Bare facts
Selenium is a trace mineral. Such minerals occur in tiny amounts but play a major role in impacting health. In the right amounts, selenium facilitates the normal functioning of the immune system and the thyroid gland.
Its deficiency can lead to cardiac problems. On the contrary, if the ingestion levels are excessively high, the element can cause a disease called selenosis. The symptoms of this ailment include gastrointestinal problems, hair loss and white blotchy nails. An acute attack of selenosis can lead to kidney and liver tissue damage. It can also affect the circulatory and nervous systems.
In terms of acceptable daily intake, the US Centers for Disease Control and Prevention pegs the safe level of selenium for humans at 5 microgrammes per kilogramme of body weight.