This important nutrient is vital to immune system function. Selenium works in conjunction with vitamin E, vitamin C, glutathione and vitamin B3 as an antioxidant to prevent free radical damage in the body. It's thought to help prevent cancer by affecting oxidative stress, inflammation and DNA repair. Selenium has been found to be important to male fertility; increasing selenium levels leads to improved sperm motility. There is preliminary research that suggests that selenium supplementation may also help with asthma symptoms, but more studies are needed.
Deficiencies of selenium can occur in areas where soil content of this mineral is low. Diets high in refined foods may also lead to deficiency, as selenium can be destroyed by food processing. Taking anti-inflammatory drugs may reduce the body's supply of selenium.
Low selenium levels can contribute to autoimmune problems, such as psoriasis and thyroid disease. Low levels have also been tied to stomach, throat and prostate cancers, although more research is needed to determine if this is a cause or a result of the disease. Some studies suggest that selenium deficiency is linked to mood disorders. There's indication that deficiencies in selenium may contribute to the progression of viral infections.
10 Selenium Food Sources
The selenium content in foods depends on the concentration of selenium in the soil where the crops were grown. The following foods are generally considered good sources of selenium:
- Brazil Nuts
- Sunflower Seeds
- Fish (tuna, halibut, sardines, flounder, salmon)
- Shellfish (oysters, mussels, shrimp, clams, scallops)
- Meat (Beef, liver, lamb, pork)
- Poultry (chicken, turkey)
- Mushrooms (button, crimini, shiitake)
- Grains (wheat germ, barley, brown rice, oats)
Recommended Daily Allowance
- Children (under 3): 20 mcg
- Children (4-8): 30 mcg
- Children (9-13): 40 mcg
- Adolescents (14-18): 55 mcg
- Adults 19 and older: 55 mcg
- Pregnant women: 60 mcg
- Lactating women: 70 mcg
Exceeding 400 mcg per day can lead to selenium toxicity. Side effects may include hair loss, white spots on fingernails, fatigue, dizziness, nausea and nerve damage. There's some evidence that high selenium levels may increase the risk of squamous cell skin cancer. Another well controlled study found a correlation between higher levels of selenium and an increased risk of developing type-2 diabetes.
Because of the possibility of toxicity, selenium supplements are controversial. The safest way to ensure a sufficient level of selenium in the diet is by eating a variety of selenium rich foods, like those listed above. Brazil nuts can be very high in selenium and should only be eaten occasionally. One Brazil nut can supply a whole day's requirement of selenium, although this can vary depending on soil conditions. A multivitamin that contains some selenium is safe for most people to take and can help to fill the gap in a diet that is lacking.