Except in the case of seafood, the selenium content in food depends on how much of the mineral is present in the soil where plants are grown or animals are raised. For example, Americans living in the high plains of northern Nebraska and the Dakotas tend to have higher levels of selenium because the soils there contain more of this mineral. Selenium deficiency is rare in the United States, and although it is needed for health, high doses can be toxic.
Why We Need It
Low levels of this mineral have been associated with higher risk for heart disease, cancer, and conditions like asthma, cataract formation, and premature aging that are linked to increased free-radical damage. Selenium also helps regulate thyroid function and appears to stimulate the immune response.
In people with lower levels of selenium in their diets, this mineral has been shown to improve mood and lessen anxiety. There is evidence that being deficient in selenium does not in itself contribute to illness but rather may cause the body to be more susceptible to illnesses caused by other nutritional or infectious stressors.