VOA常速英语:Study Shows Vitamin E Increases Prostate Cancer Risk

A number of medical studies over the years suggested that vitamin E, taken as a dietary supplement, might help prevent prostate cancer.  But new research finds not only that the earlier studies were wrong, but that taking vitamin E can actually be harmful.

For years, many doctors thought taking vitamin E could help prevent many types of cancer, including prostate cancer.  So, they told their male patients to take a daily supplement.  Some doctors also recommended selenium, an essential trace mineral, to prevent cancer.  

Then Dr. Eric Klein at the Cleveland Clinic began a study to see if vitamin E and selenium could reduce the risk of prostate cancer by up to 25 percent.  In the study of 35,000 men, researchers did not know who took vitamin E, who took selenium and who took placebos.

Pat Garrity was one of the participants.

"I thought it was an opportunity because of the large study base to get some factual data to prove or disprove the idea that selenium or Vitamin E might be beneficial," said Garrity.

The study began in 2001.  It ended early, in 2008, because the researchers saw no benefit from taking either supplement.  But the data showed something else.

"We did notice, at the time the original study was closed, that men who were taking vitamin E alone were trending toward having a higher risk of prostate cancer," noted Klein.

So the researchers continued to monitor the men after they stopped taking the supplements.  Many of the men continued to be monitored until last year.  That is when researchers realized the true impact of vitamin E.

"The results showed that men who took vitamin E were at a higher risk of developing prostate cancer by about 17 percent," added Klein.

The results on selenium are still being studied.

Dr. Klein says the effects of dietary supplements can linger after a person stops taking them.  That is why researchers are asking participants to see their doctors regularly and to take part in a long-term study on vitamin E supplements. Dr. Klein's study was published in the Journal of the American Medical Association.