Selenium 101 – Health Benefits, Best Sources, & Correct Dosage

Selenium is not a mineral you hear much about. However, this essential mineral plays a vital role in many processes in the body.  It boosts immunity, lowers oxidative stress and inflammation, and is critical to thyroid hormone metabolism and DNA synthesis. Eating food like oysters, eggs, and tuna ensures you get enough selenium in the body. In this article, we will read about the benefits of selenium and the foods rich in selenium.

What is selenium?

Selenium is a trace mineral that is nutritionally essential for humans. It is a constituent of selenoproteins that play a critical role in reproduction, thyroid hormone metabolism, DNA synthesis, and protection of oxidative damage and infection.


It exists in inorganic (selenate and selenite) and organic (selenomethionine and selenocysteine) forms. Most selenium is in the form of selenomethionine in tissues, which it is incorporated with the amino acid methionine in body proteins. The amount of selenium present in foods depends on the selenium concentration of the soil and water where farmers grow food.

Recommended intake

The recommended dietary allowance includes your total selenium intake from foods and supplements. These values can vary according to age and sex. The recommended dietary allowance for selenium is (1) –

Birth to 6 months15 mcg*15 mcg*
7 to 12 months20 mcg*20 mcg*
1 to 3 years20 mcg20 mcg
4 to 8 years30 mcg30 mcg
9 to 13 years40 mcg40 mcg
14 to 18 years55 mcg55 mcg60 mcg70 mcg
19 to 50 years55 mcg55 mcg60 mcg70 mcg
50 + years55 mcg55 mcg

* Adequate intake (AI)

Health benefits of selenium

1. Strong antioxidant properties

Selenium plays an essential role in human health as an antioxidant. It protects against oxidative stress by keeping the free radical numbers in control. Oxidative stress can lead to several diseases like heart disease, cancer, Alzheimer’s, and premature aging.

In the recent years, selenium research has attracted considerable interest because of its role in antioxidant selenoproteins for protection against oxidative stress by excess reactive oxygen species (ROS) and reactive nitrogen species (NOS) (2).

According to research from Johannes Gutenburg-University, selenium supplementation improves antioxidant capacity in patients with coronary artery disease (3). Since it is a vital component of glutathione peroxidase, selenium helps carry out critical enzyme processes that protect fats in cell membranes.

2. Boosts immunity

Selenium is essential for keeping the immune system working correctly. It helps lower oxidative stress, which lowers inflammation and boosts immunity. Selenium deficiency, on the other hand, impairs the immune function, which leads to the inability of phagocytic neutrophils and macrophages to destroy antigens. According to a study, a deficiency in selenium can cause a decreased response to poliovirus vaccination (4).

Several studies have shown an association between selenium deficiency and the progression of AIDS and mortality. Supplementation of selenium helps reduce hospitalizations, diarrheal morbidity, and improved CD4 cell counts in these patients (5). Selenium supplements also help in the treatment of various viral and bacterial infections like influenza, tuberculosis, and hepatitis (6).

3. Lowers risk of heart disease

Selenium fights inflammation, increases blood flow, and reduces oxidative stress, which is highly beneficial for heart health. According to a meta-analysis of 25 observational studies by John Hopkins University Bloomberg School of Public Health, a 50 % increase in selenium concentration was associated with a 24% reduction in coronary heart disease risk (7).

Selenium reduces the amount of LDL cholesterol that can lead to the build-up of plaque in arteries. Plaque can lead to atherosclerosis, heart attack, and strokes (8).  Oxidative stress and inflammation have also been linked to atherosclerosis.  Since selenium reduces oxidative stress, it is also helpful in preventing atherosclerosis.

According to a systematic review of 16 trials, selenium supplementation decreases serum C-reactive protein and increases the levels of glutathione peroxidase, which has a positive effect on reducing oxidative stress and inflammation in coronary heart disease (9).

4. May reduce cancer risk

In addition to improving heart health, selenium can also lower the risk of cancer. Studies have shown that selenium is effective in reducing cancer risk and reducing the progression of cancer and tumors growth in liver, prostate, colorectal, and lungs (10).

Since selenium helps to activate selenoproteins, it acts in an enzymatic role to help antioxidants to do their job. Some studies show that selenium compounds and selenoproteins inhibit cell motility, migration, and invasion, and reduce angiogenic factors in some cancer cells (11).

Selenium supplements are also beneficial for cancer patients who undergo radiotherapy. These supplements improve the general condition of the patients, improve their quality of life, and reduce the side effects of radiation (11). Some recent studies have reported that selenium does not affect reducing the risk of cancer. More detailed studies are needed to confirm the role of selenium in reducing cancer risk.

5. Improves thyroid health

The thyroid gland has the highest selenium content per gram of tissue. Selenium is essential for producing and metabolizing the thyroid hormone. A deficiency in selenium can lead to thyroid condition like Hashimoto’s thyroiditis, a type of hypothyroidism in which the immune system attacks your thyroid gland (12).

According to a 2005 study from China that involved 6152 participants, low selenium status is associated with increased risk of thyroid conditions like hypothyroidism, subclinical hypothyroidism, autoimmune thyroiditis, and enlarged thyroid (13).

Selenium supplementation can also help in the treatment of Hashimoto’s disease. According to a 2010 study, when patients of Hashimoto’s disease were given selenium supplements for three months, it resulted in lower thyroid antibodies. It also improves the mood and general well-being in patients with Hashimoto’s disease (14).

6. Helps reduce asthma symptoms

According to studies, low levels of selenium are associated with chronic asthma. Taking selenium supplements can reduce asthma symptoms. According to a 2011 study, asthmatic patients with high levels of selenium have better lung function than those with low levels of selenium (15). During a study from Slovakia, 17 corticosteroid dependent asthmatics were given 200 mg of selenium for 96 weeks. The results showed a reduction in the use of corticosteroids and no adverse effects (16).

7. Boosts fertility

Selenium is linked to increased sperm motility and increased blood flow in the body. During a 2017 study, 12 infertile men took 50 mg selenium capsules for three months. The results of the study showed a significant increase in sperm count, motility, viability, normal sperm morphology, and ejaculate volume of infertile men after treatment with selenium (17).

Selenium is incorporated in the sperm mitochondria capsule and can affect the behavior and function of the spermatozoon. Both high and low sperm selenium concentrations can have a negative influence on the number of spermatozoa and motility (18).

8. Prevents cognitive decline

Oxidative stress is one of the leading causes of the onset and progression of diseases like Alzheimer’s, Parkinson’s, and dementia. As stated earlier, selenium is an antioxidant which helps deal with oxidative stress. Selenium combines with amino acids to form small peptides which exert antioxidant activities and help prevent Alzheimer’s disease (19).

Studies also show that patients of Alzheimer’s disease have low levels of selenium (20).  According to a study published in the European Journal of Nutrition, intake of Brazil nuts restores selenium deficiency and has a positive effect on cognitive function of older adults with mild cognitive impairment (21).

9. Increases longevity

As mentioned above, selenium plays an essential role in the treatment of conditions like asthma, thyroid, cancer, and heart disease. Eating a diet rich in selenium foods can help you live a longer and healthier life. The antioxidant properties of selenium can also fight off free radicals which are linked to the aging and help prevent wrinkles, loose skin, and other signs of aging.

Foods high in selenium

The selenium content in plant-based foods depends on where they grow. Since selenium is destroyed during processing and cooking at high heat, it is best to avoid cooking food at a very high temperature. Some of the best sources of selenium include –

  1. Brazil nuts
  2. Oysters
  3. Salmon
  4. Turkey
  5. Tuna
  6. Cottage cheese
  7. Mushroom
  8. Chicken
  9. Halibut
  10. Eggs
  11. Navy beans
  12. Sardines
  13. Sunflower seeds
  14. Beef liver
  15. Oats
  16. Chia seeds
  17. Mackerel
  18. Lobster
  19. Anchovy
  20. Mussels

Side effects

Selenium does not cause any side effects if you take it in regular doses. However, chronically high doses of selenium can lead to a garlic odor in the breath and metallic taste in the mouth. Other signs of chronically high selenium intake are hair loss, brittle nails, lesions on skin, skin rashes, nausea, diarrhea, mottled teeth, fatigue, irritability, and nervous system abnormality.

Selenium supplements may be associated with skin cancer, so people who are at a high risk of skin cancer should avoid these supplements. Selenium may interact with antacids, chemotherapy medications, corticosteroids, niacin, cholesterol-lowering statin drugs, and birth control pills.


Final thoughts

Selenium is a mineral which is nutritionally essential for humans.  It has strong antioxidant properties, boosts immunity, lowers the risk of heart disease and cancer, improves thyroid health, lowers asthma symptoms, promotes fertility, prevents cognitive decline, and helps you live a longer and healthier life.

The selenium content in food depends on the concentration of selenium in the soil and water where farmers grow and raise food. Some good sources of selenium are brazil nuts, oysters, salmon, turkey, navy beans and sunflower seeds.

While selenium is not harmful when you take it in regular doses, chronically high doses can be detrimental and may cause hair loss, brittle nails, lesion on skin, fatigue and nervous system abnormality.


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