Selenium

Overview

Until the late 1950s, selenium was thought to be toxic. Although it can be toxic at high doses, it is now recognized as an important nutritional trace mineral. Selenium plays important roles in detoxification and antioxidant defense mechanisms in the body.

Dosage Info

Dosage Range

Doses used safely in clinical trials range from 21 to 200mcg daily for adults. (1) , (2)

Most Common Dosage

100mcg daily

Dosage Forms

Tablets, capsules, and liquid.

Adult RDI

70mcg

Adult ODA

200mcg

RDA

  • Infants < 6 months: 15mcg (Adequate Intake, AI)
  • Infants 7-12 months: 20mcg (AI)
  • Children 1-3 years: 20mcg
  • Children 4-8 years: 30mcg
  • Children 9-13 years: 40mcg
  • Males >14 years: 55mcg
  • Females >14 years: 55mcg
  • Pregnancy: 60mcg
  • Lactation: 70mcg

Interactions and Depletions

Depletions

Active Forms

Sodium selenite, selenomethioine, high-selenium yeast.

Absorption

Both inorganic selenium salts and organic selenium compounds appear to be readily absorbed in the small intestine but the mechanism(s) of absorption are still under investigation.

Toxicities & Precautions

General

Selenium is a trace mineral that could be toxic if excessive amounts were ingested on a regular basis. Symptoms of selenium toxicity include loss of hair and nails, skin lesions, nervous system abnormalities, digestive dysfunction, and a garlicky breath odor. (3) Although deaths from selenium toxicity have been reported in livestock, no deaths have occurred in humans.

Functions in the Body

Immune System

Selenium is a co-factor for glutathione peroxidase, which is an important antioxidant enzyme in the immune system.

Anti-cancer Benefits

Epidemiological studies have correlated low dietary selenium intakes with higher rates of cancer. (4)

Heart Disease

Selenium’s anti-oxidant activities are reported to enable it to protect against heart attacks and strokes.

Immune System

Selenium has reported anti-viral activity, may increase T-lymphocytes, and enhances natural killer cell activity. (5) , (6)

Antioxidant

Selenium helps to reduce lipid peroxidation and neutralizes destructive hydrogen peroxide radicals. Selenium also potentiates the antioxidant activity of vitamin E. However, a study involving one hundred and fifty three patients with coronary artery disease evaluated the clinical impact of antioxidant supplementation, including vitamin C, vitamin E, beta-carotene and selenium, on people with low HDL levels in an effort to improve the HDL-C:LDL-C ratio. The participants were followed for 12 months after randomization to one of three groups. They received either placebo, simvastatin and niacin, or simvastatin, niacin plus antioxidants (vitamin C, vitamin E, Beta-carotene and selenium). The treatment groups compared to the placebo group had significant reductions in plasma cholesterol, triglycerides and LDL-C. The desired increases in HDL-C were higher in the simvastatin/niacin group than in the simvastatin/niacin/antioxidant group. The investigators noted that the increases in the HDL2-C, Lp(A-I), and HDL particle size noted in the simvastatin/niacin group were apparently blunted by the additional use of the antioxidants. (7)

Detoxification

Helps detoxify heavy metal toxins such as mercury and cadmium.

Thyroid

Recently discovered that the deiodinase enzyme that converts thyroid hormone (T4) to triiodothyronine (T3, the active form) is a selenium-dependent enzyme.

Clinical Applications

Cardiomyopathy

Selenium deficiency is a recognized cause of cardiac abnormalities. (8)

Cataracts

Selenium is necessary for proper glutathione peroxidase activity in the eyes. Decreased selenium in aqueous humor and serum of patients with senile cataracts may reflect defective antioxidant defense, which leads to the formation of cataracts. (9)

Atherosclerosis.

Erythrocyte selenium-glutathione peroxidase activity has been found to be lower in patients with coronary atherosclerosis. (10) There is a decrease in both selenium content and glutathione peroxidase activity that is parallel to the increase in the severity of coronary artery disease. (11)

Aids

Selenium has been shown to inhibit reverse transcriptase activity in RNA-virus-infected animals. Researchers suggest that selenium supplementation could also prevent the replication of HIV and retard the development of AIDS in newly HIV-infected subjects. (12) Selenium appears to provide HIV-infected patients with symptomatic improvements and may slow the course of the disease. (13)

Cancer Prevention

Data collected from 27 countries reveals that increased dietary consumption of selenium is associated with lower incidence of cancers of large intestine, rectum, prostate, breast, ovary, lung and with leukemia; weak inverse associations were found for cancers of pancreas, skin and bladder. (14) , (15) , (16) , (17) , (18) , (19) In a recent 4-year study in the United States, selenium supplementation of 200mcg/day resulted in a 45 percent reduction in lung cancer, 58 percent reduction in colorectal cancer and a 63 percent reduction in prostate cancer. (20)

Bronchial Asthma

Patients were found to have decreased selenium concentrations in both plasma and erythrocytes as well as reduced glutathione peroxidase enzyme activity. (21)

Symptoms and Causes of Deficiency

The symptoms of selenium deficiency include: destructive changes to the heart and pancreas, sore muscles, increased red blood cell fragility, and a weakened immune system.

  • The primary cause of selenium deficiency is insufficient dietary intake due to either poor food choices (as in junk foods and fast foods), or eating foods grown in selenium-depleted soils.
  • Selenium is not an essential nutrient for plants and, therefore, many farmlands have become increasingly depleted of selenium because farmers see no need to add it to the soil.
  • Food processing causes substantial loss of selenium. For example, whole wheat bread has twice the selenium as white bread, and brown rice has 15 times more selenium than white rice.
  • Human breast milk contains six times more selenium than cow’s milk. A cow’s milk diet for infants can contribute to low selenium levels and depressed immune systems in infants.
  • Protein-calorie malnutrition can lead to selenium deficiency.
  • The Keshan district in China had extremely high rates of childhood cardiomyopathies until it was discovered that the soil was selenium deficient. Nutritional selenium supplementation has solved the problem.
  • Increased rates of various types of cancer are associated with low dietary intake of selenium.

Dietary Sources

Whole grains are the best dietary source of selenium followed by seafood, garlic, liver, eggs, dairy products, and some vegetables including cabbage, celery, cucumbers, and radishes.

References

  1. View Abstract: Levander OA. Selenium requirements as discussed in the 1996 joint FAO/IAEA/WHO expert consultation on trace elements in human nutrition. Biomed Environ Sci. Sep1997;10(2-3):214-219.
  2. View Abstract: Clark LC, Combs GF Jr, Turnbull BW, Slate EH, Chalker DK, Chow J, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial, Nutritional Prevention of Cancer Study Group. JAMA. Dec1996;276(24):1957-1963.
  3. View Abstract: Holness DL, Taraschuk IG, Nethercott JR. Health status of copper refinery workers with specific reference to selenium exposure. Arch Environ Health. Sep1989;44(5):291-7.
  4. View Abstract: Combs GF. Status of selenium in prostate cancer prevention. Br J Cancer. 2004 Jun 22 [Epub ahead of print]
  5. View Abstract: Ferencik M, Ebringer L. Modulatory effects of selenium and zinc on the immune system. Folia Microbiol (Praha). 2003;48(3):417-26.
  6. View Abstract: Broome CS, McArdle F, Kyle JA, et al. An increase in selenium intake improves immune function and poliovirus handling in adults with marginal selenium status. Am J Clin Nutr. Jul2004;80(1):154-62.
  7. View Abstract: Cheung MC, Zhao XQ, Chait A, Albers JJ, Brown BG. Antioxidant supplements block the response of HDL to simvastatin-niacin therapy in patients with coronary artery disease and low HDL. Arterioscler Thromb Vasc Biol. Aug2001;21(8):1320-6.
  8. View Abstract: Huttunen JK. Selenium and Cardiovascular Diseases--An Update. Biomed Environ Sci. Sep1997;10(2-3):220-26.
  9. View Abstract: Karakucuk S, et al. Selenium Concentrations in Serum, Lens and Aqueous Humour of Patients with Senile Cataract. Acta Ophthalmol Scand. Aug1995;73(4):329-32.
  10. View Abstract: Yegin A, et al. Erythrocyte Selenium-glutathione Peroxidase Activity is Lower in Patients with Coronary Atherosclerosis. Jpn Heart J. Nov1997;38(6):793-98.
  11. View Abstract: Yegin A, et al. Erythrocyte Selenium-glutathione Peroxidase Activity is Lower in Patients with Coronary Atherosclerosis. Jpn Heart J. Nov1997;38(6):793-98.
  12. View Abstract: Schrauzer GN, et al. Selenium in the Maintenance and Therapy of HIV-infected Patients. Chem Biol Interact. Jun1994;91(2-3):199-205.
  13. View Abstract: Cirelli A, et al. Serum Selenium Concentration and Disease Progress in Patients with HIV Infection. Clin Biochem. Apr1991;24(2):211-14.
  14. View Abstract: Schrauzer GN, et al. Cancer Mortality Correlation Studies--III: Statistical Associations with Dietary Selenium Intakes. Bioinorg Chem. 1977;7(1):23-31.
  15. View Abstract: Combs GF Jr, et al. Reduction of cancer mortality and incidence by selenium supplementation. Med Klin. Sep1997;92(Suppl 3):42-5.
  16. View Abstract: Federico A, et al. Effects of selenium and zinc supplementation on nutritional status in patients with cancer of digestive tract. Eur J Clin Nutr. Apr2001;55(4):293-7.
  17. View Abstract: Wong HK, et al. Effects of selenium supplementation on malignant lymphoproliferative pathologies associated with OF1 mouse ageing. Anticancer Res. Jan2001;21(1A):393-402.
  18. View Abstract: Thikkurissy S, et al. Effect of interleukin-2 and selenium on the growth of squamous cell carcinoma cells. Otolaryngol Head Neck Surg. Feb2001;124(2):142-9.
  19. View Abstract: Combs GF Jr, et al. Chemopreventive agents: selenium. Pharmacol Ther. Sep1998;79(3):179-92.
  20. View Abstract: Clark LC, et al. Effects of Selenium Supplementation for Cancer Prevention in Patients with Carcinoma of the Skin. A Randomized Controlled Trial. Nutritional Prevention of Cancer Study Group. JAMA. Dec1996;276(24):1957-63.
  21. View Abstract: Kadrabova J, et al. Selenium Status is Decreased in Patients with Intrinsic Asthma. Biol Trace Elem Res. Jun1996;52(3):241-48.