WASHINGTON, July 9 (Reuters) - People who take selenium supplements in the hope of preventing diabetes may actually worsen their odds, U.S. researchers said on Monday.
An unusually well-controlled trial showed that people who took selenium pills raised their risk of diabetes by more than half, compared to similar people taking placebos.
The trial is one of a few surprising studies that have found vitamin and mineral supplements can sometimes do more harm than good.
"I would not advise patients to take selenium supplements greater than those in multiple vitamins," said Dr. Saverio Stranges of Warwick Medical School in Britain, who led the study.
Stranges, formerly of the State University of New York at Buffalo, and colleagues were studying another idea -- whether selenium supplements could prevent skin cancer.
But there was research suggesting the mineral might help prevent diabetes.
The Stranges team looked at 1,202 people taking selenium for the skin cancer trial who did not have diabetes at the beginning of the study.
50 PERCENT GREATER RISK
Half took a 200 microgram selenium supplement and half received a placebo pill for an average of 7.7 years.
Reporting in the Annals of Internal Medicine, the researchers said 58 of 600 people taking selenium and 39 of 602 taking placebos developed type-2 diabetes over the 7.7 years.
That is an increase in relative risk of about 50 percent.
About 60 percent of Americans take multivitamin pills, many of which contain between 33 and 200 micrograms of selenium, in addition to the selenium taken in from food and the air.
The higher a person's normal blood level of selenium, the worse the risk of diabetes, the researchers said.
"The U.S. public needs to know that most people in this country receive adequate selenium from their diet," Dr. Joachim Bleys, Dr. Ana Navas-Acien and Dr. Eliseo Guallar, all of Johns Hopkins University in Baltimore, wrote in a commentary.
"By taking selenium supplements on top of an adequate dietary intake, people may increase their risk for diabetes."
The original cancer trial found that those who took selenium had a somewhat lower risk of dying from cancer, although the supplements did not lower the risk of getting skin cancer in the first place.
Another surprising study found that smokers who took beta-carotene supplements raise their risk of cancer.
