the Heart Outcomes Prevention Evaluation (HOPE) trial which was conducted between 1993 and 2003. In this study of men and women aged 55 or older with vascular disease or diabetes, men who took 400 IU of natural vitamin E every day for seven years were just as likely to be diagnosed with prostate cancer as similar men who were assigned a placebo.

      Study: JAMA. 2005 Mar 16;293(11):1338-47.
      Effects of long-term vitamin E supplementation on cardiovascular events and cancer: a randomized controlled trial.
      Lonn E, Bosch J, Yusuf S, Sheridan P, Pogue J, Arnold JM, Ross C, Arnold A, Sleight P, Probstfield J, Dagenais GR; HOPE and HOPE-TOO Trial Investigators.

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