Selenium

Selenium is a trace mineral that is essential to good health. Only small amounts are required. The human body's content of selenium is believed to be in the 13–20 milligram range. Small amounts are necessary for certain cellular functions.

Selenium is incorporated into proteins to make selenoproteins, some of which are important antioxidant enzymes that help reduce certain oxidized molecules and thereby help prevent cellular damage from free radicals.

Some selenoproteins help regulate thyroid function and play a role in the immune system.

Sources

Dietary selenium comes from nuts, cereals, meat, mushrooms, fish, and eggs.

Brazil nuts are the richest ordinary dietary source (though this is soil-dependent). High levels are also found in kidney, tuna, crab, and lobster.

Daily intake

The recommended daily intake is 55 microgram per day in adults. Here is a list of foods having the highest content of selenium.

Deficiency

Selenium deficiency is rare in healthy well-nourished individuals. Only few cases have been reported.

However, people dependent on food grown from selenium-deficient soil are at risk. There is evidence that selenium deficiency may contribute to development of a form of heart disease, hypothyroidism, and weakening of the immune system.

Usually selenium deficiency does not cause illness by itself. Rather, it can aggravate conditions caused by other nutritional, biochemical or infectious stresses.

Excess

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.

References: 1 , 2 , 3 , 4