This fact box will help you to weigh the benefits and harms of selenium supplementation for prevention of cancer. The information and numbers are based on the best scientific evidence currently available.
This fact box was developed by the Harding Center for Risk Literacy.
Selenium is an essential trace element found in fish, meat, and eggs, but also in plant products. It is important for the healthy functioning of the immune system and thyroid. A lack of selenium can lead to deficiency diseases. However, real deficiency diseases are rare in in Western industrialized countries. Selenium is freely sold as a dietary supplement.
Prior studies suggested an association between selenium status and the risk of cancer .
Selenium supplementation is said to prevent cancer .
The fact box shows the benefits and harms of selenium supplementation to prevent cancer compared to no supplementation.
The table may be read as follows:
About 9 to 10 out of every 100 men without a selenium deficiency who did or did not take supplementary selenium were diagnosed with cancer within four to seven years.
The numbers in the fact box are rounded. The data were reported in one study with around 17,800 participants .
Reliable numbers are available for men only. Selenium supplementation entailed taking of 200 micrograms of L-selenomethionine daily.
During the study,men taking selenium supplementation appeared more likely to develop type 2 diabetes. Although this result may be coincidental and there is not enough evidence to suggest that selenium supplementation is associated with an elevated risk for type 2 diabetes, the trial was nevertheless stopped as a precaution.
The total number of deaths (all causes) remained the same with or without selenium supplementation.
Results are based on one study only. Therefore, the fact box does not represent a comprehensive evaluation. However, the included study met the methodological requirements (low risk of bias).
- April 2016 (last update)
Information within the fact box was obtained from the following sources:
 Dennert G, Zwahlen M, Brinkman M, et al. Selenium for preventing cancer. Cochrane Database Syst Rev 2011(5):Cd005195. doi: 10.1002/14651858.CD005195.pub2
 Lippman SM, Klein EA, Goodman PJ, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA 2009;301(1):39-51. doi: 10.1001/jama.2008.864
Documentation on how the numbers in the fact box were determined is available on request.