What to Know About Selenium and Your Thyroid

The nutrient is essential for thyroid function

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Selenium is a mineral that is important for thyroid hormone metabolism. People who don't get enough selenium may develop thyroid problems such as thyroiditis, hypothyroidism (underactive thyroid), and Graves' disease.

Your body doesn't make selenium, so the only way you can get it is through food and/or supplements. Most people meet their requirements, but some are at greater risk for deficiency.

This article looks at why selenium is important for thyroid health and how much you should be getting each day.

Selenium’s Impact on the Thyroid

In adults, the thyroid has the highest concentration of selenium in the body. This mineral plays a key role in your thyroid gland’s ability to produce thyroid hormone.

A selenium deficiency is associated with a variety of thyroid issues, including:

Iodine is the building block and key ingredient of thyroid hormone. Iodine requires selenium in order to be synthesized properly into thyroid hormone.

Having the right amount of selenium in your diet is vital not just for preventing thyroid disease, but for your overall health. Selenium is important for reproduction and DNA synthesis. Additionally, it helps protect you from infection and damage resulting from oxidative stress.


Selenium Supplement Benefits

A number of research studies have shown key relationships between selenium supplementation and thyroid and immune function. For example:

  • Several studies have shown that supplementing with selenium reduces thyroid peroxidase antibodies (TPO) and the severity of hypothyroidism symptoms.
  • Some studies have found that treating patients who have mild to moderate thyroid eye disease (Graves' orbitopathy) with selenium supplements improved quality of life and outcomes for eye health. Selenium supplements were also associated with a dramatically slower progression of symptoms. The European Thyroid Association now recommends a six-month trial of selenium supplements for patients with Graves' orbitopathy.
  • Even for people who don't have a selenium deficiency, selenium supplements have been shown to have a considerable impact on the immune system. They may increase the production of activated T-cells and natural killer cell activity. Both of these assist in the immune response to disease, tumors, and infection.

Hashimoto's Thyroiditis

A 2016 study analyzed the impact of selenium supplementation on the thyroid antibody levels of people with Hashimoto’s thyroiditis. The study evaluated both thyroid peroxidase (TPOAb) and thyroglobulin (TgAb) antibody levels at three, six, and 12 months of selenium supplementation.

Subjects were divided into two groups:

  • Hashimoto’s patients receiving levothyroxine thyroid hormone replacement treatment
  • Newly diagnosed patients who were not receiving thyroid hormone replacement

For those treated with levothyroxine, selenium supplementation resulted in significantly lower TPOAb levels after three months. These levels continued to decrease at six months and 12 months. TgAb levels did not decrease until the 12-month point.

In the untreated Hashimoto’s group, selenium supplementation resulted in a decrease in TPOAb levels after three months, but not after six or 12 months. TgAb decreased at three months, but not at six or 12 months.

Selenium Deficiency

Selenium deficiency is fairly rare in the United States, thanks to selenium-rich soil. Most Americans easily get the amount of selenium they need on a daily basis.

While the odds of a deficiency are pretty low for most, some people have greater risk. Some of the risk factors for developing a selenium deficiency include:

  • Intestinal, digestive, or absorption issues like Crohn's disease
  • Having had gastric bypass surgery
  • Living in an area with selenium-deficient soil
  • Undergoing kidney dialysis
  • Having human immunodeficiency virus (HIV)


There are many symptoms that can occur when you aren't getting enough selenium. Some of the most common ones include:

  • Infertility
  • Hair loss
  • Fatigue
  • Weight gain
  • Compromised immune system, resulting in getting sick more often
  • Difficulty thinking and/or concentrating

Of course, it's worth noting that some of these overlap with symptoms of thyroid disease.

Your selenium levels can be measured by blood tests. A hair or nail analysis can evaluate your levels over months or years. According to the National Institutes of Health, a healthy blood level of selenium is 8 micrograms (mcg)/dL or higher.

This isn't a routine test if you have thyroid disease. It's usually only performed if a selenium deficiency or toxicity is suspected. Still, you or your healthcare provider may want to check your levels at some point to make sure they're within normal limits.

Sources and Daily Requirements

Selenium is naturally found in some of the foods we eat, and it is sometimes added to foods to fortify them. Selenium can also be taken as a dietary supplement.

There are two forms of selenium: organic (selenomethionine and selenocysteine) and inorganic (selenate and selenite). Both forms are good sources, but research has shown that using the organic form of selenium as a supplement may be more effective. This is because your body absorbs more than 90% of organic selenium but only around 50% of the inorganic form.

Foods that are good sources of selenium include:

  • Brazil nuts
  • Seafood, such as shrimp, sardines, salmon, halibut, and tuna
  • Meats like beef steak, beef liver, ground beef, and ham
  • Poultry
  • Eggs
  • Breads
  • Cereals
  • Grains

Selenium can be found in supplements either alone or in combination multivitamins. Due to its overall effects in the body, research is being conducted on whether or not selenium supplementation may have additional benefits, including:

  • Glucose metabolism
  • Cancer prevention
  • Thyroid disease
  • Heart disease
  • Age-related cognitive decline

Daily Selenium Recommendations

  • 55 mcg/day for healthy people age 14 and over
  • 60 mcg/day for pregnant people
  • 70 mcg/day for breastfeeding people

This includes all sources of selenium. You can safely take in up to 400 mcg per day between food and supplements.

Source: The Food and Nutrition Board, Institute of Medicine of the National Academies

brazil nuts

Selenium Toxicity

While low levels of selenium are a concern, high levels can result in selenium toxicity over time. Symptoms include:

  • Garlic smell to the breath
  • Metallic taste in the mouth
  • Hair and nail loss or brittleness
  • Nausea
  • Skin rashes
  • Diarrhea
  • Skin lesions
  • Fatigue
  • Irritability
  • Nervous system abnormalities

In particular, be careful with Brazil nuts. Brazil nuts contain as much as 90 mcg of selenium per nut. This means you can actually trigger selenium toxicity by eating them too often.

Benefits and Risks

Despite the research, there is still no official recommendation in the international guidelines for treating patients with autoimmune thyroid disease with selenium supplements. For those with thyroid disease and low selenium levels, supplementation can be beneficial. For those whose selenium levels are normal to high, however, supplementation could potentially result in toxicity.


Selenium is a mineral important for thyroid health. Your body doesn't make selenium, so you need to get it from your diet and/or supplementation.

Selenim deficiency can lead to a number of health problems such as hypothyroidism, Hashimoto's disease, and Grave's disease. Research also shows that selenium supplementation may help people with certain thyroid-related conditions.

It is possible to get too much selenium, which can also cause health problems. If you're concerned about your selenium levels, ask your healthcare provider about having them tested.

A Word From Verywell

Before you consider adding handfuls of Brazil nuts to your diet or taking selenium supplements, you should have your selenium levels evaluated by your healthcare provider. They can offer guidance on whether you might benefit from increasing your dietary selenium or adding supplements.

Keep in mind that if you choose to supplement with selenium, you should calculate your dietary intake. Be sure to count any selenium in multivitamins and supplements so that your daily intake doesn't exceed 400 mcg a day.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Ventura M, Melo M, Carrilho F. Selenium and thyroid disease: from pathophysiology to treatmentInt J Endocrinol. 2017;2017:1297658. doi:10.1155/2017/1297658

  2. Santos LR, Neves C, Melo M, Soares P. Selenium and selenoproteins in immune mediated thyroid disorders. Diagnostics. 2018;8(4):70. doi:10.3390/diagnostics8040070

  3. Wichman J, Winther KH, Bonnema SJ, Hegedus L. Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: a systematic review and meta-analysis. Thyroid. 2016;26(12):1681–1692. doi:10.1089/thy.2016.0256

  4. National Institutes of Health. Selenium: fact sheet for professionals.

  5. National Library of Medicine. Food and nutrition board, institute of medicine-national academy of sciences dietary reference intakes: Recommended intakes for individuals.

Additional Reading

By Mary Shomon
Mary Shomon is a writer and hormonal health and thyroid advocate. She is the author of "The Thyroid Diet Revolution."