The trace mineral selenium makes its way into our bodies because it is contained in certain foods. Over time, it becomes part of nearly every cell, with particularly high concentrations in the kidneys, liver, pancreas, spleen, and testes. The most concentrated food source for selenium is the Brazil nut; a single nut contains 120 mcg (which is about twice the RDA). Seafood in general, as well as poultry and meat, are also good sources. So are grains, especially oats and brown rice. Selenium has many tasks to perform in the body. It helps to boost the immune system and fight off infection, providing a general Increase in the body’s defense against dangerous bacteria, viruses, and cancer cells. On a basic cellular level, every cell in the body needs a particular hormone from the thyroid gland that selenium helps to convert to an active form. Perhaps the most famed use of selenium in supplement form is as an antioxidant; it helps to mop up dangerous molecules known as free radicals that can damage and alter healthy cells. It has also been recommended for staving off the effects of aging.