What is Selenium? Properties and Benefits

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  1. Selenium
    1. Description of Selenium
    2. Benefits of Selenium
  2. Nutritional references (recommended nutrient intakes)
  3. Dietary sources of selenium
    1. Deficiency and excess
    2. Anticancer
    3. Stimulates the immune system
    4. Good thyroid function
    5. The quality of the hair and nails
    6. Selenium deficiency correction ++
    7. Prostate cancer prevention ++.
    8. Prostate Cancer
    9. However, this supplement did not change skin cancer recurrence rates6.
    10. Prevention of cardiovascular disease +
  4. Risks of a selenium underdose and overdose
    1. Risks of Selenium Deficiency
    2. Risks in case of an excess of selenium
  5. You may be interested:


Selenium is also a trace element present in minute quantities in the body, but it is nevertheless indispensable.

Due to its antioxidant function, it is widely used as a dietary supplement, often in combination with vitamins A, C and E, with which it acts in synergy.

The best known role of selenium is its antioxidant role. Indeed, it helps fight against free radicals, in particular by participating in the metabolism of glutathione peroxidase (an enzyme whose function is to protect cell membranes from attack by free radicals).

Selenium Benefits

Sylvian photo on Pixabay

Because of its antioxidant function, selenium acts in synergy mainly with vitamin E, but also with vitamin C and beta-carotene (provitamin A).

It has an action on the protection of the skin, as well as on the quality of vision.

It also helps maintain the immune system, and acts as a detoxifier for the body.

Finally, it is believed to play a role in male fertility by promoting spermatogenesis.

Description of Selenium

Selenium (symbol Se in the Periodic Table of Elements) is one of the antioxidant trace elements.

In the body, it is linked to several proteins and is stored mainly in the muscles.

Benefits of Selenium

  • Selenium enters the structure of several antioxidant enzymes: glutathione peroxidase and thioredoxin reductase. These enzymes help neutralize excess free radicals present in the body, which accelerate cellular aging and promote the onset of various diseases, including cardiovascular diseases.
  • Thioredoxin reductase helps regenerate vitamins C and E, which also have an antioxidant action.
  • Selenium is a modulator of immune (especially antiviral) and anti-inflammatory responses.
  • It participates in the detoxification of certain toxic compounds, heavy metals and xenobiotics (foreign molecules).
  • It is involved in thyroid metabolism.

Nutritional references (recommended nutrient intakes)

The recommended nutrient intake, proportional to body weight, is set for children at 1 µg per kilogram of body weight per day1. For adults (women and men), it is set at 70 µg per day.

For people over 75, the recommended intake is 80 µg per day, taking into account the increase in oxidative stress with advancing age and to maintain the proper functioning of the immune system.

For athletes who train intensively, a complementary intake of 10 to 30 µg per day is proposed, proportional to the expenditure of energy, taking into account oxidative phenomena caused by muscle work.

Dietary sources of selenium

The richest foods in selenium are fish and seafood. Then there is meat, offal, eggs, legumes, whole foods and nuts.

Where do we find it?

Selenium is mainly found in nuts, meat, offal, seafood, fish, whole grains, some fruits and vegetables (tomatoes, pears, oranges, cooked leeks, cooked turnips, cooked onions, cruciferous...), etc.

It should be noted that plant sources are good sources of selenium only if they come from areas with selenium-rich soils.

The same applies to animal sources, whose content is directly related to animal feed.

Deficiency and excess

Cases of excess selenium are very rare, as selenium can only become pro-oxidant in extreme cases of overdose.

Deficiencies can be found in certain categories of the population, such as the elderly, people with intestinal absorption problems (celiac disease, Crohn's disease, etc.), vegetarians, smokers, alcoholics, sportsmen, people living in regions with poor selenium soils, etc.


Following the observation that areas with higher soil selenium concentrations had lower cancer rates, the Cancer Nutrition Prevention Study initiated experimental studies2 that showed a 41% reduction in cancer mortality and a 25% reduction in the overall incidence of cancer in people who took 200 µg selenium per day for 2 years, with better results in men and ex-smokers.

However, these results concern selenium-deficient individuals, and it would appear that over-supplementation in non-deficient individuals may be counterproductive.

Stimulates the immune system

Selenium, a powerful antioxidant, participates in the regeneration of immune system cells and helps modulate immune and inflammatory reactions. Several studies have confirmed this action345. Indeed, a low selenium intake causes a decrease in resistance to oxidative stress and an increase in sensitivity to infections.

Good thyroid function

Like iodine, selenium plays a key role in the proper functioning of the thyroid and in the biosynthesis and metabolism of thyroid hormones, as shown in this 2008 review6 .

In addition, two recent studies (Danish7 and Iranian8 ) correlate selenium supplementation with improved thyroid function.

The quality of the hair and nails

This trace element plays a role in the quality of skin, nails and hair. Many food supplements to strengthen hair and nails and limit hair loss contain selenium, among other things. Selenium deficiency is manifested in particular by abnormal hair loss and depigmentation of dandruff.

Selenium deficiency correction ++

Supplementation may protect against Keshan's disease (a heart disease related to selenium deficiency), but it does not correct heart failure once the disease has begun.

However, this condition is also believed to be related to a viral infection.

Prostate cancer prevention ++.

Observational studies suggest a protective effect of selenium against cancer, which may be explained by its antioxidant and immune response modulating effects.

A synthesis of several studies has shown a 31% reduction in cancer risk (33% for bladder cancer, 22% for prostate cancer in men) and a 45% reduction in cancer mortality in higher selenium consumers compared to lower consumers.

Another analysis of 20 studies found an inverse association between high blood selenium levels and prostate cancer risk.

Prostate Cancer

Some intervention studies have shown an interest in selenium for prostate cancer prevention.

For example, in the NPC (Nutritionnal prevention of cancer) study, initially conducted to assess the interest of selenium in preventing skin cancer recurrence.

Men who received 200 µg of selenium per day for 7 and a half years developed half the prostate cancer compared to those who received a placebo.

However, this supplement did not change skin cancer recurrence rates6.

In 2007, the World Cancer Research Fund (WCRF) reported that an intake of 200 µg of selenium per day appeared to have a protective effect against the recurrence of prostate cancer.

In contrast, the "SELECT" intervention study, conducted over 5.5 years in 35,500 men over 50, did not prevent prostate cancer with a 200 µg selenium supplement per day8 .

Prevention of cardiovascular disease +

Selenium may be of interest in cardiovascular prevention, given its antioxidant action on several enzymes.

However, observational studies are contradictory.

While some conclude that there is an association between low blood selenium levels and an increased risk of coronary heart disease, others do not find this relationship.

In an intervention study, supplementation with 100, 200, or 300 µg of selenium per day for 6 months reduced total and bad cholesterol levels in the blood of the elderly.

On the other hand, the synthesis of several studies shows that selenium supplementation has no effect on the occurrence of cardiovascular accidents.

These disappointing results could be explained by the fact that the subjects included in the studies did not initially have a selenium deficiency or deficit.

Risks of a selenium underdose and overdose

Risks of Selenium Deficiency

The essentiality of selenium was discovered with Keshan's disease, a form of heart failure linked to a deficiency of this trace element.

This cardiomyopathy can lead to death in the absence of selenium supplementation.

More frequent than deficiency, selenium deficiency may be due to insufficient intake, particularly in the case of a vegetarian diet or poor assimilation following a small intestinal disorder (celiac disease, Crohn's disease, etc.).

It can cause a cardiac arrhythmia, lower resistance to infection, muscle weakness, anemia, arthritic manifestations. Associated with iodine deficiency, it can lead to hypothyroidism (thyroid hormone deficiency).

Risks in case of an excess of selenium

Chronic excess selenium induces selenosis, resulting in skin lesions, hair and nail loss, digestive disorders, fatigue, irritability, garlicky breath and a metallic taste in the mouth.

Excess selenium may be linked to excessive supplementation or, in certain regions, to the ingestion of drinking water rich in this trace element.

The selenium content of tap water is limited to 10 µg per liter.

The safety dose limit has been set by French experts at 150 µg per day, including all intakes, including food, drinking water and even dietary supplements.

It is higher in other countries, for example 400 µg in the United States1.

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