Selenium, Se is needed in the body as the Se 2+ ion.

Deficiencies of Selenium in the diet are rare but there is a possible link between a lack of selenium in the diet and cancer. 1

Foods that are rich in selenium include nuts, cereals, meat, fish and eggs.

Too much selenium in the diet can be a problem and there have been documented cases of selenium poisoning by people who have eaten foods that are rich in the metal. The foods have become rich in the metal as they have been grown on land contaminated by selenium.

Symptoms of selenium poisoning include more minor symptoms such as gastrointestinal disorders and  hair loss with more extreme symptoms including liver cirrhosis and death.