Clinician Fact Sheet: Selenium
July 2001; Volume 4; S1-S2
The association between selenium, an essential trace mineral, and cancer gained prominence as a result of epidemiologic studies from the 1960s and 1970s that showed an inverse relationship between selenium intake and the incidence of leukemia and colon, rectal, pancreatic, breast, ovarian, prostate, bladder, lung, and skin cancers, as well as overall cancer mortality.
A retrospective study in the 1980s supported these epidemiologic findings: Subjects with the lowest serum selenium concentrations had twice the risk of several cancers, including breast cancer, as did those with the highest concentrations.1 Many recent case-control and prospective studies boast positive results,2-3 but others have not or have been confounded by the presence of multiple antioxidant agents in the intervention design.4-5
Although questions remain, the clinical evidence does point to an association between selenium levels and cancer risk. Currently, an eight-year, prospective study of 12,000 men and women is under way in France.6 This study may help clarify the effect of selenium supplementation on the incidence of many chronic diseases.
Dietary Reference Intakes (DRI)
- 15 mcg/d for children 0-6 mo
- 20 mcg/d for children 7 mo-3 y
- 30 mcg/d for children 4-8 y
- 40 mcg/d for children 9-13 y
- 55 mcg/d for children 14-18 y
- 55 mcg/d for adults 19 y and older
Food Sources
— Dietary sources of selenium include Brazil nuts, tuna canned in oil, beef liver, cod, enriched grain products, turkey, chicken, eggs, cheese, walnuts, broccoli, mushrooms, and garlic.
— The selenium content of plant foods varies depending upon the presence of selenium in the soil where the plants are grown. Variability exists within the United States.
Mechanism of Action
— Selenium is an antioxidant that regulates the activity of glutathione peroxidase enzymes.
Clinical Uses
- To prevent osteoarthritis, rheumatoid arthritis, and Kashin-Bek disease, a form of deforming arthritis.
- To prevent Osgood-Schlatter disease and Keshan disease, an endemic cardiomyopathy.
- To prevent cardiovascular disease.
- To treat asthma.
- To prevent skin, liver, hepatic, prostate, and colon cancer.
- To prevent macular degeneration and cataracts.
- To treat selenium deficiency commonly associated with HIV/AIDS.
- To improve immune function.
- To prevent liver necrosis.
- To treat abnormal testosterone metabolism.
Formulations
— It has been argued that organic selenium (selenomethionine) is absorbed better than inorganic selenium (selenite); however, there is no evidence to support this claim.
Adverse Effects/Toxicity
— Selenium can cause symptoms of acute toxicity including nausea, vomiting, nail changes, fatigue, and irritability.
— Chronic toxicity resembles arsenic toxicity. Symptoms include hair loss, white horizontal streaking on fingernails, paronychia, fatigue, irritability, hyperreflexia, nausea, vomiting, garlic odor on breath, and metallic taste. Muscle tenderness, tremor, lightheadedness, and facial flushing also may be observed.
— Selenium toxicity has been reported with mean doses greater than 800 mcg/d, with a 95% confidence limit of 600 mcg/d.
— Blood selenium levels can be used to assess the degree of toxicity: levels below 1,000 mcg/L usually are not associated with serious damage; levels above 2,000 mcg/L usually are predictive of serious damage.
— Selenium toxicity can elevate the ST segment and cause T-wave changes characteristic of myocardial infarction.
— Selenium toxicity can elevate serum creatinine kinase levels.
Interactions/Nutrient Depletion
— Selenium levels can be decreased by smoking, alcohol, and oral contraceptives.
— Vitamin E appears to decrease the oxidative damage seen in selenium deficiency; concomitant use of selenium and vitamin E may be beneficial in selenium-deficient individuals. Concomitant use also appears to have synergistic effects on the treatment of heart disease, ischemia, and cancer.
— Use of inorganic sodium selenite or selenate has been noted to interact with ascorbic acid, leading to decreased absorption of selenium.
— Concomitant use of vitamin C may produce synergistic effects; however, large doses of vitamin C may decrease selenium absorption.
— Selenium is essential for the synthesis of active thyroid hormone; therefore, selenium deficiency may affect thyroid function and may worsen the effects of iodine deficiency on thyroid function.
— In comparison to cisplatin treatment alone, concomitant use of selenium can increase the cytotoxic effects of cisplatin in the presence of chelate ethylenediaminetetraacetic acid.
— When testing blood for selenium and other trace elements, avoid powdered gloves to reduce the potential of sample contamination.
— Individuals on total parenteral nutrition or with a digestive disorder, such as Crohn’s disease, that can impair selenium absorption may require selenium supplementation.
References
1. McConnell KP, et al. The relationship of dietary selenium and breast cancer. J Surg Oncol 1980;15:67-70.
2. Clark LC, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. JAMA 1996;276:1957-1963.
3. Yoshizawa K, et al. Study of prediagnostic selenium level in toenails and the risk of advanced prostate cancer. J Natl Cancer Inst 1998;90:1219-1224.
4. Garland M, et al. Prospective study of toenail selenium levels and cancer among women. J Natl Cancer Inst 1995;87:497-505.
5. Menkes MS, et al. Serum beta-carotene, vitamins A and E, selenium, and the risk of lung cancer. N Engl J Med 1986;315:1250-1254.
6. Hercberg S, et al. Background and rationale behind the SU.VI.MAX Study, a prevention trial using nutritional doses of a combination of antioxidant vitamins and minerals to reduce cardiovascular diseases and cancer. Int J Vitam Nutr Res 1998;68:3-20.
Resources
Cirigliano MD, Szapary PO. Selenium supplementation for cancer prevention. Altern Med Alert 1999;2:3-7.
Pelton R, et al. Drug-Induced Nutrient Depletion Hand-book. Hudson, OH: Lexi-Comp; 1999.
Sunde RA. Selenium. In: Stipanuk MH, ed. Biochemical and Physiological Aspects of Human Nutrition. Philadelphia, PA: WB Saunders and Co.; 2000.
Selenium. Facts about Dietary Supplements. Office of Dietary Supplements. National Institutes of Health. Available at: www.cc.nih.gov/ccc/supplements/selen.pdf. Accessed: May 21, 2001.
Natural Medicines Comprehensive Database [database online]. Stockton, CA: Therapeutic Research Center, Inc., 2000.
July 2001; Volume 4; S1-S2
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