• Basic Info

Category

Synonyms

Atomic number 34, Na2SeO3, selenium dioxide, selenized yeast, L-selenomethionine, Se, Sele-Pak, selenate, selenite, selenious acid, selenium sulfide, seleno yeast, selenocysteine, selenomethionine (Semet), selepen, Se-methylselenocysteine (SeMCYS).

Background

Selenium is a trace mineral found in soil, water, and some foods. It is an essential element in several metabolic pathways.

Selenium deficiency can occur in areas where soil content of selenium is low, and may affect thyroid function and cause conditions such as Keshan disease. Selenium deficiency is also commonly seen in patients on total parenteral nutrition (TPN) as their sole source of nutrition. Gastrointestinal disorders may decrease the absorption of selenium resulting in depletion or deficiency. Selenium may be destroyed when foods are refined or processed.

Specific dietary sources of selenium include brewer's yeast, wheat germ, butter, garlic, grains, sunflower seeds, Brazil nuts, walnuts, raisins, liver, kidney, shellfish (lobster, oyster, shrimp, scallops), fresh-water and salt-water fish (red snapper, salmon, swordfish, tuna, mackerel, halibut, flounder, herring, smelts). Selenium is also found in alfalfa, burdock root, catnip, fennel seed, ginseng, raspberry leaf, radish, horseradish, onion, chives, medicinal mushrooms (reishi, shiitake), and yarrow.

The role of selenium in cancer prevention has been the subject of recent study and debate. Initial evidence from the Nutritional Prevention of Cancer (NPC) trial suggests that selenium supplementation reduces the risk of prostate cancer among men with normal baseline PSA (prostate specific antigen) levels, and low selenium blood levels. However, in this study selenium did not reduce the risk of lung, colorectal, or basal cell carcinoma of the skin, and actually increased the risk of squamous cell skin carcinoma. The ongoing Selenium and Vitamin E Cancer Prevention Trial (SELECT) aims to definitively address the role of selenium in prostate cancer prevention.

Evidence

Antioxidant: Selenium is a component of glutathione peroxidase, which possesses antioxidant activity, and demonstrates antioxidant properties in humans. Long-term clinical benefits remain controversial.
Grade: B

Keshan disease: Keshan disease is a cardiomyopathy (heart disease) restricted to areas of China in people having an extremely low selenium status. Prophylactic administration of sodium selenite has been shown to significantly decrease the incidence of this disorder. Selenium is used to treat and prevent selenium deficiency (for example in those with HIV or receiving enteral feedings).
Grade: B

Prostate cancer prevention: Initial evidence has suggested that selenium supplementation reduces the risk of developing prostate cancer in men with normal baseline PSA (prostate specific antigen) levels, and low selenium blood levels. This is the subject of large well-designed studies, including the Nutritional Prevention of Cancer Trial (NPC), and the ongoing Selenium and Vitamin E Cancer Prevention Trial (SELECT), as well as prior population and case-control studies. The NPC was conducted in 1,312 Americans, and reported that daily selenium reduces the overall incidence of prostate cancer - although these protective effects only occurred in men with baseline PSA levels less than or equal to 4 nanograms per milliliter, and those with low baseline blood selenium levels. The NPC trial was primarily designed to measure the development of nonmelanoma skin cancers, not other types of cancers, and therefore these prostate cancer results cannot be considered definitive. To settle this question, further study is underway: The SELECT trial is in progress, with a goal to include 32,400 men with serum PSA levels less than or equal to 4 nanograms per milliliter. SELECT was started in 2001, with results expected in 2013. Laboratory studies have reported several potential mechanisms for selenium's beneficial effects in prostate cancer, including decrease in androgen receptors and PSA production, antioxidant effects, angiogenesis inhibition, or apoptosis. It is not known if selenium is helpful in men who already have been diagnosed with prostate cancer to prevent progression or recurrence of disease. It does appear that selenium may not be beneficial in those with elevated PSA levels, or with normal/high selenium levels. It remains unclear whether men at risk (or all men) should have their serum selenium values measured; results of the SELECT study may provide additional guidance. There is evidence that low selenium levels are associated with an increased risk of prostate cancer, and several mechanisms for the beneficial effects of selenium supplementation have been suggested. In the NPC trial, no benefits were seen in reducing the risk of colorectal or lung cancers. Although an overall reduction in cancer risk was observed, it is not clear which specific types of cancer besides prostate cancer prevention may benefit.
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Asthma: Preliminary research reports that selenium supplementation may help improve asthma symptoms. Further research is needed to confirm these results.
Grade: C

Burns: Early study results suggest that supplementation with selenium and other trace elements (copper, zinc) may increase the rate of burn wound healing. Additional research is necessary before a clear recommendation can be made.
Grade: C

Cancer treatment: Several studies suggest that low levels of selenium (measured in the blood or in tissues such as toenail clippings), may be a risk factor for developing cancer, particularly prostate cancer. Population studies suggest that people with cancer are more likely to have low selenium levels than healthy matched individuals, but in most cases it is not clear if the low selenium levels are a cause or merely a consequence of disease. It remains unclear if selenium is beneficial in the treatment of any type of cancer.
Grade: C

Cardiomyopathy: Low selenium levels have been associated with the development of cardiomyopathy, and selenium supplementation is likely of benefit in such cases (for example in Keshan disease). However, most cases of cardiomyopathy are not due to low selenium levels, and therefore selenium may not be helpful. It has been suggested that low selenium levels may be a risk for coronary heart disease, although this remains unclear.
Grade: C

Cardiovascular disease (prevention): Despite the documented antioxidant and chemopreventive properties of selenium, studies of the effects of selenium intake and supplementation on cardiovascular disease yield inconsistent findings. Better-designed trials are needed to reach a firm recommendation.
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Cataracts: Preliminary research reports that selenium supplementation may affect the development of cataracts. Further research is needed before a clear conclusion can be drawn.
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Chemotherapy side effects: Study results of selenium supplementation during chemotherapy are mixed. General concern has been raised that antioxidants may interfere with radiation therapy or some chemotherapy agents, which themselves can depend on oxidative damage to tumor cells for anti-cancer activity. Therefore, patients undergoing cancer treatment should speak with their oncologist and pharmacist before taking selenium supplements.
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Cystic fibrosis : Preliminary research of selenium supplementation in cystic fibrosis patients yields indeterminate results. Further research is needed in this area before a conclusion can be drawn.
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Dandruff: Studies report that selenium-containing shampoos may help improve dandruff, and selenium is included in some commercially available products.
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Dialysis: The benefits of selenium supplementation in dialysis patients remain unclear. Some methods of dialysis may lower plasma selenium levels.
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Fatigue : Evidence of benefit is inconclusive in this area.
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HIV/AIDS: Selenium supplementation has been studied in HIV/AIDS patients, and some reports associate low selenium levels with complications such as cardiomyopathy. It remains unclear if selenium supplementation is beneficial in patients with HIV, particularly during antiretroviral therapy.
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Infection prevention: Preliminary research reports that selenium can be beneficial in the prevention of several types of infection, including recurrence of erysipelas (bacterial skin infection associated with lymphedema) orMycoplasma pneumonia.Further research is needed to confirm these results before a clear recommendation can be made.
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Intracranial pressure symptoms: Preliminary research shows a decrease of symptoms of elevated intracranial pressure (headaches, nausea, vomiting, vertigo, unsteady gait, speech disorders, and seizures). More research is needed before a recommendation can be made.
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Liver disease: Selenium supplementation has been studied in various liver disorders, including hepatitis, with mixed results.
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Infertility: Selenium supplementation has been studied for male infertility and sperm motility with mixed results. Evidence is lacking regarding potential effects on female infertility.
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Low birth weight: Selenium supplementation has been studied in low birth weight infants. Additional evidence is warranted in this area before a clear conclusion can be drawn.
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Lymphedema: Preliminary research reports that selenium supplementation may decrease lymphedema. Further research is needed to confirm these results before a clear recommendation can be made.
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Malabsorption: Low selenium status has been demonstrated in several malabsorptive syndromes and in some digestive and gastrointestinal allergic conditions. There is some evidence that children with food allergies have a higher risk of selenium deficiency. There is no clear benefit of selenium supplementation as a therapy for malabsorptive syndromes, although vitamin supplementation in general may be warranted.
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Myotonic dystrophy: Selenium and vitamin supplementation has been studied in myotonic dystrophy with mixed results.
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Pancreatitis: There is inconclusive evidence regarding the use of selenium in pancreatitis.
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Pre-eclampsia: Preliminary study in women with pregnancy-induced hypertension has reported reduced edema, without significant impact on birth outcomes. No clear conclusion can be drawn in the absence of additional well-designed research.
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Psoriasis: Research is inconclusive in this area.
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Quality of life (elderly): Studies of selenium supplementation for mood elevation and quality of life yield mixed results. Further research is needed before a firm conclusion may be reached.
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Rheumatoid arthritis: Selenium supplementation has been studied in rheumatoid arthritis patients with mixed results. Additional research is necessary before a clear conclusion can be drawn.
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Sepsis (severe bacterial infection in the blood): Study results of selenium supplementation in septic patients are mixed.
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Skin disorders (lesions): Supplementation with selenium may improve skin lesion status, although more studies are needed before a clear conclusion can be drawn.
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Sunburn prevention: Photoprotection was initially observed in preliminary research using selenium supplementation and other antioxidants, although there is some evidence of ineffectiveness in preventing light-induced erythema (skin redness).
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Thyroid conditions: An early toxic effect of selenium is disruption of endocrine function, including synthesis of thyroid hormones (T3). Selenium has been suggested to improve inflammatory activity in chronic autoimmune thyroiditis or Grave's disease. Further research is needed before a clear conclusion can be drawn.
Grade: C

Tinea capitis: Commercially available 1% selenium sulfide shampoo has been reported as equivalent to sporicidal therapy in the adjunctive treatment of tinea capitis infection, although further high quality evidence is warranted.
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Tinea versicolor: Preliminary study of topical selenium (selenium sulfide shampoo) is inconclusive.
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Colorectal cancer prevention: Evidence from the Nutritional Prevention of Cancer (NPC) trial suggests that selenium supplementation does not significantly reduce the risk of developing colorectal cancer. This randomized study was conducted in 1,312 Americans over a 13-year period, and compared the effects of daily selenium versus placebo. Although initial (interim) analysis suggested possible benefits, a later analysis found a lack of statistical significance.
Grade: D

Kashin-beck osteoarthropathy: Kashin-Beck disease is an osteoarthropathy endemic in selenium- and iodine-deficient areas. Preliminary evidence suggests that selenium supplementation does not significantly improve this disease.
Grade: D

Lung cancer prevention: Evidence from the Nutritional Prevention of Cancer (NPC) trial suggests that selenium supplementation does not significantly reduce the risk of developing lung cancer. Other evidence is inconclusive.
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Muscular dystrophy: Preliminary studies suggest that selenium supplementation is not helpful in muscular dystrophy.
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Osteoarthritis: Selenium-ACE, a formulation containing selenium with three vitamins, has been promoted for the treatment of arthritis. Research has failed to demonstrate significant benefits, with a possible excess of side effects compared to placebo.
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Skin cancer (nonmelanoma) prevention: Results from the Nutritional Prevention of Cancer (NPC) trial, conducted among 1,312 Americans over a 13-year period, suggest that selenium supplementation given to individuals at high risk of nonmelanoma skin cancer is ineffective at preventing basal cell carcinoma, and actuallyincreasesthe risk of squamous cell carcinoma and total nonmelanoma skin cancer. Therefore, selenium supplementation should be avoided in individuals at risk or with a history of nonmelanoma skin cancer.
Grade: D