November 22


How Selenium Is Important To The Thyroid

Selenium is crucial for thyroid health. Learn how to make sure you're getting enough.

By Amy Vespa, MS - Integrative Clinical Nutritionist

November 22, 2021

minutes read time


If you have Hashimoto’s, you’ve likely heard of selenium. Selenium is a trace mineral. We don’t need a lot of it but it’s crucial for certain processes in the body. Its main roles in the body are:

  • an antioxidant that protects tissues from oxidative stress (an imbalance between antioxidants and free radicals – bad things)
  • important for fetus growth and development (especially for sound and sight)
  • supporting optimal thyroid health (more on this below)
  • supporting liver function and detox
  • strengthening the immune system and regulating inflammation in some diseases 
  • anti-viral properties and helps reduce effects of certain viruses

While it is crucial for optimal thyroid health, too much can cause unwanted problems. After reading this article, you will understand the role of selenium and how to ensure your body has what it needs.

Selenium and the thyroid 

The thyroid contains the highest amount of selenium per gram of tissue in the body which is why selenium is always mentioned in relation to thyroid health and Hashimoto’s. You know it is important for optimal thyroid function, but what does it actually do?


  • is an antioxidant that protects the thyroid from free radicals 
  • helps convert T4 to T3, the active form of thyroid hormone, which provides about 80% of what the body needs each day
  • can lower TPO antibodies

Selenium also has a close relationship with iodine. Iodine is an important component of T4 and T3. And selenium is a main part of the enzyme that converts T4 to T3. Without sufficient amounts of both nutrients, thyroid levels will be off.

Getting enough selenium

It’s important to ensure your body has enough selenium to convert T4 to T3. So, how can you know? One way is to get your serum levels checked at your next doctor’s visit. 

Signs of low selenium are

  • fatigue and muscle weakness
  • brain fog
  • depression or anxiety
  • hair loss
  • weak, brittle nails
  • weakened immune system (getting sick often)

(Sounds familiar? The symptoms are similar to hypothyroidism, which is why getting a blood test is helpful!)

One of the best ways to get enough selenium is through diet. It is not difficult to get enough through food. The best consistent food sources are:

  • meat
  • seafood
  • organ meats
  • brazil nuts (quantity depends on soil quality)
  • grains and other plants can contain selenium but the amount depends on the richness of local soil

If you eat these foods and/or take a multivitamin there is a good chance you are getting enough. 

However, a few factors can alter your intake. First, if you follow a vegetarian diet and also have removed or reduced gluten or grains, there might be a decrease in selenium intake. Second, if there are some gut health issues present (leaky gut or low stomach acid), your body might not be absorbing enough. The second is a very common issue in those with Hashimoto’s.

Healing is vital to nutrient absorption…even in supplement form.

Brazil nuts

Brazil nuts are a well-known source of selenium. And they’re an easy way to increase your intake daily. The amount of selenium in each nut can vary widely based on local soil quality. However, nuts from the eastern Amazon region of Brazil have the highest concentration.

Yet, this study showed that two brazil nuts, even with the variance in concentration, were as effective as 100 mcg supplementation over a three-month period. Other studies have also shown that eating 2 brazil nuts each day increased serum levels over a three-month period in comparison to a placebo.

Should you supplement?

Sometimes when you think you might have a deficiency, taking a supplement is an easy solution. But with selenium there is more to consider because there is such a thing as too much

Excess selenium is linked to an increased incidence of insulin resistance and Type II diabetes. Since there is already a link between Hashimoto’s and these conditions, supplementing with selenium has to be carefully considered. Further, excess selenium can also inhibit immune function and add to all-cause mortality. Big reasons to not overdo selenium with supplements!

Research is mixed as to whether selenium supplementation is beneficial for Hashimoto’s. 

Studies in support of supplementation have been shown to reduce TPO antibodies and improve symptoms. It helps the thyroid reduce inflammation. And helps cells convert T4 to T3, improving thyroid function. There are also potential benefits for autoimmunity and chronic inflammation in general.

What to do about selenium

For most people, eating 1-2 brazil nuts each day is a good way to get sufficient selenium. It would be hard to overdo intake with nuts unless you ate a whole bag in one sitting or made the nuts into milk alternative, but that’s easy to avoid!

Because research has shown both positives and negatives of selenium supplementation, it’s important to work with a practitioner to know how much you need and to monitor your levels. Also, getting serum selenium levels checked will give you a much better idea of what your body needs.

To sum everything up, selenium is: 

  • important for thyroid health because it helps convert T4 to T3
  • could help bring down TPO antibodies and reduce inflammation
  • found in meat, seafood, organ meats, brazil nuts
  • important to check serum levels before supplementing
  • likely sufficient with eating 1-2 brazil nuts daily

In the comments, let us know if you’re taking a selenium supplement without ever having had your selenium levels tested. Also, let us know if you’re going to ask for a selenium test at your next appointment.

Other sources:

  • I do not take a selenium supplement. However, I eat one Brazil each day and get 40% of my recommended daily amount of selenium in my multivitamin.

  • I’m working with a functional medicine doctor who prescribed 200 mcg per day of Selenium after we did extensive blood, stool, and urine lab work. My selenium was very low.

    My TPO antibodies were high and so was inflammation.

    When I was first diagnosed with Hashimoto’s, I immediately did research and committed to a Paleo diet. So, I don’t eat many of the foods with selenium. I eat meat but not alot of it.

    We are retesting in a month or two and keeping a close watch on a variety of things in my labs.

    The first thing we focused on is healing the leaky gut and getting rid of some bad bacteria in my stomach.

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