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Selenium and Vitamin E supplementation increase prostate cancer risk (2017-10-24)

A large, randomized trial suggests that taking daily vitamin E supplements may increase a manís risk of prostate cancer.

ďI counsel all of my patients to absolutely avoid any dietary supplements that contain selenium or vitamin Eóincluding multivitaminsĒ says prostate cancer expert Dr. Marc Garnick, a clinical professor of medicine at Harvard Medical School, an oncologist at Beth Israel Deaconess Medical Center, and editor in chief of Harvardís Annual Report on Prostate Diseases.

Studies done in the 1980s and 1990s suggested that vitamin E and selenium each somehow provided protection against prostate cancer.

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was started in 2001 to see if that was true.

The 36,000 healthy, middle-aged volunteers were divided into four groups.

Each man took two pills a day: 400 international units (IU) of vitamin E plus 200 micrograms of selenium; vitamin E plus a placebo; selenium plus a placebo; or two placebos.

Neither the men nor their doctors knew who was taking what.

Although SELECT was supposed to last until 2011, it was stopped three years early because neither vitamin E nor selenium were showing any benefitóand there were hazy warning signs they might be doing some harm.

A new report in the Journal of the National Cancer Institute clarifies the picture.

A team of researchers from across the U.S. looked specifically at almost 5,000 of the SELECT volunteers who sent in toenail clippings when they joined the trial.

Toenail clippings are a great way to measure how much selenium is in a manís (or womanís) body.

The new study showed that:

Taking vitamin E alone boosted the risk of developing high-grade prostate cancer, but only in men who started the study with low selenium levels.

Taking selenium, either alone or in combination with vitamin E, increased the risk of high-grade prostate cancer in men who started the study with high selenium levels, but not in those with low selenium levels.

Among men who didnít take either vitamin E or selenium, those who started the study with high selenium levels were no more likely to have developed prostate cancer than men who started it with low selenium levels.

This means the culprit is added selenium from supplements, not selenium from food.

Men should avoid selenium or vitamin E supplementation at doses that exceed recommended dietary intakes.

For more information
Baseline Selenium Status and Effects of Selenium and Vitamin E Supplementation on Prostate Cancer Risk
The Journal of the National Cancer Institute

Harvard Medical School