One of the nicer-sounding nutrients, selenium is named after “selene,” the Greek word for “moon.” The derivation is more scientific than poetic, based on an astronomic increase in selenium’s conductive powers when taken from the dark into the light.Though only recognized in 1990 as a trace element essential for human health, selenium’s biological effects are pretty far out.

Selenium activates some of the body’s own antioxidant enzymes.Because of this, selenium boosts your ability to make glutathione, which neutralizes free radicals.Selenium also supports proper functioning of the thyroid gland and may play a role in fertility, especially in men.Here are some additional ways in which adequate selenium helps support health.

Prostate Health: Prostate cancer is the most common deadly cancer among males.One University of Arizona study of nearly 1,000 men compared those consuming 200 micrograms of selenium with a placebo-control group and found that the selenium group developed 63% fewer cases of prostate cancer.Selenium may also reduce the risk of lung, liver and colorectal cancers.

Immune Health: Selenium deficiency may impair immune function.A lack of selenium can allow an otherwise harmless virus to undermine heart muscle, possibly explaining the prevalence of a cardiac ailment know as Keshan disease in rural areas of China, where local soils lack selenium content.

Bone Health: A recent UNC study found that men and women with high dietary selenium intakes were 40% less likely to develop osteoarthritis in their knees than those with lower intakes.Selenium counters the inflammation associated with the progression of osteoarthritis and rheumatoid arthritis.

Heart Health: Researchers from the Centers for Disease Control and Prevention have linked selenium to lower levels of C-reactive protein, an inflammatory marker for heart disease.The free radicals that cause inflammation are quenched by glutathione and other antioxidants.The more antioxidants that get used up in this process, the lower the body’s antioxidant stores.

As mentioned in the DNN‘s “The Nut in Nutritious,” Brazil nuts are the highest food source of selenium (depending largely on the kind of soil in which the nuts are grown).In fact, plants have no known requirement for selenium at all and only contain it because of the soil in which they are grown.Other good sources of selenium are halibut, tuna, oysters, oat bran, shiitake mushrooms and sunflower seeds.

In contrast to many nutrients lacking in the American diet, the average person gets nearly twice the daily requirement (55 micrograms) of selenium.Ingesting more than the upper intake level (UL) of 400 micrograms/day can lead to selenium toxicity or “selenosis,” characterized by brittle hair and nails.Ingesting large (gram) quantities can be fatal.