A new study has shown that taking selenium supplements may, over time, make type 2 diabetes more likely.
The study, published in the Annals of Internal Medicine's advance online edition, doesn't prove that selenium supplements cause type 2 diabetes, however, the researchers write that selenium supplements don't appear to prevent type 2 diabetes and "may increase risk for the disease."
Selenium is a naturally occurring trace mineral present in soil and foods. The body needs selenium in minute amounts to aid in metabolism.
Saverio Stranges, MD, PhD, lead author of the study, and his team reviewed a study that was designed to assess whether selenium supplements prevented skin cancer and looked at the effects the supplement had on diabetes incidence.
Among the 1,202 participants who participated in the study, half of the group received a 200-microgram selenium supplement and half received a placebo pill for an average of 7.7 years.
The researchers found that those who took the selenium supplement had an increased risk of developing Type 2 diabetes than those who took a placebo or dummy pill.
"At this time, the evidence that people should take selenium supplements is extremely limited. We have observed an increased risk for diabetes over the long term in the group of participants who took selenium supplements," Stranges said.
By the end of the study, the relative risk rate was approximately 50 per cent higher among those in the selenium group than among those in the placebo group. The risk of developing diabetes tended to be higher in people who had higher blood selenium levels at the start of the study.
Dr. Stranges said that it's not clear why selenium would be associated with an increased risk of developing diabetes.
"No single study can provide the answer to a scientific question, but at this time, selenium supplementation does not appear to prevent type 2 diabetes, and it may increase risk of the disease. However, our understanding of the mechanisms whereby selenium would increase risk of diabetes is very limited at this time and this issue needs to be further explored. Nevertheless, I would not advise patients to take selenium supplements greater than those in multiple vitamins," Stranges said.
In an accompanying editorial, Dr. Eliseo Guallar from Johns Hopkins University Bloomberg School of Public Health, agrees that selenium seems to offer few benefits and at high levels, may be deadly.
Dr. Guallar said that most people have adequate selenium in their diet.
"Moreover, taking selenium supplements on top of an adequate dietary intake may cause diabetes."