Selenium

• Overview
• Uses
• Side Effects
• Precautions
• Interactions
• Dosing

Selenium is a mineral found in soil, water, and some foods. It is important for making many body processes work correctly.

Most of the selenium in the body comes from the diet. The amount of selenium in food depends on where it is grown or raised. Crab, liver, fish, poultry, and wheat are generally good selenium sources. The amount of selenium in soils varies a lot around the world, which means that the foods grown in these soils also have differing selenium levels. In the U.S., the Eastern Coastal Plain and the Pacific Northwest have the lowest selenium levels. People in these regions naturally take in about 60 to 90 mcg of selenium per day from their diet. Although this amount of selenium is adequate, it is below the average daily intake in the U.S., which is 125 mcg.

Selenium is used for diseases of the heart and blood vessels, including stroke, "hardening of the arteries" (atherosclerosis), complications from statin drugs, abnormal cholesterol levels, and high blood pressure during pregnancy. It is also used for various cancers including cancer of the prostate, colon and rectum, stomach, esophagus, lung, ovaries, bladder, and skin.

Selenium is also used for alcohol-related liver disease, asthma, eczema, enlarged prostate, liver disease, hepatitis C, diabetes, Kashin-Beck disease, low birth weight, muscular dystrophy, pancreas infection, swelling after surgery, itchy and scaly skin (psoriasis), selenium deficiency, blood infection, inflammatory bowel disease, Kashan disease, and Osgood-Schlatter disease.

Some people take selenium by mouth for under-active thyroid, thyroid inflammation, osteoarthritis, rheumatoid arthritis (RA), an eye disease called macular degeneration, hay fever, infertility, cataracts, gray hair, abnormal pap smears, chronic fatigue syndrome (CFS), mood disorders, arsenic and mercury poisoning, and preventing miscarriage.

Selenium is also taken by mouth for preventing serious complications and death from critical illnesses such as head injury and burns. It is also used for preventing bird flu, swine flu, treating HIV/AIDS, and reducing side effects from cancer chemotherapy and radiation.

Selenium is given through an IV when someone has experienced a trauma and is critically ill.

How does it work?

Selenium is important for making many body processes work correctly. It seems to increase the action of antioxidants.

Likely Effective for...

• Selenium deficiency. Taking selenium by mouth is effective for preventing selenium deficiency.

Possibly Effective for...

• Autoimmune thyroiditis (Hashimoto's thyroiditis). Research shows that taking 200 mcg of selenium daily along with thyroid hormone might decrease antibodies in the body that contribute to this condition. Selenium might also help improve mood and general feelings of well-being in people with this condition. Selenium also seems to improve quality of life in people with this condition. Taking selenium doses under 200 mcg daily might not be as effective, and it might be more beneficial in people with more severe cases.
• Abnormal cholesterol levels. Some research shows that taking a 100-200 mcg of a specific selenium supplement (SelenoPrecise, Pharma Nord, Denmark) daily for 6 months can modestly reduce cholesterol levels. Many people in this study had low levels of selenium in their body before the start of the study. It is not clear if taking extra selenium would have any benefit on cholesterol levels in people with normal selenium levels in the body.
• Blood infection (sepsis). Research shows that giving selenium along with other nutrients intravenously reduces the risk of death by 11% to 27% in people with a life-threatening blood infection called sepsis. But it does not seem to reduce the recovery time in the hospital or the risk of pneumonia or kidney failure.

Possibly Ineffective for...

• Asthma. Research suggests that there is no link between selenium blood levels and asthma. Additionally, research suggests that taking 100 mcg of selenium daily for up to 24 weeks does not improve quality of life, lung function, asthma symptoms, or inhaler use in people with asthma.
• Eczema (atopic dermatitis). Research suggests that taking yeast that is enriched with 600 mcg of selenium daily for 12 weeks, alone or together with vitamin E, does not improve the severity of eczema.
• Heart disease. Most research suggests that taking selenium does not reduce the risk of heart disease. In people who already have heart disease, taking 100 mcg of selenium in combination with beta-carotene, vitamin C, and vitamin E does not seem to prevent the condition from becoming worse. Also, taking 200 mcg of selenium daily for almost 8 years does not reduce the risk of developing heart disease.
• Neurotoxicity caused by chemotherapy drugs. Early research suggests that taking vitamins C and E with selenium does not prevent neurotoxicity or hearing loss caused by the chemotherapy drug cisplatin.
• Critical illness (burns, head injury, trauma). Giving 500-1000 mcg of selenium intravenously (by IV) or 300 mg of selenium (ebselen) by mouth daily to critically ill people does not seem to reduce the risk of death or infection.
• Diabetes. Some research shows that people with low selenium levels have a higher chance of developing type 2 diabetes. However, other research shows that people who have high levels of selenium also have an increased risk of type 2 diabetes. Additionally, the most reliable research shows that people who take 200 mcg of selenium daily for about 7.7 years have an increased chance of developing type 2 diabetes.
• Hepatitis C. Research shows that taking 200 mcg of selenium along with vitamin C and vitamin E for 6 months does not improve liver function or virus levels in people with hepatitis C.
• Infertility. Research suggests that taking 100-200 mcg of selenium daily, alone or together with vitamin A, vitamin C, and vitamin E, for 3-4 months, does not improve sperm function in infertile men.
• Low birth weight. Daily selenium supplementation, 7 mcg/kg by mouth or 5 mcg/kg intravenously (by IV), does not appear to improve health in low birth weight infants.
• Lung cancer. Early research showed that taking 200 mcg if selenium daily reduced the risk of lunch cancer by about 46% in people without selenium deficiency. However, a re-evaluation of this study shows that selenium did not reduce lung cancer risk in most people, but it did seem to benefit people with low selenium levels. Other research shows that taking selenium alone or with other nutrients does not reduce lung cancer risk.
• Prostate cancer. There has been a lot of interest in studying whether taking selenium lowers the chance of getting prostate cancer. The interest was triggered by the observation that prostate cancer seems to be less common in men with higher selenium levels in their bodies. To date, there have been several large, long-term scientific studies. The majority of this evidence suggests that selenium does not reduce the chance of getting prostate cancer.
• Red and irritated skin (psoriasis). Research suggests that taking yeast enriched with 600 mcg of selenium daily does not reduce the severity of psoriasis.
• Skin cancer. Taking 200 mcg of selenium does not seem to reduce the risk of getting a certain type of skin cancer called basal cell carcinoma. In fact, some scientific evidence suggests that taking extra selenium might actually increase the risk of getting another type of skin cancer called squamous cell carcinoma.

Insufficient Evidence to Rate Effectiveness for...

• Alcohol-related liver disease. Evidence shows that taking 200 mcg of selenium along with zinc and vitamin E daily can reduce the amount of time spent in the hospital and the risk of death in people with alcohol-related liver disease.
• Arsenic poisoning. Early research shows that taking yeast enriched with selenium seems to decrease how much arsenic the body absorbs in Chinese people exposed to high levels of arsenic in the environment.
• Enlarged prostate. Early research shows that taking selenium plus silymarin daily for 6 months reduces urinary tract symptoms in men with enlarged prostate. Other research shows that taking selenium along with saw palmetto, tamsulosin, and lycopene (Profluss; Ayanda AS, Norway) daily for one year improves enlarged prostate symptoms.
• Bladder cancer. A clinical study shows that taking selenium daily with or without vitamin E for around 7 years does not prevent bladder cancer in older men.
• Burns. Evidence suggests that taking 315-380 mcg of selenium along with copper and zinc daily can reduce the risk of pneumonia in people being treated in the hospital for burns. Other research suggests that this same combination might reduce the amount of time spent in the hospital but does not affect wound healing
• Cancer. Pooled research shows that taking selenium does not reduce the risk of cancer or cancer-related death. However, older studies suggest that it might reduce cancer risk by 24% and cancer-related death by 22%. Also, some research shows that taking 400 mcg of selenium daily for 2 years or 100 mcg of selenium along with zinc, vitamin C, vitamin E, and beta-carotene daily for 7.5 years does not reduce the risk of developing cancer. However, other research suggests taking selenium might reduce the risk of cancer-related death.
• Cataracts. A clinical study shows that taking 200 mcg of selenium daily with or without vitamin E daily for around 5.6 years does not reduce the risk of age-related cataracts in men.
• Destruction of the bile ducts in the liver (cirrhosis). Taking selenium with vitamin A, vitamin C, methionine, and coenzyme Q10 for 12 weeks does not seem to improve fatigue or other symptoms in people with primary biliary cirrhosis.
• Colon and rectal cancer. Early research suggests that blood levels of selenium are not linked with the risk of colon and rectal cancer. Also most research shows that taking selenium does not reduce the risk of colon and rectal cancer. But some research shows that selenium reduces the risk of colon and rectal cancer in some patients. Reasons for the conflicting findings are not clear. Different selenium formulas might have different effects. Also selenium might work better in people with lower blood levels of selenium before treatment. Some early research shows that taking selenium with other antioxidants might protect against colon cancer recurrence. But it's too soon to know if this benefit is due to selenium or other antioxidants.
• Dementia. Early research shows that taking 200 mcg of selenium daily for 4 years does not prevent dementia.
• Esophageal cancer. Taking selenium supplements does not seem to lower the risk of esophageal cancer.
• Stomach cancer. Research on the effects of selenium on stomach is mixed. Taking selenium in combination with vitamin C and vitamin E for 7-14 years does not seem to reduce the risk of developing precancerous stomach sores. But other research shows that taking selenium with vitamin C and vitamin E might reduce the risk of death from stomach or esophageal cancer. Overall, the effects of selenium alone on stomach cancer are unclear.
• HIV/AIDS. There is contradictory evidence about the effect of selenium supplements on HIV. Some evidence shows that taking selenium daily for up to 2 years can slow how quickly HIV spreads and can increase immune function. However, other early research shows that selenium has no effect.
• Low thyroid hormone levels (hypothyroidism). Some research shows that taking a selenium supplement might increase the conversion of thyroid hormones in older people. However, other research suggests that it has no benefit. Taking selenium can make hypothyroidism worse in people who are iodine deficient. Taking selenium daily during pregnancy seems to reduce the risk of developing thyroid dysfunction after pregnancy and permanent hypothyroidism.
• Stroke. Some research suggests that administering selenium (ebselen) within 24 hours of a stroke improves recovery.
• Bone and joint disease (Kashin-Beck disease). Early research suggests that selenium does not seem to improve joint pain or movement in children with Kashin-Beck disease.
• Liver cancer. Early research in China suggests that taking selenium for 2-5 years can reduce the occurrence of liver cancer. It is unclear if taking selenium will reduce the risk of liver cancer in Western countries.
• Mercury poisoning. Early research shows that taking yeast enriched with selenium seems to decrease how much mercury the body absorbs in Chinese people exposed to high levels of mercury in the environment.
• Muscular dystrophy. Early research suggests that taking a water-soluble form of selenium daily for 6 months does not benefit people with muscular dystrophy.
• Arthritis (osteoarthritis). Low selenium levels seem to be linked with an increased risk of developing osteoarthritis. However, it is not known if selenium supplements can prevent osteoarthritis.
• Ovarian cancer. Research suggests that there is no link between selenium consumption in the diet and the risk for ovarian cancer.
• Overall risk of death. Analysis of many studies suggests that taking selenium does not seem to have an effect on overall death risk. However, some research suggests that taking 100 mcg of selenium along with zinc, vitamin C, vitamin E, and beta-carotene daily for 7.5 years might lower the risk of death from any cause in men, but not women. Other research suggests that selenium, taken alone or with other nutrients, does not reduce the risk of death.
• Pancreatitis. Evidence is conflicting about the effect of selenium on pancreatitis. Some research suggests that selenium has no benefit. However, other research suggests that taking a water-soluble form of selenium daily might reduce the risk of death caused by severe pancreatitis.
• Swelling in the arms and legs after surgery. Early evidence suggests that taking selenium supplements for 15 weeks might prevent bacterial skin infections in women with swelling in the arms and legs after breast cancer surgery.
• High blood pressure caused by pregnancy. Research suggests that taking 100 mcg of selenium liquid daily for 6-8 weeks during pregnancy can reduce the occurrence of high blood pressure.
• Diarrhea from radiation treatments. Early research suggests that taking 500 mcg of selenium on days of radiation therapy and 300 mcg on days without treatments reduces diarrhea by about 54%.
• Rheumatoid arthritis (RA). Evidence on the effects of selenium on rheumatoid arthritis is inconsistent. Some research suggests that taking yeast enriched with 200 mcg of selenium does not improve RA. However, other research suggests that taking 200 mcg of selenium daily for 3 months reduces joint swelling, tenderness, and stiffness in people with RA.
• Statin-induced myopathy. Early research suggests that taking 200 mcg of selenium (SelenoPrecise; Pharma Nord, Denmark) daily with or without coenzyme Q10 for 3 months does not improve symptoms of statin-induced myopathy.
• Inflammatory bowel disease (ulcerative colitis). Early research suggests that taking selenium with fish oil, natural sweeteners, gum arabic, vitamin E, and vitamin C does not benefit people with an inflammatory bowel disease called ulcerative colitis. However, taking this same combination does seem to reduce the need for medications.
• Abnormal pap smears.
• Atherosclerosis.
• Bird flu and swine flu.
• Cataracts.
• Chemotherapy side effects.
• Chronic fatigue syndrome (CFS).
• Gray hair.
• Hay fever.
• Macular degeneration (eye disease).
• Mood disorders.
• Preventing miscarriage.
• Other conditions.

More evidence is needed to rate selenium for these uses.

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (detailed description of each of the ratings).

Selenium is LIKELY SAFE for most people when taken by mouth in doses less than 400 mcg daily, short-term.

Selenium is POSSIBLY UNSAFE when taken by mouth in high doses or for long-term. Taking doses above 400 mcg can increase the risk of developing selenium toxicity. Taking lower doses long-term can increase the risk of developing diabetes. High doses of selenium can cause significant side effects including nausea, vomiting, nail changes, loss of energy, and irritability. Poisoning from long-term use is similar to arsenic poisoning, with symptoms including hair loss, white horizontal streaking on fingernails, nail inflammation, fatigue, irritability, nausea, vomiting, garlic breath odor, and a metallic taste.

Selenium can also cause muscle tenderness, tremor, lightheadedness, facial flushing, blood clotting problems, liver and kidney problems, and other side effects.

Children: Selenium is POSSIBLY SAFE when taken by mouth appropriately. Selenium seems to be safe when used in the short-term in doses below 45 mcg daily for infants up to age 6 months, 60 mcg daily for infants 7 to 12 months, 90 mcg daily for children 1 to 3 years, 150 mcg daily for children 4 to 8 years, 280 mcg daily for children 9 to 13 years, and 400 mcg daily for children age 14 years and older.

Pregnancy and breast-feeding: Selenium use is POSSIBLY SAFE during pregnancy and breast-feeding when used short-term in amounts that are not above 400 mcg daily. Selenium is POSSIBLY UNSAFE in pregnancy and breastfeeding when taking by mouth in doses above 400 mcg daily, as this might cause toxicity, and in HIV-positive women, as this might increase virus levels in breast milk.

Autoimmune diseases: Selenium might stimulate the immune system. In theory, selenium might make autoimmune disease worse by stimulating the activity of the disease. People with autoimmune diseases such as multiple sclerosis, systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and other should avoid taking selenium supplements.

Hemodialysis: Blood levels of selenium can be low in people undergoing hemodialysis. Using a dialysis solution with selenium might increase selenium levels, but selenium supplementation might be needed for some people.

Under-active thyroid (hypothyroidism): Taking selenium can worsen hypothyroidism especially in people with iodine deficiency. In this case, you should take iodine along with selenium. Check with your healthcare provider.

Fertility problems in men: Selenium might decrease the ability of sperm to move, which could reduce fertility. If you are trying to father a child, don't take selenium supplements.

Skin cancer: Long-term use of selenium supplements might slightly increase the risk of skin cancer recurrence, but this is controversial. Until more is known about the possible increase in skin cancer risk, avoid long-term use of selenium supplements if you have ever had skin cancer.

Surgery: Selenium might increase the risk of bleeding during and after surgery. Stop taking selenium at least 2 weeks before a scheduled surgery.

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Medications that decrease the immune system (Immunosuppressants)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Selenium might stimulate the immune system. By stimulating the immune system, selenium might decrease the effectiveness of medications that decrease the immune system.

Some medications that decrease the immune system include azathioprine (Imuran), basiliximab (Simulect), cyclosporine (Neoral, Sandimmune), daclizumab (Zenapax), muromonab-CD3 (OKT3, Orthoclone OKT3), mycophenolate (CellCept), tacrolimus (FK506, Prograf), sirolimus (Rapamune), prednisone (Deltasone, Orasone), and other corticosteroids (glucocorticoids).

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Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Selenium might slow blood clotting. Taking selenium along with medications that also slow blood clotting might increase the chances of bruising and bleeding.

Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, ticlopidine (Ticlid), warfarin (Coumadin), and others.

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Medications used for lowering cholesterol (Statins)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Taking selenium, beta-carotene, vitamin C, and vitamin E together might decrease the effectiveness of some medications used for lowering cholesterol. It is not known if selenium alone decreases the effectiveness of medications used for lowering cholesterol.

Some medications used for lowering cholesterol include atorvastatin (Lipitor), fluvastatin (Lescol), lovastatin (Mevacor), and pravastatin (Pravachol).

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NiacinInteraction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Taking selenium along with vitamin E, vitamin C, and beta-carotene might decrease some of the beneficial effects of niacin. Niacin can increase levels of good cholesterol. Taking selenium along with these other vitamins might decrease how well niacin works for increasing good cholesterol.

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Sedative medications (Barbiturates)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

The body breaks down medications to get rid of them. Selenium might slow how fast the body breaks down sedative medications (barbiturates). Taking selenium with these medications might increase the effects and side effects of these medications.

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Warfarin (Coumadin)Interaction Rating: Moderate Be cautious with this combination.Talk with your health provider.

Selenium might thin the blood. Selenium might also increase the effects of warfarin in the body. Taking selenium along with warfarin might increase the chances of bruising and bleeding.

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Birth control pills (Contraceptive drugs)Interaction Rating: Minor Be cautious with this combination.Talk with your health provider.

Some research shows that women who take birth control pills might have increased blood levels of selenium. However, other research shows no change in selenium levels in women who take birth control pills. There isn't enough information to know if there is an important interaction between birth control pills and selenium.

Some birth control pills include ethinyl estradiol and levonorgestrel (Triphasil), ethinyl estradiol and norethindrone (Ortho-Novum 1/35, Ortho-Novum 7/7/7), and others.

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Gold saltsInteraction Rating: Minor Be cautious with this combination.Talk with your health provider.

Gold salts bind to selenium and decrease selenium in parts of the body. This might decrease the normal activity of selenium, possibly resulting in symptoms of selenium deficiency.

Gold salts include aurothioglucose (Solganal), gold sodium thiomalate (Aurolate), and auranofin (Ridaura).

The following doses have been studied in scientific research:

ADULTS:

BY MOUTH:

• U.S. recommended dietary allowance (RDA): 55 mcg for males and females; 60 mcg for pregnant females; 70 mcg for breast-feeding females. Currently, doses below the tolerable upper intake level (400 mcg) may be used in supplementation.
• Autoimmune thyroiditis (Hashimoto's thyroiditis): 200 mcg daily.
• Abnormal cholesterol levels: 100-200 mcg daily of a specific selenium product (SelenoPrecise, Pharma Nord, Denmark) has been used for 6 months.

BY IV:

• Blood infection (sepsis): Sodium selenite has been given in varying doses, 100-4000 mcg by IV daily for up to 28 days. Most treatments have included a loading dose followed by reduced maintenance doses.

CHILDREN:

BY MOUTH:

• U.S. recommended dietary allowance (RDA): 15 mcg for those 0-6 months old; 20 mcg daily for those 6-12 months old; 20 mcg for those 1-3 years old; 30 mcg for those 4-8 years old; 40 mcg for those 9-13 years old; and 55 mcg for those 14-18 years old. Adequate intake for infants up to six months old may be 2.1 mcg/kg daily, and for infants 7-12 months, it may be 2.2 mcg/kg daily.
• Maximum daily dose: 45 mcg for those 0-6 months old; 60 mcg for those 7-12 months old; 90 mcg for those 1-3 years old; 150 mcg for those 4-8 years old; and 280 mcg for those 9-13 years old.
• Blood infection (sepsis): Selenium has been given with zinc and glutamate along with metoclopramide by IV. Age-specific daily selenium doses include: 1-3 years = 40 mcg, 3-5 years = 100 mcg, 5-12 years = 200 mcg; adolescents 400 mcg.