The micronutrient selenium plays a protective role against oxidative injury and is important for regulating thyroid function. Dietary sources rich in selenium include whole grains, meats, seafood, poultry, and nuts. It is also available in supplement form, and marketing campaigns claim that selenium boosts immune function and prevents cardiovascular and rheumatic diseases, and cancer.
Data from epidemiologic studies and clinical trials indicate that selenium reduces the incidence of some cancers and can alleviate adverse effects associated with chemotherapy and radiation therapy. However, selenium supplementation is not effective in preventing prostate cancer, and long-term use may increase the risk of some skin cancers. Moreover, because selenium can enhance antioxidant effects, it may alter the actions of some chemotherapeutic agents.
—Barrie Cassileth, PhD
ALSO KNOWN AS: Selenocysteine, selenomethionine, selenate, selenite
SUMMARY: Selenium, an essential trace mineral, is an important component of antioxidant systems such as glutathione peroxidase. It also plays an important role in thyroid function. Selenium is obtained by consuming whole grains, meats, seafood, poultry, and nuts. It is also marketed as a supplement with claims that it boosts immune function and prevents cardiovascular and rheumatic diseases, as well as cancer.
Despite several studies, the role of selenium in reducing the risk of cardiovascular disease remains uncertain.1 Selenium supplementation was found to reduce the viral load in individuals infected with HIV.2 Research also indicates that selenium may improve glucose metabolism; it was not useful in preventing type 2 diabetes, and may increase risk.3
The importance of selenium in cancer prevention has been documented in epidemiologic studies and clinical intervention trials. Data suggest it may prevent gastrointestinal4 and lung cancers.5 Selenium supplementation resulted in significant reduction of side effects including hair loss, abdominal pain, and loss of appetite in ovarian cancer patients undergoing chemotherapy.6 It also reduced head and neck lymphedema7 and diarrhea associated with radiation therapy.8
However, the large Selenium and Vitamin E Cancer Prevention Trial (SELECT), based on previous data indicating that selenium and vitamin E reduced the incidence of prostate cancer, failed to support the protective effects of selenium. The trial was suspended in January 2009, when initial data analysis showed no reduction in the risk of prostate cancer with selenium alone or with vitamin E.9
For additional information, visit the Memorial Sloan-Kettering Cancer Center Integrative Medicine Service website, "About Herbs," at http://www.mskcc.org/AboutHerbs.
A cross-sectional analysis of men with prostate cancer indicated that selenium levels may influence the risk of aggressive prostate cancer.10 Long-term use of selenium may increase the risk of certain types of skin cancer.11
ADVERSE REACTIONS: Case Report: Oral consumption of a sodium selenite supplement for treatment of prostate cancer resulted in the death of a 75-year-old man.12
Chronic Selenosis: Doses greater than 1,000 μg/d may result in muscle weakness, fatigue, peripheral neuropathy, dermatitis, nail and hair changes/loss, garlic breath/body odor, irritability, growth retardation, and hepatic necrosis.
Toxicity: Acute toxicity via selenium poisoning has occurred with either accidental or suicidal ingestion of gun bluing solution or sheep drench. Consumption of gram quantities of selenium can cause severe gastrointestinal and neurologic disturbances, acute respiratory distress syndrome, myocardial infarction, and renal failure.13
HERB-DRUG INTERACTIONS: High doses of selenium may decrease vitamin C absorption.13
1. Mozaffarian D: Int J Environ Res Public Health 6:1894-1916, 2009.
2. Hurwitz BE et al: Arch Intern Med 167:148-154, 2007.
3. Stranges S et al: Ann Intern Med 147:217-223, 2007.
4. Bjelakovic G et al: Lancet 364:1219-1228, 2004. 5. Zhuo H et al: Cancer Epidemiol Biomarkers Prev 13:771-778, 2004.
6. Sieja K et al: Gynecol Oncol 93:320-327, 2004.
7. Bruns F et al: Med Princ Pract 13:185-190, 2004.
8. Muecke R et al: Int J Radiat Oncol Biol Phys Feb 2, 2010 (epub ahead of print).
9. Lippman SM et al: JAMA 301:39-51, 2009.
10. Chan JM et al: J Clin Oncol 27:3577-3583, 2009.
11. Duffield-Lillico AJ et al: J Natl Cancer Inst 95:1477-1481, 2003.
12. See KA et al: Med J Aust 185:388-389, 2006.
13. Pronsky ZM: Power's and Moore's Food-Medication Interactions, 11th ed. Pottstown, Pa; Food Medication Interactions; 2000.