Selenium

​Function: 
Selenium works together with Glutathione to aid in antioxidant function, is involved in iodine metabolism and therefore thyroid function, and is involved in energy production.
 
Deficiency: 
Selenium deficiency may lead to abnormal cell death in heart and joint tissues leading to congestive heart failure and degeneration of the joints.  It may also lead to symptoms of poor growth, muscle pain and weakness, loss of pigmentation of hair and skin, and whitening of the nail beds.
 
Absorption:
Selenium is easily absorbed.  Absorption is improved when vitamins C, A, and E are consumed at the same time.
 
Sources:
Selenium levels in soil vary greatly and therefore the amount of Selenium in food also varies greatly.  Brazil nuts are considered an excellent source of Selenium.  Other sources include mushrooms, animal products, and whole grains.
 
Toxicity:
Selenium toxicity is called selenosis and is caused by over supplementation.  Symptoms include nausea, vomiting, fatigue, diarrhea, hair and nail brittleness and loss, and paresthesia.  Do NOT self-supplement Selenium!

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* This information is not intended to encourage self-supplementation.   As you will read in individual nutrient content, self-supplementation can be unnecessary or even dangerous.  I highly recommend micro-nutrient blood testing before choosing to take any supplements that are not whole-foods based.
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References:
Gropper SS, Smith JL, Groff JL. Advanced nutrition and human metabolism. 5th ed. Belmont, CA: Wadsworth; 2009.
Mahan L, Escott-Stump S, Raymond J. Krauses's food and the nutrition care process. 13th ed. St. Louis, Missouri: Elsevier Saunders; 2012.