Selenium: Overview

Selenium is an essential mineral which works closely with vitamin E.  Selenium is absorbed fairly easily in the upper portion of the GI tract.

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Selenium is considered a trace mineral.  Found in minute amounts in soil, selenium is considered essential to health.  Deficiencies include cardiomyopathy and Keshan disease.  While deaths are rare, low selenium intakes are often seen in countries where the soil is depleted of selenium.

Selenium enters the body when food containing selenium is eaten.  The selenium contained in grains and meat is associated with proteins.  The human body easily absorbs the organic selenium compounds that are eaten and makes them available where they are needed in the body.  The selenium in drinking water is usually in the form of inorganic sodium selenate and sodium selenite, which are also easily absorbed in the digestive tract.  The human body can change these inorganic selenium compounds into forms the body can use.

Selenium can build up in the human body, mostly in the liver and kidneys and, to a lesser extent, in the blood, lungs, heart, and testes.  It also can build up in hair, depending on the length of time and amount of exposure.  Selenium leaves the body mainly in the urine, and less in feces and breath.  Selenium in the urine increases as the amount of selenium to which a person is exposed increases.

Selenium closely interacts with vitamin E in the body.  The antioxidant properties of selenium are related to this interaction as well as its active selenoprotein involvement in glutathione metabolism.  These activities have made selenium one of the key players, albeit in trace amounts, in antioxidant, anti-aging, and immune enhancing products.  There are many ongoing research projects investigating selenium, as well as other antioxidants, for the ability to slow the growth of various cancers.


Organic and inorganic forms of selenium may have different properties.  Organic forms include selenomethionine, selenocysteine, amino acid chelates, yeast, and kelp-bound selenium.  Inorganic forms include sodium selenite and sodium selenate.

Selenium is naturally found in foods high in protein, such as fish, meat, poultry, cereals, seeds and other grains.  It can also be found in vegetables like garlic, mushrooms and asparagus.  Brazil nuts, especially with their shells on, are very high in selenium.  Some experts believe that vegetarians may not be getting enough selenium unless supplemented.

Natural selenium levels in the soil are highly variable throughout the world.  In the U.S., the Eastern Coastal Plain and the Pacific Northwest have the lowest selenium levels and people in these regions naturally ingest about 60 to 90mcg per day.  This compares to a range of 60 to 200mcg across the U.S. with 125mcg being average.

Why it is Recommended

Selenium is useful in the prevention of several cancers.  As deficient selenium levels are associated with an increased risk of cancers in general, ensuring adequate selenium intake and maximizing selenium status in the presence of an elevated cancer risk is highly recommended.

Incrementally increasing doses of sodium selenite are being used for decreasing sensitivity to environmental toxins.  Your local Naturopath should be familiar with this protocol.


At the time of writing, there is no clear agreement on how to supplement with selenium – exactly who should use it, how much, or in what form.

The normal intake of selenium in food, about 50-150mcg per day, is enough to meet the daily need for this essential nutrient.  Selenium compounds can be harmful, however, at daily levels that are only somewhat higher than needed.

The National Academy of Sciences' Food and Nutrition Board has stated that a daily intake of between 50 to 300mcg of selenium is "safe and adequate".  Therapeutic doses often range from 200 to 400mcg daily.

The current USRDA recommendation is between 50 and 200mcg of selenium.


Toxicity is more of a problem with selenium than most nutrients, and doses over 800 to 1000mcg should be used with caution or under a doctor's supervision only.

The seriousness of the effects of excess selenium depends on how much is eaten and how often.  Swallowing a lot of sodium selenate or sodium selenite (for example, part of a bottle of sodium selenate prepared for a flock of sheep, or large numbers of selenium supplement pills) could be life-threatening without immediate treatment.

If amounts of selenium only somewhat higher than needed were eaten over long periods of time, several health effects could occur, including brittle hair, deformed nails, and, in extreme cases, loss of feeling and control in arms and legs.  These health effects were seen in several villages in the People's Republic of China where people were exposed to foods high in selenium for months to years.  No populations in the United States have been reported with symptoms of serious, long-term selenium poisoning.

There is a warning: "We must be careful not to encourage overconsumption of selenium supplements.  While an intake of selenium of around 15mcg per kg of bodyweight per day is thought to be without prolonged impact on human health, it must be remembered that selenium is a toxic mineral with a fairly small therapeutic window.  In some sensitive individuals, the maximum safe dietary intake may be as low as 600mcg per day.  It would therefore seem prudent to restrict adult intake from all sources to an upper limit of 400-450mcg per day as recommended by several expert panels."

Persons considering supplementation should note that the multivitamins they are taking may already include selenium – in addition to their dietary intake, which tends to be higher in the U.S. than in many countries.

Selenium can help with the following:


Cigarette Smoke Damage

An Italian study of men who smoked found that heavy smokers had lower levels of selenium than lighter smokers and non-smokers. [Atherosclerosis, 1991;87: pp.129-34]


Premature/Signs of Aging

Considered to be from 200 to 500 times more potent an antioxidant than vitamin E, selenium and vitamin E are synergistic as antioxidants and inhibit or prevent the damage to tissues by free radicals which have been cited as causal factors in heart disease, atherosclerosis, arthritis and aging.


Chronic Thyroiditis

Three months of supplementation with 200mcg selenium daily reduced thyroid peroxidase antibodies (TPOAb) but had no effect on Tg antibodies (TgAb) in a well-controlled study of 70 women with autoimmune thyroiditis.  TPOAb and/or TgAb levels were above 350 IU/ml. [ J Clin Endocrinol Metab 2002;87(4): pp.1687-1691]


Coronary Disease / Heart Attack

Selenium is considered to be from 200 to 500 times more potent an antioxidant than Vitamin E.  Selenium and Vitamin E are synergistic as antioxidants and inhibit or prevent the damage to tissues by free radicals which have been cited as causal factors in heart disease.


Considered to be from 200 to 500 times more potent an antioxidant than vitamin E, selenium and vitamin E are synergistic as antioxidants and inhibit or prevent the damage to tissues by free radicals which have been cited as causal factors in heart disease, atherosclerosis, arthritis and aging.  Dosage: 200mcg per day.

Dental / Oral

Environment / Toxicity

Mercury Toxicity (Amalgam Illness)

Selenium chelates heavy metals such as cadmium, lead, mercury and silver.

Heavy Metal Toxicity

Selenium is able to combine with metals such as cadmium and mercury to reduce their toxicity.

Eyes / Ocular

Macular Degeneration

Selenium is sometimes recommended, but you should always consult your physician to determine appropriate dosages.


Pregnancy-Related Issues

A small study of infertile women and women with a history of miscarriage suggests that low levels of magnesium may impair reproductive function, and may contribute to miscarriage.  Oxidation, a process that is damaging to cell membranes, can lead to loss of magnesium.  The same study suggests that the antioxidant selenium protects the cell membrane, thereby maintaining appropriate levels of magnesium.  The authors of the study suggest taking both magnesium and selenium supplements.

Women who have miscarried have lower levels of selenium than women who carry a pregnancy to full term.  Although the authors of the above-mentioned study do not specify the exact amount to take, the recommended doses are generally 300 to 400mg per day of magnesium and 200mcg per day of selenium.

Female Infertility

A deficiency of selenium can lead to infertility in women.




A review of medical literature that focused on 69 articles published between 2000 and 2016 concluded that the maintenance of proper selenium levels in the body (not too high and not too low) is a prerequisite not only to prevent thyroid disease but also to maintain overall health. [Mara Ventura et al., Int J Endocrinol. 2017; 2017: art.1297658]

The thyroid gland contains the highest concentration of any organ in the body.  Selenium is vital for the production of thyroid hormone and is involved in the conversion of T4 (inactive thyroid hormone) to T3 (the active form).  Two important groups of enzymes within the thyroid are selenoproteins, which depend on selenium.  Mercury and cadmium are major thyroid disruptors but not when sufficient selenium is available: selenium binds to mercury and makes it completely inert; it also binds to cadmium and facilitates its excretion through bile.  Selenium and iodine are both essential for thyroid hormone production and a deficiency in either will cause problems.

On June 22, 2001 Dr. Barbara Gasnier reported the findings at the 83rd Annual Meeting of the Endocrine Society in Denver, Colorado that selenium supplementation may prevent progression of autoimmune thyroid disease, especially during the onset of the disease.

According to the researchers, selenium deficiency appears to contribute to the development and maintenance of autoimmune thyroiditis because of its effect on the function of selenium-dependent enzymes, which can modulate the immune system.

Selenium supplementation with 200mcg of sodium selenite may improve the inflammatory activity seen in patients with autoimmune thyroiditis, but whether this effect is specific for autoimmune thyroiditis or may also be effective in other organ-specific autoimmune diseases remains to be investigated.  Selenium supplementation may lower free radical activity, which contributes to inflammation.

It appears that taking selenium without iodine will result in a decrease in production of Thyroxine (T4), although there may be an initial transient increase in T4 to T3 conversion and hence higher T3 and seemingly worse hyperthyroidism.


Selenium and iodine are two minerals which are important in the proper functioning of the thyroid.  While the importance of iodine has been known for a long time, the importance of selenium has only been discovered and explored since 1990.

The following is a summary of the possible interactions of selenium and iodine to consider when dealing with thyroid abnormalities:

  • A selenium deficiency causes an iodine deficiency to worsen
  • When both are deficient, giving selenium alone results in a worsening of existing hypothyroidism
  • If iodine intake is low, selenium intake should also be kept low or the two should be supplemented together
  • If iodine intake is high and selenium is low, the thyroid may over-produce thyroid hormone (Grave's hyperthyroidism), the thyroid can be damaged from oxidation and hypothyroidism may result (Hashimoto's thyroiditis)

The solution to nutrient supplementation for hypothyroidism may be to take both selenium and iodine simultaneously and gradually increase the dose.  A good recommendation may be to start with 100mcg of selenium and 1 kelp tablet per day and gradually work up to 400-600mcg of selenium and 2-4 tablets of kelp per day.



Lab Values

High Total Cholesterol

A selenium deficiency is associated with hypercholesterolemia.


Syndrome X / Metabolic Syndrome

Selenium is a mineral that works alongside vitamin E as part of the antioxidant protection against free radical damage caused by high insulin levels.  It may also help prevent heart disease.


Rheumatoid Arthritis

Selenium levels are generally low in patients with rheumatoid arthritis.  Low selenium levels in joint tissues may be a significant factor contributing to the inflammatory process in rheumatoid arthritis.  Selenium plays an important role as an antioxidant and serves as the mineral cofactor in the free-radical scavenging enzyme glutathione peroxidase.  This enzyme is also important in reducing the production of inflammatory compounds that cause much of the damage to tissues seen in rheumatoid arthritis.  A deficiency of selenium would result in even more significant damage.


Organ Health


Optimal selenium status should be ensured for both prevention and treatment: 200mcg per day is needed to keep your liver healthy.  When the micronutrient selenium was added to the diet of 20, 847 people in a Chinese town, the number who became infected with hepatitis B virus was 50% less than for villagers not receiving dietary selenium.  Supplementation also markedly reduced the risk of liver cancer among HBV sufferers.

"Selenium also appears to be protective in individuals infected with hepatitis virus (B or C) against the progression of the condition to liver cancer." [Rayman MP. The importance of selenium to human health. The Lancet. July 15, 2000; volume 356, pp.233-41]




People with low levels of selenium have a high risk of asthma. [Clin Sci 1989;77: pp.495-500]  Asthma involves free-radical damage [N Engl J Med 1991;325: pp.586-7 (letter)] that selenium might protect against.  In a small double-blind trial, supplementation with 100mcg of sodium selenite (a form of selenium) per day for 14 weeks resulted in clinical improvement in six of eleven patients, compared with only one of ten in the placebo group. [Allergy 1993;48: pp.30-6]  Most doctors recommend 200mcg per day for adults (and proportionately less for children) – a higher, though still safe, level.


Adult Acne

See the link between Adult Acne and Vitamin E.

Adolescent Acne

Acne in both men and women can show improvement with vitamin E and selenium treatment.

Tumors, Malignant

Chronic Lymphocytic Leukemia (CLL)

In evaluating 59 patients with lymphoid malignancies such as Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma and chronic lymphocytic leukemia, serum selenium concentrations were significantly lower in patients than in controls.  Clinical stage was inversely associated with selenium levels.

Non-Hodgkin's Lymphoma

In evaluating 59 patients with lymphoid malignancies such as Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma and chronic lymphocytic leukemia, it was found that serum selenium concentrations were significantly lower in patients than in controls.  The lower the selenium levels were, the worse the cancer turned out to be.

As deficient selenium levels are associated with an increased risk of cancers in general, ensuring adequate selenium intake and maximizing selenium status in the presence of an elevated cancer risk is appropriate.


Serum selenium levels were inversely related to the degree of disease severity in 200 cases of melanoma studied.  As selenium has established cancer prevention effects, its use to reduce the risk of melanoma is advisable.

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Selenium can help prevent the following:


Alzheimer's Disease

See the link between Alzheimer's Disease and Zinc.

Eyes / Ocular

Tumors, Malignant

Lung Cancer

A double-blind study demonstrated that supplementation with 200 mcg/day of selenium (in the form of high-selenium brewer's yeast) reduced the incidence of prostate, colorectal and lung cancer, and reduced overall cancer mortality by 50%. [JAMA 1996;276: pp.1957-63]

Prostate Cancer

In one study, the risk of prostate cancer for men receiving a daily supplement of 200mcg per day of selenium was found to be one-third that of those receiving a placebo.

Ovarian Cancer

20,305 American women were followed prospectively for 20 years.  Initial serum selenium levels were inversely related to the risk of ovarian cancer. [J Natl Cancer Inst 88(1): pp.32-7, 1996]

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