MONDAY, July 9, 2007 (HealthDay News) -- Selenium supplements appear to increase the risk of type 2 diabetes, a new study suggests.
The chances of developing the blood sugar disease was higher in people who had high blood selenium levels, according to the report in the July 10 online edition of the Annals of Internal Medicine.
"The hypothesis was that, because of its antioxidant properties, selenium could be beneficial in diabetes prevention," explained lead researcher Dr. Saverio Stranges, from the Warwick Medical School, in Coventry, U.K. "Actually, long-term selenium supplementation did not have any benefits in diabetes prevention and actually increased the risk for this disease."
Selenium is a mineral found in soil and foods. Selenium is used by the body to aid in metabolism. Selenium supplements have been widely promoted for conditions such as cold sores, shingles, arthritis and multiple sclerosis. These supplements are also sold to prevent aging, enhance fertility, prevent cancer and get rid of toxic minerals such as mercury, lead and cadmium.
Selenium supplements have shown some promise in preventing cancer, including prostate cancer and lung cancer, Stranges noted. "There are ongoing clinical trials to determine if selenium can be beneficial in cancer prevention," he said.
In the study, Stranges and his colleagues collected data on 1,202 patients who participated in the Nutritional Prevention of Cancer Trial. During the trial, half the patients received a daily 200 microgram selenium supplement or placebo.
The researchers found that 58 out of 600 people in the selenium group and 39 of the 602 in the placebo group developed type 2 diabetes. During 7.7 years of follow-up, Stranges' team noted that the risk of developing type 2 diabetes was approximately 50 percent higher among those taking selenium compared with those taking a placebo.
"Most people in the United States have adequate selenium in their diet," Stranges said. "Taking selenium on top of an adequate dietary intake may cause diabetes."
Some 60 percent of Americans take multivitamin pills, many containing between 33 and 200 micrograms of selenium. The recommended dietary allowance for selenium varies by age. For people aged 14 and over, 55 micrograms per day is recommended.
"Right now, there is no conclusive evidence of the benefits of selenium in chronic disease prevention," Stranges said. "People can get all of the antioxidants they need from the diet."
One expert thinks that, while not proven, the increased risk of developing diabetes by taking selenium supplements is concerning.
"We probably get enough selenium in our diet, and there is no reason to take supplements," said Dr. Eliseo Guallar, from Johns Hopkins University Bloomberg School of Public Health and author of an accompanying editorial.
Guallar doesn't think that this single study proves that selenium increases the risk for diabetes. "But it's enough to say this is worrisome. The risk appears high enough that people should be concerned," he said. "Until we know for sure that there are benefits from these supplements, it doesn't make sense to be taking them."
Another expert also thinks there is probably no value in taking supplemental selenium.
"We Americans are so quick to take stuff," said Dr. Larry Deeb, president for medicine and science at the American Diabetes Association. "If they put it in a pill, we'll take it. But it doesn't always work for you."
Deeb isn't sure that taking selenium is dangerous. "But why would you take selenium for something to do?" he said. "I don't see a good reason to take selenium. It's certainly not to prevent diabetes -- that's for sure."
The National Institutes of Health can explain selenium.