Selenium

What is selenium?

Selenium is a trace mineral that is an essential nutrient to human health.

The chemical symbol for selenium is Se.

Selenium Function

In the human body, selenium is incorporated into the amino acid selenocysteine, which is part of selenoproteins ^[1]:

• Selenoproteins act as antioxidants, which may protect cells against free radicals
• Selenoproteins are required for conversion of the inactive thyroid hormone (T4) into its active form (T3).

Selenium Rich Foods

Selenium in foods is in the form of an amino acid selenomethionine. Selenium content of foods greatly depends on amount of selenium in soil.

• Plant foods high in selenium: nuts, rice, whole-wheat bread
• Animal foods high in selenium: fish, poultry, eggs
• Human breast milk contains 18 mcg selenium/liter ^[2]. An Adequate Intake (AI) for selenium for 0-6 months old infants is 15 mcg/day and for 7-12 months old infants 20 mcg/day ^[1].

Chart 1. Foods High in Selenium
PLANT FOODS	Selenium (mcg)
Brazil nuts (1 oz, 28 g)	537
Nuts, mixed (1 oz, 28 g)	120
Couscous (1 cup, 237 mL)	45
Spaghetti, whole wheat (1 cup, 237 mL)	35
Bagel (4″ dia)	27
Bread, whole-wheat (2 slices, 50 g)	25
Sunflower seed kernels (1 oz, 28 g)	22
Cereals: barley, cornmeal, oatmeal, rice (white/brown) (1 cup, 237 mL)	10-20
Walnuts, black, dried (1 oz, 28 g)	5
ANIMAL FOODS
Organ meats: kidney, liver (3 oz, 85 g)	90-186
Tuna (yellowfin) (3 oz, 85 g)	90
Mollusks (3 oz, 85 g)	85
Most other fish and seafood (3 oz, 85 g)	30-60
Beef, lamb, pork (3 oz, 85 g)	Up to 40
Turkey, light meat (3 oz, 85 g)	27
Chicken breast, meat only (3 oz, 85 g)	17
Egg, whole (1 large, 50 g)	15

Chart 2 source: USDA.gov ^[2] All listed foods are ready to eat.

Recommended Selenium Intake

The Recommended Dietary Allowance (RDA) for selenium for adults is 55 micrograms/day ^[1].

Selenium Supplements

Oral selenium supplements without prescription include ^[5]:

• Inorganic selenium in the form of sodium selenite (Na₂SeO₃) and sodium selenate (Na₂SeO₄)
• Organic selenium in the form of selenomethionine. Organic forms are better absorbed.
• Selenium-enriched yeast may contain both organic and organic selenium.

Selenium Health Benefits

Selenium supplements are EFFECTIVE in preventing and treatment of selenium deficiency, and POSSIBLY EFFECTIVE in treatment of autoimmune thyroiditis (Hashimoto’s thyroiditis) ^[6].

Selenium supplements are POSSIBLY INEFFECTIVE or there is INSUFFICIENT EVIDENCE about their effectiveness in prevention or treatment of atherosclerosis, bird flu, burns, cancer of any type, cataracts, chemotherapy side effects, chronic fatigue syndrome (CFS), diabetes mellitus, gray hair, hay fever, heart disease, HIV/AIDS, infertility, macular degeneration (eye disease), miscarriage, mood disorders, osteoarthritis, rheumatoid arthritis or swelling after surgery ^[6].

Selenium Safety: Side Effects, Toxicity

The Tolerable Upper Intake Level (UL) for selenium–the amount that should not cause side effects–for adults, is 90 micrograms/day for small children, and 400 micrograms (mcg)/day for adults ^[5].

Acute Selenium Toxicity

Ingestion of one oz of Brazil nuts, which can contain more than 500 micrograms of selenium, could already have a toxic effect. Brazil nuts, sapucaia nuts, or coco de mone nuts (all grown in South America) or selenium supplements taken in excessive amounts may cause ^[7]:

• within few hours: nausea, vomiting, diarrhea, metallic taste, garlic odor, facial flushing, lightheadedness, muscle tenderness, tremor
• within few weeks: hair loss, horizontal streaks on nails.

Chronic Selenium Toxicity

Regular selenium intake at doses as low as 850 micrograms/day may result in selenosis (blood selenium level >100 µg/dL) with white blotchy nails, hair loss, rash, stomach upset, garlic breath odor, fatigue, and tingling due to a mild nerve damage ^[7].

Selenium may increase the risk of bleeding during surgery, so stop taking selenium supplements at least two weeks before scheduled surgery. Selenium may also cause blood clotting problems and liver and kidney problems. There is some concern that long-term high selenium intake might increase the risk of diabetes 2, skin cancer and prostate cancer ^[6]. Selenium, taken without iodine, may worsen the symptoms of hypothyroidism. Selenium may reduce sperm motility, so men who try to father a child should not take selenium ^[6].

Selenium-Drugs Interactions

An anticonvulsant drug valproic acid lowers the blood selenium levels ^[5]. Zinc supplements may decrease selenium absorption ^[6]. Taking selenium with blood thinners, such as aspirin, clopidogrel, dalteparin, heparin, ticlopidine or warfarin, may increase the risk of bleeding or bruising ^[6]. Selenium may increase the effect of barbiturates ^[6].