Selenium Benefits, Foods, Dosage and Side Effects - Dr. Axe

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Selenium Benefits for Overall Health, Plus Dosage Recommendations


Selenium - Dr. Axe

Selenium is a vital mineral for the human body that has numerous roles. What is selenium used for? It increases immunity, takes part in antioxidant activity, 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 a daily selenium supplement can have positive effects, including workign as an antiviral, support fertility and reproduction, and may even reduce the risk of some types of cancer, autoimmune diseases and thyroid disorders.

What Is Selenium?

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

There are actually four naturally occurring types of this trace mineral. The four natural states of selenium are:

  1. elemental selenium
  2. selenide
  3. selenite
  4. selenate

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

As a component of antioxidant enzymes, particularly glutathione reductase, it supports maintenance of healthy tissues throughout the body.

Because it both increases antioxidant capabilities and the quality of blood flow, it can help enhance resistance against diseases and negative effects of stress. Its ability to fight oxidative stress and excessive inflammation is thought to be due to different types of selenoproteins found in this mineral.

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 at increased risk of having low selenium levels.


What are the health benefits of taking selenium? Here’s more about the roles that this essential mineral has:

1. Acts as an Antioxidant and Defends Against Oxidative Stress

This mineral helps fight the aging process and supports a strong immune system by reducing free radical damage.

It has a synergistic effect with other antioxidants like vitamin E, enabling the body to defend against oxidative stress. Stress, of course, contributes to many conditions, including heart disease, neurological conditions and some cancers.

For example, a 2016 review found that having a higher level of selenium exposure could offer protection against breast, lung, colon, gastric, esophageal and prostate cancers.

As an essential component of glutathione peroxidase, selenium also 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 may be especially helpful if you have a weakened immune system or a history of cancer in your family. Taking high dose selenium supplements 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 some types of cancer — 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 it may also help slow down existing cancer progression and tumor growth.

Studies have shown that a high dose 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 Against Viruses

Selenium supports immunity because it’s needed for the proper functioning of the immune system — plus it’s a key nutrient in counteracting the development of viruses, including HIV.

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

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

Low selenium levels are associated with an increased risk of developing cardiovascular disease, potentially along with suffering from a stroke or heart attack. Supplements, or an increase of selenium-rich foods, may be able to help prevent coronary heart disease by protecting arteries against plaque buildup and damage.

It’s believed that dietary selenium may 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

Is selenium good for your thyroid? Yes, because this mineral acts as a catalyst for the production of active thyroid hormones.

Research now suggests that there is a link between thyroid metabolism and selenium deficiency. Having too little in your diet can impair how your thyroid, and therefore metabolism, works.

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.

Acquiring proper amounts of selenium helps the thyroid and body in many important ways:

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

For these reasons, selenium may be able to help those with Hashimoto’s disease, Grave’s disease and pregnant women with anti-TPO antibodies.

Does selenium cause weight gain? It shouldn’t. In fact, because it can help with thyroid function, research suggests it supports a normal metabolism and can aid in weight maintenance.

If you’re deficient, it might lead to a sluggish thyroid, which can sometimes cause weight gain.

One study even found that selenium helps protect against obesity — and that higher intake led to significant increases in lean body and muscle mass, along with significant decreases in “hunger hormones” after three months of use among overweight adults.

6. May Help Increase Cognitive Health Into Older Age

Certain studies have investigated the use of selenium supplements for the treatment of dozens of conditions that range from asthma to arthritis, thyroid disorder and Alzheimer’s. The risk of these conditions increase as we age, but high-antioxidant intake and consumption of essential vitamins and minerals can help defend the body and may contribute to a longer life.

For example, a number of studies suggest that higher intake of selenium (and other antioxidants) offers protection against cognitive decline and conditions such as Alzheimer’s disease. A 2019 meta-analysis uncovered evidence for a significant decrease of selenium status in adults with Alzheimer’s compared to to those without it, supporting the mineral’s antioxidant role and the involvement of oxidative stress in neurological impairment.

7. Helps Reduce Asthma Symptoms

Observational studies have demonstrated that patients with chronic asthma may have lower amounts of selenium in their diets and therefore may be prone to deficiency. According to studies, when people with asthma take selenium supplements, they experience less asthma-related symptoms than those who take placebos.

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. These are two key components involved in conception and beating infertility.

This mineral is incorporated into the sperm’s 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 selenium concentrations can have a negative influence on the number of sperm, therefore aiming to meet the recommended dietary intake, but not to far exceed it, is important for fertility.

Some studies also show that meeting the recommended dietary intake may even potentially reduce the risk of miscarriage, but more data is still needed.

Dosage Recommendations

Selenium is a trace mineral, meaning we only need a small amount of selenium from our diets each day. 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.

It’s particularly important maintain normal selenium levels as you age in order to take advantage of its antioxidant benefits.

It is important to note that if you already consume the proper amount of selenium from a healthy diet, consuming more may not be beneficial. 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 National Institutes of Health:

  • 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, it 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.

Based on available research, the tolerable upper limit of selenium (the amount taken before side effects will occur) is 400 mcg per day.

It’s best to meet your needs through dietary intake if possible (eating foods with selenium). No one should exceed recommendations by supplementing with very high doses without consulting a healthcare professional.

Note: Selenium sulfide is another form of this mineral you may come across. This type is the active ingredient often found in shampoos used for the treatment of dandruff, but it’s not taken orally.


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

What food is highest in selenium? That would be Brazil nuts. Just one Brazil nut provides more than 100 percent of the recommended daily value of selenium (roughly 68 to 91 micrograms per nut).

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
  16. Tofu


Certain groups of people are more likely to be deficient in selenium due to factors like a poor diet and trouble with absorption.

Suffering from a selenium deficiency has been correlated in studies 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 far more than the recommended daily amount.

What are the symptoms of selenium deficiency? Some contributing causes to a 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 foods 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.
  • According to research, populations in the U.S. of the Eastern Coastal Plain and the Pacific Northwest have the lowest levels of selenium. These populations average consuming 60 to 90 micrograms per day, which is still considered to be adequate intake but less than other populations.
  • Being affected by Kashin-Beck disease, a chronic bone disorder.
  • Undergoing kidney dialysis and living with HIV.

Risks and Side Effects

Is it safe to take selenium every day? Taken at normal doses, it does not usually have negative side effects.

What are possible side effects of taking selenium? 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 very high doses.

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 or that this poses a serious risk in everyday situations.

This mineral may also interact with other medicines and supplements. These include:

  • antacids
  • chemotherapy drugs
  • corticosteroids
  • niacin
  • cholesterol-lowering statin drugs
  • 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 certain foods and even in water.
  • The two main sources are supplements and selenium-rich foods. To boost your dietary intake, each these foods regularly: Brazil nuts, eggs, liver, tuna, cod and sunflower seeds, in addition to poultry and certain types of meat.
  • Selenium supports overall health thanks in large part to its role acting as an antioxidant. Other roles of this mineral include defending against oxidative stress, heart disease and cancer; boosting immunity; regulating thyroid function; increasing longevity; reducing asthma symptoms; and boosting fertility.
  • It’s recommended that adults over 14 aim to get at least 55 micrograms per day.
  • While generally well-tolerated, in high doses, such as 400 to 900 mcg/day, it can be harmful and even toxic.

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