Drugs A - Z
Generic Name: selenium
CategoryHerbs & Supplements
Adrusen zinco, atomic number 34, DL-selenomethionine, high-selenium yeast, L-selenium methionine, L-selenomethionine, Na2SeO3, peaselenium, Se, Se-EMP, selen, selenate, selenious acid, selenite, selenite-exchangeable metabolic pool, selenium dioxide, selenium disulfide, selenium sulfide, selenium supplementation, selenium-enriched wheat, selenium-enriched yeast, selenium-rich pea flour, selenium-zinc, selenized yeast, seleno yeast, selenocysteine, selenoenzymes, selenomethionine, selenoproteins, selenous acid, Sele-Pak, selepen, Selmevit, Se-malt, SeMCYS, Seme, SeMet, Se-methylselenocysteine, SeO3(2-), SeO4(2-), SeS, se-spirulina, se-yeast, sodium selenite, Spirulin-Sochi-Selen, wheat selenium.
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 the soil content of selenium is low and it 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), and 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.
EvidenceDISCLAIMER: These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Selenium is a component of glutathione peroxidase, which possesses antioxidant
activity and demonstrates antioxidant properties in humans. Long-term clinical benefits remain controversial.
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. Organic forms of selenium (such as selenized yeast or Se-yeast) may have better bioavailability than selenite and thus may be better preventative treatments for Keshan disease.
Selenium is used to treat and prevent selenium deficiency (for example in those with HIV or receiving enteral feedings).
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. However, 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 decreases 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 the 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 what specific types of cancer, besides prostate cancer, may be prevented by selenium supplementation.
Preliminary research reports that selenium supplementation may help improve asthma symptoms. Further research is needed to confirm these results.
Selenium supplementation may offer benefits in patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency and chronic hemolysis. Selenium supplementation may also affect platelet function and coagulation.
Because selenium is proposed to have a role in immune function, selenium supplementation has been studied in patients with various infections. Some evidence suggests that selenium may promote recovery from bronchitis and pneumonia caused by respiratory syncytial virus (RSV). Though selenium may correct selenium deficiency in patients with bronchitis, more studies are needed to show its effectiveness in treating respiratory infections.
Several studies suggest that low levels of selenium may be a risk factor for developing cancer, particularly gastrointestinal, gynecological, lung, colorectal, and esophageal cancer. Studies have shown significantly reduced risk of some (but not all) cancers in subjects taking selenium supplements. Selenium supplementation may reduce cancer incidence in men more than women. Ongoing trials are examining the precise role of selenium in reducing cancer risk.
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, gastrointestinal, gynecological, and colorectal 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.
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 and Chagas' 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.
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.
Central nervous system disorders:
Studies have consistently shown that antioxidants have no clinical benefits in motor neuron diseases such as amyotrophic lateral sclerosis (ALS). Although the research thus far does not discourage selenium supplementation in patients, more research is needed before selenium is recommended as a treatment for central nervous system disorders.
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.
Selenium is known to play important roles in human health. Though some studies have produced promising results, many showed no evidence that selenium can improve health or decrease mortality in critically ill patients. Research is ongoing, though presently there is not enough evidence to recommend the use of selenium therapy in critical illnesses.
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.
Studies report that selenium-containing shampoos may help improve dandruff, and selenium is included in some commercially available products.
The benefits of selenium supplementation in dialysis patients remain unclear. Some methods of dialysis may lower plasma selenium levels.
Although selenium appears to be involved in cataract development and uveitis (eye inflammation), it is not known whether selenium supplements may affect the risk of developing these disorders. Research in this area is warranted.
Evidence of benefit is inconclusive in this area.
High blood pressure:
Some studies have reported that low serum selenium levels may be related to increased blood pressure. Furthermore, known anti-hypertensive therapies (such as ACE-inhibitors) do not appear to affect the activity of serine-dependent enzymes.
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.
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), sepsis, or Mycoplasma pneumonia. Selenium may help prevent infection by stimulating immune function. Further research is needed to confirm these results before a clear recommendation can be made.
Selenium supplementation has been studied for male infertility and sperm motility with mixed results. Evidence is lacking regarding the potential effects on female infertility.
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.
Because antioxidant supplements are thought to slow aging and prevent disease, selenium supplementation may increase longevity. However, results from clinical trials are mixed, and it is still unclear whether selenium supplementation can affect mortality in healthy individuals.
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.
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.
There is inconclusive evidence regarding the use of selenium in pancreatitis.
The anti-oxidant effects of selenium have been suggested to improve physical endurance. However, the available evidence suggests that selenium supplementation does not affect physical performance or endurance training.
There is some evidence that selenium may aid postoperative recovery and reduce edema (swelling) after surgery. Patients with severe inflammation, resulting from surgeries or extensive burns, may benefit from supportive selenium therapy. More studies are needed to determine whether selenium is a suitable addition to post-operative therapy and care.
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.
Quality of life:
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.
Radiation side effects:
Selenium supplementation has been used as an adjunct therapy to treat radiation side effects. Additional research is necessary before a clear conclusion can be drawn.
Selenium supplementation has been studied in rheumatoid arthritis patients with mixed results. Additional research is necessary before a clear conclusion can be drawn.
It is unclear whether serum selenium levels are related to seizures in patients with epilepsy or brain tumors. More research needs to examine whether selenium supplementation can affect the frequency or severity of seizures.
Sepsis (severe bacterial infection in the blood):
Study results of selenium supplementation in septic patients are mixed.
Taking selenium by mouth has been studied for its effects on psoriasis and lesions induced by arsenic or the human papilloma virus (HPV). Selenium has also been used to treat eczema and to increase the rate of burn wound healing. Although some results appear promising, the overall results are mixed. Additional study is needed in this area.
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).
Thyroid function is thought to depend on selenium, and thyroid problems are common in patients with selenium deficiency. Selenium has been suggested to improve goiter, as well as inflammatory activity in chronic autoimmune thyroiditis or Grave's disease. Further research is needed before selenium supplementation can be recommended for thyroid conditions.
Because selenium levels and thyroid hormones are disrupted in trauma patients, selenium supplementation has been suggested as a treatment for critically injured patients. Presently, there is not enough evidence to recommend the use of selenium therapy in severe injuries.
Commercially available 1% selenium sulfide shampoo has been reported as equivalent to sporicidal therapy in the adjunctive treatment of tinea capitis and tinea versicolor infections, although further high quality evidence is warranted.
Arthritis (osteoarthritis, rheumatoid arthritis):
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.
Some studies have suggested that selenium supplementation may help prevent type 2 diabetes by improving glucose metabolism. However, results from the Nutritional Prevention of Cancer (NPC) trial showed increased rates of type 2 diabetes in subjects taking selenium supplements. Although diabetes was not the primary focus of this study, these results indicate a potential risk of selenium supplementation that needs further examination.
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.
Muscle and joint disorders:
Selenium and vitamin supplementation has been studied in patients with Duchenne muscular dystrophy (DMD), myotonic dystrophy, and exercise-induced muscle injury. However, selenium does not appear to improve muscle strength or motor performance in patients with myotonic dystrophy. Despite promising early evidence, selenium supplementation does not appear to affect muscle strength or disease progression in muscular dystrophy.
Skin cancer (nonmelanoma) prevention:
Results from the Nutritional Prevention of Cancer (NPC) trial, conducted among 1,312 Americans over a 13-year period, suggested that selenium supplementation given to individuals at high risk of nonmelanoma skin cancer is ineffective at preventing basal cell carcinoma and actually increases the 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.
TraditionWARNING: DISCLAIMER: The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.
Abnormal pap smears, acne, alcoholism, allergic rhinitis, altitude sickness, anemia, arsenic poisoning, atherosclerosis (hardening of the arteries), bone density, burns, cardiac arrhythmia, celiac disease, childhood growth promotion, cognitive dysfunction, colitis, depression, diabetic retinopathy, Down's syndrome, gray hair, growth disorders (growing pains), helminth re-infection, hypersensitivity to electricity, inflammation, inflammatory bowel disease, lupus, macular degeneration, menopausal symptoms, metabolic enhancement, miscarriage prevention, non-Hodgkin's lymphoma, organ dysfunction, Osgood-Schlatter disease, otitis media, pain, phenylketonuria, poor elasticity of poison prophylaxis, Raynaud's phenomenon, sleep apnea, stroke, sudden infant death syndrome (SIDS), ulcerative colitis, vaccine adjunct, vasculitis.
Adults (over 18 years old)
The U.S. Recommended Dietary Allowance (RDA) for adults is 80-200 micrograms taken by mouth. Specifically: 55 micrograms for female adults; 70 micrograms for male adults; 40-70 micrograms for adolescent males, 45-55 micrograms for adolescent females; 65 micrograms for pregnant females; and 75 micrograms for breastfeeding females.
Some forms of selenium, such as organic L-(+) selenomethionine), may have better bioavailability than selenite and selenate. Bioavailability may also be affected by vitamin C. Selenium absorption may be lower in those adapted to low selenium diets.
A common dosing range studied is 80-200 micrograms daily. However, these doses have not been proven effective. The dose of selenium associated with a reduced risk of prostate cancer in the NPC trial is 200 micrograms daily. Although the maximum daily dose recommended is 200 micrograms, other trials have used 200, 400, or 800 micrograms of selenized yeast in the prevention of prostate cancer. Selenized yeast (200 or 800 micrograms daily) is being tested as a treatment for prostate cancer.
Intravenous doses have been given, but should only be used under the direction of a qualified healthcare professional.
Children (under 18 years old)
The U.S. Recommended Dietary Allowance (RDA) for infants and children is 10 micrograms taken by mouth daily for 0-6 months; 15 micrograms daily for 6-12 months; 20 micrograms for 1-6 years; 30 micrograms for 7-10 years; 45 micrograms for 11-14 years; and 50 micrograms for 5-18 years. Adequate intake for infants up to six months old may be 2.1 micrograms per kilogram per day and for infants 7-12 months it may be 2.2 micrograms per kilogram per day.
The maximum daily dose recommended is 45 micrograms for 0-6 months; 60 micrograms for 7-12 months; 90 micrograms for 1-3 years; 150 micrograms for 4-8 years; and 280 micrograms for 9-13 years.
Intravenous doses have been given, but should only be used under the direction of a qualified healthcare professional.
SafetyDISCLAIMER: Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.
Selenium is a trace element and hypersensitivity is unlikely. Avoid individuals with a known allergy/hypersensitivity to products containing selenium.
Side Effects and Warnings
The level of selenium exposure that will cause chronic toxicity is not known. Selenium toxicity may cause gastrointestinal symptoms (nausea, vomiting, abdominal pain, diarrhea, garlic-like breath odor, and metallic taste), neuromuscular-psychiatric disturbances (weakness/fatigue, lightheadedness, irritability, hyperreflexia, muscle tenderness, tremor, and peripheral neuropathy), dermatologic changes (skin rash/dermatitis/flushing, fingernail loss/thickening/blotching/streaking/paronychia, and hair changes/loss), liver dysfunction, kidney dysfunction, thrombocytopenia (low blood platelets), immune alterations (natural killer cell impairment), thyroid dysfunction (decreased T3), reduced sperm motility, or growth retardation.
Acute selenium poisoning may cause fever, gastrointestinal symptoms (nausea, vomiting, pain, anorexia), liver or kidney functional impairment, respiratory distress, cardiac complications (EKG changes, increased creatine kinase levels, heart damage), and even death if levels are high enough. Other symptoms similar to chronic selenium toxicity may also occur.
Chronic low selenium levels are associated with the development of cardiomyopathy and possibly with coronary artery disease. Selenium supplementation in selenium-deficient rats may lead to increased serum homocysteine, which is linked to cardiovascular disease. However, human studies suggest that this does not occur in healthy humans.
There have been numerous reports of adverse reactions to shampoos and lotions containing 2.5% selenium sulfide. Selenium applied topically apparently is not absorbed significantly into the bloodstream.
In animals, selenium deprivation can result in cataracts. Cataracts can be induced by administering selenium in doses several hundred times higher than the daily requirement. At present, there is not enough human evidence that selenium supplementation beyond the normal dietary requirement will affect the rate of cataract formation.
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 actually increases the 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.
Researchers have reported high levels of selenium in children with behavioral problems, although causality has not been established.
Pregnancy and Breastfeeding
No pregnancy category has been established for supplemental selenium intake although it is generally believed to be safe during pregnancy when consumed in amounts normally found in foods. Studies suggest that a daily intake of 50-75 micrograms is adequate during lactation.
Animal research reports that large doses of selenium may contribute to birth defects.
Selenium is excreted in breast milk, but it is generally believed to be safe to consume during lactation in amounts commonly found in foods. Studies have shown that different types of selenium consumed may have varying affects on the selenium content of breast milk. For example, selenomethionine appears to increase milk selenium concentrations more significantly than selenium-enriched yeast.
Interactions with Drugs
Agents that alter the pH of the stomach may decrease the absorption of selenium.
Concern has been raised that antioxidants may interfere with radiation therapy or some chemotherapy agents (such as alkylating agents, anthracyclines, or platinums), which themselves can depend on oxidative damage to tumor cells for anti-tumor effects. Studies of the effects of antioxidants on cancer therapies yield mixed results, with some reporting antagonistic effects (interference), others noting synergism (benefit), and most suggesting no significant interaction. This remains an area of study and controversy. In particular, selenium may reduce toxic side effects associated with chemotherapy drugs including cisplatin, doxorubicin, irinotecan (Camptosar®), or bleomycin. However, until better evidence is available, selenium supplementation is not recommended during chemotherapy or radiation therapy due to potential interference. Patients considering the use of selenium during chemotherapy or radiation therapy should discuss this choice with their medical and radiation oncologists.
High-dose steroid therapy may decrease plasma selenium levels.
Chronic high selenium levels may decrease sperm motility, although effects on fertility are not known.
Taking selenium in combination with beta-carotene and vitamins C and E appears to decrease the effectiveness of the combination of simvastatin (Zocor®) and niacin, although long-term effects are not known. This may be due to antioxidant effects associated with selenium use. Theoretically, selenium could reduce the effectiveness of other HMG-CoA reductase inhibitors such as atorvastatin (Lipitor®), fluvastatin (Lescol®), lovastatin (Mevacor®), and pravastatin (Pravachol®).
Selenium levels may vary in the female life cycle and may be related to estrogen status. Selenium levels may be increased in patients taking birth control pills.
Interactions with Herbs and Dietary Supplements
Selenium is a component of glutathione peroxidase, which possesses antioxidant activity and demonstrates antioxidant properties in humans. Long-term clinical benefits remain controversial. Selenium may add to the effects of other antioxidants in the body, such as vitamins A, C, and E, lycopene, green tea, soy, grape seed extract, or melatonin. The antioxidant activity of selenium may be affected by n-3 polyunsaturated fatty acids (n-3 PUFA).
There is preliminary evidence that vitamin C may be necessary for maintaining selenium levels in the body. Vitamin C appears to increase the absorption of natural selenium (found in foods) but not sodium selenate (found in supplements).
Selenium supplementation may affect the absorption of calcium and magnesium.
This information is based on a systematic review of the medical literature, edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com): Ethan Basch, MD (Memorial Sloan-Kettering Cancer Center); Wendy Chao, PhD (Natural Standard Research Collaboration); Dawn Costa, BA, BS (Natural Standard Research Collaboration); Shaina Tanguay-Colucci, BS (Natural Standard Research Collaboration); Catherine Ulbricht, PharmD (Massachusetts General Hospital); Wendy Weissner, BA (Natural Standard Research Collaboration).
BibliographyDISCLAIMER: Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.
Arnaud J, Arnault N, Roussel AM, et al. Relationships between selenium, lipids, iron status and hormonal therapy in women of the SU.VI.M.AX cohort. J Trace Elem Med Biol 2007;21 Suppl 1:66-9.
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Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.