Selenium is an essential mineral and micronutrient. It is fundamental to human health and found in many foods. It is found in meat, seafood (hence, selenium levels are high in populations with high intake of seafood, like the Inuit population), grain cereals, egg yolk, milk, brazil nuts, mushrooms and garlic. Concern has been raised for some years about falling levels of selenium intake and a possible relationship to the incidence of some diseases, including some cancers.
Selenoproteins are important constituents of a number of enzymes with a range of functions including antioxidant function, thyroid hormone metabolism, male fertility and immune mechanisms. A decline in blood selenium levels in the UK and other European countries has raised concern about possible public health implications, particularly in relation to cancer and cardiovascular disease. Whilst there is some understanding of the role of these proteins in health and disease (and some interesting theories and research), there are many unanswered questions and much debate about supplementation. More research is repeatedly called for. Deficiency is linked with Keshan disease but excessive intake can have toxic effects and may even be carcinogenic.