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The long-term effect of selenium on diabetes risk

An article in the Annals of Internal Medicine reports, “Selenium supplementation does not seem to prevent type 2 diabetes, and it may increase risk for the disease.”

First, the details.

  • 1202 participants were randomly assigned to take 200 mcg of selenium daily or placebo.
  • Treatment averaged 7.7 years.
  • The study was conducted in areas of the eastern US where there is low selenium consumption.

And, the results.

  • Type 2 diabetes developed in 58 selenium and 39 placebo recipients.
  • The lack of benefit of selenium on the incidence of type 2 diabetes persisted after re-analysis of the results for potentially confounding factors (ie, age, gender, body mass index, smoking status).
  • There was a significant increased in the risk for type 2 diabetes among those who had the highest selenium blood levels at the start of the study.

The bottom line?
This is the largest study of its kind to report on the effect of selenium supplementation alone on the prevention of type 2 diabetes. And the results raise concerns about the prolonged use of selenium in terms of blood sugar metabolism and resistance to the effects of insulin.

There are some caveats. It should be mentioned that these findings are based on data originally collected for another reason — diabetes was not the primary reason for this study.

Also, the researchers depended on the study participants to report their diagnosis of type 2 diabetes. This might have led to misclassification of patients. In addition, some potentially confounding variables (ie, family history of diabetes, body fat distribution, and physical activity) were not considered. On both counts, the authors think these variables would have balanced out between groups, but they can’t be sure.

In an accompanying editorial, Dr. Eliseo Guallar from Johns Hopkins University in Baltimore, Maryland points to other supplements like beta-carotene and vitamin E, which were widely believed to be safe only to be shown to increase mortality and morbidity when studied more closely. “The US public needs to know that most people in this country receive adequate selenium from their diet. By taking selenium supplements on top of an adequate dietary intake, people may increase their risk for diabetes.”

7/10/07 19:15 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at www.Vicus.com, a complementary and alternative medicine website.