High Selenium Levels May Raise Diabetes Risk, Review Says

Supplements of selenium, a trace mineral that may help prevent some cancers, might increase the risk of Type 2 diabetes if taken in large quantities, according to a review of existing studies.

To help prevent raising the chance of developing diabetes, people with selenium levels of 122 micrograms per liter or higher in their blood shouldn’t take selenium supplements, Margaret Rayman, a professor of nutritional medicine at the University of Surrey in the U.K., said in the review published today in The Lancet medical journal. Rayman surveyed studies published between January 1990 and February 2011.

Selenium is a naturally occurring mineral found in soil and foods and is essential in small amounts for good health. A low selenium level in the blood has been linked with an increased risk of death, poor immune function, and cognitive decline. A healthy level has been shown to enhance male fertility, have antiviral effects and provide some protection against cancers of the prostate, lung, colon and bladder.

“Over the last 10 years, the use of selenium supplements has become widespread, largely due to the belief that selenium can reduce the risk of cancer and other diseases,” The Lancet said in a statement today. “But the evidence also suggests that selenium has a narrow therapeutic range and at high levels might have harmful effects such as increasing the risk of Type 2 diabetes.”

Varied Levels

People who take a 200-microgram daily dose of the mineral for seven years have a 50 percent higher risk of developing Type 2 diabetes, compared with those on a placebo, according to a 2007 study at the Warwick Medical School in the U.K.

Selenium levels vary significantly worldwide, with higher intake in the U.S., Canada and Japan and less consumption in Europe, said Rayman, the researcher. Average intake for Britons is below recommended levels, said Graham Keen, executive director of the Health Food Manufacturers Association in the U.K., in an e-mailed statement.

“This shows that for many in the U.K., there is a strong need to increase selenium in their diet,” Keen said.

Diabetes is a chronic illness in which the body either doesn’t produce enough insulin to process blood sugar or fails to use insulin effectively. About 552 million people, or one in 10 adults, may have diabetes by 2030, compared with about 366 million now, if nothing is done to curb the epidemic, the International Diabetes Federation said in a report in November. As many as 183 million people have the disease and don’t know it, the Brussels-based federation said.

Type 2 diabetes, often the result of excess body weight and lack of physical activity, accounts for at least 90 percent of all cases of the disease, according to the federation. Type 1 diabetes develops early in life and robs people of their ability to make insulin, according to the World Health Organization. While the exact cause of Type 1 is unknown, scientists believe it occurs when the immune system attacks the pancreatic cells that produce insulin.

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