Selenium Facts

Selenium books Selenium supplements

Selenium also plays a role in the functioning of the thyroid gland and in every cell that utilizes thyroid hormone, by participating as a cofactor for the three known thyroid hormone deiodinases, which activate and then deactivate various thyroid hormones and their metabolites. It may inhibit Hashimotos's disease, in which the body's own thyroid cells are attacked as alien.

Dietary selenium comes from nuts, cereals, meat, fish, and eggs. Brazil nuts are the richest ordinary dietary source (though this is soil-dependent, since the Brazil nut does not require high levels of the element for its own needs). In descending order of concentration, high levels are also found in tuna, crab, and lobster.

Selenium Deficiency

Selenium deficiency is relatively rare in healthy, well-nourished individuals. It can occur in patients with severely compromised intestinal function, those undergoing total parenteral nutrition, and also on advanced-aged people (over 90). Also, people dependent on food grown from selenium-deficient soil are also at risk. However, although New Zealand has low levels of selenium in its soil, adverse health effects have not been detected. Several studies have suggested a possible link between cancer and selenium deficiency.

Selenium Toxicity

Exceeding the Tolerable Upper Intake Level of 400 micrograms per day can lead to selenosis. Symptoms of selenosis include a garlic odor on the breath, gastrointestinal disorders, hair loss, sloughing of nails, fatigue, irritability, and neurological damage. Extreme cases of selenosis can result in cirrhosis of the liver, pulmonary edema, and death.

Sources: 

http://en.wikipedia.org/wiki/Selenium
Understanding Nutrition Eleventh Edition

Books on Selenium for further research. Selenium supplements