Selenium is a trace mineral that our bodies use to produce glutathione peroxidase. Glutathione peroxidase is part of the body's antioxidant defense system; it works with vitamin E to protect cell membranes from damage caused by dangerous, naturally occurring substances known as free radicals.
China has very low rates of colon cancer, presumably because of the nation's low-fat diet. However, in some parts of China where the soil is depleted of selenium, the incidence of various types of cancer is much higher than in the rest of the country. This fact has given rise to a theory that selenium deficiency is a common cause of cancer, and that selenium supplements can reduce this risk.
As we will see, there is some preliminary evidence that selenium supplements might provide some protection against some types of cancer among people living in the US, but this evidence is far from definitive.
The official US and Canadian recommendations for daily intake of selenium are as follows:
Selenium content of food varies depending on the selenium content of the soil in which it was grown. Studies suggest that many people in certain developed countries, including New Zealand, Belgium, and Scandinavia, do not get enough selenium in their diets.3-6 However, most people in the US and Canada are believed to consume sufficient quantities of selenium.46
Foods containing significant and reliable amounts of selenium include animal products like meat, seafood, and dairy foods, as well as whole grains and other foods grown in selenium-rich soils, especially Brazil nuts. The table below from the Office of Dietary Supplements provides a more complete list of the selenium content in certain foods and the percent daily value.69
|% Daily Value|
|Brazil nuts, dried||1 ounce||544||777|
|Tuna, light, canned in water, drained||3 ounces||68||97|
|Cod, cooked||3 ounces||32||46|
|Turkey, roasted||3 ounces||27||39|
|Chicken breast, roasted||3 ounces||24||34|
|Beef chuck roast, lean, roasted||3 ounces||23||33|
|Sunflower seed, dry roasted||1 ounce||23||33|
|Enriched egg noodles, boiled||½ cup||19||27|
|Enriched macaroni, boiled||½ cup||19||27|
|Ground beef, broiled||3 ounces||18||26|
|Hard-boiled egg||1 large||15||21|
|Fortified instant oatmeal||1 cup||12||17|
|Low-fat cottage cheese||½ cup||11||16|
|Whole-wheat bread||1 slice||11||16|
|Long-grain brown rice||½ cup||10||14|
|Enriched long-grain white rice||½ cup||6||9|
|White bread||1 slice||6||9|
|Black walnuts||1 ounce||5||7|
|Cheddar cheese||1 ounce||4||6|
Certain digestive conditions, such as Crohn’s disease, short-bowel syndrome, and ulcerative colitis may impair selenium absorption.47 In addition, medications that reduce stomach acid such as proton pump inhibitors or H2blockers may reduce absorption of selenium.12
In controlled trials of selenium, typical dosages were 100 mcg to 200 mcg daily.
The two general types of selenium supplements are available to consumers are organic and inorganic forms. These terms have a very specific chemical meaning and have nothing to do with "organic" foods. In chemistry, organic means a substance's chemical structure includes carbon. Inorganic chemicals have no carbon atoms.
The inorganic form of selenium, selenite, is essentially selenium atoms bound to oxygen. Some research suggests that selenite is harder for the body to absorb than organic forms of selenium, such as selenomethionine (selenium bound to methionine, an essential amino acid) or high-selenium yeast (which contains selenomethionine).13,14 However, other research on both animals and humans suggests that selenite supplements are about as good as organic forms of selenium.15,16 These contradictory results suggest that any differences in absorption, if they exist at all, are relatively minor.
Selenium is required for a well-functioning immune system.24 Based on this, selenium has been suggested as a treatment for people with HIV. Early studies showed little to no benefit.25-32,62 A large trial reported in 2007 reported that use of selenium supplements reduced viral load.62 However, this study suffered from numerous flaws in its statistical methods. For reasons that are not clear, another study found that selenium supplements decreased symptoms of psychological anxiety in patients undergoing highly active retroviral therapy (HAART).56
One study of healthy people in the UK (where marginally low selenium intake is common) found that use of selenium supplements improved general immune function, as measured by response to poliovirus immunization.57
A preliminary double-blind trial suggests that selenium supplements may improve fertility in males who are selenium deficient.54 Weak evidence suggests that selenium might be helpful for diabetic neuropathy.23
Selenium has also been recommended for many other conditions, including acne, anxiety, cataracts, cervical dysplasia, fibromyalgia, gout, multiple sclerosis, osteoarthritis, psoriasis, and ulcers, but there is no real evidence as yet that it is actually helpful.
A small study among nursing home residents found that low levels of the mineral selenium was associated with depression. Moreover, 8 weeks of supplementation tended to improve the mood of the most seriously depressed patients with low selenium levels.67 The same was not true of the two other nutrients investigated, folate and vitamin C.
Low selenium levels have been associated with increased likelihood of developing certain kinds of rheumatoid arthritis.34 However, selenium supplements don't appear to help rheumatoid arthritis once it has developed.35,36,44,45
Selenium may offer some benefits for people with hypothyroidism.68 A review of 6 randomized trials, involving 339 people with low thyroid hormone level from Hashimoto's thyroiditis, compared selenium (200 mcg daily for 3 months) to placebo. Those in the selenium group reported improvements in their mood and well-being, and lab tests found lower levels of the antibodies that attack the thyroid.
Somewhat inconsistent evidence suggests that selenium supplements may help prevent cancer.
Evidence from observational studies indicates that low intake of selenium is tied to increased risk of cancer.39,40 However, such studies are notoriously unreliable as guidelines to therapy. Only double-blind trials can truly determine whether selenium supplements can help prevent cancer. (For information on why this is so, see Why Does This Database Rely on Double-blind Studies?)
The most important double-blind study on selenium and cancer was conducted by researchers at the University of Arizona Cancer Center.37 In this trial, which began in 1983, 1,312 people were divided into two groups. One group received 200 mcg of yeast-based selenium daily; the other received placebo. Participants were not deficient in selenium, although their selenium levels fell toward the bottom of the normal range. The researchers were trying to determine whether selenium could lower the incidence of skin cancers.
As it happened, no benefits for skin cancer were seen. (In fact, careful analysis of the data suggests that selenium supplements actually marginally increased risk of certain forms of skin cancer.58 ) However, researchers saw dramatic declines in the incidence of several other cancers in the selenium group. For ethical reasons, researchers felt compelled to stop the study after several years and allow all participants to take selenium.
When all the results were tabulated, it became clear that the selenium-treated group developed almost 66% fewer prostate cancers, 50% fewer colorectal cancers, and about 40% fewer lung cancers as compared with the placebo group. (All these results were statistically significant.) Selenium-treated subjects also experienced a statistically significant (17%) decrease in overall mortality, a greater than 50% decrease in lung cancer deaths, and nearly a 50% decrease in total cancer deaths. A subsequent close look at the data showed that only study participants who were relatively low in selenium to begin with experienced protection from lung cancer or colon cancer; people with average or above average levels of selenium did not benefit significantly.55, 60 It has not yet been reported whether this limitation of benefit to low-selenium participants was true of the other forms of cancer as well.
While this evidence is promising, it has one major flaw. The laws of statistics tell us that when researchers start to deviate from the question their research was designed to answer, the results may not be trustworthy. Currently, other studies are underway in an attempt to validate the findings accidentally discovered in this trial.
Interestingly, combining the results of 12 recent placebo-controlled trials investigating the association between antioxidant supplementation and cancer, researchers found that men who took selenium experienced an overall reduction in the incidence of cancer. No similar effect, however, was observed in women.65 This difference cannot be explained without more research. In addition, selenium supplementation appeared to modestly lower cancer mortality in both men and women.
Other evidence for the possible anticancer benefits of selenium comes from large-scale Chinese studies showing that giving selenium supplements to people who live in selenium-deficient areas reduces the incidence of cancer.38 In addition, animal trials have found anticancer benefits.41,42
However, one study published in 2007 reported negative results in transplant patients.63 People who undergo organ transplants are at particularly high risk of skin cancer linked to the human papilloma virus (HPV). In this double-blind study, 184 organ transplant recipients were given either placebo or selenium at a dose of 200 mg daily. The results over two years failed to show benefit; both the placebo and the selenium group developed precancerous and cancerous lesions at the same rate.
The US Institute of Medicine issues guidelines for the maximum total daily intake of various nutrients, based on estimations of what should be safe for virtually all healthy individuals. These tolerable upper intake levels (ULs) are, thus, conservative guidelines. For selenium, they have been set as follows:43
Note that these dosages apply to combined dietary and supplemental intake of selenium. When deciding how much selenium it’s safe to take, keep in mind that most adults already receive about 100 mcg of selenium in the daily diet.
Maximum safe doses of selenium for individuals with severe liver or kidney disease have not been established. There is some evidence that supplementing selenium over the long-term in areas where selenium is already adequate in the diet may increase the risk of diabetes and perhaps hypercholesterolemia.66
Highly excessive selenium intake, beginning at about 900 mcg daily, can cause selenium toxicity.46 Signs include depression, nervousness, emotional instability, nausea, vomiting, and in some cases loss of hair and fingernails.
1. Gallegos A, Berggren M, Gasdaska JR, et al. Mechanisms of the regulation of thioredoxin reductase activity in cancer cells by the chemopreventive agent selenium. Cancer Res. 1997;57:4965-4970.
2. Harrison PR, Lanfear J, Wu L, et al. Chemopreventive and growth inhibitory effects of selenium. Biomed Environ Sci. 1997;10:235-245.
3. Tolonen M. Finnish studies on antioxidants with special reference to cancer, cardiovascular diseases and aging. Int Clin Nutr Rev. 1989;9:68-75.
4. Neve J, Vertongen F, Capel P. Selenium supplementation in healthy Belgian adults: response in platelet glutathione peroxidase activity and other blood indices. Am J Clin Nutr. 1988;48:139-143.
5. Thomson CD, Robinson MF. The changing selenium status of New Zealand residents. Eur J Clin Nutr. 1996;50:107-114.
6. Duffield AJ, Thomson CD, Hill KE, et al. An estimation of selenium requirements for New Zealanders. Am J Clin Nutr. 1999;70:896-903.
7. Swanson CA, Longnecker MP, Veillon C, et al. Selenium intake, age, gender, and smoking in relation to indices of selenium status of adults residing in a seleniferous area. Am J Clin Nutr. 1990;52:858-862.
8. Levander OA. Scientific rationale for the 1989 recommended dietary allowance for selenium. J Am Diet Assoc. 1991;91:1572-1576.
9. Pennington JA, Wilson DB, Newell RF, et al. Selected minerals in foods surveys, 1974 to 1981/82. J Am Diet Assoc. 1984;84:771-780.
10. Pennington JA, Young BE, Wilson DB. Nutritional elements in US diets: results from the Total Diet Study, 1982 to 1986. J Am Diet Assoc. 1989;89:659-664.
11. Thompson JN, Erdody P, Smith DC. Selenium content of food consumed by Canadians. J Nutr. 1975;105:274-277.
12. Sturniolo GC, Montino MC, Rossetto L, et al. Inhibition of gastric acid secretion reduces zinc absorption in man. J Am Coll Nutr. 1991;10:372-375.
13. Stewart MS, Spalholz JE, Neldner KH, et al. Selenium compounds have disparate abilities to impose oxidative stress and induce apoptosis. Free Radical Biol Med. 1999;26:42-48.
14. Shiobara Y, Yoshida T, Suzuki KT. Effects of dietary selenium species on Se concentrations in hair, blood, and urine. Toxicol Appl Pharmacol. 1998;152:309-314.
15. Wen HY, Davis RL, Shi B, et al. Bioavailability of selenium from veal, chicken, beef, lamb, flounder, tuna, selenomethionine, and sodium selenite assessed in selenium-deficient rats. Biol Trace Elem Res. 1997;58:43-53.
16. Neve J. Human selenium supplementation as assessed by changes in blood selenium concentration and glutathione peroxidase activity. J Trace Elem Med Biol. 1995;9:65-73.
17. Clark LC, Combs GF Jr, Turnbull BW, 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. 1996;276:1957-1963.
18. Yu SY, Zhu YJ, Li WG. Protective role of selenium against hepatitis B virus and primary liver cancer in Qidong. Biol Trace Elem Res. 1997;56:117-124.
19. National Research Council, Diet and Health. Implications for Reducing Chronic Disease Risk. Washington, DC: National Academy Press; 1989:376-379.
20. Hocman G. Chemoprevention of cancer: selenium. Int J Biochem. 1988;20:123-132.
21. Tanaka T, Makita H, Kawabata K, et al. 1,4-phenylenebis(methylene)selenocyanate exerts exceptional chemopreventive activity in rat tongue carcinogenesis. Cancer Res. 1997;57:3644-3648.
22. Yan L, Yee JA, McGuire MH, et al. Effect of dietary supplementation of selenite on pulmonary metastasis of melanoma cells in mice. Nutr Cancer. 1997;28:165-169.
23. Kahler W, Kuklinski B, Ruhlmann C, et al. Diabetes mellitus—a free radical-associated disease. Results of adjuvant antioxidant supplementation [in German; English abstract]. Z Gesamte Inn Med. 1993;48:223-232.
24. Schrauzer GN, Sacher J. Selenium in the maintenance and therapy of HIV-infected patients. Chem Biol Interact. 1994;91:199-205.
25. Constans J, Pellegrin JL, Sergeant C, et al. Serum selenium predicts outcome in HIV infection. [letter]. J Acquir Immune Defic Syndr Hum Retrovirol. 1995;10:392.
26. Baum MK, Shor-Posner G, Lai S, et al. High risk of HIV-related mortality is associated with selenium deficiency. J Acquir Immune Defic Syndr Hum Retrovirol. 1997;15:370-374.
27. Campa A, Shor-Posner G, Indacochea F, et al. Mortality risk in selenium-deficient HIV-positive children. J Acquir Immune Defic Syndr Hum Retrovirol. 1999;20:508-513.
28. Olmsted L, Schrauzer GN, Flores-Arce M, et al. Selenium supplementation of symptomatic human immunodeficiency virus infected patients. Biol Trace Elem Res. 1989;20:59-65.
29. Constans J, Delmas-Beauvieux MC, Sergeant C, et al. One-year antioxidant supplementation with beta-carotene or selenium for patients infected with human immunodeficiency virus: a pilot study [letters]. Clin Infect Dis. 1996;23:654-656.
30. Look MP, Rockstroh JK, Rao GS, et al. Sodium selenite and N-acetylcysteine in antiretroviral-naive HIV-1-infected patients: a randomized, controlled pilot study. Eur J Clin Invest. 1998;28:389-397.
31. Zazzo JF, Chalas J, Lafont A, et al. Is nonobstructive cardiomyopathy in AIDS a selenium deficiency-related disease? [letter] JPEN J Parenter Enteral Nutr. 1988;12:537-538.
32. Dworkin BM. Selenium deficiency in HIV infection and the acquired immunodeficiency syndrome (AIDS). Chem Biol Interact. 1994;91:181-186.
33. Baeten JM, Mostad SB, Hughes MP, et al. Selenium deficiency is associated with shedding of HIV-1-infected cells in the female genital tract. J Acquir Immune Defic Syndr. 2001;26:360-364.
34. Knekt P, Heliovaara M, Aho K, et al. Serum selenium, serum alpha-tocopherol, and the risk of rheumatoid arthritis [abstract]. Epidemiology. 2000;11:402-405.
35. Tarp U. Selenium in rheumatoid arthritis. A review. Analyst. 1995;120:877-881.
36. Peretz A, Siderova V, Neve J. Selenium supplementation in rheumatoid arthritis investigated in a double blind, placebo-controlled trial. Scand J Rheumatol. 2001;30:208-212.
37. Clark LC, Combs GF Jr, Turnbull BW, 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. 1996;276:1957-1963.
38. Yu SY, Zhu YJ, Li WG. Protective role of selenium against hepatitis B virus and primary liver cancer in Qidong. Biol Trace Elem Res. 1997;56:117-124.
39. National Research Council, Diet and Health. Implications for Reducing Chronic Disease Risk. Washington, DC: National Academy Press; 1989: 376-379.
40. Hocman G. Chemoprevention of cancer: selenium. Int J Biochem. 1988;20:123-132.
41. Tanaka T, Makita H, Kawabata K, et al. 1,4-phenylenebis(methylene)selenocyanate exerts exceptional chemopreventive activity in rat tongue carcinogenesis. Cancer Res. 1997;57:3644-3648.
42. Yan L, Yee JA, McGuire MH, et al. Effect of dietary supplementation of selenite on pulmonary metastasis of melanoma cells in mice. Nutr Cancer. 1997;28:165-169.
44. Petersson I, Majberger E, Palm S, et al. Treatment of rheumatoid arthritis with selenium and vitamin E [abstract]. Scand J Rheumatol. 1991;20:218.
45. Jantti J, Vapaatalo H, Seppala E, et al. Treatment of rheumatoid arthritis with fish oil, selenium, vitamins A and E, and placebo [abstract]. Scand J Rheumatol. 1991;20:225.
46. Institute of Medicine. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids. Washington, DC: National Academy Press; 2000.
47. Rannem T, Ladefoged K, Hylander E, Hegnhoj J, Staun M. Selenium depletion in patients with gastrointestinal diseases: Are there any predictive factors? Scand J Gastroenterol. 1998;33:1057-1061.
48. Kardinaal AF, Kok FJ, Kohlmeier L, et al. Association between toenail selenium and risk of acute myocardial infarction in European men. The EURAMIC Study. European Antioxidant Myocardial Infarction and Breast Cancer. Am J Epidemiol. 1997;145:373-379.
49. Korpela H, Kumpulainen J, Jussila E, et al. Effect of selenium supplementation after acute myocardial infarction. Res Commun Chem Pathol Pharmacol. 1989;65:249-252.
50. Lapenna D, de Gioia S, Ciofani G, Mezzetti A, Ucchino S, Calafiore AM, Napolitano AM, Di Ilio C, Cuccurulo F. Glutathione-related antioxidant defenses in human atherosclerotic plaques. Circulation. 1998;97:1930-1934.
51. Neve J. Selenium as a risk factor for cardiovascular diseases. J Cardiovasc Risk. 1996;3:42-47.
52. Salvini S, Hennekens CH, Morris JS, et al. Plasma levels of the antioxidant selenium and risk of myocardial infarction among US physicians. Am J Cardiol. 1995;76:1218-21.
53. Trankmann P, Thiele R, Winnefeld K, et al. Effect of administration of selenium and vitamin E on heart failure and ventricular arrhythmias in patients with acute myocardial infarct. Med Klin. 1999;94(suppl 3):78-80.
54. Scott R , MacPherson A, Yates RWS, et al. The effect of oral selenium supplementation on human sperm motility. Br J Urol. 1998;82:76-80.
55. Reid ME, Duffield-Lillico AJ, Garland L, et al. Selenium supplementation and lung cancer incidence: an update of the nutritional prevention of cancer trial. Cancer Epidemiol Biomarkers Prev. 2002;11:1285-1291.
56. Shor-Posner G, Lecusay R, Miguez MJ, et al. Psychological burden in the era of HAART: impact of selenium therapy. Int J Psychiatry Med. 2003;33:55-69.
57. 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. 2004;80:154-162.
58. Duffield-Lillico AJ, Slate EH, Reid ME, et al. Selenium supplementation and secondary prevention of nonmelanoma skin cancer in a randomized trial. J Natl Cancer Inst. 2003;95:1477-1481.
59. Rayman M, Thompson A, Warren-Perry M, et al. Impact of selenium on mood and quality of life: a randomized, controlled trial. Biol Psychiatry. 2005 Sep 19. [Epub ahead of print]
60. Reid ME, Duffield-Lillico AJ, Sunga A, et al. Selenium supplementation and colorectal adenomas: an analysis of the nutritional prevention of cancer trial. Int J Cancer. 2005 Oct 10. [Epub ahead of print]
61. Shaheen SO, Newson RB, Rayman MP, et al. Randomised, double-blind, placebo-controlled trial of selenium supplementation in adult asthma. Thorax. 2007 Jan 18. [Epub ahead of print]
62. Hurwitz BE, Klaus JR, Llabre MM, et al. Suppression of human immunodeficiency virus type 1 viral load with selenium supplementation, a randomized controlled trial. Arch Intern Med. 2007;167:148-154.
63. Dreno B, Euvrard S, Frances C, et al. Effect of selenium intake on the prevention of cutaneous epithelial lesions in organ transplant recipients. Eur J Dermatol. 2007;17:140-145.
64. Stranges S, Marshall JR, Natarajan R, et al. Effects of long-term selenium supplementation on the incidence of type 2 diabetes. Ann Intern Med. 2007 July 9. [Epub ahead of print]
65. Bardia A, Tleyjeh IM, Cerhan JR, et al. Efficacy of antioxidant supplementation in reducing primary cancer incidence and mortality: systematic review and meta-analysis. M ayo Clin Proc. 2008;83:23-34.
66. Navas-Acien A, Bleys J, Guallar E. Selenium intake and cardiovascular risk: what is new? Curr Opin Lipidol. 2008;19:43-49.
67. Gosney MA, Hammond MF, Shenkin A, et al. Effect of micronutrient supplementation on mood in nursing home residents. Gerontology. 2008 May 8.
68. Toulis KA, Anastasilakis AD, Tzellos TG, Goulis DG, Kouvelas D. Selenium supplementation in the treatment of Hashimoto's thyroiditis: a systematic review and a meta-analysis. Thyroid. 2010;20(10):1163-1173.
69. Dietary supplement fact sheet: selenium. Office of Dietary Supplements website. Available at: http://ods.od.nih.gov/factsheets/Selenium-HealthProfessional/. Accessed September 10, 2012.
Last reviewed December 2015 by EBSCO CAM Review Board
Last Updated: 12/15/2015