Selenium is an essential trace mineral that humans need for proper bodily functions that can be found in foods such as brazil nuts, fish, and eggs. It is available as a nutrition supplement, considered by many to have antioxidant properties, and is said to prevent cardiovascular diseases, cognitive decline, thyroid disorders, and cancers.

However, according to the National Institutes of Health, clinical evidence is inconclusive to support routine use of selenium in cancer prevention, and does not support use in other disease prevention areas. Furthermore, a recent meta-analysis by Vinceti and colleagues published in the European Journal of Epidemiology raises concerns for adding selenium to a person’s diet due to an increased risk of developing type 2 diabetes (T2D).

The connection between T2D and selenium intake was first noted in 2007 when supplementation with selenium in a trial was found to increase T2D risk. There have since been numerous studies on this subject, including both observational and experimental studies. Vinceti and colleagues conducted a systematic review to analyse published data that examined the linkage between T2D and selenium intake. The authors found a clear dose-response trend in the studies, where the more selenium in a person’s body, the higher the risk was for T2D. Relative risk of developing diabetes ranged between 1.11–3.6 times depending on how much selenium the test subjects were exposed to.

T2D is already a global public health crisis. GlobalData epidemiologists estimated that for adults ages 20 and older in the seven major markets (US, France, Germany, Italy, Spain, UK, and Japan), the number of diagnosed prevalent cases of T2D is expected to nearly double in just 20 years, from around 20.9 million cases in 2006 to around 41 million cases in 2026. Vinceti and colleagues cautioned for potential impact on public health burden given the high diabetes incidence worldwide and the ubiquity of selenium supplements. Many multivitamins currently on the market contain added selenium and there is currently a largely favourable media coverage for selenium supplementation.