Healthy Hormones

Selenium Deficiency and the Thyroid

Selenium is crucial for normal thyroid function.

In fact, if you have undiagnosed selenium deficiency, it could be making your thyroid function worse.

If you have chronic digestive issues, there is a good chance that you have inadequate selenium levels.

Selenium is especially important if you have an autoimmune thyroid disease such as Hashimoto's or Grave's Disease.

In this article, I will discuss selenium deficiency and the thyroid, how to know if you are selenium deficient, give you some great food sources of selenium, and discuss how and when you should consider using a supplement.

Let's get started...


Why is Selenium Important for Normal Thyroid Function?

Bear with me as I quickly describe the science behind selenium and its important role in the body.

Selenium is required for the proper function of some proteins in our body called selenoproteins.

These proteins perform many important functions in the body including:

     - Conversion of T4 to T3

     - Production of antioxidants

     - Energy productions and metabolism

Let's discuss some of these functions in a little more detail:

1.  Increases T4 to T3 Conversion

Selenium is required for the optimal conversion of T4 into T3 in the peripheral tissues.

Selenium is needed for the proper function of the deiodinase enzymes which perform the conversion process.

As a quick reminder, the thyroid gland produces primarly T4, which is a thyroglobulin molecule with 4 iodine molecules attached to it.  This is the transport form of thyroid and is mostly inactive.

In order for the body to be able to use the thyroid hormone, an iodine molecule must be cleaved off of the T4 by the deiodinase enzyme, which converts it into T3.  T3 is the active thyroid hormone.

2.  Decreases Autoimmunity

Selenium has been shown in studies that it reduces autoimmune inflammation in patients with Hashimoto's Thyroiditis.  It has been shown to reduce the TPO antibody levels.

3.  Strengthens Your Immune System

Having a deficiency of selenium does not in itself cause illness.

It appears instead that being deficient in selenium just makes us more susceptible to illnesses due to its role in normal immune function. 

In other words, having an optimal selenium level helps to ensure that our immune system is working at its maximal level.

This is because selenium plays a huge role in increasing antioxidant levels in the body.

In fact, selenium supplementation has been shown to improve immune function in patients that were deficient.

4.  Reduces Thyroid Damage from Iodine

Iodine is a controversial issue in regards to thyroid health.

There is plenty of evidence that shows that low iodine is a huge cause of thyroid disease worldwide.

However, there is also evidence that excessive iodine can also damage the thyroid gland and may even increase the incidence of autoimmune thyroid disease such as Hashimoto's.

One study showed that taking iodine in the presence of LOW levels of selenium may actually increase your risk for thyroid tissue damage.

Conversely, if you supplement with selenium in the presence of low iodine levels, it can also worsen hypothyroidism.

It appears that iodine is dangerous to the thyroid ONLY when selenium levels are low or high.

Optimizing the selenium level allows the thyroid to tolerate a wide range of iodine levels.

The selenium appears to protect the thyroid from iodine at least in some part because it increases regulatory T cell levels.

What if you have Hashimoto's?  

I believe the evidence shows that it is okay to take iodine if you have Hashimoto's as long as you are also supplementing with selenium.

How Do You Know if You Have Selenium Deficiency?

Selenium deficiency doesn't necessarily cause any obvious symptoms, but there are some signs to look for that can indicate that you may be low. 

Let's discuss some of the big ones below:

1.  You have a history of digestive problems

Selenium deficiency is common in patients that have chronic digestive issues such as Crohn's disease, Celiac disease, etc.

This is felt to be due to malabsorption caused by the inflammation that is occurring in the gut.

Selenium deficiency is commonly associated with vitamin B12 deficiency because they both are affected by poor gut absorption.

So if you have B12 deficiency or any type of chronic gut inflammation, there is a strong chance that you are deficient in selenium.

2.  You have a low free T3 level

As I discussed earlier, selenium is important for the conversion of T4 to T3.

When that conversion process is reduced, the free T4 levels will begin to rise and the free T3 levels will begin to fall.

To make matters worse, if you go see your doctor and he or she only checks your TSH and T4 and not your free T3 level, it will look like your thyroid levels are "normal" or even "high."

Meanwhile, your hypothyroid symptoms continue to worsen because you are low in active thyroid hormone.

Not a good situation at all.

That's why it is critical that you find a doctor that will check a complete thyroid panel and will listen to you and your symptoms, and not solely depend on lab results to manage your thyroid problem.

3.  You have hair loss or brittle nails

Let me start with an obvious statement:  Not all hair loss is caused by selenium deficiency (you've seen my photo and my selenium level is good!).

However, selenium deficiency has been shown to cause changes in hair.

It also can cause your nails to get brittle and crack easily.

Replacing low selenium levels has been shown to improve hair growth and nail growth.

If you suffer from unexplained hair loss or brittle nails, you should consider getting a further workup.

At a minimum, you should look at these micronutrients as possible culprits:  iron, zinc, selenium, and biotin.

You should also get a complete thyroid panel.

4.  Your RBC Selenium level is low

There is a lab test to measure the selenium level in the body, specifically in the red blood cells.

It is called an RBC Selenium Level.

I do not routinely check this on patients.  If I suspect a selenium deficiency, I start treatment.

However, if a patient continues to have signs or symptoms of selenium deficiency, it can be checked to make sure they are absorbing the selenium from their food or supplements.

How to Treat Selenium Deficiency

So if you think you have a selenium deficiency, what should you do about it?

Selenium is a micronutrient, meaning only small amounts are needed.

It can be replaced in your body either through increasing your consumption of foods that are high in selenium and/or by taking a selenium supplement.

Food Sources of Selenium

Without a doubt, it is always safest to use food to increase nutrient levels in our body.

Most Americans eat so poorly that simply improving their diet can do wonders for helping them to regain their health.

The food with the highest amount of selenium is brazil nuts.

Eating 2 brazil nuts per day will increase your selenium level as much as 100mcg of selenomethionine.

Other foods with good selenium content include:

  • mushrooms
  • fish - cod, halibut, tuna, salmon
  • shrimp
  • chicken
  • eggs
  • turkey

It's always best to start with natural food sources such as these.

However, that is not always possible.  

For instance, I am personally allergic to brazil nuts and I don't have a big fondness for fish (unfortunately). Therefore, I use a supplement periodically to keep my selenium level optimized.

Selenium Supplements

When using supplements, it is always critical to use a good quality supplement from a respected company that uses quality control standards when making their products.

My preferred brand for supplementing selenium is below:

How to Supplement with Selenium

Why I Like It

May reduce antibodies in patients with Hashimoto's

Also acts as an  anti-inflammatory

May help reduce anxiety symptoms

Helps boost T4 to T3 conversion (helpful in those with high reverse T3)

Who Should Use It

    • Patients with hair loss or hair thinning
    • Patients with a known thyroid disorder and hair loss
    • Patients with other nutrient deficiencies like zinc or iodine
    • Patients who frequently take acid blockers for acid reflux
    • Patients with other GI related issues (IBS, gas/bloating, IBD)
    • Patients also taking zinc

How to Use

    • Take 200-400 mcg per day (do not exceed 400 mcg daily)

My Recommended Brand and Product

I prefer selenomethionine because of it's high bioavailability.

I typically recommend supplementing for only a few months (3-6) which should restore the levels in the body to the optimal range.

Like most things, you can overdo selenium supplementation as well.

Excess selenium can cause a variety of symptoms, including GI upset, white blotchy nails, hair loss, fatigue, irritability, and mild nerve damage.

One study even showed a possible increased risk of prostate cancer in patients with excessive selenium.

Once you have repleted the tissues and changed your diet, continued supplementation should be unnecessary.

The only exceptions would be if you have poor absorption from chronic digestive tract conditions such as inflammatory bowel disease, IBS, Celiac diease, etc.


Selenium is a vital micronutrient for normal thyroid function, immune system function, energy production, and metabolism.

Selenium deficiency is common but can be difficult to diagnose.

It is always best to treat selenium deficiency by eating food rich in selenium.

If that isn't possible or if you have absorption issues due to chronic GI issues, adding a good quality selenium supplement may be necessary.

You should not take a selenium supplement indefinitely.  Usually taking it for a few months is sufficient unless you have a chronic GI problem.

If you have a selenium deficiency, it is also important to look for other micronutrient deficiencies such as iron, zinc and iodine.

Now it's your turn...

Do you think you have a selenium deficiency?

What have you used to treat it.  Has it helped?

Leave your comments below.

About the Author Dr. Jeff Whelchel

Dr. Whelchel is a family physician who specializes in functional medicine, especially hormone optimization. He has over 20 years experience in private practice managing patients with various medical issues. His passion is helping patients reach their full potential of wellness and quality of life. He grew up in the Texas Panhandle where he currently lives. He is married and has 3 awesome children.

Leave a Comment:

Peter Vongphrachanh says February 8, 2018

Dr Jeff whelchel thank you so much for sharing amazing article for me to read MayGod bless u and your family.

Gregory L. Mouser says July 8, 2018

Thanks for posting this information Dr. Whelchel. I was born back in 1952 with congential hypothyroidism… in West Virginia… I posted this on my facebook pages for those who want to know more… I too have allergies to nuts, and some seafood but I can get my natural daily supply of selenium via mushrooms, fish & Veggies.. I apply selenium and iodine to my plants when watering… I also filter my water 3 times… It is of my opinion that many physicians are not helping with ways that could help their patients as it relates to how many sources of exposure to fluorides that are antagonist to the thyroid IF, we have underactive thyroid glandular health risks..

    Dr. Jeff Whelchel says July 8, 2018

    Thank you for the nice comments, Greg. I am glad that you have taken control of your own health. It is past time for ALL of us to do that.

Kris Vrooman says October 29, 2020

I have been losing my hair, brittle nails. I have IBS and take a protonic. I had surgery for Herd in the early 90s, but sty needed pepcid. However Herd was much better.
Your article is the first information I have found ( actually my husband) that mentioned selenium as a possible cause. My T3 is low, T4 high. I eat all the food you listed except Brazil nuts. I really like them but are hard to get. I will search. I take a daily vitamin that has selenium and zinc. I will restart Biotin. I took that for years with no help. Thank you for the article. If this is the right fix, will my hair grow back? My hair has been falling out for several months, and is now quite thin.

    Dr. Jeff Whelchel says November 11, 2020

    Hello. I’m sorry for your symptoms. If selenium deficiency is truly the cause of your hair loss, the hair should grow back. If it doesn’t, something else is likely going on. Best of luck.

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