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  • Writer's pictureGavin Guard, Medical Director

How your gut health affects your thyroid

Updated: Jan 23, 2022

Key Takeaways

  • There is a key relationship between your gut and thyroid health, and vice versa

  • This relationship is exhibited through an association between thyroid status and many gut disorders

  • It’s important to first fix your gut health before making drastic changes in your thyroid management

How your thyroid health?

Many people feel tired, run down, and low on energy. They may feel like their gas tank is running out of fuel and they are looking for ways to increase their energy levels and sense of vitality.

A major cause of these symptoms is low thyroid (hypothyroidism). In fact, 12% of Americans will develop a thyroid condition in their lifetime. And up to 60% of people with thyroid disease are unaware of their condition. Thus, it’s important to assess thyroid status and to fix the underlying cause of any dysfunction.

What we are going to cover in this article is the key relationship between the gut and the thyroid. You may be wondering how two (seemingly unrelated) organs are related. It’s important to know that almost all body systems affect each other in one way or another. Unfortunately, this fact goes unnoticed many times in conventional medical care.

As I alluded to, a major connection between body systems is the gut and the thyroid. Many people are on thyroid medication these days. However, some still suffer from thyroid-related symptoms:

  • Low energy

  • Weight gain

  • Constipation

  • Brittle hair and nails

  • Chronic fatigue

Even though they are on thyroid medication, these symptoms either persist or can even get worse. What’s often missed is how gut health affects thyroid health. Instead, many patients are placed on higher doses of thyroid or switched from one medication to another. These decisions are often done prematurely without first addressing other factors that affect overall thyroid health.

SIBO and Thyroid

The first connection we will make is between thyroid health and Small Intestinal Bacteria Overgrowth (SIBO). Normally, gut bacteria should be high in the large intestine and low in the small intestine. SIBO is a condition where the small intestine starts to get crowded with too much or the wrong type of gut bacteria. It characterized by symptoms such as:

  • Bloating

  • Abdominal discomfort

  • Diarrhea and/or constipation

  • Excessive flatulence, usually after meals

SIBO is considered a malabsorption syndrome where “bad” bacteria adhere and damage the lining of the small bowel.

One study concluded that 54% of those who are hypothyroid have SIBO, compared to only 5% who did NOT have SIBO. The authors noted that “overt hypothyroidism is a risk factor for SIBO development.”

In a study looking at 1,800 patients with confirmed SIBO, thyroid replacement therapy was the strongest predictor of having SIBO. In other words, those patients who were taking thyroid medication, were also the most likely to have SIBO. PPI (e.g. Prilosec, Nexium) and opioid use were other predictors.

The correlation between SIBO and thyroid is interesting. Thyroid hormone increases gut motility which plays a large role in controlling overgrowth of bacteria in the gut. Thyroid hormone also is needed for gastric acid production which also limits bacteria growth in the small intestine. Thus, low thyroid hormone may play a role in the development of SIBO.

Lactose Intolerance and Thyroid

Lactose intolerance is characterized by a deficiency of the lactase enzyme that breaks down lactose found in the diet (e.g. butter, milk, yogurt). Interestingly, those who have lactose intolerance have a higher need for thyroid hormone medication. Only 5 of 34 patients reached thyroid hormone goals with a normal dose. They needed about 33% more thyroid hormone to reach goal and 2x more if they have another diagnosed gut issue.

When patients restricted lactose, they improved thyroid hormone status without changing their medication dose. This means, this relationship goes beyond just a correlation and points to causation

H. pylori and Thyroid

Almost 50% of the world and 33% of those in the United States is infected with a bacteria called H. pylori. It’s well-established that those with autoimmune thyroid disease have a higher prevalence of H pylori. A recent study took 10 people with H. pylori and treated half of them. The 5 that were treated for this infection had reduced thyroid antibodies and other thyroid markers.

In a research article published in the New England Journal of Medicine, 123 patients with goiter had 22-34% higher need for thyroid medication if they had H. pylori or atrophic gastritis. These findings were repeated in another study.

The reason those infected with H. pylori might exhibit thyroid issues is mainly because the infection causes an immune response not only to it but the thyroid gland as well. This process is called “molecular mimicry” where the bacteria/virus/parasite looks a lot like our own tissue. Thus, our immune system attacks our own body in a process of “friendly fire”.

H. pylori may also decrease gastric acid production, increase inflammation, damage the gut lining, and lower iodine absorption. All of these factors can lead to thyroid dysfunction.

PPI Use and Thyroid

Proton pump inhibitors (PPI) are a stable of many American medicine cabinets. PPIs include brand names like Prilosec and Nexium. These medications are great at reducing stomach acid secretion and improving symptoms of heart burn/GERD. Unfortunately, PPIs often go abused when used long-term. Even the makers of these drugs suggest to only take them for no longer than 8 weeks.

Many papers note that PPI use increases the need for more thyroid medication and can decrease medication absorption. You may want to reconsider taking PPIs long-term especially if you have a thyroid condition. You may not be surprised the cause of heart burn/GERD can be exacerbated by the regular use of PPIs. Patients can get stuck in an endless pattern of taking these medications which only lead to more gut dysfunction causing their symptoms in the first place.

Celiac Disease and Thyroid

Celiac disease is an autoimmune condition that affects about 1% of the American population. Another 10% of the population has a condition called “Non-Celiac Gluten Sensitivity” which is a milder version of the disease without autoimmunity. An astounding statistic shows that for every 1 person diagnosed with Celiac disease, there are another 6.4 who go undiagnosed. This means that we are doing a really bad job of catching this disease. This may be because only around 50% of those with Celiac have typical gut symptoms.

30% of those with Celiac disease have autoimmune thyroid disease as well. In a study looking at 50 patients with atypical celiac disease (no gut symptoms), they required less thyroid hormone medication when they were properly diagnosed with Celiac disease and went on a gluten-free diet. Those who do have Celiac disease but are still eating gluten may need a thyroid hormone dose increase by up to 50%. Celiac disease not only impedes absorption of thyroid hormone but also the nutrients needed for natural thyroid hormone production. Some authors even recommend routine screening of Celiac disease if someone has autoimmune thyroid disease.

Parasite Infections and Thyroid

Parasite infections are more common than you may think. This is because you don’t have to travel to another country to acquire a parasitic illness. A parasite called Blastocystis hominis (B. hominis) is the most common parasite that affects 5-75% of the world population (depending on country).

It is highly associated with chronic urticaria (hives). In fact, 61% of those infected with B. hominis have a chronic history of hives. In one case study, a 49 year-old man with chronic hives and gut symptoms developed an autoimmune thyroid disease and was placed on thyroid replacement therapy. When his clinician treated the parasite with an antibiotic, his hives not only resolved, but he also did not require thyroid medication any more.

Another study showed that inflammatory markers were higher in hypothyroid patients infected with B. hominis. After these people had the B. hominis eradicated, thyroid hormone and inflammation levels all improved.

Similar results have also been noted in those infected with Giardia. Both types of parasites are capable of increasing inflammation, shifting immune system balance, and inducing autoimmune processes.

How does gut health affect thyroid health?

We have already touched on the many mechanisms linking gut health and thyroid health, but let’s examine it a little more.

As noted earlier, a healthy gut means better thyroid hormone absorption. Thyroid medication absorption occurs in the small intestine. Generally, 60-80% of medication is absorbed, with the remaining being excreted. It’s no surprise than an infection, inflammation, or a damaged gut lining is going to require you to increase your thyroid hormone dose and will decrease the medication’s efficacy greatly.

The microbiome is the term used to describe the bacteria that live in our gut. A whopping 39 trillion bacteria compose an average of 4 pounds of bacteria that reside within our gastrointestinal tract. The microbiota plays a key role in affecting key nutrients for thyroid health such as selenium, iodine, iron, and zinc. It has been noted that “bad” bacteria express proteins that soak up iron, leaving it unable to process natural thyroid hormone production.

Finally, our gut is a key driver of autoimmune processes. If you have the genetic set up for autoimmunity, a bad gut ecosystem may tip you over the edge to develop an autoimmune condition such as autoimmune thyroid diseases. The gut can do this by

  1. Tagging your own tissue for immune system destruction

  2. Promoting inflammation

  3. Reducing gut lining integrity allowing the wrong type and amount of substances to travel across the gut barrier

With all of this said, you can see why a healthy gut means a healthy thyroid.

The Bottom Line

There is a wealth of research pointing to the importance of your gut with your thyroid. Unfortunately, this association often goes ignored or missed altogether. You can see why fixing your gut is an important first step in improving the health of your thyroid. If you want to better manage your thyroid health or get down to the root cause of your fatigue and low energy, then fixing your gut is the right place to start.

I hope you found this information useful and helpful in your journey back to a healthier and happier life.

Learn more about how to use probiotics

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Resources Cited

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2. Brechmann T, Sperlbaum A, Schmiegel W. Levothyroxine therapy and impaired clearance are the strongest contributors to small intestinal bacterial overgrowth: Results of a retrospective cohort study. World J Gastroenterol. 2017;23(5):842-852. doi:10.3748/wjg.v23.i5.842

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9. Rajič B, Arapović J, Raguž K, Bošković M, Babić SM, Maslać S. Eradication of Blastocystis hominis prevents the development of symptomatic Hashimoto's thyroiditis: a case report. J Infect Dev Ctries. 2015;9(7):788-791. Published 2015 Jul 30. doi:10.3855/jidc.4851

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