~ what is Selenium?
What is Selenium?
Selenium is a trace element essential for human wellbeing (1). It is integral to a number of proteins with important functional roles in the maintenance of health, including antioxidant enzymes which protect the body against free radical attack. Free radicals generated in the body can be increased by some diets and may cause significant degenerative diseases.
It is the 17th most common element on earth and is found in inorganic form in the soil. However, its concentration varies considerably across geographical regions. High concentrations occur in some parts of Russia, China, USA and Venezuela, while New Zealand, Australia, Finland, and other regions of China have areas which are significantly depleted of selenium (2).
How long have we known about selenium?
Discovered in 1818, its importance in biology didn't become apparent until 1957 when it was demonstrated that selenium, along with vitamin E, became known in the 1970s, and knowledge of how this occurs is still developing.
What other foods provide selenium?
It is believed that grain foods, depending on their source, currently provide about 30% of our normal dietary intake of Selenium (12), with meat and seafood (eg octopus, squid, tuna) providing about the same. Dairy foods are a variable source (11).
Brazil nuts provide one of the richest natural sources of selenium known. However, the amount of selenium present in any food also depends on where and how it was produced. There is a shortage of information on the selenium content of common foods in the Australian diet (8).
Do Australians need extra selenium?
There has been no comprehensive research into selenium levels in the population across Australia, but studies in US and elsewhere suggest higher levels than present RDI recommendations might be required to achieve significant reduction in risk of some diseases. (3).
Several small surveys of blood samples indicate Australians and New Zealanders are marginally deficient in selenium by North American standards (8, 9, and 13). There needs to be more comprehensive study and surveying of the food and population.
This is probably due to the selenium deficiency in some Australian soils, the nature of those soils e.g. acidic and some modern farming practices.
Obviously, there can be an immense variation in diet from one person to another and the selenium levels in the food you eat varies naturally as well.
Why is Selenium important to my health?
Selenium is needed to create a number of proteins which are important antioxidant enzymes. In the human body, Selenium is present within at least 20 identifiable proteins, some with significant biological functions in the maintenance of health. It is also found in the 21st amino acid selenocysteine.
Some of these proteins are Antioxidants, which help control free radicals which cause cellular damage which contributes to the development of chronic diseases (1 & 4).
Research has shown that in some parts of the world e.g. UK and Europe selenium levels in the diet are decreasing. While the exact reasons for this are still being studied, some experts believe that it could be linked to environmental pollutants arising from the burning of fossil fuels and the smelting industry (7). There is some evidence to suggest this may also be occurring in Australia (9). Pollutants such as sulphur dioxide and nitrate can significantly reduce selenium availability and uptake by plants and crops. The use of sulphates associated with some fertilizer practices may also be having a similar impact, leading to depletion of selenium in the plant foods we eat.
Can we have too much selenium?
Yes we can. Selenium is toxic at high intakes. With a number of nutrients, vitamins, trace elements and minerals if you ingest too much there are potential harmful effects.
Several experts have recommended that an upper limit of 400-450 micrograms of Selenium per day is prudent, with the maximum safe dietary intake for sensitive individuals thought to be below 600 micrograms (2, 5, and 10) depending on the form of selenium ingested.
