If you are a health news junkie, you’ve probably found yourself frustrated by what seems like completely contradictory information. For example, one day a perfectly sound study will show that a certain supplement does something great, and the next day another study will show that it’s no better than a sugar pill. Results that don’t agree make it hard to know what to believe. But we can find the truth if we really know how to look. And that’s the case right now with the mineral selenium. If you are interested in preventing cancer—particularly prostate cancer—you’ll want to see exactly how some conflicting studies about selenium supplements can be unraveled to get to the truth.


Selenium has strong antioxidant properties, and many studies have shown that cancer is less likely to develop in people who have more selenium in their diets. But there has been a lot of controversy about how effective it is in preventing prostate cancer. One large study showed selenium supplementation cut risk of prostate cancer by up to two-thirds, while another large study showed that it was no better than a placebo.

Where does the truth lie? In the not-so-fine print, actually, because some new research has brought to light what may be obvious but easily missed. It turns out that the particular type of selenium supplement used may make it a hit or miss when it comes to protection against prostate cancer.

The study that showed a drastic reduction in prostate cancer used a supplement made of selenium yeast, which is yeast that has been enriched with selenium. The study that showed no effect used a supplement made of selenomethionine, which is the amino acid that contains selenium. To find out why one type of a selenium supplement was effective and another not in terms of prostate cancer protection, a research team recruited 69 healthy men between the ages of 23 and 78 to participate in a year-long study. The men were divided into four groups—one group received a placebo, one group received the maximum daily recommended dosage of selenium (200 micrograms per day) in the form of selenomethionine, another group received the maximum daily dosage in the form of selenium yeast and, because higher doses of selenium yeast are currently being studied as therapy for prostate cancer, the last group received a higher dosage (285 micrograms per day) of selenium yeast.

Before starting the study and at three, nine and 12 months, all of the men had blood and urine tests to evaluate levels of selenium and prostate specific antigen (PSA, a marker for prostate cancer) as well as signs of oxidative stress related to prostate cancer development.

The results: Although blood levels of selenium increased in all of the men taking any form or dose of selenium, they substantially increased in the men taking selenomethionine (by 93%) and high-dose selenium yeast (86%). You would think that the higher the blood level, the higher the prostate cancer protection, but the study findings hinted that this may not be the case—the only form of selenium that had an impact on oxidative stress in this particular study was high-dose selenium yeast. The researchers theorized that, although selenomethionine may be able to get more selenium into the blood than selenium yeast, it may be missing the compounds that reduce oxidative stress in the prostate gland or allow sufficient absorption of selenium into prostate gland tissue.

Selenium is naturally found in seafood, meats, grains and eggs. Adults should get at least 55 micrograms per day, according to the National Institutes of Health. Most people in the United States who maintain well-balanced diets get enough selenium, although studies show that selenium levels are commonly low in men with prostate cancer. But if you are a man concerned about prostate health, get your selenium level checked first to find out whether taking a selenium yeast supplement is right for you. Getting too much selenium, such as from going overboard with supplement use, can cause gastrointestinal, cardiovascular and kidney problems.