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.
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.
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
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.
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.
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.
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
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.
Selenium supplementation has been studied in various liver disorders, including hepatitis, cirrhosis, and liver cancer, with mixed results.
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