Selenium

Definition

Selenium is a trace element that is considered a micronutrient, meaning it is a nutrient needed in very small amounts. It is an essential cofactor for many antioxidant enzymes of the body, which counteract the damaging effects of reactive oxygen in tissues. Taken in large amounts, it is toxic to humans.

Purpose

The body requires selenium for the function of a special class of enzymes called selenoproteins. Proteins are long folded chains of amino acids. Selenoproteins are made by the body by incorporating dietary selenium into a very specific location in their amino acid sequence. Animals and humans both require selenium, but plants do not. Plants can, however, incorporate selenium present in the soil into compounds that usually also contain sulfur. Since the amount of selenium in the ground varies from region to region, the amount of selenium in plants grown in each region will vary.

The major function of selenoproteins is to prevent or reduce the damage (oxidative stress) caused by free radicals, such as peroxides. There are many types of selenoprotein enzymes that protect cells from these damaging molecules. For instance, some convert peroxides into nontoxic alcohols, thus protecting cells from membrane damage, while others protect against other types of free radicals. Selenoproteins are also required to:

Selenium

Age

Recommended dietary allowance (μg/day)

Tolerable upper intake level (μg/day)

Infants 0-6 mos.

15 (AI)

45

Infants 6-12 mos.

20 (Al)

60

Children 1-3 yrs.

20

90

Children 4-8 yrs.

30

150

Children 9-13 yrs.

40

280

Adolescents 14-18 yrs.

55

400

Adults 19≥ yrs.

55

400

Pregnant women

60

400

Breastfeeding women

70

400

Food

Selenium (μg)

Brazil nuts, 1 oz. (6-8 nuts)

544

Tuna, canned in water, 3 oz.

68

Enriched noodles or macaroni, 1 cup

37

Turkey, 3 oz.

27

Sunflower seeds, ¼ cup

25

Cod, 3 oz.

24

Cinnamon raisin bagel, 3 ½ in.diameter

22

Couscous, ½ cup

22

Mushrooms, shiitake, ½ cup

18

AI = Adequate intake

μg = microgram (mcg)

SOURCE: Office of Dietary Supplements. National Institutes of Health. “Selenium: Fact Sheet for Health Professionals.” U.S. Department of Health and Human Services. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional (accessed April 2, 2018).

There have been claims for selenium in the treatment and prevention of many disorders, including cancer and depression. The Natural Medicines Comprehensive Database uses rigorous scientific evidence to rate natural medicines in the following ways: effective, likely effective, possibly effective, possibly ineffective, likely ineffective, ineffective, and insufficient evidence to rate. In 2012, selenium supplementation was rated as follows:

Description

Selenoproteins are found in cell membranes, blood, organs, and the prostate gland and testicles.

The richest food sources of selenium are Brazil nuts, organ meats, and fish, followed next by muscle meats. As for plants and grains, there is wide variation in their selenium content because it depends on the selenium content of the soil in which they grow. For example, Brazil nuts grown in areas of Brazil with selenium-rich soil provide more selenium than those grown in a selenium-poor soil. In the United States, grains are a good source of selenium, but not fruits and vegetables.

Some good food sources of selenium include (per 1 oz. serving or as indicated):

The U.S. Institute of Medicine (IOM) of the National Academy of Sciences has developed values called dietary reference intakes (DRIs) for many vitamins and minerals. The DRIs consist of three sets of numbers. The recommended dietary allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97%–98% of the population. The adequate intake (AI) is an estimate set when there is not enough information to determine an RDA. The tolerable upper intake level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

KEY TERMS
Antioxidant—
A molecule that protects cells against damage by free radicals.
Free radical—
A molecule with an unpaired electron that has a strong tendency to react with other molecules in DNA (genetic material), proteins, and lipids (fats), resulting in damage to cells. Free radicals are neutralized by antioxidants.
Oxidative stress—
A condition when free radicals build up faster than antioxidants can neutralize them, resulting in damage to cells.

The RDAs for selenium are:

Selenium in nutritional supplements is available mostly in the form of sodium selenite and sodium selenate, two inorganic forms of selenium, or as selenomethionine in “high selenium yeasts,” generally considered to be the best absorbed and utilized form of selenium.

Precautions

Selenium is a trace element that is essential in small amounts, but is toxic in larger amounts. Intake of less than 400 μg per day is likely safe for most people when taken by mouth for a short time. Excessive or long-term supplementation may result in symptoms including fatigue and irritability, with increased toxicity leading to loss of hair and nails, white blotchy nails, and garlic breath odor. If not corrected, it leads to a condition called chronic selenium toxicity (selenosis), with symptoms of vomiting, nausea, nerve damage, skin rashes, and brittle bones.

On the other hand, gastrointestinal problems, such as Crohn's disease, or surgical removal of part of the stomach can lead to selenium deficiency.

Interactions

Selenium supplements should not be taken by people who are taking blood-thinning drugs, including aspirin, or anti-clotting drugs as these drugs interact with selenium to slow blood clotting and increase the risk of bruising. Selenium also may interact with cholesterol-lowering drugs (statins), niacin, barbiturates, oral contraceptives, and gold salts. Zinc supplements may make it more difficult for the body to absorb selenium from food. Some species of Astragalus accumulate large amounts of selenium. When Astragalus and selenium supplements are both taken, selenium overdose may occur. Other interactions may not yet have been identified. Individuals should always check with their physician before beginning selenium supplementation.

Aftercare

When the diet is corrected for selenium imbalance, most symptoms tend to disappear with intake of recommended levels. People at risk of selenium deficiency due to gastrointestinal disease or severe infection are evaluated by physicians for depleted selenium blood levels to determine the need for supplementation.

Complications

Acute and fatal complications have occurred with accidental ingestion of gram quantities of selenium. Significant selenium toxicity was reported in 13 individuals who took supplements that contained 27,300 μg per tablet due to a manufacturing error. Selenosis may occur with smaller doses of selenium over long periods. Overall, selenium deficiency is rare in the United States. Selenium deficiency has also been suggested as a probable cause of Keshan's disease and Kashin-Beck disease, both rare in the United States.

Parental concerns

Maintaining good nutrition in the home includes providing children with a varied diet to ensure that all nutritional needs are met. Parents should also be aware of the risks associated with both selenium deficiency and overconsumption.

See also Acne diet ; ADHD diet ; Antioxidants ; Cancer ; Cancer-fighting foods .

QUESTIONS TO ASK YOUR DOCTOR

Resources

BOOKS

Mason, Pamela. Dietary Supplements. 4th ed. Chicago: Pharmaceutical Press, 2011.

Prasad, Kedar N. Micronutrients in Health and Disease. Boca Raton, FL: CRC Press/Taylor & Francis, 2010.

Pressman, Alan H., and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals. 3rd ed. Indianapolis, IN: Alpha Books, 2007.

PERIODICALS

Mohkber, N., et al. “Effect of Micronutrient Supplementation on Mood in Nursing Home Residents.” Gerontology 54, no. 5 (2008): 292–99.

Mokhber, N., et al. “Effect of Supplementation with Selenium on Postpartum Depression: A Randomized Double-Blind Placebo-Controlled Trial.” Journal of Maternal-Fetal Neonatal Medicine 24, no. 1 (January 2011): 104–108.

WEBSITES

Higdon, Jane, Victoria J. Drake, and Barbara Delage. “Selenium.” Linus Pauling Institute, Oregon State University. http://lpi.oregonstate.edu/mic/minerals/selenium (accessed April 17, 2018).

MedlinePlus. “Selenium Sulfide.” U.S. National Library of Medicine, National Institutes of Health. https://medlineplus.gov/druginfo/meds/a682258.html (accessed April 17, 2018).

Office of Dietary Supplements. “Fact Sheet for Health Professionals: Selenium.” National Institutes of Health. https://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/ (accessed April 17, 2018).

ORGANIZATIONS

Academy of Nutrition and Dietetics, 120 South Riverside Plz., Ste. 2000, Chicago, IL, 60606-6995, (312) 899-0040, (800) 877-1600, amacmunn@eatright.org, http://www.eatright.org .

British Nutrition Foundation, High Holborn House, 52-54 High Holborn, London, UK, WC1V 6RQ, +44 20 7404 6504, Fax: +44 20 7404 6747, postbox@nutrition.org.uk, http://www.nutrition.org.uk .

Office of Dietary Supplements, National Institutes of Health, 6100 Executive Blvd., Rm. 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845, ods@nih.gov, http://ods.od.nih.gov .

Monique Laberge, PhD
Revised by Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.