High levels of selenium may increase type 2 diabetes risk

Selenium at high levels might increase the risk of type 2 diabetes, according to a Bloomberg News report on a scientific review published in The Lancet journal.

The study from University of Surrey in the UK warns that people who want to avoid increasing their risk of developing diabetes should avoid selenium supplements if their selenium levels are 122 micrograms per liter or higher in the blood.

People who take a 200 microgram daily dose of selenium for seven years have a 50 percent higher risk of developing type 2 diabetes than people on a placebo, according to a 2007 study at the Warwick Medical School in the UK.

Selenium is a trace mineral that is essential to good health but is required only in small amounts, according to the National Institutes of Health (NIH).

Selenium incorporates into proteins to make selenoproteins, important antioxidant enzymes. Selenoproteins help prevent cellular damage from free radicals that may contribute to developing cancer and heart disease.

Other selenoproteins help regulate thyroid function and play a role in the immune system, according to NIH.

“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,” according to The Lancet. “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.”

Food sources
Plant foods grown in selenium-rich soil are the major sources of naturally occuring selenium. Some meats and seafood also have the mineral. The selenium content in food depends on the mineral content of the soil where plants are grown or animals graze.

Brazil nuts have a particularly high level of selenium and should be eaten only occasionally. Other food sources of selenium include tuna, cod, turkey, chicken breast, sunflower seeds, pasta, eggs, oatmeal, and cottage cheese.

Selenium intake is higher in the US, Canada and Japan. Intake is lower in Europe. Selenium deficiency is rare in the US but seen in other countries like China, where soil concentration of selenium is low and consumers eat only locally grown foods.

Selenium deficiency makes the body more susceptible to illnesses caused by other nutritional, biochemical or infectious stresses, according to NIH.

Selenium deficiency may contribute to developing hypothyroidism, a heart disease called Keshan Disease, and a weakened immune system.

Sources: National Institutes of Health, Bloomberg News