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Hashimoto’s and Gut Health: Understanding the Critical Connection

Writer's picture: Dr. Tediana TorrensDr. Tediana Torrens
Women holding neck, over thyroid.

Hashimoto's thyroiditis is a complex autoimmune disorder that impairs thyroid function and causes symptoms like fatigue, weight gain, constipation, and depression. While genetics and environmental factors play a role, emerging research highlights the critical connection between gut health and autoimmune thyroid conditions. The thyroid-gut-microbiome axis links digestive and thyroid function, showing how gut and microbiota imbalances can perpetuate Hashimoto’s symptoms. Understanding this interplay is essential for addressing the root causes of thyroid dysfunction and optimizing treatment approaches.


 

What is Hashimoto's Thyroiditis?

Key Points:

  • Hashimoto's thyroiditis is an autoimmune condition causing low thyroid function 

  • Symptoms include fatigue, weight gain, constipation, dry skin, hair loss, and depression.

  • Underlying cause is likely multifactorial, including genetics, immune dysfunction, inflammation, and environmental factors.

  • Gut microbiota imbalances (dysbiosis) are now known to play a role in autoimmune thyroid disorders.


Hashimoto's thyroiditis is an autoimmune disorder that impairs thyroid function, leading to symptoms like fatigue, weight gain, depression, constipation, dry skin and hair loss, cold intolerance and irregular periods. It is the most common cause of hypothyroidism in the U.S., disproportionately affecting women. Hashimoto's is often linked to other autoimmune conditions, most prominently Celiac disease, an autoimmune condition that damages the small intestine in response to gluten. While the exact cause is unclear, it is likely multifactorial, including a combination of genetic susceptibility, immune system dysfunction, increased inflammation, and environmental factors.


Environmental factors associated with the development of Hashimoto's are many, including iodine excess; deficiencies in selenium, zinc, iron, and vitamin D; bacterial or viral infections such as EBV; cigarette smoke and toxins; endocrine disruptors; and stress. Although iodine deficiency is linked to hypothyroidism globally, its relationship with Hashimoto's is complex and often misunderstood.


Iodine deficiency is rare in the U.S., but excessive iodine intake can harm gut health by increasing intestinal permeability, disrupting microbiota balance, and impairing immune function. These changes, collectively called dysbiosis, contribute to inflammation and immune dysregulation, fueling the autoimmune process. Newer research into the microbiome has started to shed some light on the relationship between gut and microbiome health and autoimmune hypothyroidism.


 

The Thyroid-Gut-Microbiome Axis and Its Role in Hashimoto’s

Key Points:

  • Dysbiosis can increase intestinal permeability ("leaky gut"), allowing microbial products to enter the bloodstream, trigger an immune response and harm the thyroid through molecular mimicry.

    • Molecular mimicry occurs when the immune system mistakes bacterial antigens, the intended target, with self. In this case, the immune system attacks the thyroid.

  • Dysbiosis can interfere with thyroid hormone metabolism, preventing the activation of thyroid hormones.

  • Beneficial gut bacteria support the absorption of minerals essential for thyroid health, such as iodine, selenium, zinc, copper, and iron, and produce beneficial short-chain fatty acids (SCFAs.)

  • SCFAs from gut bacteria strengthen the gut barrier to prevent increased intestinal permeability, regulate immunity, and reduce inflammation.

  • T3, the active thyroid hormone, supports gut barrier integrity, creating a positive feedback loop between gut and thyroid health.


Mechanisms of Interaction

Several robust studies have identified causal links between specific microbiota species and Hashimoto’s development, clearly establishing the relationship between Hashimoto's and gut health. When comparing individuals with Hashimoto's to their healthy counterparts, consistent differences have been seen between their microbiota compositions and functions.


SCFA: SCFAs are created by gut bacteria via fermentation of carbohydrates in our diet. Bacterial species associated with higher SCFA production are protective, as SCFAs strengthen intestinal barrier integrity, reduce inflammation, and support immune function. Decreased levels of these beneficial bacteria are linked to increased intestinal permeability, or "leaky gut," due to poor gut lining and mucosal health.


Increased Intestinal Permeability: Increased intestinal permeability allows microbial products that typically stay within the gut to enter the bloodstream. Once in the bloodstream, these microbial products activate the immune system and negatively impact the thyroid through a process called molecular mimicry. Bacterial antigens, antigens being anything that can trigger an immune response, closely resemble thyroid tissue, causing the immune system to attack thyroid tissue. This process perpetuates inflammation and destruction of the thyroid gland. Research has shown that patients with Hashimoto’s have higher levels of zonulin, a protein regulating tight junctions in the intestinal lining, indicating increased intestinal permeability compared to healthy individuals.


Lipopolysaccharides (LPS): LPS can become elevated in the gut when there is an overgrowth of certain microbiota species. As long as LPS remain within the gut, there is usually minimal harm - though excessively elevated LPS may cause local inflammation. In the context of increased intestinal permeability, LPS not only will trigger an inflammatory response that can result in destruction of the thyroid, it can also inhibit enzymes responsible for converting T4 (inactive thyroid hormone) into T3 (active thyroid hormone). Reduced T3 levels not only result in more symptoms of hypothyroidism, but it also weakens the gut barrier, perpetuating intestinal permeability and autoimmune activity.


Nutrients: Beneficial gut bacteria are essential for absorbing minerals critical for healthy thyroid activity and hormone production. Dysbiosis disrupts this process, leading to deficiencies that further impair thyroid health by impacting thyroid hormone production and metabolism.


 

Treatment Considerations for Hashimoto's and Gut Health

Dietary Modifications:

  • High-fiber foods: Vegetables, fruits, whole grains – promote SCFA production, supporting gut barrier function and reducing inflammation.

  • Polyphenol-rich foods: Berries, green tea, olive oil – provide antioxidants that combat oxidative stress and support the growth of beneficial bacterial.

  • Probiotic-rich and fermented foods: Yogurt, kefir, sauerkraut – restore beneficial gut bacteria and improves immune function.

  • Diverse diet: Ensures microbiome diversity, which is critical for gut and immune health.


Improving Intestinal Barrier Function:

  • Glutamine: Helps repair the gut lining and supports intestinal barrier integrity.

  • Zinc carnosine: Plays a role in maintaining tight junctions and reducing intestinal permeability.


Lowering Inflammation:

  • Curcumin: From turmeric, known for its potent anti-inflammatory effects.

  • Omega-3 fatty acids: Found in fish oil, reduce systemic and gut inflammation.


Nutrient Supplementation for Hashimoto’s:

It's very important to test vitamin and mineral levels before considering supplementation to confirm supplementation is necessary, determine an optimal dose, and to ensure there is no overdosing and toxicity. Vitamin D is particularly crucial to test as vitamin D is a fat-soluble vitamin and will build up in the body.

  • Vitamin D: Supplementation is typically needed, as food sources do not contain appreciable amounts. Liver and egg yolks have small amounts and milk is sometimes fortified with vitamin D.

  • Selenium: Brazil nuts, fish, poultry, eggs, and whole grains.

  • Zinc: Oysters, fish, seafood, eggs, beans, nuts, and whole grains.

  • Iron: Animal proteins provide the most bioavailable form. Plant-based sources include legumes, whole grains, nuts and seeds.


Medication:

  • Levothyroxine: The standard medication for Hashimoto’s, providing synthetic, bioidentical T4 to improve thyroid hormone levels and alleviate symptoms.

  • Desiccated Thyroid: A T4/T3 combination medication derived from the thyroid glands of animals, typically pigs or cows. As it comes from animal thyroid, the T4 to T3 ratio differs from what is found in humans. Some individuals find greater benefit with desiccated thyroid over levothyroxine, while some experience worse side effects.


These interventions, including dietary changes and supplementation, can improve thyroid health by addressing the gut-thyroid connection, reducing inflammation, and supporting nutrient balance.


 

Conclusion

The gut-thyroid connection provides valuable insights into the development and management of Hashimoto’s thyroiditis. By addressing gut health through diet, lifestyle, and targeted therapies, individuals can mitigate autoimmune processes and improve thyroid function, paving the way for better overall health.



 

Disclaimer

The information provided in this blog and throughout the website is intended for educational purposes only and should not be considered, or used as a substitute for, medical advice. The content is not meant to diagnose, treat, or cure any medical condition. This blog does not constitute the practice of any medical, nursing or other professional health care advice, diagnosis or treatment. Always consult with a qualified healthcare provider before making any changes to your health regimen or starting new treatments, and never disregard professional medical advice or delay seeking care because of something that you have read on this blog, website or in any linked materials. Your individual needs and circumstances should be evaluated by a medical professional to ensure safe and appropriate care. If you are experiencing a medical emergency, please call 911 or call for emergency medical help on the nearest telephone immediately.


 

References

“Association Between Gut Microbiota and Autoimmune Thyroid Disease: A Systematic Review and Meta-Analysis - PMC.” Accessed December 13, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC8635774/.

“Causal Relationship between Gut Microbiota and Autoimmune Thyroiditis: A Mendelian Study - PMC.” Accessed December 14, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10865322/.

“Detection of Alterations in the Gut Microbiota and Intestinal Permeability in Patients With Hashimoto Thyroiditis - PMC.” Accessed December 13, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC7973118/.

“Effects of Iodine Intake on Gut Microbiota and Gut Metabolites in Hashimoto Thyroiditis-Diseased Humans and Mice - PMC.” Accessed December 15, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10824742/.

“Exploring the Role of Gut Microbiota in Autoimmune Thyroid Disorders: A Systematic Review and Meta-Analysis - PMC.” Accessed December 13, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10641821/.

“Exposure to Proton Pump Inhibitors Is Associated with the Development of Pediatric Autoimmune Diseases - PMC.” Accessed December 15, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10083351/.

“Hashimoto Thyroiditis: An Evidence-Based Guide to Etiology, Diagnosis and Treatment - PMC.” Accessed December 13, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC9478900/.

“Investigating Causal Associations among Gut Microbiota, Metabolites and Autoimmune Hypothyroidism: A Univariable and Multivariable Mendelian Randomization Study - PMC.” Accessed December 15, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10794377/.


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