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What is selenium?

Although seemingly unknown by many for so long, selenium jumped into the spotlight a couple of decades ago when researchers identified that a mysterious type of heart disease in Asia was actually caused by selenium deficiency—another example of how a small amount of a mineral can have a huge impact on the normal functioning of the body.

 

What foods provide selenium?

Like many of the trace minerals, the quantity of selenium in foods is often a reflection of the soil content in which plants were grown and the animals grazed. Animal products, including seafood, seem to be better sources of dietary selenium than plants.

What are current recommendations for selenium intake?

The RDA for selenium is the same for adult men and women at 55 µg daily. However during pregnancy and lactation the RDA increases to 60 µg and 70 µg daily.

 

What does selenium do in the body?

Selenium is absorbed well from our digestive tract. Therefore, absorption may not be the primary site of body selenium regulation. Selenium is a necessary component of a couple enzymes with the following functions:

 

  • Antioxidant protection – As part of the enzyme called glutathione peroxidase selenium helps protect cells from free radical damage. Glutathione peroxidase inactivates free-radical substances such as hydrogen peroxide and organic peroxides. Glutathione peroxidase is a water-soluble molecule, its antioxidant activities will usually take place in the watery portion of the cells rather than in and around cell membranes like vitamin E. However, the peroxides that glutathione peroxidase inactivate typically travel to and assault cell membranes. In fact, selenium and vitamin E have co-­protective function against oxidative damage to cells.

  • Thyroid hormone activity - Selenium also appears to be incorporated into an enzyme (deiodi­nase) that is involved in iodide metabolism. This function of selenium is still unclear and scientists are currently engaged in trying to understand its function better. It appears that this selenium-containing enzyme helps convert the less potent form of thyroid hormone, thyroxine (T4), to the more active form, triiodothyronine (T3), in certain organs.

 

What happens if we get too little selenium?

Mild selenium deficiency can reduce antioxidant capabilities as well as compromise efficient thyroid hormone action. Meanwhile, extreme selenium deficiency has been determined to be the cause of Keshan disease. The major medical problem associated with Keshan disease is an enlargement and abnormal functioning of the heart and eventual heart failure. The disease was observed in discrete regions of Asia where the selenium content of the soil is extremely low. The people within this region relied exclusively on crops and livestock grown in that area for food yet both of these food sources had very low selenium contents. Keshan disease is preventable with selenium supple­men­tation.

 

Can we get too much selenium?

Selenium intakes greater than 750 micrograms/day over time can produce toxic alterations such as hair and nail loss, fatigue, nausea and vomiting, and a hindrance of proper protein manufacturing. Selenium toxicity is rare and seems likely only with excessive supplementation.