Selenium

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What is it?

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 selenium deficiency, a disease that causes underactive thyroid (autoimmune thyroiditis), and high blood pressure during pregnancy. It is also used for diseases of the heart and blood vessels, including stroke, complications from statin drugs, and abnormal cholesterol levels, as well as for many other conditions, but there is no good scientific evidence to support these uses.

Coronavirus disease 2019 (COVID-19): There is no good evidence to support using selenium for COVID-19. Follow healthy lifestyle choices and proven prevention methods instead.

It is effective?
Natural Medicines rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

Probably Effective for …

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

Possibly Effective for …

  • A disease that causes underactive thyroid (autoimmune thyroiditis). Research shows that taking up to 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, general feelings of well-being, and 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.
  • A disorder that affects the bones and joints, usually in people with selenium deficiency (Kashin-Beck disease). Some research shows that adding salt enriched with selenium to food can prevent Kashin-Beck disease in children. But selenium does not seem to improve joint pain or movement in children with Kashin-Beck disease.
  • A pregnancy complication marked by high blood pressure and protein in the urine (pre-eclampsia). Pregnant women with low levels of selenium in the blood might have a higher chance of developing pre-eclampsia. Pre-eclampsia is a serious complication of pregnancy. Pregnant women taking selenium 60-100 mcg daily for up to 6 months during pregnancy might have a lower chance of having pre-eclampsia.

Possibly Ineffective for …

  • Asthma. There is no link between selenium blood levels and asthma. Taking 100 mcg of selenium daily for up to 24 weeks does not seem to improve quality of life, lung function, asthma symptoms, or inhaler use in people with asthma.
  • Eczema (atopic dermatitis). Taking yeast that is enriched with 600 mcg of selenium daily for 12 weeks, alone or with vitamin E, does not improve the severity of eczema.
  • Bladder cancer. Taking selenium does not appear to prevent bladder cancer.
  • Heart disease. Taking selenium does not appear to 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 chance of developing heart disease.
  • Colon cancer, rectal cancer. Most research shows that taking selenium does not reduce the risk of colon and rectal cancer.
  • Diabetes. Most research shows that people with high levels of selenium, people who eat diets high in selenium, and people who take selenium supplements for many years have an increased risk of type 2 diabetes. For people who already have diabetes, taking selenium for 2-3 months does not improve blood sugar levels.
  • Abnormal levels of cholesterol or blood fats (dyslipidemia). Most research shows that taking selenium supplements does not improve cholesterol levels in people with dyslipidemia.
  • Infants born weighing less than 2500 grams (5 pounds, 8 ounces). Selenium does not appear to reduce the chance of death in low birth weight infants. But it might reduce the chance of an infection called sepsis.
  • Lung cancer. Research shows that taking selenium alone or with other nutrients does not reduce the risk of lung cancer. But some research suggests that selenium might benefit people with lower selenium levels.
  • Prostate cancer. Most large, long-term scientific studies show that selenium does not reduce the chance of getting prostate cancer.
  • Scaly, itchy skin (psoriasis). Taking yeast enriched with 600 mcg of selenium daily does not seem to reduce the severity of psoriasis.
  • Blood infection (sepsis). Most research shows that giving selenium along with other nutrients intravenously (by IV) does not reduce the risk of death in people with sepsis.
  • Skin cancer. Taking 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 Make a Determination for …

  • Decline in memory and thinking skills that occurs normally with age. It’s unclear if selenium improves memory and thinking skills in older adults.
  • 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.
  • Cancer. Most 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 especially in men and in people with lower selenium levels.
  • Cataracts. Early research shows that taking selenium daily for around 5.6 years does not reduce the risk of age-related cataracts in men.
  • Abnormal cells on the surface of the cervix (cervical dysplasia). Early research shows that taking 200 mcg of selenium daily might reduce the amount of abnormal cells in people with this condition.
  • Non-cancerous growths in the large intestine and rectum (colorectal adenoma). Some research shows that taking selenium does not protect against the return of polyps in the intestines or rectum. However, selenium might protect against the return of advanced polyps.
  • Surgery to improve blood flow to the heart (CABG surgery). It’s unclear if giving selenium improves outcomes in people after CABG surgery.
  • Critical illness (trauma). It’s unclear if giving selenium intravenously (by IV) or by mouth reduces the risk of death or infection in critically ill people.
  • Diseases, such as Alzheimer disease, that interfere with thinking (dementia). Early research suggests that taking 200 mcg of selenium daily for 4 years might not prevent dementia.
  • Kidney damage in people with diabetes (diabetic nephropathy). It’s unclear if giving selenium improves kidney function in people with this condition.
  • Weakened and enlarged heart (dilated cardiomyopathy). Early research has found that taking selenium is linked with a lower risk of heart death in people with a specific type of dilated cardiomyopathy called Keshan disease. It’s unclear if selenium helps to improve outcomes in pregnant people with dilated cardiomyopathy.
  • Cancer of the esophagus. Taking selenium supplements is not linked to less risk of getting this cancer.
  • 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.
  • Overactive thyroid (hyperthyroidism). Early research shows that giving selenium with drug therapy does not improve symptoms in people with this condition.
  • Underactive thyroid (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.
  • An inflammatory condition that causes rash or sores on the skin or mouth (lichen planus). Using a selenium gel on the skin might improve pain in people with this condition. But it is unclear if taking selenium by mouth is helpful.
  • 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.
  • A group of inherited disorders that cause muscle weakness and muscle loss (muscular dystrophy). Early research suggests that taking a water-soluble form of selenium daily for 6 months does not benefit people with muscular dystrophy.
  • Obesity. Early research suggests that adding selenium supplements to a low-calorie diet does not help with weight loss.
  • Swelling (inflammation) and sores inside the mouth (oral mucositis). Early research suggests that taking selenium does not reduce sores inside the mouth in people receiving radiation therapy for cancer.
  • 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.
  • Death from any cause. 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.
  • Pancreatic cancer. Increased selenium intake has been linked with a reduced risk of cancer of the pancreas. But other research has found that selenium levels in the blood are not linked with the risk of cancer of the pancreas.
  • Swelling (inflammation) of the pancreas (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.
  • A hormonal disorder that causes enlarged ovaries with cysts (polycystic ovary syndrome or PCOS). Early research shows that taking a selenium supplement along with a probiotic supplement improves depression, anxiety, and stress by a small amount in women with PCOS. But it’s not clear if this effect is from selenium, the probiotic, or the combination.
  • Swelling in the arms or legs caused by damage to the lymph system (lymphedema). 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 during pregnancy. Early 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 caused by radiation therapy. 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 mixed. 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.
  • Muscle weakness caused by statin drugs (statin-induced myopathy). Early research suggests that taking 200 mcg of selenium daily with or without coenzyme Q10 for 3 months does not improve symptoms of statin-induced myopathy.
  • Thyroid cancer. One small study suggests that taking selenium supplements is linked with a reduced risk for thyroid cancer.
  • Liver disease in people who drink alcohol.
  • Flu (influenza).
  • Swelling (inflammation) of the liver caused by the hepatitis C virus (hepatitis C).
  • Burns.
  • Cataracts.
  • Kidney damage caused by cancer drugs.
  • Chronic fatigue syndrome (CFS).
  • Liver scarring (cirrhosis).
  • Gray hair.
  • Hay fever.
  • Hearing loss caused by the drug cisplatin.
  • Heart failure.
  • A type of inflammatory bowel disease (ulcerative colitis).
  • Conditions in a man that prevent him from getting a woman pregnant within a year of trying to conceive (male infertility).
  • Stomach cancer.
  • Toxicity from cancer drugs.
  • Other conditions.

More evidence is needed to rate selenium for these uses.

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

Is there concern for the safety of its use?
When taken by mouth: Selenium is LIKELY SAFE for most people when taken by mouth in doses less than 400 mcg daily, short-term. However, selenium is POSSIBLY UNSAFE when taken by mouth in high doses or for a long time. Taking doses above 400 mcg can increase the risk of developing selenium toxicity. Taking lower doses for a long time, such as doses that are higher than the recommended dietary allowance (RDA), can also increase the risk of developing diabetes.

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

Special Precautions & Warnings:

Pregnancy and breast-feeding: Selenium 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 taken by mouth in doses above 400 mcg daily. This dose might cause toxicity, and in HIV-positive women, it might increase virus levels in breast milk.

Children: Selenium is POSSIBLY SAFE when taken by mouth appropriately. Selenium seems to be safe when used 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.

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.

Are there any drug interactions?

Birth control pills (Contraceptive drugs)

Interaction Rating=Minor Be watchful with this combination.

Some research shows that women who take birth control pills might have increased blood levels of selenium. But 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.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Interaction Rating=Moderate Be cautious with this combination.

Selenium might slow blood clotting. Taking selenium along with medications that also slow 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.

Medications used for lowering cholesterol (Statins)

Interaction Rating=Moderate Be cautious with this combination.

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 some medications used for lowering cholesterol.

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

Niacin

Interaction Rating=Moderate Be cautious with this combination.

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

Sedative medications (Barbiturates)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down medications to get rid f 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.

Warfarin (Coumadin)

Interaction Rating=Moderate Be cautious with this combination.

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.

Are there any interactions with herbs and supplements?
Astragalus: Some species of astragalus accumulate large amounts of selenium, especially when grown in selenium-rich soils. Taking products made from these plants along with selenium supplements could cause selenium poisoning. However, most astragalus supplements contain Astragalus membranaceus, which is not a selenium accumulator.
Copper: Selenium might increase how quickly the body processes removes copper. In theory, taking selenium might reduce copper levels in the body.
Herbs and supplements that might slow blood clotting: Using selenium with other herbs that can slow blood clotting might increase the risk of bleeding in some people. These other herbs include angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, and others.
Niacin: Niacin can increase good cholesterol levels. Taking selenium along with beta-carotene, vitamin E, and vitamin C might decrease the effects of niacin on good cholesterol levels. It is not known if selenium alone decreases the effects of niacin on good cholesterol levels.
Omega-3 fatty acids: Taking selenium with omega-3 fatty acids might reduce how much selenium the body absorbs.
Vitamin C: Taking vitamin C might affect how much selenium the body absorbs from some supplements. However, it is unlikely that this potential interaction is a big concern.
Zinc: Zinc might make it more difficult for the body to absorb selenium from food.

Are there any interactions with food?
Ketogenic diet: Following the high-fat, low-carbohydrate ketogenic diet might lead to vitamin and mineral deficiencies, including selenium deficiency.

What dose is used?
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.
  • A disease that causes underactive thyroid (autoimmune thyroiditis): 80-200 mcg daily.
  • A pregnancy complication marked by high blood pressure and protein in the urine (pre-eclampsia): 60-100 mcg daily for up to 6 months while pregnant.

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.

By what other names is the product known?
Atomic number 34, Dioxyde de Sélénium, Ebselen, L-Selenomethionine, L-Sélénométhionine, Levure Sélénisée, Numéro Atomique 34, Se, Selenio, Selenite, Sélénite de Sodium, Sélénium, Selenium Ascorbate, Selenium Dioxide, Selenized Yeast, Selenomethionine, Sélénométhionine, Sodium Selenite.

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