What Are Selenium’s Benefits and Uses?

by jamespereiramadsa
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By Dr. Mercola

Selenium (Se) was first discovered nearly 200 years ago by Swedish chemist Baron Jöns Jacob Berzelius. Many decades later, scientists deem selenium to be essential in improving human health. This page will help you learn more about selenium: its health benefits, foods rich in this mineral and potential side effects to watch out for.1

What Is Selenium?

Selenium is an essential trace mineral found in human tissue, mostly in skeletal muscles, and in different foods,2 and is said to deliver numerous health benefits to the body (more on this to come later). While researchers emphasized that selenium is highly essential, selenium deficiency remains a big issue. Nearly 1 billion people worldwide suffer from it, while more people consume less than the daily recommended amount needed to provide protection against diseases.3,4

To help offset risks linked to a selenium deficiency, taking selenium supplements can be recommended. Usually, selenium can be taken as a component of a vitamin-mineral supplement or as a nutritional antioxidant formula.

Most selenium supplements contain a form of selenium called selenomethionine.5 Should you come across a product called selenium sulfide, don’t use it to address selenium deficiency, given that it comes in lotion form and is applied as a shampoo to aid with alleviating dandruff and addressing tinea versicolor, a fungal skin infection.6

Selenium-Rich Foods You Should Try

Apart from taking selenium supplements, you can also combat the negative effects of a selenium deficiency by eating foods high in selenium. Examples of foods abundant in selenium include:7

Brazil nuts

Fish like sardines, wild-caught Alaskan salmonand herring


Sunflower seeds and chia seeds

Pastured organic eggs

Pasture-raised organic chicken and turkey

Grass fed liver (lamb or beef)


Take note that selenium levels in some foods depend on the amount of this mineral present in the soil where they were grown. Ideally, eat these foods raw or slightly cooked, or look for organic items that didn’t undergo further processing, because selenium can be destroyed when foods are refined or processed.

Health Benefits of Selenium

Selenium has been linked to various benefits, with some already being proven by research:8

Serving as an essential component of glutathione peroxidase: This is an enzyme that can convert hydrogen peroxide to water.

Possessing antioxidant and anti-inflammatory properties for improved immune function:

When selenium is utilized for producing glutathione peroxidase, the mineral delivers antioxidant properties and serves as a first line of defense against free radical build-up in the cells.

Selenium also has the potential to influence immune response via selenoproteins (selenium-containing proteins), which can help regulate excess immune responses and chronic inflammation.

Assisting with combatting infectious diseases and viral infections: Selenium may be beneficial in inhibiting HIV, as patients with this disease have low selenium levels.9

Taking selenium supplements was shown to decrease hospitalizations and improve white blood cell count among HIV patients.

Several studies also emphasized that selenium may help combat viral infections, such as influenza, and bacterial infections such as Coxsackie, which can mutate to highly pathogenic strains.10

Aiding in maintaining proper thyroid function: Although its definite effects are still being studied, selenium is said to play a role in preserving proper thyroid function.11

The thyroid contains more selenium per gram of tissue than any other organ in the body and can express specific selenoproteins.

Promoting a healthy pregnancy: Selenium has been suggested to lower the risk of miscarriage.12

Addressing fertility concerns among men: It has been found to have a favorable effect on male fertility.13

Helping people with chronic asthma: Observational studies demonstrated that those with chronic asthma may have lower selenium levels compared to those without this condition.14

Helping mitigate cancer risk: This is due to selenium’s potential to prevent build-up of free radicals, a known cancer precursor.

Numerous studies highlighted that low selenium levels were linked to an increased risk of death from cancer and all causes.15,16,17,18

Remember that greatly increasing your selenium intake must be done properly to prevent health risks. I suggest consulting a doctor first before taking selenium supplements or increasing your intake of selenium-rich foods.

Ideal Dosage of Selenium

Selenium is needed in very small microgram (mcg) amounts. I suggest that you moderate your selenium intake, whether from food sources or supplements, because it can lead to a selenium toxicity. Ideally, I recommend not exceeding a 200 mcg serving of selenium daily.

Most research surrounding selenium supports the 200 mcg daily serving and highlights that no significant benefits were recorded at higher dosages.

If you want to increase selenium levels by eating Brazil nuts, consuming two to three nuts daily can be sufficient. Supplements can also be taken to increase selenium levels, provided that you consult a doctor first. Once you get the go signal, make sure you get the correct form of selenium supplements. A high-selenium yeast form, which is the scientifically tested and most recommended version, is ideal.

Side Effects of Selenium

Although it's difficult to "overdose" on selenium from foods, the case isn't the same for selenium supplements. Selenium poisoning, or selenium toxicity, is a major health risk linked to selenium. Ingesting too much selenium can trigger various selenium toxicity symptoms. Selenium poisoning can either be acute or chronic:19

Acute selenium poisoning: People develop this condition through inhalation (usually in the form of selenium dioxide or hydrogen selenide) or oral exposure to selenium. Different side effects are linked to these two methods of exposure:20

Acute Selenium Poisoning Through InhalationAcute Selenium Poisoning Through Oral Exposure
Irritation of mucous membranes in the nose and throatPulmonary edema
CoughingLung lesions
Dyspnea or difficulty breathingNausea
Bronchial spamsVomiting
Chemical pneumoniaAbdominal pain
VomitingEffects on the liver
Irritation of the eyesIrritability
Cardiovascular effects 

Chronic selenium poisoning: This can arise because of exposure to high levels of selenium in food and water. Chronic selenium poisoning can result in complications such as:21,22

Discoloration of the skin

Deformation and loss of nails


Excessive tooth decay and discoloration

“Garlic breath”


Lack of mental alertness


Skin rashes



Weight loss

Excessive amounts of selenium have also been linked to an increased risk of high cholesterol levels and diabetes. If you belong to any of the following groups, avoid taking selenium supplements without consulting a doctor:23

People diagnosed with hypothyroidism

People who have had skin cancer

People at risk for skin cancer

Medications to Avoid If You Plan on Taking Selenium Supplements

If you or someone you know is taking any of these medicines, do not take selenium supplements without consulting or informing your doctor, because of the risk of contraindications such as:24

Reduced levels of selenium: These drugs are known to lower your body’s levels of this mineral:

Cisplatin (a known chemotherapy drug)

Clozapine (Clozaril)

Corticosteroids like prednisone

Valproic acid (Depakote)

Anticoagulants and antiplatelet drugs, or blood thinners

Increased risk of bleeding: Taking selenium supplements alongside these medicines can raise the risk for internal bleeding:

Clopidogrel (Plavix)

Warfarin (Coumadin)




Longer-lasting sedative effects: Some animal studies showed that selenium can make the sedative effects of these medicines last longer:

Butabarbital (Butisol)

Mephabarbital (Mebaral)

Phenobarbital (Nembutal)

Secobarbital (Seconal)

Interference with chemotherapy: Patients undergoing chemotherapy are advised to talk to an oncologist or doctor before taking selenium supplements, as this mineral can interfere with the treatment’s effects.

Decreased effectivity of cholesterol-lowering medications: Selenium was suggested to reduce the effectiveness of statin drugs.

If you’re a woman taking birth control pills but want to try selenium supplements, consult a doctor or OB-GYN first. Researchers proposed that women taking birth control pills may already have high selenium levels, and further selenium intake can trigger selenium poisoning or toxicity.

Meanwhile, gold salts, which are chemical compounds, were said to reduce selenium levels in the body and cause symptoms of selenium deficiency.

Selenium: This Mineral Is Worth the Praise

When something is deemed "essential," there must be a list of reasons why it deserves this accolade. Selenium has proven its worth as an essential nutrient, thanks to its health benefits for people of various conditions.

Unfortunately, you must exercise caution when optimizing your levels, given the risk of selenium poisoning or selenium toxicity caused by excessively high levels, as well as the potential side effects associated with selenium supplements. As I mentioned earlier, it would be wise to consult a doctor first before supplementing with selenium to help reduce your risk of these complications.

Frequently Asked Questions (FAQs) About Selenium

Q: What is selenium good for?

A: Selenium has been linked to health benefits such as:

Serving as an essential component of the glutathione peroxidase enzyme

Having antioxidant and anti-inflammatory properties to boost immune function

Helping combat infectious diseases and viral infections

Assisting with maintaining proper thyroid function

Assisting pregnant women

Addressing fertility concerns among men

Aiding people with chronic asthma

Helping mitigate cancer risk

Q: Which foods contain high amounts of selenium?

A: There are food sources of selenium that you can benefit from. These include Brazil nuts, sunflower and chia seeds, garlic, pastured organic eggs, pasture-raised organic chicken and turkey, grass fed liver (from beef or lamb), fish like wild-caught Alaskan salmon and herring, and mushrooms.

Q: How much selenium should you take per day?

A: I highly advise taking a 200 mcg daily dose of selenium. Avoid going over this amount, because this can raise your risk for selenium toxicity or poisoning. When buying selenium supplements, purchase the high-selenium yeast form, which is scientifically tested and is the most recommended. Talk to a doctor as well to know how much of this mineral your body will need.

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