Where is it found?
Brazil nuts are the best source of selenium. Yeast, whole grains, and seafood are also good sources. Animal studies have found that selenium from yeast is better absorbed than selenium in the form of selenite.1
Selenium has been used in connection with the following conditions (refer to the individual health concern for complete information):
| Science Ratings | Health Concerns |
|---|---|
 |
Burns (zinc, copper, and selenium, intravenously, for extensive burns) Colon cancer (reduces risk) Immune function (for elderly people) Infections (to prevent hospital-acquired infections in very low birth weight infants) Lung cancer (reduces risk) Phenylketonuria (if deficient) Prostate cancer (reduces risk) Thyroiditis (autoimmune) |
 |
Cardiomyopathy (only for Keshan’s cardiomyopathy) Halitosis (if gum disease) Hypothyroidism (if deficient) Retinopathy (combined with vitamin A, vitamin C and vitamin E) |
 Reliable
and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies
suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal
or no scientific evidence. For a supplement, little scientific support and/or minimal health
benefit. |
|
Who is likely to be deficient?
While most people probably don’t take in enough selenium, gross deficiencies are rare in Western countries. Soils in some areas are selenium-deficient and people who eat foods grown primarily on selenium-poor soils are at risk for deficiency. People with AIDS have been reported to be depleted in selenium.2 Similarly, limited research has reported an association between heart disease and depleted levels of selenium.3 People who are deficient in selenium have an increased risk of developing certain types of rheumatoid arthritis.4
How much is usually taken?
While the Recommended Dietary Allowance for most adults is 55 mcg per day, an adult intake of 100–200 mcg of selenium per day is recommended by many doctors.
Are there any side effects or interactions?
Selenium is safe at the level people typically supplement (100–200 mcg); however, taking more than 900 mcg of selenium per day has been reported to cause adverse effects in some people.5 Selenium toxicity can result in loss of fingernails, skin rash, and changes in the nervous system. In the presence of iodine-deficiency-induced goiter, selenium supplementation has been reported to exacerbate low thyroid function.6 Although most research suggests that selenium prevents cancer, one study found an increased risk of a type of skin cancer (squamous cell carcinoma) in people taking selenium supplements.7 The National Academy of Sciences recommends that selenium intake not exceed 400 mcg per day, unless the higher intake is monitored by a healthcare professional.8 In a double-blind study of people who took 200 mcg of selenium per day for several years to prevent recurrences of skin cancer, the incidence of diabetes was higher in people who received selenium (9.7%) than in those who received a placebo (6.5%).9 While this difference was statistically significant, this finding should be considered preliminary, since the study was not originally designed to test whether selenium influences the risk of developing diabetes.
Selenium enhances the antioxidant effect of vitamin E.
Are there any drug
interactions?
Certain medicines may interact with selenium. Refer to drug interactions for a list of those medicines.
1. Yoshida M, Fukunaga K, Tsuchita H, Yasumoto K. An evaluation of the bioavailability of selenium in high-selenium yeast. J Nutr Sci Vitaminol 1999;45:119–28.
2. Dworkin BM. Selenium deficiency in HIV infection and the acquired immunodeficiency syndrome (AIDS). Chem Biol Iteract 1994;91:181–6.
3. Moore JA, Noiva R, Wells IC. Selenium concentrations in plasma of patients with arteriographically defined coronary atherosclerosis. Clin Chem 1984;30:1171–3.
4. Knekt P, Heliovaara M, Aho K, et al. Serum selenium, serum alpha-tocopherol, and the risk of rheumatoid arthritis. Epidemiology 2000;11:402–5.
5. Yang GQ, Zhou RH. Further observations on the human maximum safe dietary selenium intake in a seleniferous area of China. J Trace Elem Electrolytes Hlth Dis 1994;8:159–65.
6. Contempre B, Dumont JE, Ngo B, et al. Effects of selenium supplementation in hypothyroid subjects of an iodine and selenium deficient area: The possible danger of indiscriminate supplementation of iodine deficient subjects with selenium. J Clin Endocrinol Metabol 1991;73:213–5.
7. 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;95:1477–81.
8. Panel on Dietary Antioxidants and Related Compounds, Food and Nutrition Board, Institute of Medicine, National Academy of Sciences. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. National Academy Press, Washington, D.C., 2000.
9. Stranges S, Marshall JR, Natarajan R, et al. Effects of long-term selenium supplementation on the incidence of type 2 diabetes: a randomized trial. Ann Intern Med 2007;147:217–23.
