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An Update on Selenium and Thyroid Health

Published April 3 2017

Each of the minerals have multiple important functions in the body.  But when it comes to thyroid health, one of the most important minerals is selenium.  Sure, there are other minerals that are essential for optimal thyroid health, such as iodine, iron, and zinc.  But when I consult with someone for the very first time, selenium is one the most commonly listed supplements on the health history form.  In other words, many of my patients have been taking a selenium supplement for months, and sometimes even years prior to working with me.  And the reason for this is because many people are already aware of the benefits of selenium supplementation prior to working with me.

Although selenium has numerous roles in the body, the predominant biochemical action of this mineral in both animals and man is to serve as an antioxidant via the selenium-dependent enzyme, glutathione peroxidase, and thus protect cellular membranes and organelles from peroxidative damage (1) [1].  In other words, if someone is low in selenium, they will also be low in glutathione.  And while taking precursors such as N-acetylcysteine (NAC) can increase glutathione levels, you also need to have healthy selenium levels.

How Does Selenium Relate To Thyroid Health?

With regards to thyroid and autoimmune thyroid conditions, there are a few different ways in which selenium can be beneficial.  I’m going to discuss three of them here.

1. Selenium plays a role in the conversion of T4 to T3.  Certain deiodinase enzymes play a role in the conversion of T4 into T3.  And there are a few studies which show that having a selenium deficiency can result in a decrease in this conversion (2) [2] (3) [3] (4) [4].  On a blood test, a person with a conversion problem will usually have normal levels of T4 and low or depressed levels of T3.  Keep in mind that there can be other factors which can affect the conversion process, and in most cases a selenium deficiency isn’t the primary reason for a conversion problem.  I spoke about this in a blog post entitled “6 Factors Which Can Affect The Conversion of T4 to T3 [5]“.

2. Selenium can help to decrease thyroid peroxidase (TPO) antibodies.  A few studies have demonstrated that supplementing with 200 mcg of selenium can result in a decrease in TPO antibodies (5) [6] (6) [7].  These antibodies are commonly found in those with Hashimoto’s Thyroiditis, although a lot of people with Graves’ Disease also have elevated TPO antibodies.  But why is this the case?  Well, hydrogen peroxide is a necessary substrate for TPO activity.  But the production of thyroid hormone can result in excess hydrogen peroxide, which results in oxidative stress and can increase TPO antibodies.  Earlier I mentioned that selenium is a cofactor of glutathione, and so having sufficient selenium levels can increase glutathione levels, which in turn will reduce the hydrogen peroxide levels, and this in turn can help to reduce TPO antibodies.

3. Selenium can benefit people with thyroid eye disease.I mentioned how selenium can reduce thyroid peroxidase antibodies by helping to increase glutathione levels.  And the same concept applies to thyroid eye disease, as taking selenium can reduce oxidative stress and help to decrease the TSH receptor antibodies associated with Graves’ Disease.  I spoke about this in a separate blog post entitled “Can Taking Selenium Help Reverse Thyroid Eye Disease? [8]

What Are Some of The Signs and Symptoms of a Selenium Deficiency?

A severe selenium deficiency is characterized by cardiomyopathy, while a moderate deficiency usually results in symptoms such as muscular weakness and pain (7) [1], along with dry skin (8) [9].  Since selenium is important for the conversion of T4 to T3, having a selenium deficiency can lead to symptoms of hypothyroidism, including fatigue, brain fog, cold hands and feet, and weight gain, just to name a few.

What Are Some of The Signs and Symptoms of a Selenium Toxicity?

Although having a selenium deficiency isn’t a good thing, you do want to be careful about supplementing with high doses of selenium supplements.  Doing this can result in a selenium toxicity.  A few years ago, 201 people were affected by an error in a liquid dietary supplement that contained 200 times the labeled concentration of selenium (9) [10].  Fortunately only one person was hospitalized.  The symptoms associated with the selenium toxicity include diarrhea (78%), fatigue (75%), hair loss (72%), joint pain (70%), nail discoloration or brittleness (61%), and nausea (9) [10].

Food Sources of Selenium

Seafood and organ meats are considered to be the richest food sources of selenium (10) [11].  Many people reading this are aware that Brazil nuts are also a good source of selenium, and one study showed that the consumption of two Brazil nuts is as effective for increasing selenium status and enhancing glutathione peroxidase activity as 100 mcg of selenomethionine (11) [12]. However, the amount of selenium in a Brazil nut is dependent on the amount of selenium in the soil, along with other factors, including soil pH.  So for example, according to the U.S. Department of Agriculture Food Composition Database, Brazil nuts have 544 mcg of selenium per ounce, but values from other analyses vary widely (10) [11].  This is why one can’t assume that they are getting plenty of selenium by eating a few Brazil nuts, as this isn’t always the case.  In addition, those following a strict autoimmune paleo diet are not allowed to eat Brazil nuts, as nuts and seeds are excluded from this diet.

Types of Selenium Supplements           

If you take a selenium supplement, which form should you take?  Here is a breakdown of a few of the more common types of selenium you’ll find in supplements:

Selenomethione.  This consists of selenium bound to the amino acid methionine, and is the main form of selenium found in Brazil nuts, legumes, and fish. It is a well-absorbed form of selenium, and is one I commonly recommend to my patients.

Selenocysteine.  This consists of selenium bound to the amino acid cysteine.  Although I don’t usually recommend this form of selenium to my patients, this form is also well absorbed and can improve selenium status.

Sodium selenite.  This is an inorganic form of selenium, and is not something I commonly recommend to my patients.

Selenium-enriched yeast.  This consists of selenium bound to yeast, and consists mainly of selenomethionine, but also has some other forms of selenium.  This is also something I commonly recommend to my patients.

Which Of These Forms of Selenium Are The Best?

If you choose to take a selenium supplement, which one should you take?  All of these forms of selenium will help to increase selenium levels.  When I recommend a selenium supplement to my patient I usually recommend either selenomethionine or selenium-enriched yeast, and I usually will give multiple options.

Checking Selenium Status

There is no perfect test for determining the levels of selenium.  RBC selenium is a common method of determining selenium status.  Although serum selenium isn’t considered to be a good measurement of selenium in the tissues, some sources claim that this is the most useful test for assessing selenium tissue status (12) [13]. Many question the accuracy of hair mineral analysis testing.  And while hair testing does have limitations, a few studies show that hair testing does have some value with regards to selenium (13) [14] (14) [15].

In summary, selenium is one of the most important minerals with regards to thyroid health.  First of all, selenium is important for the conversion of T4 to T3.  Selenium also can help to decrease thyroid peroxidase antibodies, and can also help with thyroid eye disease as well.  Although many people are deficient in selenium, one also needs to be cautious about selenium toxicity.  Seafood and organ meats are considered to be the richest sources of selenium, and Brazil nuts are also a good source.  With regards to selenium supplements, some of the common types include selenomethionine, selenocysteine, and selenium-enriched yeast.