NEW YORK (Reuters Health) - Contrary to researchers' expectations, high blood levels of selenium are positively associated with diabetes in adults, according to findings published in the medical journal Diabetes Care.

The results of some animal studies have suggested that oxidative stress reduces insulin secretion and increases insulin resistance, Dr. Joachim Bleys and colleagues from Johns Hopkins University Bloomberg School of Public Health, Baltimore, point out. They therefore hypothesized that because selenium has antioxidant properties, high levels of selenium in the body may prevent diabetes.

Selenium is a mineral required in small amounts to maintain good health. This mineral is necessary to generate antioxidant proteins that help prevent cell damage from free radicals, which are thought to contribute to the development of chronic diseases. Selenium also has a role in regulating thyroid gland function and the immune system.

To test their hypothesis, the researchers conducted an analysis of data from 8,876 subjects, at least 20 years of age, who participated in the Third National Health and Nutrition Examination Survey.

The team defined diabetes as a fasting blood sugar level of at least 126 milligrams per deciliter; patient reports of a physician's diagnosis of diabetes; or the current use of insulin or an oral diabetes medication.

The results of the study ran counter to what was anticipated. After accounting for the potential effects of age, sex, race, and weight, the researchers found that blood levels of selenium were 126.8 nanograms per milliliter in diabetics and 124.7 nanograms per milliliter in subjects without diabetes, a statistically significant difference.

Upon further analysis, the researchers found that subjects with the highest levels of selenium were 57 percent more likely to have diabetes than those with the lowest levels.

The authors call for more research to investigate high blood levels of selenium as factor that can increase the risk of diabetes.

Until the findings of additional studies are available, increased levels of selenium, through the diet or in supplements, should not be recommended for diabetes prevention in individuals with normal selenium levels, Bleys and colleagues advise. "Furthermore, diabetic patients should avoid selenium supplementation" until evidence showing a benefit becomes available.