Men who have a relatively high amount of selenium in their blood are less subject to prostate cancer. This discovery was made by nutritionists at the University of East Anglia, who compared and reanalysed data from 12 epidemiological studies of more than 13,000 men.
The file on selenium is a problematic one. On the one hand, there are indications that a high intake of selenium protects against diseases accompanying ageing. That isn’t very surprising since selenium is a building block of detoxifying enzymes.
But on the other hand, a high intake of selenium is anything except healthy. If people who consume a lot of selenium in their food are given a selenium supplement, their chance of developing type 2 diabetes increases. [Ann Intern Med. 2007 Aug 21;147(4):217-23.]
With some exceptions, Europeans consume too little rather than too much selenium. The average European consumes about 60 micrograms of selenium daily. An adult male should consume 100 micrograms of selenium each day.
Once the British researchers had analysed all of the usable data, they produced the figures below. The first shows the relation between prostate cancer and the selenium concentration, and the second shows the relation between advanced prostate cancer and the selenium concentration.
According to the figures, more selenium is better for the prostate. But that picture is incomplete because studies have shown that the prostate may be affected by too much selenium. Evidently, the researchers didn’t find enough men with such a high concentration of selenium to be able to show this.
Most Europeans have a selenium concentration of less than 80 nanogram/millilitre. Using the British information, you could assume that the average European man’s chance of developing prostate cancer decreases when his consumption of selenium increases by tens of micrograms daily. That can be achieved by a careful use of supplements containing organic selenium, but also by adding Brazil nuts to the diet. As far as we know, Brazil nuts are the best nutritional source of selenium. Two Brazil nuts supply about 50 microgram of selenium. [Am J Clin Nutr. 2008 Feb;87(2):379-84.]
Other metastudies have found similar relations between selenium and cancer. For example, a recent metastudy suggested that selenium supplements reduce the chance of developing lung cancer if your selenium concentration is lower than 106 nanogram/millilitre. But if your concentration is above 122 nanogram/millilitre, selenium supplements increase your chance of developing lung cancer. [PLoS One. 2011;6(11):e26259.]