Micronutrients: Selenium

A bunch of nuts on a white background.

Essential to many of the body’s regulatory and metabolic functions, selenium is part of at least 25 proteins called selenoproteins, many of which are oxidant defense enzymes.

Roles in health
Selenium is involved in reproduction, metabolism, thyroid function, DNA production and protection from oxidative damage and infection. Studies have associated low levels with increased risk for cancer, cardiovascular disease, cognitive decline and thyroid disease. Low dietary consumption of selenium may be associated with obesity.

Selenium’s antioxidant properties and its effect on DNA repair and the endocrine system may play a role in the prevention of certain cancers. However, the relationship between selenium and cancer is debated worldwide. In 2003, a qualified health claim for reduction of certain cancers was approved by the U.S. Food and Drug Administration for dietary supplements containing selenium. A 2016 meta-analysis suggested high selenium exposure through dietary sources may have varying effects on cancer prevention.

A 2006 meta-analysis showed high selenium concentrations were associated with a reduction in coronary heart disease risk. Some experts recommend selenium supplements for patients with or at risk for coronary heart disease and for those undergoing cardiac surgery.

Food sources* mcg/serving
1 ounce Brazil nuts 544
3 ounces cooked yellowfin tuna 92
3 ounces roasted ham 42
1 cup cooked egg noodles 38
3 ounces cooked beef liver 28
1 cup 1% cottage cheese 20
1 large cooked egg 15

*All foods listed here are rated “excellent” sources.

Immune function may be boosted with increased selenium levels, which can help protect against infectious diseases caused by viruses such as HIV, influenza and hepatitis C.

Since aging is characterized by loss of muscle mass and selenium plays a key role in muscle function, reduced serum selenium levels may be associated with age-related decline in brain function.

Studies indicate supplementation may offer benefits only to those whose selenium consumption already is inadequate, and emerging research suggests genetic factors may affect how people respond to supplementation.

Current recommendations
The Institute of Medicine uses Adequate Intake, or AI, for infants due to insufficient evidence to develop a Recommended Dietary Allowance. The daily AI is 15 micrograms for infants 0 to 6 months and 20 micrograms for infants 7 to 12 months.

The RDA is 20 micrograms for children ages 1 to 3, 30 micrograms for ages 4 to 8, 40 micrograms for ages 9 to 13, and 55 micrograms for ages 14 and older. Pregnant and lactating women require 60 micrograms and 70 micrograms, respectively.

Daily Tolerable Upper Intake Levels are 45 micrograms for infants 0 to 6 months, 60 micrograms for infants 7 to 12 months, 90 micrograms for children 1 to 3 years, 150 micrograms for ages 4 to 8, 280 micrograms for ages 9 to 13, and 400 micrograms for ages 14 and older.

Sources of selenium
Selenium is found naturally in many foods. However, the amount depends on the selenium concentration of soil and water. Most Americans get enough selenium from their diet, primarily from grains, meat, poultry, fish and eggs.

Selenium is available as a supplement and in multivitamins in the highly absorbable form of selenomethionine.

Signs of deficiency
Rare in the United States and estimated to effect 1 billion people worldwide, selenium deficiency is measured by concentration in serum and plasma. Deficiency may increase the risk of thyroid disease and can cause Keshan disease (cardiomyopathy), Hashimoto’s thyroiditis, male infertility and possibly Kashin-Beck, a type of osteoarthritis.

Populations at risk
Diarrhea, malabsorption and poor intake by people with HIV can lead to deficiency. Kidney dialysis also increases deficiency risk. Selenium may interact with medications such as Cisplatin, a chemotherapy drug that can lower selenium levels.

Selenium toxicity is uncommon in the United States. Consuming excess selenium can cause symptoms such as garlic breath, nausea, diarrhea and skin rash. Hair and nail loss are common signs of chronic overconsumption. Dangerously high intakes can cause kidney failure, heart attack and heart failure.

Bottom line
Selenium is important in many aspects of health and may boost the immune system, slow mental decline and reduce risk of some diseases, but more research is needed to confirm this.


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Kathleen Zelman
Kathleen Zelman, MPH, RDN, is the nutrition director of WebMD.