What is selenium in?



Algotar AM, Stratton MS, Ahmann FR, et al. Phase 3 clinical trial investigating the effect of selenium supplementation in men at high-risk for prostate cancer. Prostate. 2013;73(3):328-35.

Bleys J, Navas-Acien A, Guallar E. Selenium and diabetes: more bad news for supplements.Ann Intern Med. 2007 Aug 21;147(4):271-2.

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Duffield-Lillico AJ, Slate EH, Reid ME, Turnbull BW, Wilkins PA, Combs GF Jr, et al. Nutritional Prevention of Cancer Study Group. Selenium supplementation and secondary prevention of nonmelanoma skin cancer in a randomized trial. J Natl Cancer Inst. 2003 Oct 1;95(19):1477-81

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Faghihi T, Radfar M, Barmal M, et al. A randomized, placebo-controlled trial of selenium supplementation in patients with type 2 diabetes: effects on glucose homeostasis, oxidative stress, and lipid profile. Am J Ther. 2014;21(6):491-5.

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Kristal AR, Darke AK, Morris JS, et al. Baseline selenium status and effects of selenium and vitamin e supplementation on prostate cancer risk. J Natl Cancer Inst. 2014;106(3):djt456.

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Why do we need selenium?

Unlike other minerals which we may need in larger amounts, humans only require small amounts of selenium. However, these small amounts are absolutely crucial to our overall health and wellbeing as selenium has been linked to a number of vital functions throughout the body. The mineral is capable of increasing our antioxidant capabilities as well as enhancing our immune system.

This makes it very important for our cardiovascular health as it helps to prevent oxidative stress and reduce inflammation, improving our blood flow. It also plays a key role when it comes to our thyroid function, helping to regulate the production of active thyroid hormones and protect against antibodies that may cause problems.

Finally, selenium has also been linked to reproductive health as the mineral is required for proper sperm motility, warding off damaging molecules known as ‘free radicals’ and improving sperm quality.

Natural sources of Selenium

As I mentioned earlier, humans only need small amounts of selenium, with NHS recommending just 0.075mg a day for men between the ages of 19-64 and 0.06mg for women in the same age range, although this can increase if you are pregnant. This is one of the reasons why selenium-deficiencies are so rare and you should be able to get all the selenium you need from your diet.

Food sources Selenium (micrograms, mcg)
Brazil nuts, 28g 536mcg
Yellowfin Tuna, 85g 92mcg
Turkey, 85g 28mcg
Sunflower seeds, 50g 26.5mcg
Chicken breast, 85g 22mcg
Eggs, 1 15.9mcg

Selenium deficiency

Selenium deficiency is rare, given the small amounts of selenium that we need to intake each day. Nevertheless, it does exist, particularly in areas where levels of the mineral are low in the soil. It’s also possible that certain medications can hinder your absorption of selenium too, so it’s important to be aware of the side-effects!

Some of the more pronounced symptoms selenium-deficiency include; fatigue, skin discolouration and low immunity. In more severe cases, low levels of selenium have been linked to fertility issues, particularly in men. Since your thyroid also depends on selenium, it’s not unheard of to experience thyroid issues such as hypothyroidism.

Too much selenium

Unfortunately, cases of selenium toxicity are becoming more common due to supplementation and the results are not good. The upper limit set for selenium is generally around 400mcg – any more than that and you can risk selenosis, which may cause you to exhibit symptoms such as hair loss, mood swings, fatigue and weight loss. It’s believed that prolonged episodes of selenosis can even cause nerve damage!

A-Z Index

Public Health Statement for Selenium


September 2003

CAS#: 7782-49-2

PDF Version, 72 KB

This Public Health Statement is the summary chapter from the Toxicological Profile for Selenium. It is one in a series of Public Health Statements about hazardous substances and their health effects. A shorter version, the ToxFAQsTM, is also available. This information is important because this substance may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present. For more information, call the ATSDR Information Center at 1-800-232-4636.

This public health statement tells you about selenium and the effects of exposure.

The Environmental Protection Agency (EPA) identifies the most serious hazardous waste sites in the nation. These sites make up the National Priorities List (NPL) and are the sites targeted for long-term federal cleanup activities. Selenium has been found in at least 508 of the 1,623 current or former NPL sites. However, the total number of NPL sites evaluated for selenium is not known. As more sites are evaluated, the sites at which selenium is found may increase. This information is important because exposure to selenium at high levels may harm you and because these sites may be sources of exposure. A minimum dietary level of selenium is required for good health.

When a substance is released from a large area, such as an industrial plant, or from a container, such as a drum or bottle, it enters the environment. This release does not always lead to exposure. You are exposed to a substance only when you come in contact with it. You may be exposed by breathing, eating, or drinking the substance, or by skin contact.

If you are exposed to selenium, many factors determine whether you’ll be harmed. These factors include the dose (how much), the duration (how long), and how you come in contact with it/them. You must also consider the other chemicals you’re exposed to and your age, sex, diet, family traits, lifestyle, and state of health.

1.1 What is selenium?

Selenium is a naturally occurring, solid substance that is widely but unevenly distributed in the earth’s crust. It is also commonly found in rocks and soil. Selenium, in its pure form of metallic gray to black crystals, is often referred to as elemental selenium or selenium dust. Elemental selenium is commercially produced, primarily as a by-product of copper refining. Selenium is not often found in the environment in its elemental form, but is usually combined with other substances. Much of the selenium in rocks is combined with sulfide minerals or with silver, copper, lead, and nickel minerals. Selenium also combines with oxygen to form several substances that are white or colorless crystals. Some selenium compounds are gases. Selenium and its compounds are used in some photographic devices, gun bluing (a liquid solution used to clean the metal parts of a gun), plastics, paints, anti-dandruff shampoos, vitamin and mineral supplements, fungicides, and certain types of glass. For example, selenium sulfide is used in anti-dandruff shampoos by the common trade name Selsun Blue. Selenium is also used to prepare drugs and as a nutritional feed supplement for poultry and livestock. More information on the chemical and physical properties, production, and uses of selenium are found in Chapters 4 and 5.

1.2 What happens to selenium when it enters the environment?

Selenium occurs naturally in the environment. As an element, selenium cannot be created or destroyed, although selenium can change forms in the environment. Weathering of rocks and soils may result in low levels of selenium in water, which may be taken up by plants. Weathering also releases selenium into the air on fine dust-like particles. Volcanic eruptions may release selenium in air. Selenium commonly enters the air from burning coal or oil. Selenium that may be present in fossil fuels combines with oxygen when burned, which may then react with water to form soluble selenium compounds. Airborne particles of selenium, such as in ash, can settle on soil or surface water. Disposal of selenium in commercial products and waste could also increase the amount of selenium in soil. The forms and fate of selenium in soil depend largely on the acidity of the surroundings and its interaction with oxygen. In the absence of oxygen when the soil is acidic, the amount of selenium that can enter plants and organisms should be low. Elemental selenium that cannot dissolve in water and other insoluble forms of selenium are less mobile and will usually remain in the soil, posing smaller risk of exposure. Selenium compounds that can dissolve in water are sometimes very mobile. Thus, there is an increased chance of exposure to these compounds. Selenium may enter surface water in irrigation drainage waters. Some evidence indicates that selenium can be taken up in tissues of aquatic organisms and possibly increase in concentration as the selenium is passed up through the food chain. Selenium concentrations in aquatic organisms have been a problem as a result of irrigation runoff in some dry areas of the United States. Chapter 6 contains more information on what happens to selenium in the environment.

1.3 How might I be exposed to selenium?

People are exposed to low levels of selenium daily through food, water, and air. Selenium is also an essential nutrient for humans and animals. However, selenium can be harmful when regularly taken in amounts higher than those needed for good health. People receive the majority of their daily intake of selenium from eating food, and to a lesser extent, from water intake. Estimates of the average intake of selenium from food for the U.S. population range from 71 to 152 millionths of a gram of selenium per person per day. Low levels of selenium can also be found in drinking water. Selenium levels are less than 10 parts of selenium in a billion parts of water (10 ppb) in 99.5% of drinking water sources tested. People may be exposed to higher-than-normal levels of selenium at hazardous waste sites by swallowing soil or water, or by breathing dust. In some parts of the United States, especially in the western states, some soils naturally have higher levels of selenium compounds. Some plants can build up selenium to levels that harm livestock feeding on them. In these areas, people could be exposed to too much selenium if they eat a lot of locally grown grains and vegetables or animal products that have built up high levels of selenium. People may also be exposed to selenium from industrial sources. Humans are normally not exposed to large amounts of selenium in the air, unless selenium dust or volatile selenium compounds are formed in their workplace. Occupations in which humans may be exposed to selenium in the air are the metal industries, selenium-recovery processes, paint manufacturing, and special trades. Chapter 6 contains more information on how people can be exposed to selenium.

1.4 How can selenium enter and leave my body?

Selenium from the environment mainly enters the body when people eat food containing selenium. The human body easily absorbs the organic selenium compounds (for example, selenoamino acids) when eaten, and makes them available where needed in the body. The selenium in drinking water is usually in the form of inorganic sodium selenate and sodium selenite; these forms of selenium are also easily absorbed from the digestive tract. The human body can change these inorganic selenium compounds into forms that it can use. Selenium in the air may also enter your body when you breathe it.

Hazardous waste sites at which selenium is present could represent a major source of exposure. The way that selenium can enter the body from a particular site depends on such factors as whether vegetables are grown in soil in which selenium from the site has been deposited, whether water at the site contains selenium and is able to flow into drinking water supplies, and whether selenium dust blows into the air. As mentioned earlier, specific conditions at a site can greatly influence which selenium compounds form and whether they can move in the environment to places where people might be exposed. Therefore, it is important to know that the presence of selenium at a site does not necessarily mean that people are being exposed to it. Specific tests of locally grown food, drinking water, and air must be done to find out whether exposure is occurring. You should also be aware that selenium compounds, including those used in some medicated dandruff shampoos, are not easily absorbed through the skin.

Most of the selenium that enters the body quickly leaves the body, usually within 24 hours. Beyond what the body needs, selenium leaves mainly in the urine, but also in feces and breath. Selenium in the urine increases as the amount of the exposure goes up. Selenium can build up in the human body, however, if exposure levels are very high or if exposure occurs over a long time. The amount that builds up in the body depends on the chemical form of the selenium. It builds up mostly in the liver and kidneys but also in the blood, lungs, heart, and testes. Selenium can build up in the nails and in hair, depending on time and amount of exposure. Chapter 3 contains more information on how selenium enters and leaves the human body.

1.5 How can selenium affect my health?

To protect the public from the harmful effects of toxic chemicals and to find ways to treat people who have been harmed, scientists use many tests.

One way to see if a chemical will hurt people is to learn how the chemical is absorbed, used, and released by the body; for some chemicals, animal testing may be necessary. Animal testing may also be used to identify health effects such as cancer or birth defects. Without laboratory animals, scientists would lose a basic method to get information needed to make wise decisions to protect public health. Scientists have the responsibility to treat research animals with care and compassion. Laws today protect the welfare of research animals, and scientists must comply with strict animal care guidelines.

The general public rarely breathes high levels of selenium, although some people may be exposed to selenium dust and selenium compounds in workplace air. Dizziness, fatigue, and irritation of mucous membranes have been reported in people exposed to selenium in workplace air at concentrations higher than legal levels. In extreme cases, collection of fluid in the lungs (pulmonary edema) and severe bronchitis have been reported. The exact exposure levels at which these effects might occur are not known, but they become more likely with increasing amounts of selenium and with increasing frequency of exposure.

The normal intake of selenium by eating food is enough to meet the Recommended Daily Allowance (RDA) for this essential nutrient. However, as discussed in Chapters 2 and 3 of this profile, selenium compounds can be harmful at daily dietary levels that are higher than needed. The seriousness of the effects of excess selenium depends on how much selenium is eaten and how often. Intentional or accidental swallowing of a large amount of sodium selenate or sodium selenite (for example, a very large quantity of selenium supplement pills) could be life-threatening without immediate medical treatment. Even if mildly excessive amounts of selenium are eaten over long periods, brittle hair and deformed nails can develop. In extreme cases, people may lose feeling and control in arms and legs. These health effects, called selenosis, were seen in several villages in China where people were exposed to foods high in selenium for months to years. No human populations in the United States have been reported with long-term selenium poisoning, including populations in the western part of the country where selenium levels are naturally high in the soil. Because most people in the United States eat foods produced in many different areas, overexposure to selenium in food is unlikely to occur.

In some regions of China where soil levels of selenium are very low, not eating enough selenium has resulted in health effects. Selenium is used by the body in antioxidant enzymes that protect against damage to tissues done by oxygen, and in an enzyme that affects growth and metabolism. Not eating enough selenium can cause heart problems and muscle pain. Muscle pain has also been noted in people fed intravenously for a long time with solutions that did not contain selenium. Babies born early may be more sensitive to not having enough selenium, and this may contribute to lung effects. In the United States, selenium in food is sufficient to meet the RDA and prevent harmful effects from not enough selenium.

Upon contact with human skin, industrial selenium compounds have been reported to cause rashes, redness, heat, swelling, and pain. Brief, acute exposure of the eyes to selenium dioxide as a dust or fume in workplace air may result in burning, irritation, and tearing. However, only people who work in industries that process or use selenium or selenium compounds are likely to come into contact with levels high enough to cause eye irritation.

Studies of laboratory animals and people show that most selenium compounds probably do not cause cancer. In fact, some studies of cancer in humans suggest that lower-than-normal selenium levels in the diet might increase the risk of cancer. Other studies suggest that dietary levels of selenium that are higher than normal might reduce the risk of cancer in humans. However, taking selenium so that your daily amount is greater than that required might just increase your risk of selenium poisoning.

Based on studies done until 1987, the International Agency for Research on Cancer (IARC) determined that selenium and selenium compounds could not be classified as to their ability to cause cancer in humans. However, since then, the EPA has determined that one specific form of selenium, called selenium sulfide, is a probable human carcinogen. Selenium sulfide is the only selenium compound shown to cause cancer in animals. Rats and mice that were fed selenium sulfide daily at very high levels developed cancer. Selenium sulfide is not present in foods, and it is a very different chemical from the organic and inorganic selenium compounds found in foods and in the environment. Also, if introduced into the environment, selenium sulfide does not dissolve readily in water and would probably bind tightly to the soil, further reducing any chance of exposure. Because selenium sulfide is not absorbed through the skin, the use of anti-dandruff shampoos containing selenium sulfide is generally considered safe.

Very high amounts of selenium have caused decreased sperm counts, increased abnormal sperm, changes in the female reproductive cycle in rats, and changes in the menstrual cycle in monkeys. The relevance of the reproductive effects of selenium exposure in animals studied to potential reproductive effects in humans is not known. Selenium compounds have not been shown to cause birth defects in humans or in other mammals.

Chapter 3 contains more information on the health effects of selenium and selenium compounds in humans and animals.

1.6 How can selenium affect children?

This section discusses potential health effects from exposures during the period from conception to maturity at 18 years of age in humans.

Children living near selenium waste sites or coal burning plants are likely to be exposed to higher environmental levels of selenium through breathing, touching soil, and eating contaminated soil. Children living in areas of China with high selenium in the soil had higher levels of selenium in the blood than adults from that area. Very few studies have looked at how selenium can affect the health of children. Children need small amounts of selenium for normal growth and development. Children will probably show the same sort of health effects from selenium exposure as adults, but some studies suggest that they may be less susceptible to health effects of selenium than adults.

We do not know if exposure to selenium could result in birth defects in people. Selenium compounds have not been shown to cause birth defects in humans or in other mammals. We have no information to suggest that there are any differences between children and adults in where selenium is found in the body or in how fast it enters or leaves the body. Studies in laboratory animals have shown that selenium crosses the placenta and enters the fetus. Studies in humans show that infants are supplied with selenium through breast milk, and therefore, women who were exposed to selenium by living near a waste site might transfer selenium to their babies. However, babies in areas of China with high selenium in the soil did not show any signs of health effects due to selenium, even though some of their parents did.

1.7 How can families reduce the risk of exposure to selenium?

If your doctor finds that you have been exposed to significant amounts of selenium, ask whether your children might also be exposed. Your doctor might need to ask your state health department to investigate.

Since selenium occurs naturally in the environment, we cannot avoid exposure to it. Certain dietary supplements and anti-dandruff shampoos contain selenium in high levels. You should not exceed the recommended dosages when using these products.

Children living near selenium waste sites or coal burning plants are likely to be exposed to higher environmental levels of selenium through breathing, touching soil, and eating contaminated soil. Some children eat a lot of dirt. You should discourage your children from eating dirt. Make sure they wash their hands frequently and before eating. Discourage your children from putting their hands in their mouths or from other hand-to-mouth activity.

The primary route of human exposure to selenium is through eating food. People who irrigate their home gardens with groundwater containing high levels of selenium may grow and eat plants that contain high levels of selenium because this element is taken up in some plants. Fishermen and hunters of waterfowl who regularly eat fish and game from waterways with high selenium content may also consume above average levels of selenium. To reduce your family’s exposure to selenium, obey any wildlife advisories issued by your state. Information on fish and wildlife advisories in your state is available from your state public health or natural resources department.

1.8 Is there a medical test to determine whether I have been exposed to selenium?

Selenium can be measured in the blood, urine, and fingernails or toenails of exposed individuals. However, since selenium is an essential nutrient normally present in foods, low levels of selenium are normally found in body tissues and urine. Tests for selenium are most useful for people who have recently been exposed to high levels. Samples of blood, urine, or nails can be properly collected in a physician’s office and sent to a laboratory that has the special equipment needed to measure selenium. Urine can be used to determine short-term exposure. Because red blood cells last about 120 days before they are replaced by newly made red blood cells, the presence of selenium in red blood cells can show whether a person was exposed to selenium during the 120 days before testing, but not if exposed more than 120 days before testing. Toenail clippings can be used to determine longer-term exposure.

Many methods are available to measure selenium levels in human tissue and the environment. However, none of the methods that are routinely available can measure or detect each selenium compound in one test, and better tests that measure lower levels of different selenium compounds are needed. Also, these tests cannot determine the exact levels of selenium you may have been exposed to or predict whether health effects will occur, even though very high amounts of selenium in blood are clearly related to selenosis. Some human as well as animal studies suggest that when people are exposed over a long period to higher-than-normal amounts of selenium, their bodies adjust to the higher amounts. Chapter 3 contains more information on studies that have measured selenium in blood and other human tissues.

The length of time that selenium stays in the body after exposure stops depends on the form of selenium to which the person was exposed. Thus, it is difficult to predict how useful a test will be if some time has gone by since exposure stopped. Chapter 7 contains more information on the methods available to measure selenium in human tissues and in the environment.

1.9 What recommendations has the federal government made to protect human health?

The federal government develops regulations and recommendations to protect public health. Regulations can be enforced by law. Federal agencies that develop regulations for toxic substances include the Environmental Protection Agency (EPA), the Occupational Safety and Health Administration (OSHA), and the Food and Drug Administration (FDA). Recommendations provide valuable guidelines to protect public health but cannot be enforced by law. Federal organizations that develop recommendations for toxic substances include the Agency for Toxic Substances and Disease Registry (ATSDR) and the National Institute for Occupational Safety and Health (NIOSH).

Regulations and recommendations can be expressed in not-to-exceed levels in air, water, soil, or food that are usually based on levels that affect animals; then they are adjusted to help protect people. Sometimes these not-to-exceed levels differ among federal organizations because of different exposure times (an 8 hour workday or a 24 hour day), the use of different animal studies, or other factors.

Recommendations and regulations are also periodically updated as more information becomes available. For the most current information, check with the federal agency or organization that provides it. Some regulations and recommendations for selenium include the following:

The EPA Office of Drinking Water regulates the amount of selenium allowed in drinking water. Public water supplies are not allowed to exceed 50 ppb total selenium.

The FDA regulations allow a level of 50 ppb of selenium in bottled water. OSHA is responsible for setting regulations on selenium levels allowable in the workplace. The exposure limit for selenium compounds in the air for an 8 hour period is 0.2 mg selenium/m3. Chapter 8 contains other regulations and guidelines for selenium.

Agency for Toxic Substances and Disease Registry (ATSDR). 2003. Toxicological profile for Selenium. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.

Selenium: What it does and how much you need

Share on PinterestSelenium is an essential trace mineral that assists with cognitive function and fertility.

Selenium may help prevent cardiovascular disease, thyroid problems, cognitive decline, which means disorders related to thinking, cancer, and others.

Cardiovascular disease: According to the Office for Dietary Supplements, selenoproteins can protect against cardiovascular disease, because they prevent the oxidative modification of lipids, or fats, in the body.

This reduces inflammation and prevents the buildup of platelets.

However, clinical evidence does not support the use of selenium supplements for this purpose.

Cognitive decline: Selenium’s antioxidant activity may help reduce the risk of cognitive, or mental, decline, as people get older.

Evidence from studies is mixed, however, and selenium supplements are not yet prescribed for people at risk of diseases such as Alzheimer’s, although it may have a role in prevention that is still under investigation.

Thyroid disorders: Selenium has an important role in producing and metabolizing thyroid hormone.

There is some evidence that women with higher selenium levels have fewer thyroid problems, but this has not been proven for men, and other studies have produced mixed results.

More studies are under way to decide whether selenium supplements might support thyroid health.

Cancer: The role played by selenium in DNA repair and other functions may mean that is can help prevent cancer. However, studies have produced mixed results.

The U.S. Food and Drug Administration (FDA) concluded in 2003:

“Some scientific evidence suggests that consumption of selenium may reduce the risk of certain forms of cancer.”

Studies have suggested that selenium may also help to:

  • prevent HIV from progressing to AIDS
  • reduce the risk of miscarriage
  • protect against asthma

There has been some investigation into whether a woman’s selenium levels during pregnancy might predict her child’s risk of asthma.

While selenium is clearly element for many aspects of human health, there is too little evidence to indicate that supplements could be of use in preventing these conditions.


Published: July 2000


Prescriber Update 20: 39-42
July 2000

Medsafe Editorial Team

Selenium is an essential trace element. Although concentrations in New Zealand soils are low, there is no indication that this has resulted in any detrimental effects on the health of New Zealanders. With current levels of animal and poultry supplementation of selenium and consumption of imported plant foods, especially wheat and legumes, it appears that intake of selenium by most New Zealanders is at or around recommended levels, as indicated by the 1997 National Nutrition Survey and the 1997/98 New Zealand Total Diet Survey. The current recommended daily intake in the US for adults is 55µg.
Some New Zealanders take selenium supplements with the intention of reducing the oxidative damage of free radicals. The daily dose recommended on the label of these supplements is usually 50-200µg. The Dietary Supplements Regulations 1985 require supplements to have a maximum adult dose of 150µg/day. The maximum safe daily intake is 400µg.
Symptoms of selenium toxicity include a garlicky odour in the breath, fatigue, gastrointestinal symptoms, transverse lines on the nails, alopecia, and peripheral neuropathy. Treatment is by supportive care. There is no known effective antidote. Symptomatic recovery may be quite rapid, occurring within 2 weeks in one case.

Selenium is an essential trace element

Selenium is an essential trace element, used in particular in the glutathione peroxidase enzyme system which protects intracellular structures against oxidative damage. In foods it is present largely as the amino acids selenomethionine and selenocysteine, in which it replaces the usual sulphur atom.

Most New Zealand diets have low but sufficient levels of selenium

A deficiency of selenium in an area of China has resulted in an endemic form of cardiomyopathy, called Keshan disease. Selenium has low concentrations in most New Zealand soils, but there has been little indication that the low intake has resulted in any detrimental effects on the health of New Zealanders. The disease patterns for coronary artery disease, hypertension and cancer are similar to those in Western countries with far higher selenium intakes.1

An evaluation of selenium requirements completed in 2000 by the US Institute of Medicine revised the American recommended adult intake to 55µg/day, the level at which the enzymes with antioxidant functions are at maximum activity.2 A recent study3 conducted in New Zealand estimated that a suitable minimum intake for New Zealanders, achievable without use of supplements, is 39µg/day. At this level plasma glutathione peroxidase is at two-thirds of maximal activity which was thought to be sufficient by the WHO/IAEA/FAO Expert Committee.4

The 1997 New Zealand National Nutrition Survey,5 based on recall of food consumed during the previous day, calculated a mean daily selenium for men aged ≥ 15 years of 60µg/day and for women aged ≥ 15 years of 44µg/day. The 1997/98 Total Diet Survey6 examined selenium intake in two groups of men (young male 19-24 years and adult male > 25 years) and two groups of women (adult female > 25 years and lacto-ovo vegetarian female 19-40 years) using simulated diets. Estimated intakes for both groups of men were in excess of the US recommendation, while the estimated intakes for the women coincided with the US recommended level, 55µg/day. The intake calculated in the National Nutrition Survey is considered to be a more representative indication of dietary intake of selenium by New Zealanders.

The intake of selenium by New Zealanders has increased since the earlier Total Diet Surveys in 1982 and 1987/88.6 To prevent animal diseases, farm animals are drenched with selenium-enriched products and the meal fed to poultry has selenium added. Generally bread made in the South Island is lower in selenium than bread made in the North. Since deregulation of the grain industry much North Island bread has a significant proportion of imported, largely Australian wheat which is selenium-rich. But South Island bread is made predominantly with wheat grown locally in low-selenium soils. Current practices need to continue for the selenium intake of New Zealanders to remain around recommended levels.

Meats, eggs, dairy products and bread are the main sources of selenium in New Zealand diets.6 Kidney, liver and seafood, and for the vegetarian, imported legumes are rich in selenium.

Some New Zealanders take selenium supplements

Some people use selenium supplements as a prophylactic against cancer and cardiovascular disease, but its value for either purpose is not well established.4,7 One placebo-controlled study of patients with a history of basal cell or squamous cell carcinomas of the skin found a significantly lower rate of total cancer incidence among the group taking selenium.8 These results need to be confirmed by further large scale long term studies.8.9

The dose recommended on the label of selenium supplements is usually 50-200µg daily. The Dietary Supplements Regulations 1985 require selenium supplements to be manufactured and labelled so that the recommended daily dose is no more than 150µg.

A maximum safe daily dietary intake has been estimated at 400µg.2,4 At an intake of 750-850µg functional signs of toxicity can be expected.4 In an American publication, the normal range in serum is said to be 0.84-1.3 µmol/L,10 but what is regarded as ‘normal’ will vary from country to country and region to region.

Symptoms of toxicity: garlicky breath, alopecia, peripheral neuropathy

Selenium, like arsenic, inactivates the sulphhydral groups of amino acids. Toxicity has been associated with a garlicky odour in the breath (caused by methylated selenium), fatigue, gastrointestinal disturbances, transverse lines on the nails, alopecia and peripheral neuropathy. Treatment involves discontinuation of the source of excessive intake and supportive care. There is no known antidote or suitable chelator.

In a published11 case of selenium poisoning, the patient took 10 tablets a day for 2 weeks following a loading dose of a supplement containing an unknown amount of selenium. During this time he developed diarrhoea, worsening fatigue, a tingling sensation in the extremities and became completely bald. Two weeks after discontinuing the supplement he had a serum selenium level of 8.26 µmol/L and appeared healthy with regrowth of hair and normal neurological examination.

  1. Robinson MF. Selenium in human nutrition in New Zealand. Nutr Rev 1989;47:99-107.
  2. Antioxidants’ role in chronic disease prevention still uncertain; huge doses considered risky. Institute of Medicine, Food and Nutrition Board, Standing Committee on the Scientific Evaluation of Dietary Reference. Media release, 10 April 2000. http://www.nationalacademies.org/news
  3. Duffield AJ, Thomson CD, Hill KE, Williams S. An estimation of selenium requirements for New Zealanders. Am J Clin Nutr 1999;70:896-903.
  4. Selenium. In Trace elements in human nutrition and health, Geneva: World Health Organisation, 1996, p.105-122.
  5. Russell D, Parnell W, Wilson N, and the principal investigators of the 1997 National Nutrition Survey. NZ Food: NZ People. Key results of the 1997 National Nutrition Survey. Wellington, NZ: Ministry of Health, August 1999, pp.24, 56-7.
  6. Vannoort R, Cressey P, Silvers K. 1997/98 New Zealand Total Diet Survey Part 2: Elements. Selected contaminants and nutrients. Wellington, NZ: Ministry of Health, February 2000, pp.41-46.
  7. Foster LH, Sumar S. Selenium in health and disease: A review. Crit Rev Food Science & Nutr 1997;37:211-28.
  8. Clark LC, Combs GF, Turnbull BW, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. JAMA 1996;276:1957-63.
  9. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board. Dietary reference intakes for vitamin C, vitamin E, selenium, and beta-carotene, and other carotenoids. National Academy Press, 2000, p.290-1. Accessed through the internet at http://books.nap.edu/catalog/9810.html.
  10. Baselt RC. Disposition of toxic drugs and chemicals in man. 5th Ed. Foster City, California: Chemical Toxicology Institute, 2000, p.778-81.
  11. Clark RF, Strukle E, Williams SR, Manoguerra AS. Selenium poisoning from a nutritional supplement. JAMA 1996;275:1087-8.

Selenium Supplements: Too Much of a Good Thing?

A new review adds to mounting evidence that dietary supplements may do more harm than good.

Selenium, a mineral found in fish, meat, eggs, grains and certain nuts, helps boost antioxidant activity in the body to potentially ward off chronic diseases. But too much selenium can cause selenosis, a condition marked by hair and nail loss, garlic breath, fatigue and nerve damage.

The recommended daily intake of selenium is 60 micrograms for men and 53 micrograms for women, according to the review published today in The Lancet. But men and women in the U.S., where 50 percent of the population takes supplements, get an average 134 and 93 micrograms per day, respectively.

“Additional selenium intake may well benefit people with low ,” Margaret Rayman, a professor of nutritional medicine at the University of Surrey in the U.K., wrote in the review. “However, people of adequate or high status could be affected adversely and should not take selenium supplements.”

Adults should not consume more than 400 micrograms of selenium per day, according to the National Institutes of Health Office of Dietary Supplements. Some selenium supplements contain 200 micrograms. And the daily multivitamin Centrum contains 55 micrograms, enough to exceed the recommended daily intake in a person who gets sufficient selenium from a balanced diet.

“People who take dietary supplements are the least likely to need them,” said Dr. Donald Hensrud, associate professor of preventive medicine and nutrition at the Mayo Clinic in Rochester, Minn. “People who have a bad diet typically can’t afford them or tend not to take them.”

Hensrud credited “Mother Nature” with making the concentrations of vitamins and minerals in fruits, vegetables, whole grains and lean sources of protein “optimal for health.”

“We like to believe if we can concentrate something and put it in pill form, it must be good for us,” he said. “And supplements are a multibillion dollar industry, so this belief is fueled by marketing and advertising.”

But some people have difficulty getting enough selenium, despite a healthy diet. People with Crohn’s disease and other gastrointestinal disorders, as well as people with iodide deficiency, may need to take selenium supplements, according to the NIH.

“Obviously, if someone has a deficiency then they do need a supplement,” said Hensrud.

Some studies have suggested selenium supplements can reduce the risk of cancer, cardiovascular disease and type 2 diabetes. But Rayman said more research is needed to tease out the mineral’s benefits and risks.

“The effects of selenium on human health are multiple and complex, necessitating further research to optimize the benefits and reduce the risks of this potent trace mineral,” she wrote.

Selenium is a vital mineral for the human body that has numerous roles, and there is no shortage of selenium benefits.

What is selenium used for? It increases immunity, takes part in antioxidant activity that defends against free radical damage and inflammation, and plays a key role in maintaining a healthy metabolism.

According to studies, consuming foods with selenium — such as Brazil nuts, eggs, liver, tuna, cod and sunflower seeds — and/or taking supplements can have positive antiviral effects, supports fertility and reproduction, and may even reduce the risk of cancer, autoimmune and thyroid diseases.

What Is Selenium?

Selenium is a trace mineral that is found naturally in the soil and also appears in certain foods. There are even small amounts in the water you drink.

What is selenium good for in the body? Something that makes it valuable is its role in antioxidant activity. As a component of antioxidant enzymes, particularly glutathione reductase, it’s key for repairing tissues throughout the body.

Because it both increases antioxidant capabilities and the quality of blood flow, it can help to enhance resistance against diseases and effects of stress. Its ability to fight oxidative stress and and inflammation are thought to be due to different types of selenoprotein found in selenium.

Among healthy people in the U.S., a selenium deficiency is believed to be uncommon. However, people with certain health conditions, such as HIV, Crohn’s disease and other disorders that impair nutrient absorption, are associated with having low levels that can lead to deficiency.

Top 8 Selenium Benefits

1. Acts as an Antioxidant and Defends Against Oxidative Stress

Selenium benefits include the ability to fight the aging process and help the immune system by reducing free radical damage. It has a synergistic effect with other antioxidants like vitamin E, enabling the body to defend against cancers like prostate and colon cancer.

As an essential component of glutathione peroxidase, it helps carry out important enzyme processes that protect lipids (fats) in cell membranes. It’s needed to fight oxidative degradation of cells and protect against mutation and DNA damage that can cause disease.

2. May Help Defend Against Cancer

Selenium benefits are especially helpful if you have a weak immune system or a history of cancer in your family. Supplementation at high doses has been shown to potentially have anti-cancer effects.

According to studies, it may be effective at reducing the risk of cancer incidence, cancer-caused mortality and severity of cancers — specifically in the liver, prostate, colorectal and lungs.

Because it has the special job of activating selenoproteins, this mineral acts in an enzymic role that helps antioxidants to do their job best. There is evidence that selenium benefits include not only being able cut cancer risk, but also help to slow down existing cancer progression and tumor growth.

Studies have shown that a high dose of 200 milligrams a day can be effective in protecting DNA, which can reduce the risk for cell mutation and cancer development.

Other studies show that in areas of the world where the soil is lowest in selenium, cancer risk is increased when compared to areas that have higher levels naturally available.

3. Can Help Boost Immunity

According to recent research, selenium benefits immunity because it is needed for the proper functioning of the immune system and can also be a key nutrient in counteracting the development of viruses, including HIV.

In patients who already contracted HIV, it’s been shown to also be useful in slowing down the progression of the disease into AIDS.

4. Improves Blood Flow and May Lowers Risk for Heart Disease

Low selenium concentrations are associated with an increased risk of cardiovascular disease. Supplements or an increase of selenium-rich foods may be able to help prevent coronary heart disease.

It’s believed that it can benefit heart health due to its ability to fight inflammation, increase blood flow, reduce free radical oxidative stress and help with antioxidant activity.

5. Helps Regulate Thyroid Function

Research now suggests that there is a link between thyroid metabolism and selenium deficiency. This mineral acts as a catalyst for the production of active thyroid hormones.

If you imagine that your body is a manufacturing facility, then your thyroid would be the main boss in charge of regulating the whole operating system, so when the thyroid isn’t working properly, there are many serious, noticeable consequences.

The thyroid gland controls numerous important everyday body functions, including appetite, sleep, temperature, weight, energy and more.

A problem with proper thyroid function can result in negative symptoms, such as irritability, muscle weakness, fatigue, weight gain or loss, trouble sleeping, and many other reactions — therefore acquiring proper amounts of selenium benefits the thyroid and body in many important ways.

It acts as a powerful protector of the thyroid, and it regulates the production of reactive oxygen within the gland and protects it from antibodies that can create thyroid disease.

For these reasons, selenium benefits are also being investigated to see if they can help patients with Hashimoto’s disease, Grave’s disease and in pregnant women with anti-TPO antibodies.

6. May Help Increase Longevity

Certain studies have investigated the use of selenium for the treatment of dozens of conditions that range from asthma to arthritis, thyroid disorder and heart disease. The risk of these conditions increase as we age, so consuming it can help defend the body and may contribute to a longer life.

7. Helps Reduce Asthma Symptoms

Observational studies have demonstrated that patients with chronic asthma may have lower levels of selenium. According to studies, when people with asthma took selenium supplements, they experienced less asthma-related symptoms than those who took a placebo.

Experts think that supplementation may be a useful add-on treatment to medication for patients with chronic asthma. However, more research is needed before this becomes a regular practice, as researchers have yet to determine the mineral’s full effect on lung function.

8. Can Help Boost Fertility

Selenium benefits fertility because it is required for proper sperm motility and also increases blood flow, two key components involved in conception and beating infertility. It is incorporated in the sperm mitochondria capsule and may affect the behavior and function of the sperm as they move through the vaginal canal.

It appears that both low and high sperm selenium concentrations can have a negative influence on the number of sperm, therefore aiming to meet the recommendation, but not to far exceed it, is important for fertility.

Some studies also show that this may even reduce the risk of miscarriage, but at this point more research has been dedicated to infertility in men than in women when it comes to selenium supplementation.

Supplementation and Dosage Recommendations

Selenium is a trace mineral, which means we only need a small amount of it. However, the body is able to flush it out of your system somewhat quickly since it plays an actionable role in many important body functions — therefore it’s important to consume it regularly, especially as you age, in order to take advantage of its benefits.

Some doctors, such as naturopaths, may recommend selenium supplements to treat acne, asthma, tendinitis, male infertility problems and postmenopausal disorders in women, among other conditions.

It is important to note that if you already consume proper amounts of selenium from a healthy diet, consuming more may not be beneficial, and high doses reaching 400 micrograms can even be harmful.

The recommended daily allowance for selenium depends on your age and is as follows, according to the USDA:

  • Children 1–3: 20 micrograms/day
  • Children 4–8: 30 micrograms/day
  • Children 9–13: 40 micrograms/day
  • Adults and children 14 and up: 55 micrograms/day
  • Pregnant women: 60 micrograms/day
  • Breastfeeding women: 70 micrograms/day

In supplement form, selenium is available in the form of selenomethionine and selenium selenite. Selenomethionine is usually easier for most people to digest and absorb properly.

When taking selenium supplements, most adults should take up to 55 micrograms daily (such as of selenomethionine), while pregnant women can take up to 60 micrograms and lactating women can take up to 70 micrograms.

The tolerable upper limit of selenium is 400 mcg per day.

Experts warn that it’s crucial that the public understands that selenium benefits work best when levels are met through eating foods with selenium. No one should exceed recommendations by supplementing with very high doses without consulting a physician.

Selenium sulfide is another form you may come across. This type is the active ingredient often found in shampoos used for the treatment of dandruff.


Whole foods are the best sources of selenium, especially when these foods are handled and prepared in a delicate way, since the mineral may be destroyed during processing and very high-heat cooking methods.

What food is highest in selenium? That would be Brazil nuts.

Just one single nut provides more than 100 percent of the daily selenium you need, roughly 68 to 91 micrograms (mcg).

Here are the top foods high in selenium:

  1. Brazil nuts
  2. Salmon
  3. Tuna
  4. Turkey
  5. Cottage Cheese
  6. Chicken
  7. Mushrooms
  8. Halibut
  9. Eggs
  10. Navy beans
  11. Sardines
  12. Sunflower seeds
  13. Grass-fed beef
  14. Oats
  15. Beef Liver

To add more selenium to your diet naturally, try any of the recipes below that feature foods rich in selenium.

  • Salmon Cakes or Teriyaki Salmon
  • Chicken Salad or Coconut Curried Chicken
  • Mushroom Soup or this Green Bean Casserole
  • Grainless Granola which you can add Brazil nuts or sunflower seeds to

Causes of Deficiency

Selenium can be found in soil and from food sources, however certain groups of people are more likely to be deficient.

There are actually four naturally occurring types of this trace mineral. The four natural states of selenium are: elemental selenium, selenide, selenite and selenate.

Two types, selenate and selenite, are found predominantly in water, whereas the other two types are the kinds found in soil and therefore in food sources. For humans, the primary pathway of consuming it is through food, followed by water and then by air.

Suffering from a selenium deficiency is correlated with an increased risk of health problems including mortality due to inflammation, infertility, poor immune function and cognitive decline. While not as serious, deficiency symptoms can include reproductive issues, muscle weakness, fatigue, brain fog, thyroid dysfunction, and hair loss.

While the RDA for selenium for adults is 55 micrograms/daily, the average daily intake in the U.S. is believed to be 125 micrograms per day, which far meets the daily requirements.

Some contributing to causes to selenium deficiency can include:

  • Not eating selenium foods very often.
  • Living in the U.S, certain parts of Europe, China, or Africa — The content of selenium in soil differs a lot depending on the location. For example, certain studies show concern that parts of Europe such as the U.K, and Africa, have soil low in selenium levels and the populations living in those areas may be suffering from compromised immunity because of this.
  • Consuming foods grown in poor quality soil — Even in food sources, the amount of selenium is largely dependent on soil conditions that the food grew in — therefore even within the same food, levels of selenium can vary widely, and selenium benefits may be found in crops grown in certain locations more so than others.
  • According to research, populations in the U.S. of the Eastern Coastal Plain and the Pacific Northwest have the lowest levels due to the soil in those areas. These populations average consuming 60 to 90 micrograms per day, which is still considered to be adequate intake but less than other populations where the soil is more selenium-rich.
  • Being affected by Kashin-Beck disease, a chronic bone disorder.
  • Undergoing kidney dialysis and living with HIV.

Testing for selenium deficiency:

If you have a condition that puts you at risk for selenium deficiency, you may want to have your levels tested to see if you can experience additional selenium benefits by taking a supplement. To find out your current levels, you can have a blood or hair test done by your doctor, however these are not believed to always be very accurate.

Here’s the good news: Because experts don’t often find deficiencies in populations that are generally not malnourished or who have compromised immunity, you probably don’t need to be tested unless at your high risk. It’s believed that as long as you include natural food sources of selenium in your diet regularly and are otherwise healthy, there is only a small chance you could suffer a deficiency that could lead to any serious risks.

Risks and Side Effects

What are the side effects of taking selenium? Taken at normal doses, it does not usually have negative side effects.

An overdose of selenium (selenium toxicity) may possibly cause reactions like bad breath, fever, nausea and potentially liver complications — or even kidney and heart problems — although these only occur at very high levels that reach “poisoning” status.

Again, the toxicity of most forms of selenium is rare and usually only experienced in people who supplement with high doses. Too high of levels can lead to potentially fatal complications including heart attack and respiratory (lung) depression.

The U.S. National Toxicology Program also lists certain types of selenium as an animal carcinogen, but there is no evidence that all types can harm animals and that this poses a serious risk in everyday situations.

It may also interact with other medicines and supplements. These include antacids, chemotherapy drugs, corticosteroids, niacin, cholesterol-lowering statin drugs and birth control pills.

If you take any of these medications, it’s best to speak with your doctor before supplementing.

Final Thoughts

  • What is selenium? It’s is a trace mineral found naturally in the soil that also appears in certain foods and even in water.
  • The two main sources are supplements and selenium-rich foods. The best way to get it from foods is to regularly eat: Brazil nuts, eggs, liver, tuna, cod and sunflower seeds, in addition to poultry and certain types of meat.
  • What is it used for? It helps the body thanks in large part to its role acting as an antioxidant.
  • Uses and benefits of selenium include: defending against oxidative stress, heart disease and cancer; boosting immunity; regulating thyroid function; increasing longevity; reducing asthma symptoms; boosting fertility.
  • Adults over the age of 14 should aim to get 55 micrograms (mcg) per day. While generally well-tolerated, in high doses, such as 400 to 900 mcg/day, it can be harmful and even toxic.

Selenium is an essential mineral needed for immunity, thyroid health, antioxidant protection, and more. Its intake needs to be just right – too much or too little can both have adverse effects. This article covers all the benefits of selenium supplementation, optimal dosage, and toxicity.

What is Selenium?

Intro & Roles

Selenium (Se) is a mineral found in Brazil nuts, poultry, fish, cereal, and eggs. It was considered a toxin until 1957 when its health benefits started to be discovered. Balanced selenium intake is crucial. Both selenium deficiency and excess are harmful while taking in just the right amount can have wide-ranging health benefits .

The recommended daily allowance – 55 µg/day – is based on the amount needed to maximize the activity of the selenium-dependant master antioxidant enzyme glutathione.

Selenium also binds to the sulfur-containing amino acid cysteine and forms antioxidant selenoproteins in the body. Selenoproteins carry selenium to the tissues, reduce inflammation, support a healthy immune system and thyroid gland .



  • Fights inflammation and improves the immune response
  • Vital for a healthy thyroid
  • May help prevent cancer
  • Can reset the circadian rhythm
  • Supports a balanced mood


  • Narrow optimal range, you need to be careful not to take in too much
  • May contribute to type 2 diabetes and lower antioxidants in excess
  • May lower thyroid hormones in men

Intake & Deficiency

Plants take in selenium from the soil, making selenium intake dependant on its concentration in the surrounding soil. People who live within a selenium-poor geographical belt – spanning from northeast to southwest China – are at a greater risk of selenium deficiency .

Deficiency can cause serious health problems, including Keshan disease, an extreme weakening of the heart that can result in heart failure .

On the other hand, very high blood selenium is associated with diabetes, high short-term (fasting blood glucose) and long-term diabetes markers (HbA1c) .

Intake of selenium is also low in Eastern Europe, while it can exceed the recommended daily amounts in Venezuela, parts of the US, Canada, and Japan. The average person living in the US takes in 107 – 151 µg/day of selenium from food and supplements, which is 2-3x the official recommended daily allowance (RDA) .

Anti-inflammatory and Antioxidant Effects

Selenium forms selenoproteins, key players in antioxidant defense, and increases the activity of genes that make them .

Selenium blocks the activation of NF-kB, the main controller of inflammation in the body. As a result, fewer inflammatory substances are released into the bloodstream (including IL-6, IL-8, and TNF-alpha) .

Adequate selenium intake may also lower the inflammatory marker CRP, which is high in many inflammatory and autoimmune diseases .

Effects on the Circadian Rhythm

Selenium is a powerful zeitgeber – a cue that synchronizes your internal clock to the natural 24-hour light/dark cycles of the Earth (zeit=time, geber=giver). Selenium helps restore an imbalanced circadian rhythm, which often affects people with insomnia.

The selenium- and sulfur-containing amino acid methyl selenocysteine could reset circadian rhythm genes in cell-based studies. It caused the activity of these genes to peak at nighttime, as they normally should. This amino acid is found in garlic, astragalus, onions, and broccoli .

Health Benefits of Selenium

Possibly Effective:

Selenium is most concentrated in the thyroid and helps regulate its function. Severe selenium deficiency may impair its function and is linked to different thyroid disorders .

Hashimoto’s Disease

Selenium supplementation can be useful for people with Hashimoto’s thyroiditis or autoimmune hypothyroidism. In a review of four clinical studies, selenium improved mood, general well-being, and thyroid peroxidase antibodies in people with Hashimoto’s. The direct benefits on thyroid structure and function were less clear, though .

Grave’s Disease

Graves’ disease (GD) is an autoimmune disease in which the thyroid becomes enlarged and overactive. In 38 selenium-deficient patients with Grave’s disease, Se supplementation significantly reduced thyroid hormones .

However, it showed no short-term benefits in another trial of 30 GD patients with normal selenium levels .

The benefits of Se supplementation for Graves’ disease may be limited to Se-deficient patients.


Some pregnant women experience mildly reduced thyroid function, also known as subclinical hypothyroidism (increased TSH, normal T4).

In an analysis of over 300 pregnant women, lower selenium blood levels were linked to thyroid enlargement and damage. Selenium supplements helped restore thyroid health, especially after birth. Selenium was used in the form of Selenomethionine, a naturally-occurring selenium-bound amino acid .

In mice with autoimmune thyroiditis, selenium increased T-reg immune cells, which are crucial for overcoming the destructive autoimmune response. It also lowered blood levels of disease-related antibodies (thyroglobulin TgAb) .

2) Viral Infections

Lack of selenium can set off the immune system and cause even harmless virus infections to progress and become dangerous. In the most severe cases, this can result in complete heart failure (Keshan disease) .

Adequate selenium intake protects immune cells and aids in producing antibodies. Lower selenium levels can increase damage (via oxidative stress) in healthy cells, reducing immune defense, activating viruses, and triggering their faster division.

HIV infections can trigger selenium deficiency, while supplementation may help fight HIV and improve outcomes. In one trial of 18 HIV-positive people, selenium in combination with conventional drugs improved the quality of life. Selenium also blocked the replication of the virus in cellular and animal studies .

Selenium levels may predict the disease outcome in HIV-positive people. In one study, selenium-deficient HIV patients were almost 20 times more likely to die from HIV than those with normal selenium levels .

In one study on children, low selenium levels not only increased the likelihood of dying from HIV but were also linked to faster spreading of the disease .

3) Kashin-Beck Disease Prevention

Kashin-Beck disease (KBD) is an endemic disease of the joints and bones, mainly occurring in certain China regions, particularly Tibet. Selenium deficiency plays an important role, along with different environmental and genetic factors .

According to a meta-analysis of 11 Chinese clinical trials with 2652 patients, adding Se-enriched salt to a diet reduces the odds of Kashin-Beck disease by 84% in healthy children, compared with iodized salt .

However, Se supplementation didn’t improve joint pain or mobility in 324 children with Kashin-Beck disease. The authors emphasized the role of iodine deficiency in KBD .

4) Preeclampsia

Preeclampsia is characterized by high blood pressure, swelling, and the presence of protein in the urine during pregnancy .

In a meta-analysis of 3 trials with 439 pregnant women, Se supplements (60-100 mcg daily for up to 6 months) reduced the risk of preeclampsia by 72% compared with placebo. According to 13 observational studies (1,515 participants), pregnant women with low Se levels have a higher risk of preeclampsia .

Insufficient Evidence:

No valid clinical evidence supports the use of selenium for any of the conditions in this section. Below is a summary of up-to-date animal studies, cell-based research, or low-quality clinical trials which should spark further investigation. However, you shouldn’t interpret them as supportive of any health benefit.

5) Brain Protection

The benefits of fish consumption are often attributed to polyunsaturated fatty acids, omega-3s, but high amounts of selenium found in fish may be equally important. Selenium works in synergy with the fatty acids, preventing their breakdown and enhancing their beneficial effects on cognition.

In one study on 200 older people, fish intake increased selenium blood levels more than omega-3 levels. According to the authors, better cognitive function in the elderly may depend directly on selenium .

Selenium is very important for your brain health. Low selenium levels are linked to poor cognition, memory problems, and low neurotransmitter levels in the brain. Alzheimer’s patients had only 60% of the brain selenium levels of healthy people in one study .

6) Cancer Prevention

The role of selenium in cancer prevention is a hot topic of debate and the findings are conflicting. Selenium supplements aren’t approved for cancer prevention or treatment.

Supportive Research

Ever since the 70s, studies have been reporting that increased selenium intake reduces cancer deaths and vice versa. In one study, the dietary intake of selenium in 27 countries was linked to fewer deaths from cancer. In the US, deaths from cancer were much higher in low selenium counties, in which people are more likely to be deficient .

Early studies of up to 11,000 people reported that low selenium status is linked with an increased cancer risk of cancer and death. The estimated risk ranged from two to six-fold and was at times only applicable to men .

Some recent studies support early findings. Slightly increased selenium intake – still well below toxic levels – was associated with a lower risk of colorectal and prostate cancer .

In 37 men, a combination of Milk thistle (Silymarin) and selenium reduced LDL, inflammation, and total cholesterol after prostate removal surgery, potentially preventing prostate cancer relapse and progression .

Conflicting Research

A significant limitation is that most studies of selenium intake and cancer risk are observational. Observational studies can make associations, but can’t attribute any causation.

There have been very few clinical trials using selenium as a therapeutic agent, which are needed to determine its effects. Many other factors – including lifestyle, genetics, gender, and age, stage, and type of cancer – will affect cancer outcomes and the preventive action of selenium .

In one clinical trial of over 1,000 people with a history of nonmelanoma skin cancer, 200 µg/day of selenium (as selenium yeast) didn’t reduce the chances of relapse. But it did lower all-type cancer mortality by 50% and cancer rates by 37%. It especially reduced the rates of prostate, colon, and lung cancer .

According to a meta-analysis of 15 clinical trials, Se supplementation may lower the risk of lung cancer in deficient patients but increase the risk in patients with normal Se levels .

Once again, the benefits of Se supplementation actually stemmed from fixing a deficiency.

Discouraging Research

Despite a couple of promising clinical trials, the largest review up-to-date concluded that there is no evidence to support increased selenium intake through diet or supplements in preventing cancer in humans. This review included 83 studies and emphasized the above-mentioned drawbacks of the available studies .

Selenium supplementation or increased dietary intake would undoubtedly provide benefits to Se-deficient individuals. But given that deficiency is quite rare, it would be best to check selenium blood levels before taking supplements. Whether or not selenium prevents cancer is still unknown while taking in excessive selenium can only be harmful.

More clinical research is needed, taking into account genetics, nutritional status, and various forms of selenium supplements.

7) Immune Response

Selenium deficiency impairs immune function. Accordingly, selenium supplementation stimulates the immune system, even in people who are not deficient. Lymphocytes of people who supplemented with selenium (200 µg/day) were more active and efficient at destroying foreign invaders and tumor cells .

Selenium may be more important for proper immunity than was previously realized. Activated immune cells have an increased need for selenium and its amino-acid bound form (selenocysteine), according to recent studies .

Good for Th2-Dominant People

Selenium supplementation may help divert the immune response away from the Th2-type and promote the Th1-type, which protects against asthma, allergic reactions, viral infections and cancer .

More studies are needed to evaluate the immune-stimulating properties of selenium.

8) Fertility and Reproductive Health

Balanced selenium levels are important for reproductive health in both men and women. In men, selenium is important for producing sperm and testosterone.

In a study of 69 men with fertility issues, selenium supplements mildly increased sperm motility but didn’t improve sperm density. 11% of the men who took selenium achieved paternity, compared to none in the placebo group .

However, Se supplementation had no benefits on sperm count, motility, or quality in a similar trial of 33 patients .

In studies on male rats, selenium increased testosterone levels but only in rats who were selenium-deficient .

In women, adequate selenium levels are especially important during early pregnancy. In one study, women who suffered from recurrent miscarriages were more likely to have lower selenium blood levels. Selenium deficiency was also linked to an increased likelihood of miscarriages in animal studies .

9) Heart Health

Selenium may protect against heart disease, probably by boosting the antioxidant glutathione, reducing oxidative stress and preventing platelet clumping .

Selenium deficiency eventually causes harmful, reactive substances to build up, making blood vessels less flexible and platelets more “sticky”. For example, in men with heart disease, low selenium may cause platelets to clump together and narrow blood vessels, potentially worsening heart health .

The clinical results are still mixed, though. In one study, low selenium was linked to a two- to three-fold increase in heart disease, while in another study men with low selenium were at an increased risk of heart attacks or stroke. But other small studies didn’t find any clear link between heart disease risk and selenium levels .

In 668 elderly Swedish people, supplementation with selenium (200 μg) and coenzyme Q10 (200 mg) for four years significantly reduced the risk of heart failure. It dropped by 50% in previously Se-deficient patients and by 62% in patients with moderate Se levels .

Patients with high Se levels didn’t benefit from supplementation, suggesting once again that the benefits might be limited to Se-deficient individuals .

Further research should determine whether selenium supplementation protects against heart disease and under which occasions.

10) Mood and Anxiety

Low selenium levels have been linked to depression, anxiety, tiredness, and mental confusion. In one study of 50 people, selenium supplementation (100 mcg/day) over 5 weeks improved mood, energy levels, and lessened anxiety .

Selenium supplementation over 8 weeks noticeably improved depression and mildly reduced anxiety in a study on seniors living in nursing homes .

Selenium Blood Test & Normal Ranges

The margin between selenium deficiency, optimal and above-optimal levels and toxicity is very narrow. Knowing your selenium status can be helpful in identifying potential health problems.

The most common way to measure selenium status is using blood biomarkers that reflect selenium intake, which can include the following :

  • Elemental selenium (normal range: 70 – 160 ng/mL)
  • Glutathione peroxidase
  • Selenoprotein P, the main supplier of selenium to tissues

To increase longevity, fight inflammation, and aid in cancer prevention, even higher blood levels have been researched. Slightly above-optimal intake may reduce the risk of lung, prostate and colorectal cancers, but the evidence is inconclusive .

Aside from blood tests, long-term selenium status can alternatively be assessed by measuring selenium concentrations in toenails and hair.

Low Selenium

Selenium levels are a marker of antioxidant protection and overall health. Low or high levels don’t necessarily indicate a problem if there are no symptoms or if your doctor tells you not to worry about it.


Causes of low selenium include:

  • Lack of selenium in the diet
  • Inflammatory bowel disease (ulcerative colitis and Crohn’s disease)
  • Parenteral nutrition, in ill people who receive nutrients through the veins
  • Kidney disease
  • Alzheimer’s disease
  • Grave’s disease (hyperthyroidism) or an underactive thyroid (hypothyroidism)
  • Specialized diets for people with health conditions (such as phenylketonuria, a rare birth defect that causes phenylalanine amino acid buildup in the body)

The following drugs may also decrease selenium levels:

  • Corticosteroids, drugs used to reduce inflammation
  • Birth Control pills
  • Clozapine (Clozaril, FazaClo, Versacloz), antipsychotic medication used to treat schizophrenia

Associated Conditions

Low selenium levels may be associated with:

High Selenium

Selenium levels are a marker of antioxidant protection and overall health. Low or high levels don’t necessarily indicate a problem if there are no symptoms or if your doctor tells you not to worry about it.

While optimal selenium intake has many health benefits, excess selenium can be dangerous.

Causes of high selenium levels include:

  • Excess selenium intake, either from a diet high in selenium or from selenium supplements

If you have high selenium levels, stop taking selenium supplements. You should also make sure that your total selenium intake from any other supplements does not exceed the recommended daily intake .

Curcumin supplements may reduce the damage from high selenium in the body .

Type 2 Diabetes

Higher selenium levels were linked to type 2 diabetes and high blood sugar, independent of other factors .

However, the relationship between diabetes and selenium is not that straightforward. The association was much stronger in men who supplement with selenium despite getting sufficient amounts from food. On the other hand, women who develop diabetes during pregnancy are often selenium-deficient .

Excess selenium supplementation in non-deficient people may increase the risk of type 2 diabetes.

Lower Active Thyroid Hormone (T3) in Men

Excess selenium supplementation (300 mcg/day) lowered T3 in men in one study. However, a larger study couldn’t replicate these results .

Prostate Cancer Mortality

Selenium supplementation of 140 μg/day or more in people with prostate cancer (non-metastatic) was linked to increased mortality in one observational study. Blood selenium levels were not measured, so it’s hard to draw meaningful conclusions .

Increased Blood Fats

High blood selenium levels may be associated with increased blood levels of total, LDL, and HDL cholesterol, apo-B, and apo-A1 .


General symptoms selenium toxicity include :

  • Nausea
  • Vomiting
  • Diarrhea
  • Stomach pain
  • Skin rash (dermatitis)
  • Low blood pressure
  • Fast heartbeat

Selenium toxicity may also cause :

  • Garlic-like breath
  • Metallic taste in the mouth
  • Tremors
  • Muscle spasms
  • Confusion
  • Delirium
  • Coma

Symptoms of selenium toxicity can persist for a long time, even up to 3 months after stopping a supplement .

That said, short-term supplementation with an appropriate dosage of Se is safe and well-tolerated, even in children and pregnant women .

Selenium Sources & Dosage


Selenium exists naturally in a variety of foods, but it can also be purchased as a supplement.

Some food sources include :

  • Brazil nuts
  • Fish
  • Shellfish
  • Beef
  • Chicken
  • Young barley seedlings
  • Brewer’s yeast
  • Wheat germ
  • Shiitake and button mushrooms
  • Oats
  • Whole-wheat bread
  • Bran
  • Brown rice
  • Red swiss chard

Fish is an especially good source of selenium because it’s also high in omega 3s and iodine, which all work in synergy.


The below doses may not apply to you personally. If your doctor suggests using a selenium supplement, work with them to find the optimal dosage according to your health condition and other factors.

Although the RDA is 55 mcg, most clinical studies used selenium doses of 100-200 mcg/day, taking into account all sources.

For example, one brazil nut already contains 50 mcg of selenium on average. If you eat 2 brazil nuts per day and plenty of fish, you probably don’t need to supplement with selenium as you are already taking in 100-150 mcg/day through diet.

However, the selenium content in Brazil nuts can vary depending on the soil they were grown on, which is why supplements may be a more reliable option for some people .

The Tolerable Upper Intake Level for selenium in adults is 400 mcg/day. This is the maximum daily intake at which no adverse health effects are expected in most people .

Certain things in life are just better together: chocolate and peanut butter, you and your BFF, iron and vitamin C. And another power duo that deserves major recognition is selenium and antioxidants.

Woah, selenium what? While not given as much press time as magnesium or calcium, selenium is another essential trace mineral that your bod needs to be in tip-top shape. It’s found in soil, water, and foods like brazil nuts, eggs, tuna, cod, poultry, and mushrooms. While overdoing it on selenium can be dangerous (more on that later), for the most part, selenium can work wonders for the human body. Here’s everything you need to know about this super mineral.

Keep reading to find out the top selenium benefits.

Photo: Getty Images / Claudia Totir

1. It helps antioxidants do their job.

“In humans, selenium functions as a cofactor for antioxidant enzymes including glutathione peroxidase, whose main role is to protect our tissues from oxidative damage,” says nutritionist Tamar Samuels, RDN. Basically, your body needs selenium in order to get the most benefits out of certain antioxidants that fight inflammation and free radical damage in your body.

2. It’s important for a healthy immune system.

The mineral also helps facilitate cell growth, says Samuels, and is an important part of immune system health. “Selenium is also needed for the proper functioning of neutrophils, macrophages, NK cells, T lymphocytes, and other immune mechanisms.” All of these parts play an important role in protecting your body from infection and disease. Take that, cold season.

3. It may boost thyroid health.

Selenium helps your body metabolize thyroid hormones, which help regulate your metabolism, digestive function, and mood. For anyone who’s ever struggled with thyroid issues, you may want to allow selenium to be your new best friend—because it can help a lot. “Clinical research shows that selenium taken in combination with thyroid medication helps to lower autoimmune thyroid antibodies,” says Samuels. She says the mineral might also help improve postpartum thyroid function.

4. It might help fight cancer.

Remember how selenium helps antioxidants do their job? That may translate into some cancer-fighting benefits, too. “Selenium may reduce the risk of colorectal cancer,” says Samuels—although a 2016 study found that the mineral offers only moderate benefits in this area. She also notes one study which found that selenium may decrease cancer risk and overall mortality in men.

Is there such a thing as too much selenium?

In a word, yes. The recommended daily allowance (RDA) of selenium is 55 milligrams per day, although a 2012 study found that most people get more than they need from diet and supplementation. People can safely take up to 400 milligrams per day, says Samuels, but anything more than that can be harmful. Consuming too much selenium is linked with a number of health consequences, she says, including nausea, vomiting, abdominal pain, dermatitis, nail changes, fatigue, irritability, alopecia, impaired endocrine function, neurotoxicity, and weight loss.

And if you suffer from an autoimmune disease, be careful. “Selenium might have immunostimulant effects, meaning it could worsen an autoimmune disease by stimulating disease activity,” says Samuels.

Another thing to be wary of? Adverse effects on male fertility. “High amounts of selenium, including through getting it through diet, might decrease sperm motility potentially impacting male fertility,” explains Samuels.

So if you’re already getting a lot of selenium through your diet (like eating lots of poultry and eggs), it may be best to keep it that way to avoid overdoing it. A separate selenium supplement probably isn’t necessary for most people, unless their doctor recommends it. Which is great, because I have so many vitamins already in my lineup as it is.

While we’re on the subject of supplements, here’s the lowdown on why omega-3s are so freaking great for your bod. And here’s what you should know before getting crazy with medicinal mushrooms and herbs.


Shop Selenium

Staff Picks: Megafood Selenium 60 Tablets – recommended universally by our sales staff!

If you want a stronger immune system, a sharp mind, and a youthful appearance start consuming foods enriched with selenium. There is no question that it is essential for your well-being. It contains antioxidants that not just treat inflammation, but fight dangerous free radicals as well. It assist the reproductive system, detoxify your body, aid in cardiovascular health, contribute to good thyroid health as well as boost the body immunity.

It is a mineral that is naturally present in a number of food items. You can find supplements made with selenium as well. It has two types; organic and inorganic. However, both are effective and necessary to maintain a healthy body. Since it is mainly obtained from a natural source, risks of adverse reactions are fewer.

Food Sources of Selenium

  • Shrimp 40mcg
  • Tuna 92mcg
  • Beef 33 mcg
  • Cottage cheese 20 mcg
  • Chicken 22 mcg
  • Hard-boiled egg 15 mcg
  • Brown Rice 19 mcg
  • Whole wheat bread 13 mcg
  • Plain yogurt 8 mcg
  • Milk 8 mcg
  • Lentils 6 mcg
  • Cashew nuts 3 mcg
  • Potato 1 mcg
  • Peaches 1 mcg
  • Banana 2 mcg

11 Amazing Health Benefits of Selenium

. Selenium for Reproductive System

Several studies have concluded that regular consumption of selenium can enhance fertility in both males and females. These studies have also confirmed that regular intake promotes sperm locomotion. It is considered as one of the essential minerals for your wellbeing and its deficiency can cause male infertility. Some studies even suggest that lack of selenium adversely affects fetal growth and female fertility.

2. It Works as a Detoxifier

You can find a number of ways to detoxify your body, which is good as your body builds up toxins from the diet that people normally consume, which mainly consists of processed foods. It is essential to detoxify your body to keep the liver and other organs healthy. You need to consume foods that fight pollutants such as heavy metals. Your body also suffers plenty of environmental damage, which is why it is even more important to incorporate selenium supplements or a diet rich with the mineral in order to detoxify your liver.

3. For Cardiovascular Health

There are countless reasons that negatively affect your cardiovascular health and the best thing that you can apart from being active and eating healthy is to include foods that contain selenium. It is naturally present in chicken, turkey, and tuna, which are all foods that are good for the heart as well, if eaten in moderation. According to cardiologists, people with selenium deficiency usually fall prey to heart disease and hypertension. Several studies have also concluded that when combined with other nutrients such as beta-carotene and Vitamin E, selenium normalizes higher cholesterol levels, which is good for the arteries.

4. It Fights Free Radicals

It is evident that free radical cells are the root cause of harrowing diseases such as cancer. You are required to fight these free radicals as they may cause further health problems. More than that, these cancerous cells eliminate healthy cells and create an acidic environment inside your body, where the bad cells thrive and keep on multiplying and metastasizing. This leads to numerous health conditions such as a weak immune system and premature aging. Being a powerful antioxidant, selenium fights free radical cells effectively.

5. For Thyroid Health

Thyroid health is an under-discussed topic. A slight problem in your thyroid can lead you to developing a slew of health complications totally disrupting your hormones. These hormones contribute to metabolic and growth processes. Your thyroid gland needs selenium to adequately produce all the necessary hormones in your body.

6. Relieve Asthma Symptoms

Being a chronic disease, asthma gets troublesome if not dealt with adequately. According to a recent study, selenium is a potent mineral that helps reduce symptoms associated with asthma. Since this respiratory disorder is a common health problem, it will be even better if you include selenium in the diet of your children to avoid risks of asthma later in life.

7. It Works as an Immunity Booster

Your immune system protects you from a number of health issues naturally, but only if it is strong enough. So, what should you do to keep it stronger? Consume fresh vegetables, fruits, dairy products and proteins that are loaded with selenium. Your immune system fights various bacteria steering you clear of infections, fever, and flu.

8. It fights Cancerous Cells

You will be surprised to learn how a single mineral is potent enough to fight cancerous cells. Selenium is that miraculous mineral – it has a capability to prevent risks of cancers in several ways. It is noteworthy that after a thorough research, scientists have concluded that if taken adequately, selenium can reduce the risks of lung, prostate, and colorectal cancer as well. The study also suggests that it has potential to destroy cancerous cells and the regular consumption of selenium can even stop the free radical cell cycle.

9. Selenium for Psychological Health

Due to stress and mental pressure, psychological problems are becoming common day by day. They are considered harmful because they can take a toll on both your mental and physical health, leading to a weak immune system. Plus, stress can also induce eating disorders that can lead to obesity and diabetes. Experts have associated disturbed psychological health with selenium deficiency. In an experiment, people suffering with severe depression were given selenium supplements. Improvements in their mood and behavior gradually begun to change, proving that selenium deficiency can lead to mental disorders.

10. For Beautiful Skin

The phrase “you become what you eat” is quite common and true. It is absolutely same for the skin as a healthy diet appears on your face whereas processed foods and lack of water can lead to acne breakouts. Plus, you end up splurging on skin care products and treatment. However, treating your skin with harsh chemicals is not a smart idea as your skin is naturally delicate. It should be nourished in a natural way instead of chemical-filled substances. This is why beauty experts stress on consuming a healthy diet. By a healthy diet, they mean consuming all the minerals and vitamins that are needed for a youthful skin. In this case, selenium can help you as well as the mineral is in every food that beauticians suggest.

11. For Hair Health

It is heartbreaking to see dry and damaged hair. It happens due to dying your hair frequently, using hair tools without a heat protector, etc. There are treatments that provide a temporary solution to your dry hair, but they don’t last long. However, consuming selenium supplements can do wonders for you.

Bottom Line

Selenium is powerful mineral and treats various health problems. Incorporating it into your diet is a good way to benefit from it’s various health benefits and enhance the quality of your life.

7 Science-Based Health Benefits of Selenium

Though you may have never heard of selenium, this amazing nutrient is vital to your health.

Selenium is an essential mineral, meaning it must be obtained through your diet.

It’s only needed in small amounts but plays a major role in important processes in your body, including your metabolism and thyroid function.

This article outlines 7 health benefits of selenium, all backed by science.

1. Acts as a powerful antioxidant

Antioxidants are compounds in foods that prevent cell damage caused by free radicals.

Free radicals are normal byproducts of processes like metabolism that are formed in your body daily.

They often get a bad rap, but free radicals are essential for your health. They perform important functions, including protecting your body from disease.

However, things like smoking, alcohol use, and stress can cause an excess of free radicals. This leads to oxidative stress, which damages healthy cells (1).

Oxidative stress has been linked to chronic conditions like heart disease, Alzheimer’s, and cancer, as well as premature aging and the risk of stroke (2, 3, 4, 5, 6).

Antioxidants like selenium help reduce oxidative stress by keeping free radical numbers in check (7).

They work by neutralizing excess free radicals and protecting cells from damage caused by oxidative stress.

Summary Selenium is a powerful antioxidant that fights oxidative stress and helps defend your body from chronic conditions, such as heart disease and cancer.

2. May reduce your risk of certain cancers

In addition to decreasing oxidative stress, selenium may help lower the risk of certain cancers.

This has been attributed to selenium’s ability to reduce DNA damage and oxidative stress, boost your immune system, and destroy cancer cells (8).

A review of 69 studies that included over 350,000 people found that having a high blood level of selenium was associated with a lower risk of certain types of cancer, including breast, lung, colon, and prostate cancers (9).

It’s important to note that this effect was only associated with selenium obtained through foods, not supplements.

However, some research suggests that supplementing with selenium may reduce side effects in people undergoing radiation therapy.

For example, one study found that oral selenium supplements improved overall quality of life and reduced radiation-induced diarrhea in women with cervical and uterine cancer (10).

Summary Higher blood levels of selenium may protect against certain cancers, while supplementing with selenium may help improve quality of life in people undergoing radiation therapy.

3. May protect against heart disease

A diet rich in selenium may help keep your heart healthy, as low selenium levels have been linked to an increased risk of heart disease.

In an analysis of 25 observational studies, a 50% increase in blood selenium levels was associated with a 24% reduction in the risk of heart disease (11).

Selenium may also lower markers of inflammation in your body⁠ — one of the main risk factors for heart disease.

For example, a review of 16 controlled studies including over 433,000 people with heart disease showed that taking selenium supplements decreased levels of the inflammatory marker C-reactive protein (CRP).

Additionally, it increased levels of glutathione peroxidase, a powerful antioxidant (12).

This indicates that selenium may help lower heart disease risk by reducing inflammation and oxidative stress in your body. Oxidative stress and inflammation have been linked to atherosclerosis, or the buildup of plaque in arteries.

Atherosclerosis can lead to dangerous health problems like strokes, heart attacks, and heart disease (13).

Incorporating selenium-rich foods into your diet is a great way to keep levels of oxidative stress and inflammation to a minimum.

Summary Selenium may help keep your heart healthy by keeping oxidative stress in check and reducing your risk of heart disease.

4. Helps prevent mental decline

Alzheimer’s disease is a devastating condition that causes memory loss and negatively affects thinking and behavior. It’s the sixth-leading cause of death in the United States.

The number of people with Alzheimer’s disease is growing. Thus, finding ways to prevent this degenerative disease is imperative.

Oxidative stress is believed to be involved in both the onset and progression of neurological diseases like Parkinson’s, multiple sclerosis, and Alzheimer’s (14).

Several studies have shown that patients with Alzheimer’s disease have lower blood levels of selenium (15, 16).

Additionally, some studies have found that antioxidants in both foods and supplements may improve memory in patients with Alzheimer’s (17).

One small study found that supplementing with one selenium-rich Brazil nut per day improved verbal fluency and other mental functions in patients with mild cognitive impairment (18).

What’s more, the Mediterranean diet, which is rich in high-selenium foods like seafood and nuts, has been associated with a lower risk of developing Alzheimer’s disease (19, 20).

Summary A diet rich in selenium may help prevent mental decline and improve memory loss in people with Alzheimer’s disease.

5. Is important for thyroid health

Selenium is important for the proper functioning of your thyroid gland. In fact, thyroid tissue contains a higher amount of selenium than any other organ in the human body (21).

This powerful mineral helps protect the thyroid against oxidative damage and plays an essential role in the production of thyroid hormones.

A healthy thyroid gland is important, as it regulates your metabolism and controls growth and development (22).

Selenium deficiency has been associated with thyroid conditions like Hashimoto’s thyroiditis, a type of hypothyroidism in which the immune system attacks the thyroid gland.

An observational study including over 6,000 people found that low serum levels of selenium were associated with an increased risk of autoimmune thyroiditis and hypothyroidism (23).

Additionally, some studies have shown that selenium supplements may benefit people with Hashimoto’s disease.

One review concluded that taking selenium supplements daily for three months resulted in lower thyroid antibodies. It also led to improvements in mood and general well-being in those with Hashimoto’s disease (24).

However, more research is needed before selenium supplements can be recommended for those with Hashimoto’s disease.

Summary Selenium protects the thyroid gland from oxidative stress and is necessary for thyroid hormone production. Selenium may help people with Hashimoto’s disease and other types of thyroid disease, but more research is needed.

6. Boosts your immune system

Your immune system keeps your body healthy by identifying and fighting off potential threats. These include bacteria, viruses, and parasites.

Selenium plays an important role in the health of your immune system. This antioxidant helps lower oxidative stress in your body, which reduces inflammation and enhances immunity.

Studies have demonstrated that increased blood levels of selenium are associated with enhanced immune response.

On the other hand, deficiency has been shown to harm immune cell function and may lead to a slower immune response (25).

Studies have also associated deficiency with an increased risk of death and disease progression in people with HIV, while supplements have been shown to lead to fewer hospitalizations and an improvement in symptoms for these patients (26).

Additionally, selenium supplements may help strengthen the immune system in people with influenza, tuberculosis, and hepatitis C (27).

Summary Selenium is crucial for the health and proper functioning of your immune system. Higher levels of selenium may help boost the immune systems of people with HIV, influenza, tuberculosis, and hepatitis C.

7. May help reduce asthma symptoms

Asthma is a chronic disease that affects the airways that carry air in and out of the lungs.

These airways become inflamed and begin to narrow, causing symptoms like wheezing, shortness of breath, chest tightness, and coughing (28).

Asthma has been associated with increased levels of oxidative stress and inflammation in the body (29).

Due to selenium’s ability to reduce inflammation, some studies suggest that this mineral may help reduce asthma-related symptoms.

Research suggests that people who have asthma have lower blood levels of selenium.

In fact, one study showed that asthmatic patients with higher levels of blood selenium had better lung function than those with lower levels (30).

Selenium supplements may also help reduce asthma-related symptoms.

For example, one study found that giving people with asthma 200 mcg of selenium per day reduced their use of the corticosteroid medications used to control their symptoms (31).

However, research in this area is conflicting, and larger studies are needed to fully understand selenium’s role in the development and treatment of asthma (32).

Summary Selenium may benefit people with asthma due to its ability to lower inflammation in the body. However, more research is needed.

Best dietary sources of selenium

Fortunately, many healthy foods are high in selenium.

The following foods are great sources (33), (34):

The amount of selenium in plant-based foods varies depending on the selenium content of the soil in which they were grown.

Thus, selenium concentrations in crops depend largely on where they are farmed.

For example, one study showed that the selenium concentration in Brazil nuts varied widely by region. While a single Brazil nut from one region provided up to 288% of the recommended intake, others provided only 11% (35).

Therefore, it’s important to consume a varied diet that includes more than one good source of this important mineral.

SummaryFoods rich in selenium include seafood, nuts, and mushrooms. It’s important to consume a variety of foods that contain this mineral, as selenium content can vary depending on growing conditions.

Dangers of excessive selenium intake

Although selenium is necessary for good health, getting too much can be dangerous. In fact, consuming high doses of selenium can be toxic and even fatal.

While selenium toxicity is rare, it’s important to stay close to the recommended amount of 55 mcg per day and never exceed the tolerable upper limit of 400 mcg per day (36).

Brazil nuts contain a very high amount of selenium. Consuming too many could lead to selenium toxicity.

However, toxicity is more likely to happen from taking supplements rather than eating selenium-containing foods.

Signs of selenium toxicity include:

  • hair loss
  • dizziness
  • nausea
  • vomiting
  • facial flushing
  • tremors
  • muscle soreness

In severe cases, acute selenium toxicity can lead to serious intestinal and neurological symptoms, heart attack, kidney failure, and death (37).

SummaryWhile selenium toxicity is rare, overconsumption of this mineral through diet or supplements can have dangerous side effects.

The bottom line

Selenium is a powerful mineral that is essential for the proper functioning of your body.

It plays a critical role in metabolism and thyroid function and helps protect your body from damage caused by oxidative stress.

What’s more, selenium may help boost your immune system, slow age-related mental decline, and even reduce your risk of heart disease.

This micronutrient can be found in a wide variety of foods, from oysters to mushrooms to Brazil nuts.

Adding more selenium-rich foods to your diet is an excellent way to maintain good health.

The Selenium Dosage you ChooseShould be ‘Just Right’

For those who choose to get their selenium dosage from supplements, getting the RIGHT Selenium Dosage is extremely important. While there are MANY selenium benefits, long-term exposure to high doses can cause very real cases of selenium overdose that can undo any or all of the beneficial effects that you are seeking from taking this vital mineral.

Do You Even Need Selenium Supplements?

This is a question that no one is going to be able to answer for you. With some supplements, it is almost a ‘no brainer’ to decide. For instance, there is almost no vitamin D in any commonly eaten foods and most people stay out of the sun. Therefore, taking Vitamin D Supplements is practically required to prevent the long term Symptoms of Vitamin D Deficiency.

But the need for your selenium dosage from supplements is more subtle. Blood testing does not give adequate information about need for selenium,

and unlike Vitamin B12 Supplements which have few, if any, toxic effects even at massively high doses- you CAN take too much selenium and impair your health. So, my warning to you is to read the Selenium Overdose page as well as doing your own due diligence, reading the literature and being aware of toxicity symptoms – and be fully aware of the risks and benefits of selenium supplementation before you begin to supplement on your own.

Why Supplement anyway if there are risks of selenium overdose? There are many Selenium Benefits and most of us are far removed from where our food is grown. If you eat many servings of unprocessed whole foods per day and you KNOW that the plants you are eating were grown in selenium rich soils (you can not assume that organic foods were grown in selenium-rich soil), or you know that the animal products you are eating grazed on plant material high in selenium, then you probably don’t need to supplement. But if you do not eat large quantities of fresh, unprocessed foods grown or raised in selenium-rich soil, then there is really no way to know for sure if you are getting adequate selenium.

The Facts About Selenium suggest that even seemingly ‘adequate’ selenium in the diet may not be enough:

  • This Study took a group of people with NORMAL selenium blood levels and supplemented them with 200 mcg of selenium per day and concluded, “The results indicated that the immunoenhancing effects of selenium in humans require supplementation above the replete levels produced by normal dietary intake.”
  • Antioxidant researcher Beldeu Singh states,”It is well established that in most industrialized countries, selenium intake is so low and that it might limit GPx (glutathione) synthesis….” And glutathione is an antioxidant produced INSIDE of each and every cell of the body that is CRITICAL for good health- and can only be produced in the presence of adequate selenium.

So, immune enhancing effects, including Selenium’s Role in Influenza and cancer, are only a few of the many Selenium Benefits that you may not be able to get except by taking selenium supplements. But if you were to take selenium supplements, what dose would be beneficial.

Selenium Dosage in Nature

Selenium comes entirely from the plant kingdom and humans get selenium by ingesting plants or by drinking water that contains selenium. But intake varies GREATLY from region to region depending upon soil and water conditions. In areas with LOW selenium levels, humans get diseases like:

  • Heart Failure from Selenium Deficiency
  • Some cancers
  • Thyroid problems
  • Immune System Problems

But in regions that get too high of a selenium dosage or in people who Overdose on Selenium, they get neurologic and endocrine diseases. So there is a ‘Goldilocks’ effect of not getting too much and not getting too little- but getting the ‘Just Right’ Selenium Dosage for optimal health.

Selenium Dosage in Studies

Many studies have attempted to determine the ‘Just Right’ selenium dosage, and while there are no clear cut answers as to the exact optimal dose for optimal health, the studies that HAVE been done give us some clues.

200 mcg (micrograms) is the most frequently used dose in studies that obtained beneficial results. Most of these studies were done over relatively short periods of time, but some were done over long periods of time, so it seems that 200 mcg per day is a relatively safe dosage to take for relatively long periods of time.

One study that analyzed many other studies on selenium found that dosages of about 300 mcg per day of selenium began to show ill effects on the thyroid gland as well as hair and nail weakening and loss.

So from this study, we can determine that 300 mcg per day of selenium is likely to be unnecessary and may cause harm over the long term. So, taking between about 100 mcg to 200 mcg seems to be the ‘just right’ selenium dosage that is beneficial for health, but that does not cause problems in MOST people. Again, this will be dependent upon how much you ALREADY get in your diet, your specific metabolism and other factors that science may not even know about.

What are the Best Selenium Supplements

There are several different forms of Selenium Supplements

The ‘organic’ forms of selenium, in studies, seemed to raise blood levels more effectively than did synthetic forms of selenium and were less toxic.

The preferred types of selenium are:

  • Selenomethionine
  • Selenium enriched yeast
  • Methylselenocysteine
  • Chelated Formulations

Importantly, though, there are many many studies that mention the ‘Synergistic’ effects of Selenium when taken with Vitamin E. That means that even though selenium showed benefits alone and Vitamin E showed some benefits alone- the COMBINED effects of Selenium and Vitamin E TOGEHTHER were greater than the effects of either one by itself.

That’s one of the reasons that I recommend Jigsaw Health’s Essential Daily Packs

. It contains 400 mcg of natural Selenium along with Vitamin E in the form of tocopherols- the only form of vitamin E that you should take.

The forms of selenium that are NOT recommended are:

  • Selenites
  • Selenates

So, if you choose to take Selenium Supplements, it is vital that you are fully aware of the benefits- as well as the risks of Overdose on Selenium that can occur with a too high Selenium Dosage.

Also, selenium deficiency- as with most other nutrients- does not occur all by itself. If you believe that you may be selenium deficient, selenium seems to work better with other antioxidants- particularly Vitamin E and Vitamin C. However, getting a ‘balance’ of nutrients is ALWAYS the recommended way of taking supplements.

In our ‘One Drug for One Problem’ society, most people want to know what ONE SPECIFIC supplement to take for their problem. They want the MAGIC BULLET that will solve their problems. Unfortunately, it’s likely that you will never find that ‘Magic Bullet’ because the SYNERGY between multiple nutrients is often what is required to solve health problems.

If you have health problems (or don’t yet and want to keep it that way), I highly recommend taking a look at Jigsaw Health’s Essential Daily Packs

. It is really one of the best supplements on the market. Don’t skimp on cheap products when it comes to your multivitamin, your health is worth more than that.

Keep reading to see how Selenium could also influence your risk of the Flu- as well as how everyone’s else’s intake of selenium could influence YOUR risk….

Selenium and Influenza
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