People who take selenium supplements to prevent type 2 diabetes may increase their risk of developing it, according to news reports. An article in the Daily Mail on 11 July 2007 entitled "Selenium supplements could increase risk of diabetes" stated that it was "possible that some selenium compounds might themselves generate harmful free radicals capable of hampering the insulin-producing function of the pancreas" (11 July 2007).
The study was conducted by Saverio Stranges and colleagues at the State University of New York at Buffalo and was published in the Annals of Internal Medicine.
This randomised, double blind, placebo-controlled trial recruited 1,312 people between 1983 and 1991 from dermatology clinics in the eastern United States for a study investigating whether selenium supplementation prevents cancer. When the study started 1,202 participants did not have diabetes, and it is data relating to these people that has been used for "secondary analysis" and informed Dr Stranges’s study.
Participants were chosen at random to receive either 200 micrograms per day of selenium or a placebo for over 7 years. During the study period, these people visited the clinic every six months for blood tests and to update the researchers about their general health.
What were the results of the study?
The authors found that there were 58 new cases of type 2 diabetes in the 600 people given selenium and 39 new cases of type 2 diabetes in the group given the inert tablets. The chance of developing diabetes was about 1.5 times higher in the group taking selenium supplementation compared with the group not taking it.
As this is a secondary analysis of the data, the possibility that the results are a chance finding is increased. The authors say they have carefully examined the data for other possible causes of this finding.
The authors concluded that selenium supplementation does not seem to prevent type 2 diabetes and may increase the risk of developing the disease.
The authors acknowledge some of the limitations of this study and have been cautious in their conclusions as it was based on a ’secondary analysis‘.
This study presents evidence of an association between taking selenium and the development of type 2 diabetes, but it is not clear if this is a causal relationship or not.
There is no good evidence that selenium deficiency is common, as a mixed diet eaten in the UK does not appear to result in selenium deficiency.