Selenium deficiency is one of the most common nutrient deficiencies that I see in people with Hashimoto’s, and research suggests that thyroid disease is linked to selenium deficiency.

In my clinical experience, most people with Hashimoto’s have a deficiency in selenium, and being deficient in this key thyroid nutrient is a very common and widely recognized trigger of autoimmune thyroid conditions!

The good news is that supplementing with selenium at a therapeutic dosage, has been found to reduce thyroid antibodies, reduce thyroid symptoms, and improve overall well-being. (1-3)

When I surveyed my Root Cause readers, 63 percent of respondents said that taking a selenium supplement helped them feel better.

As an added bonus, selenium has been shown to help reduce anxiety as well. I remember my own disbelief when, after taking selenium supplements, my frequent panic attacks completely disappeared! You may not have even realized that the anxiety you are being treated for is a very common thyroid symptom, but it is.

Interestingly, a 2004 study found an association between the presence of an anxiety or mood disorder, and the presence of thyroid peroxidase (TPO) antibodies. (4)

Because selenium can reduce thyroid antibodies, I believe this is why it can help with thyroid-related anxiety. Many of my clients who come to me already taking anxiety medications, have been able to wean off them completely, under the guidance of their physicians, after implementing my recommended interventions.

Beyond Hashimoto’s, other populations at risk for selenium deficiency include: people on certain diets (grain-free, gluten-free – just the type of diets that we usually find to be helpful for those with Hashimoto’s!), people with celiac disease or gluten sensitivities, those with IBS or Graves’ disease, women who are pregnant or experiencing postpartum thyroiditis, and people with thyroid eye disease. (5-8)

Why such an impact on so many? Selenium is vital to our body’s ability to convert T4 to T3, and has a balancing effect on our thyroid and immune health. It also plays an important role in managing our oxidative stress within the thyroid, through a complex relationship with iodine, which I’ll discuss in more detail in this article. Additionally, new research has shown that selenium may have synergistic benefits, when used alongside myo-inositol. (9-12)

Research has shown that the optimal intake of selenium is difficult to get through diet alone, especially if you are like many people with Hashimoto’s who experience gut issues that cause poor nutrient absorption.

Absorption challenges can even be seen with supplementation, so it’s important to address this issue for optimal selenium levels.

In this article, you’ll discover:

• The link between selenium and thyroid health
• How selenium supplementation can reduce your symptoms
• The connection between selenium levels and anxiety symptoms
• How to optimize your intake of selenium
• Synergistic benefits of selenium and myo-inositol

The Link Between Selenium and Thyroid Health

Selenium is an important trace element and antioxidant required for healthy thyroid hormone synthesis and metabolism. The human thyroid gland has been found to have the highest content of selenium per gram of tissue among all the organs in the human body. Selenium supports the conversion of your body’s inactive thyroid hormone thyroxine (T4) into triiodothyronine (T3), the biologically active form your body needs. It protects your body’s thyroid cells from oxidative damage during this process. (13)

I’ll talk more about selenium’s role during the thyroid hormone conversion process, its relationship with iodine levels, and how it can be a trigger for Hashimoto’s. But first, let me review why selenium deficiencies are so commonly seen in Hashimoto’s in the first place.

We see many nutrient deficiencies in people with Hashimoto’s. I also believe that these types of nutrient issues are not just happening in Hashimoto’s, but are generally applicable to just about everyone these days. Unfortunately, too many people in the United States eat an overly processed and gut-unfriendly Western diet, which often leads to food sensitivity reactions, digestion issues, gut permeability problems, and other nutrient absorption challenges. Add to that the toxins in our everyday environment, stress, and other real world impacts… and it is no wonder that our bodies are not functioning optimally.

Most of my clients come to me with one or more deficiencies in the key nutrients important for proper thyroid function, including: iron/ferritin and B12 (both associated with anemia), vitamin D, thiamine, and magnesium. Selenium is also high on this list.

The three-legged stool of autoimmune disease theory states that you need to meet three requirements in order to have an autoimmune disease such as Hashimoto’s: a genetic predisposition, gut permeability issues (like leaky gut), and one or more environmental triggers. So, gut permeability problems are inherent in someone with Hashimoto’s, which leads to poor nutrient extraction and absorption. (14)

When people with Hashimoto’s embark on a gluten-free diet to heal their gut permeability issues, they may inadvertently worsen their selenium deficiency. While the gluten-free diet has been found to improve Hashimoto’s symptoms and reduce the autoimmune attack on the thyroid, it’s important to note that selenium deficiency can be caused or worsened by gluten and grain-free diets, as demonstrated in nutritional studies involving people with celiac disease. (15, 16)

Thus, a selenium deficiency may prevent someone who is already on a gluten-free diet from feeling better.

We also know from the research that many symptoms of Hashimoto’s, such as my own experience with low stomach acid while dealing with acid reflux and trying every acid blocker known to mankind, are correlated with nutrient deficiencies. The list of symptoms and root causes is long here (gut infections, stress, toxins, etc.), and so many of them can affect nutrient absorption!

Selenium absorption and intake are affected by many of these same triggers and conditions, likely resulting in the deficiency being seen so often in Hashimoto’s.

How Selenium Deficiency Can Trigger Hashimoto’s

It can be a bit complicated, but it’s worth spending a few minutes talking about how a deficiency in selenium can be a trigger for Hashimoto’s. It’s also important to understand the iodine piece of this, as high levels of iodine can increase the risk for selenium deficiency.

Adequate levels of both iodine and selenium are required for optimal thyroid hormone metabolism. Thyroxine (T4) is produced by the thyroid gland in ample amounts, but is relatively biologically inactive. Therefore, triiodothyronine (T3), the biologically active thyroid hormone, must be produced by a hormone conversion process, converting T4 to T3. This conversion occurs mostly in the liver and is the process that iodine supports.

The antioxidant selenium is required during this conversion process, its role being to neutralize the toxic build-up of hydrogen peroxide (H2O2) which is produced as a by-product of the hormone conversion.

Remember I mentioned that the thyroid contained the highest amount of selenium in the body?

This high concentration of selenium in the thyroid gland is incorporated into proteins called selenoproteins. There are many different types of selenoproteins that focus on different functions relating to thyroid and immune system support. Some types of selenoproteins make the antioxidant glutathione peroxidase, which specifically removes the excess hydrogen peroxide produced during the thyroid hormone T4 to T3 conversion process. Glutathione peroxidase breaks down the hydrogen peroxide into water particles. This allows for the removal of any cells affected by oxidative damage.

This removal process is important, as hydrogen peroxide is a reactive oxygen species, which causes oxidative damage and inflammation. The build-up of reactive oxygen species in cells can cause damage to DNA or even cell death. Selenium’s job of neutralizing the hydrogen peroxide produced during thyroid hormone conversion (via the actions of glutathione peroxidase), becomes even more critical when a person has high iodine levels.

In the case of too much iodine, a greater amount of hydrogen peroxide is created. So even if your selenium levels are “normal,” too much iodine creates a relative selenium deficiency in the body. (i.e. There is too much iodine and too much hydrogen peroxide for the “normal” level of selenium/glutathione peroxidase to deal with, so a toxic build-up of hydrogen peroxide occurs.) And that is worsened even more if a person is also deficient in selenium.

When the reactive hydrogen peroxide is left unchecked, it causes oxidative damage and inflammation of the surrounding thyroid tissues. This inflammation triggers lymphocytes or white blood cells (WBCs) to converge for clean-up. (17-20)

As the WBCs converge, small amounts of antibodies are formed to help mark the damaged cells that need to be cleaned up. In instances of higher turnovers of cells seen with excess oxidative damage (due to iodine excess and selenium deficiency), more antibodies are produced, and an immune system shift can be induced. The shift can result in the failure to distinguish self from non-self.

This is how autoimmunity starts. Thus, selenium deficiency has also been recognized as a risk factor for Hashimoto’s. In fact, selenium deficiency has been particularly associated with autoimmune disorders in general. But selenium supplementation has also been shown to halt this progression. (21-23)

In a study performed using mice, autoimmune thyroiditis was induced by iodine, but the development of the autoimmune disease was prevented when selenium was administered. Selenium reduced the number of thyroid antibodies while increasing the number of regulatory T cells (which help the immune system recognize itself and prevent WBC infiltration of the thyroid cells). (24)

Here’s a helpful graphic which shows what is going on during thyroid hormone synthesis when there is both selenium deficiency as well as excess iodine:

After autoimmunity occurs, this T4 to T3 conversion can continue to be impaired, leading to decreased production of thyroid hormones. The decreased production results in the stimulation of the hypothalamic-pituitary axis, increasing TSH production. This in turn stimulates the selenoproteins to convert more T4, and the hydrogen peroxide continues to build up instead of being neutralized. More of it accumulates in thyroid tissue, creating further damage. (25, 26)

With this explanation in hand, let’s now talk about some of the research that has been done regarding the optimization of selenium in people with various thyroid issues, including Hashimoto’s, selenium’s synergistic effects with myo-inositol, hypothyroidism relating to pregnancy, and autoimmune hyperthyroidism (Graves’ disease). We’ll also talk about the connection between selenium deficiency and anxiety.

Thyroid Benefits of Selenium Supplementation

Selenium Supplementation and Hashimoto’s

Research suggests that selenium supplementation for people with Hashimoto’s is associated with a reduction in TPO antibody levels, improved thyroid ultrasound features, and improved quality of life. In fact, thyroid antibodies in people with Hashimoto’s have been shown to be reduced by 40 percent in three to six months, with therapeutic doses of selenium. (27)

But before digging into the research on this topic, let’s remember the importance of reducing thyroid antibodies, even if TSH levels may be telling us that we don’t have a thyroid problem.

I’ve found antibodies are an early warning system for Hashimoto’s, with positive antibody levels seen years before someone may see abnormal levels for their TSH. Research suggests that 80 to 90 percent of people with Hashimoto’s will have elevated TPO or TG antibodies, or both. (28)

A reduction in antibodies can result in people feeling better, and interventions such as nutrient supplementation can have fast results!

Years ago, before I was diagnosed with my own thyroid issues, I had not had my antibodies tested, only my TSH, which was deemed normal (even though it was 4.5 μIU/mL and I now know that the optimal range is 0.5-2.0 μIU/mL for most women of childbearing age). I struggled for almost a decade until finally being tested for TPO antibodies. At that time, my antibodies tested in the 2000 IU/mL range. (Note: the optimal range is less than 2 IU/mL!) Once I was diagnosed and started focusing on addressing my root causes, I was able to reduce my antibodies and finally start feeling better.

There are many interventions that are associated with a reduction in both antibodies as well as symptoms. If you’d like to read more about antibodies (how you can easily test for them, and interventions to reduce them, for example), check out this article on the importance of thyroid antibodies.

Now on to the research showing that selenium supplementation – at consistent, therapeutic levels – has been shown to reduce thyroid antibodies, improve thyroid symptoms, and make people feel better.

In a 2002 study led by Dr. Roland Gärtner, 71 patients with Hashimoto’s (who also had high levels of antibodies) were treated. Half of the participants were given selenium supplementation at a dosage of 200 mcg per day, along with levothyroxine, for a 90-day period. The other half was only given levothyroxine and a placebo. Those with selenium supplementation showed a 40 percent decrease in TPO antibodies. The other group (placebo group) only showed a 10 percent decrease. In 24 percent of those taking a selenium supplement, antibody levels completely normalized! Those taking supplementation also reported better well-being compared to the placebo group. (29, 30)

In a follow-up study by the same researchers, four groups were created from the initial 71 patients who agreed to participate in the first study. One group continued to take selenium, and their TPO concentrations continued to decrease. Another group who had been taking selenium supplementation was removed from it, and their antibodies significantly increased. A group who had not been originally taking supplementation started it, and their antibodies decreased. The final group had not been taking selenium, continued to not take it, and their antibodies remained the same. (31)

Another study from Greece evaluated the effects of selenium supplementation (200 mcg/day) in patients suffering from amiodarone-induced thyrotoxicosis (AIT). AIT is a side effect for people taking the antiarrhythmic drug amiodarone, as the drug contains iodine. After 6 months of treatment, a 9.9 percent reduction of TPO antibodies was observed. Afterwards, supplementation in one group was continued, resulting in further decreases in antibodies; while in the other group, supplementation was stopped, and an increase in antibodies occurred. (32)

(I’ve written an article about thyroid toxic drugs and their alternatives if you want to cross-check it with your medication list.)

Findings that suggest that thyroid antibodies can be reduced with therapeutic dosages of selenium supplementation (despite an increased intake of iodine) have been supported by additional studies relating to Hashimoto’s.

Synergistic Effects With Myo-Inositol

In most of the studies on myo-inositol and Hashimoto’s, myo-inositol has been evaluated in conjunction with selenium.

Research has shown that a combination of selenium and myo-inositol can have a synergistic effect that maximizes the benefit to thyroid function — consuming both of these together may not just reduce thyroid antibodies, but can also reduce TSH by an average of 30 percent. In some cases, this can normalize TSH levels (both for low and high TSH levels), reduce the risk of developing overt hypothyroidism, and improve overall well-being for those who have Hashimoto’s. (33-37)

Today’s research strongly points to the benefits of taking both together. (38)

In one study done in 2013, patients with autoimmune thyroiditis were split into two groups, with one group being treated with 600 mg of myo-inositol and 83 mcg of selenium (selenomethionine) per day for 6 months, and the other being treated with just 83 mcg of selenium. While both groups showed a decrease in thyroid antibodies, the group treated with myo-inositol also experienced a 31 percent reduction in TSH levels! The selenium group showed no change in TSH levels.

The group taking the myo-inositol and selenium also showed a 44 percent reduction in thyroid antibodies, while the group taking selenium alone showed a 42 percent reduction in antibodies — not a huge difference here; however, interestingly, thyroglobulin was reduced by 48 percent with the myo-inositol/selenium combination, versus 38 percent with just selenium alone.

Some people actually went into remission after starting the myo-inositol, with thyroid antibodies testing below the levels associated with Hashimoto’s. The results weren’t just in the numbers either. Improvements were seen in people’s assessment of their personal well-being. (39)

Selenium Supplementation and Pregnancy

It is estimated that up to 10 percent of pregnant women are positive for TPO antibodies, and that about 8 percent of all pregnant women develop postpartum thyroiditis. So the research relating to pregnant women with TPO antibodies is important, as selenium supplementation can significantly decrease the percentage of those with postpartum thyroiditis and hypothyroidism.

In an interesting study involving 2143 pregnant women with autoimmune thyroiditis in euthyroidism (this is when people have thyroid symptoms or thyroid antibodies but their TSH level may still test as normal), selenium supplementation was given during and after pregnancy. Of the original group, 169 were positive for thyroid peroxidase (TPO) antibodies and were divided into two groups: 77 pregnant women received 200 mcg of selenomethionine a day, and 74 received placebo doses. (40, 41)

The group that supplemented with selenium during their pregnancy as well as postpartum, showed a decrease in the progression of autoimmune thyroiditis, including a reduction in TPO antibody levels. They also showed a decreased incidence of thyroid dysfunction in the postpartum period, better thyroid ultrasound patterns, and decreased permanent hypothyroidism.

This suggests that selenium supplementation for pregnant women with TPO antibodies can lead to a reduction in antibodies and a decrease in postpartum thyroiditis and hypothyroidism. There have also been studies focused on pregnant women, suggesting that selenium administration may have a protective role relating to pregnancy loss.

Selenium Supplementation for Autoimmune Hyperthyroidism

Selenium supplementation has also resulted in thyroid improvements in a few studies relating to Graves’ disease, and appears to also have a beneficial effect on Graves’ orbitopathy or ophthalmopathy (which is when antibodies are directed at the receptors presented behind the eyes, leading to a bulging eye appearance). (42)

In one study, serum selenium levels in patients with remission and relapse of Graves’ disease were compared. The authors found that the highest serum selenium levels (>120 mg/L) were seen in the remission group, indicating a positive effect of selenium levels on the outcome of Graves’ disease.

Regarding Graves’ orbitopathy, one study found that treatment with selenium was associated with less eye involvement, improved quality of life, and delayed progression of Graves’ orbitopathy at six months.

As of 2018, there have been at least two active studies underway to gain more definitive results, the GRASS (Graves’ Disease Selenium Supplementation) and the CATALYST (The Chronic Autoimmune Thyroiditis Quality of Life Selenium Trial). These trials are focused on obtaining data concerned with the optimal amount of selenium supplementation necessary for patients with Graves’ hyperthyroidism that will provide the fastest remission and improved quality of life. (43, 44)

Even without this definitive data, however, a recommendation for selenium’s use in mild cases was incorporated into the recent guidelines for the European Group On Graves’ Orbitopathy (EUGOGO). This is very significant and suggests that selenium may be recommended for Graves’ disease-related conditions in the near future.

Why Selenium Levels May Be Connected to Anxiety Symptoms

Along with seeing a reduction in thyroid antibodies, I have found that selenium supplementation also often results in a reduction in anxiety in many people with Hashimoto’s. (45)

Anxiety, irritability, and moodiness are all symptoms which are frequently associated with Hashimoto’s and Graves’ disease. As I mentioned earlier, I suffered from significant anxiety myself, but taking selenium supplements and balancing my blood sugar worked wonders at providing me a renewed sense of calm. (You can read more about anxiety and Hashimoto’s.)

When the thyroid is under attack by the immune system, and as thyroid cells are broken down, they release thyroid hormones into the bloodstream. This causes transient hyperthyroidism, otherwise known as thyroid hormone surges. This can result in making people extremely anxious, irritable, and on edge.

Some studies have linked selenium deficiency with anxiety and depression, which are also common symptoms seen in those with Hashimoto’s. A study in New Zealand found that low selenium intakes were associated with the most depressive symptoms in young adults. The researchers theorized that oxidative damage to the brain and nervous system was due to the inability of the body to neutralize excess hydrogen peroxide. (46-48)

This research underscores a point I will make in the next section, and that is that the nutrient content of foods can differ dramatically depending on where it is grown! Let’s take the New Zealand study as an example. New Zealand’s soil is low in mineral content such as selenium. Gaining consistent levels of any given nutrient through diet is difficult for a number of reasons, one of them being unknown nutrient levels (depending on where the food has been grown) — you can’t look at a chart to know the nutrient levels of the particular food you are eating.

So whether we are attempting to reduce our antibodies, reduce anxiety symptoms, or just feel better, we want to ensure our selenium intake is at an optimal and therapeutic level, as demonstrated by the research. So how do we do that if food sources alone are often inadequate?

Let’s discuss how you can achieve the optimal level of selenium to improve your thyroid health.

Dietary Sources of Selenium

Our bodies do get selenium from the foods we eat. According to one study, the main sources of selenium are meat products (31 percent), fish (19 percent), pasta or rice (12 percent), and bread or cereals (11 percent). Note that this study was done in Belgium, so the US diet – or the diet you are personally following – may not be reflective of these percentages. (49)

Many people with Hashimoto’s may turn to a gut-friendlier diet such as a gluten-free or grain-free diet, so they will actually lower their selenium intake through such a diet. Reduced selenium levels have also been associated with the consumption of eggs, white rice, alcohol, and coffee, in addition to smoking.

The average intake of selenium in the United States was reported to be 93 mcg per day in women, and 134 mcg per day in men. Given that the RDA (recommended daily allowance) for selenium in the United States is only 55 mcg daily, what’s the issue then, you might ask? (50-52)

The issue is that the RDA of 55 mcg will not be sufficient for TPO antibody reduction.

Studies have shown that the minimal dose of selenium necessary for TPO antibody reduction is 200 mcg daily. Even a 100 mcg dose did not produce a statistically significant TPO antibody reduction. (53)

And you are unlikely to get to that daily dose through your diet.

Some nutrition charts suggest that one serving of certain foods like Brazil nuts, contains more than enough selenium, so you might think that all you need to do is eat a few Brazil nuts each day, but I don’t suggest this strategy.

While it may be tempting to increase selenium intake by increasing your consumption of selenium-rich foods such as Brazil nuts, it is important to realize that selenium content varies widely for foods grown in different soils. Remember my earlier comment on New Zealand?

While the Dakotas have selenium-rich soils, other areas such as Russia and China have deficient levels of selenium.

The importation of foods further complicates these issues. The amounts of selenium in a single Brazil nut have been reported to vary tenfold depending on where the nut was grown. This means there could be anywhere from 55 mcg to 550 mcg per ounce of nuts.

Additionally, absorption issues due to gastrointestinal (GI) problems and food sensitivities may limit the availability of selenium from food sources.

Supplementation

For these reasons, I routinely recommend selenium supplementation in order to get the therapeutic level of selenium that addresses antibody reduction. Supplementation also allows for a consistent dose each day. I’ve tested Brazil nuts vs. selenium supplements personally and with clients, and have always found a more significant impact on symptoms and antibodies by using a supplement.

You might wonder if you can easily test your selenium levels so you see where they are at as you progress through your healing journey. I don’t routinely recommend testing for selenium levels; rather, I’ve found that selenium supplementation in the studied range of 200 to 400 mcg per day is generally safe and effective for most people with Hashimoto’s.

Remember, in my Root Cause survey, 63 percent of respondents said that taking a selenium supplement helped them feel better. Thirty-four percent saw no difference, while only 3.5 percent felt worse.

There is also research that shows selenium supplementation has significant immune-stimulatory effects even outside of Hashimoto’s, and I have found toxicity problems to be very rare. (54) Talk with your practitioner if you are curious as to whether selenium supplementation may be right for you.

While multivitamins may contain the RDA of selenium, keep in mind that it won’t be the correct therapeutic dose. Multivitamins also have so many different ingredients in them, and sometimes even fillers, resulting in reduced absorption of selenium.

Additionally, please note that while many prenatal vitamins contain up to 200 mcg of selenium, some only contain 100 mcg, and others do not contain any selenium. Nonetheless, even if they contain selenium, an additional standalone supplement may be required to ensure adequate absorption.

If you are thinking about adding a standalone selenium supplement, I have had a lot of success with recommending Selenium from Pure Encapsulations, at a dose of 200 mcg per day. In my clinical experience, I have observed that it can take 3-5 days for symptoms to show improvement, and three full months to see the full impact on reduced thyroid antibodies. This version is generally very well tolerated and helpful. Some individuals use this product along with an additional myo-inositol supplement (find more information on myo-inositol in this article).

Because of new emerging research on the synergistic benefits of selenium with myo-inositol, because I know it’s easier to take one supplement instead of multiple supplements per day, and because some of my more sensitive readers were reporting side effects with even 200 mcg of selenium when used as a standalone dose, I was excited to create a new supplement, that combined selenium and myo-inositol, in the same exact doses that were studied by researchers. (55)

Introducing Rootcology Selenium + Myo-inositol, which delivers the therapeutic range of both selenium and myo-inositol. This formula is compliant with an Autoimmune Paleo diet. It is free of dairy, gluten, GMOs, shellfish, and soy, and has been tested for purity.

Please note that both versions of selenium contain methionine, which is a sulfur-containing amino acid. Some individuals may react to or be sensitive to sulfur. However, selenium methionine is the form of selenium that has been studied in Hashimoto’s, so I am unable to vouch for the effectiveness of other forms of selenium in autoimmune thyroid conditions. Additionally, sulfur and selenium are closely related, and processed in the same way by the body. As such, those with sulfur sensitivities may react to other forms of selenium as well.

How to Ensure Proper Absorption of Selenium

Because of the absorption issues many people have with their gut, I do always recommend people take a selenium supplement with a vitamin E supplement, as it works in synergy with selenium to ensure proper absorption. I recommend taking selenium and vitamin E together on an empty stomach.

Be aware, however, that many vitamin E supplements are soy-based. (Soy is a common sensitivity that I’ve seen in those with Hashimoto’s!)

Finding a soy-free version of vitamin E has actually been a big challenge for me over the last few years. I would often recommend a brand, and then the brand would be reformulated or discontinued.

I’ve found that NOW brand’s Sun-E 400 offers a soy-free, natural vitamin E, which is derived from Identity Preserved (IP) non-GMO sunflower seed oil. It contains 400 IU vitamin E (as D-Alpha Tocopherol).

Optimal vs. Toxic Doses of Selenium

Selenium has a narrow therapeutic index, and doses of under 100 mcg per day may not be sufficient for improving Hashimoto’s symptoms and markers, while doses in excess of 800 mcg per day can be toxic. (56)

As I mentioned earlier, the RDA for selenium has been defined as 55 mcg in the United States, and an upper limit of 400 mcg has been suggested.

A study done in South Dakota did not find any signs of selenium toxicity at levels as high as 724 mcg. However, changes in nail structure, a sign of toxicity, were reported with a selenium intake of 900 mcg per day in China. (57)

That said, everyone’s chemistry is different, and you may have an underlying health issue that adds risk to you reacting to selenium supplements, so I always recommend that you discuss any type of supplementation with your practitioner. They will be able to help guide you as to what dosage is most appropriate for you.

In my clinical practice and in listening to what my readers tell me about their own experiences, I have found selenium toxicity to be extremely rare. When taken in therapeutic doses, selenium does not typically have side effects.

But it is always important to understand the flip side of optimal results. While most reported toxicity cases have been associated with industrial accidents and manufacturing errors, it is important to at least be aware of the symptoms of selenium toxicity.

Some symptoms of selenium toxicity that have been reported included GI disturbances, hair loss, changes in hair and nails, fatigue, peripheral neuropathy, irritability, garlic-smelling breath, fever, nausea, and a jaundice-like yellow tint to the skin. Potentially serious side effects include liver, kidney, and heart problems. At high enough levels, selenium can cause death (reports of this level of toxicity exist, but are extremely rare). (58, 59)

It’s important to note that selenium may also interact with other supplements and medications, such as cholesterol-lowering statin drugs, antacids, chemotherapy drugs, corticosteroids, niacin, and even birth control pills.

Those with a CBS gene mutation have difficulty breaking down selenium. (Research has found that selenomethionine needs to be converted into its active form via the CBS gene. So, if this gene is mutated, the body cannot break down selenomethionine properly.) (60) Thus, those with a CBS gene mutation may have excess levels of selenium compared to those without this mutation, even with the same supplemental dose taken.

If you know you have a CBS gene mutation, then regularly monitoring your selenium levels is necessary. If you suspect that you may have this mutation, be sure to test for it using a genetic test like the one offered by 23andMe. You’ll also want to check out the Sulfur Toxicity Protocol in the Advanced Protocols section of Hashimoto’s Protocol. I heard from one reader, who had the CBS mutation, and this individual ended up with selenium toxicity due to this very reason.

Selenium supplements are also associated with a risk of non-melanoma skin cancer (squamous cell carcinoma), so people at high risk of skin cancer should not take these supplements.

There is conflicting data on the connection between selenium and prostate cancer. A study by the National Cancer Institute shows that men who already have high concentrations of selenium in their bodies are nearly twice at risk of aggressive prostate cancer if they take selenium supplements. (61) But other research suggests that selenium supplements can help prostate cancer. Selenium-enriched yeast has been researched as a supplement that may reduce the risk of prostate cancer. (62, 63) (I recommend that men concerned with prostate cancer consult with their practitioner before supplementing with selenium, and get annual PSA screenings and prostate exams starting at age 40.)

Selenium intake may also cause side effects in those with diabetes. One study found that people who took 200 micrograms a day of selenium, were 50 percent more likely to develop type 2 diabetes. (64) So far, it’s unknown whether it’s the selenium that actually caused the disease (as opposed to a factor that was co-occurring along with the selenium supplementation).

It is also important to note that herbal supplements, such as those taken for lactation support, may be sources of selenium. These include burdock root, alfalfa, fenugreek, fennel seed, catnip, chamomile, garlic, cayenne, nettle, oat-straw, yarrow, peppermint, sarsaparilla, lemongrass, ginseng, hawthorn berry, rose hips, and raspberry-leaf. Thus, you may need to adjust your supplementation dosage to avoid having too much selenium.

As mentioned previously, food sources that are rich in selenium can also contribute to excess selenium, especially if your typical diet includes Brazil nuts in addition to a selenium supplement. If you are consuming Brazil nuts from selenium-rich soils (like New Zealand), you could be consuming up to an additional 550 mcg of selenium, on top of your 200-400 mcg dose of selenium supplementation.

My best advice is to work with your practitioner to determine the appropriate dosage for you.

Additionally, most product recommendations are intended for adults. Please consult with your pediatrician before giving supplements to children. The tolerable upper limit for children, ages 9-13, is 280 mcg. Since one of the supplements I recommend, Pure Encapsulations Selenium, can contain up to 320 mcg per capsule (specifications state that the product can contain up to 160 percent of the label claim), it is not recommended for children.

This is one of the reasons I was super excited to create a selenium and myo-inositol supplement with a lower dose of selenium that has still shown benefits. The Rootcology Selenium + Myo-Inositol supplement contains 83 mcg and 600 mg, respectively, and can be a great starting place for many individuals.

What to Do If You Have Low Levels of Iodine

Many people come to me already in the midst of iodine supplementation (which I generally do not support without other root cause investigations). However, most people with Hashimoto’s are not deficient in iodine. Furthermore, too much iodine can be a bad thing as we’ve seen, especially if you have not addressed the underlying issues triggering your Hashimoto’s.

That said, I have heard from a few clients and readers that adding selenium in the presence of low iodine levels has made them feel worse. (You can read more about iodine, and the different views on iodine supplementation in Hashimoto’s, in my article on iodine and Hashimoto’s.)

If you do have an adverse reaction to selenium (again, this is very rare), you may find that you have an iodine deficiency. While I don’t usually recommend taking iodine supplements until addressing other root causes, you can certainly talk with your practitioner about whether a low-dose iodine supplement might be right for you. (Up to 250 mcg a day has been well-tolerated in people with Hashimoto’s.)

Some potential factors that may lead me to suspect an iodine deficiency include: eating a diet low in seafood, eating a vegan diet, having fibrocystic breasts (though this could be caused by magnesium deficiency), or having low reverse T3 levels. You can find out more about iodine in the Advanced Protocols section of my book Hashimoto’s Protocol.

Monitoring Your Thyroid Hormones When Taking Selenium (with or Without Myo-Inositol)

Whenever you start a lifestyle or complementary intervention to address Hashimoto’s, I encourage you to work with your doctor to monitor your thyroid symptoms, thyroid hormones, and thyroid antibodies. This is a great idea for any lifestyle intervention, but a must for lifestyle changes that could impact your TSH, like myo-inositol, especially if you are already taking thyroid medications.

Studies have shown that selenium can reduce thyroid antibodies by at least 40 percent over three months. Additionally, myo-inositol can lower TSH by an average of 30 percent within six months. (65, 66)

What this means is that myo-inositol could lower/normalize TSH in some cases, thus potentially reducing your requirement (or need) for thyroid meds. So as you move forward with supplementation, please look out for the following symptoms of being overmedicated: rapid or irregular heartbeat, nervousness, irritability or mood swings, muscle weakness or tremors, diarrhea, heat intolerance, menstrual irregularities, hair loss, weight loss, insomnia, chest pain, and/or excessive sweating.

I recommend testing thyroid hormone levels every six to 12 weeks while using complementary therapies, including root cause approach-based medicine, diet, or supplements, to ensure your thyroid medication dosage is optimized, or sooner, if you are showing any of the above symptoms. Thyroid medications are goldilocks hormones — they need to be used in just the right dose — and there are risk factors of being overmedicated.

Testing TSH, T4, T3, and the two most common Hashimoto’s antibodies (TPO and TG antibodies) is an important part of ensuring that the lifestyle changes you are making are both safe and helpful. 🙂 You can read more about thyroid tests here.

If your doctor is ordering these thyroid labs for you, be sure to request a copy so that you can see them for yourself and ensure that they are interpreted correctly. If you aren’t able to use your physician for ordering, or have a high deductible insurance plan like I do, you may also wish to self-order your own thyroid monitoring labs. I recommend the Ulta Labs thyroid panel for monitoring your progress, which can be ordered anywhere in the U.S. (Some, but not all, insurance companies may reimburse you for self-ordered labs. Please be sure to check with your plan.)

What You Can Do Today to Start Feeling Better

If you have Hashimoto’s, you likely have one or more nutrient deficiencies. And while you do need to investigate and correct any underlying root causes (such as gut issues or food sensitivities), in the meantime, selenium supplementation could make you feel better.

While there isn’t specific testing I would recommend relating to measuring selenium levels, taking a consistent, therapeutic dosage of selenium each day has been shown to reduce thyroid antibodies, reduce symptoms (including anxiety), and improve overall well-being.

Selenium is necessary for thyroid hormone conversion of T4 to T3, promotes blood flow, and may support immune health. Selenium and myo-inositol together may help to optimize TSH levels, reduce thyroid antibodies, help you reduce your risk of developing more severe forms of hypothyroidism, and even promote a more balanced mood. In synergy with vitamin E, selenium can protect normal cell function, and enhance the function of certain energy-producing cells.

I created an infographic that you can use on social media to share the benefits of selenium:

Even if you haven’t yet been diagnosed with thyroid disease due to having a “normal” TSH level, you could still have thyroid antibodies, and I recommend testing for those. It is easy and inexpensive, and antibody testing provides you with “early warning” information that can help you prevent further damage to your thyroid.

I hope this helps you on your healing journey! Let me know how taking selenium works for you. 🙂

Looking for more info? Supplements can help or hurt your thyroid! Download my FREE eBook to learn about safe and effective supplements that can help your thyroid symptoms naturally.

You can also download a free Thyroid Diet Guide, 10 thyroid-friendly recipes, and the Nutrient Depletions and Digestion chapter from my first book for free by signing up for my weekly newsletter. You will also receive occasional updates about new research, resources, giveaways, and helpful information. And, for future updates, make sure to follow us on Facebook and Instagram!

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Note: Originally published in February 2015, this article has been revised and updated for accuracy and thoroughness.