Seattle Scientists: Supplements Thought To Protect Against Cancer Increase Risk

Feb 21, 2014

Two nutrient supplements once thought to protect against cancer may actually increase the risk of prostate cancer, according to a study led by researchers at Seattle’s Fred Hutchinson Cancer Research Center.

The randomized, double-blind, placebo-controlled study looked at 4,856 men taking large doses of vitamin E and selenium, either alone or together, or a placebo.

Lead author Alan Kristal says taking the supplements appears to significantly raise the risk of prostate cancer.

“For both of these micronutrients, we have no evidence whatsoever that taking these micronutrients is beneficial in any way,” said Kristal, associate program head of the Cancer Prevention Program at Fred Hutch. “And now we begin to identify subgroups of people among whom there’s clear harm.”

How much harm depends on what men’s baseline levels of selenium already were. If they were high, taking selenium supplements nearly doubled their risk of an aggressive kind of prostrate tumor. If the men’s baseline levels were low, taking Vitamin E alone more than doubled their risk (though adding selenium for this group dampened the increase).

“Men using these supplements should stop, period,” Kristal said.

The study is just the latest to link high-dose single-nutrient supplements with a higher risk of cancer. Earlier studies have implicated folate and beta carotene, and more recently, omega-3 fatty acids. In the case of vitamin E and selenium, researchers say the doses present in common multivitamins don’t seem to pose a problem. 

The findings are published in the Journal of the National Cancer Institute