Your Gut Microbiota and Your Thyroid

Can your gut microbiota affect your thyroid? Studies suggest that it can and with thyroid conditions on the rise, especially for women, it is worth looking into. Your microbiota in your gut is a complex arrangement of microorganisms in your intestinal tract. So what does that have to do with your thyroid gland? What connection does it have to diseases of the thyroid?

What is your thyroid?

Your thyroid is a gland located in the front of your throat (just below your Adam’s apple) that is shaped like a butterfly. The thyroid secretes a couple of hormones, including thyroxine (T4), triiodothyronine (T3), and thyroid-stimulating hormone (TSH). These thyroid hormones influence metabolism, growth and development, body temperature, and brain development from infancy and throughout childhood.

There is a range of conditions and diseases that can happen to the thyroid including:

• Goiter – thyroid swelling
• Hyperthyroidism – too much thyroid hormone production
• Hypothyroidism – too little thyroid production
• Grave’s disease – an autoimmune disease of the thyroid
• Thyroid cancer – a form of cancer found in the thyroid and usually curable
• Thyroid nodule – small abnormal lump or mass in the gland

What is gut microbiota?

Within your intestines lives the largest population of microorganisms, an average person has about 100 trillion microorganisms. Humans have about approx. 23,000 genes, however, our microbiome encodes over 3 million genes – making humans about 99% microbial.

• Gut microbiota hallmarks for healthiness
• Increased species richness and diversity
• Resilience and stability over time
• High gut microbial gene richness

Gut microbiota plays an important role in our bodies – including defending against harmful microorganisms, assisting the immune system, and degrading toxic compounds. Besides, it helps us digest and break down dietary fibers, facilities absorption of minerals, and synthesizes vitamins. It has even been shown to affect mood and behavior!

Your thyroid function and how gut microbiota affect it

Studies have shown that people with thyroid disorders also have altered microbiota compositions, suggesting that it can affect the thyroid. Since the microbiota influences, the uptake of iodine, selenium, and iron and thyroid physiology includes iodine uptake, hormone recycling, and drug uptake and metabolism – the two functions are connected.

Some of the relationships include:

• Iodine may be toxic to the microbiota so it influences its uptake
• Those with autoimmune thyroid disease have shown to have altered microbiota populations
• Leaky gut syndrome induced bacterial overgrowth and also increased the chance of autoimmune thyroid disease
• Estrogen recycling carries out microbiota and the composition is different in males and females
• Altered microbiota is found in those with obesity

Autoimmune Thyroid Diseases and Gut Microbiota

Autoimmune thyroid diseases affect 2-5% of the population, this is mostly women (5-15%) and less so for men (1-5%). These diseases include Hashimoto thyroiditis (HT), Grave’s disease (GD), and others. Hypothyroidism and hyperthyroidism are most commonly caused by these diseases.

Altered microbiota composition has been shown to increase the chance of Hashimoto’s thyroiditis and Grave’s disease because microbiota may affect L-thyroxine uptake and influence the propylthiouracil – medication used for hyperthyroidism. The microbiota has also been associated with insufficient iodine intake and the prevalence of a goiter.

Altered microbiota composition in the gut can cause the development of an autoimmune disorder by a few mechanisms:

• Generation of self-antigens by post-translational modification of proteins
• Lipopolysaccharide (LPS)-induced Toll-like receptor 4 activation
• Induction of type 1 (Th1) to type 2 (Th2) T helper cell shift
• Reducing the integrity of intercellular junctions (leaky gut)
• Inducing transcriptomic, proteomic
• Metabolic changes

Thyroid Diseases Linked to the Microbiome

Since the bacterial environments are connected to 80% of the immune system response. “Approx. 90% of hyperthyroid conditions have an autoimmune component and are triggered by microbiome dysbiosis”, according to Dr. Gilbert, the Orlo & Carol Clark Distinguished Lecturer in Endocrine Surgery and director of the Microbiome Center at the University of Chicago in Illinois. He also links “decreases in Bifidobacterium and Lactobacillus, but with increases in Enterococcus presumably via thyroid-reactive antigenic molecular mimicry.”

Gut microbiota can also be affected by a range of other factors including:

• Environment – where you live
• Diet including iodine intake
• Obesity
• Age
• Sex hormones
• How autoimmunity impacts microbiota

Your Gut Microbiota and Hashimoto’s Disease

When hormones from the thyroid and a healthy gut barrier are imbalanced the chances of having Hashimoto’s disease increases. Research shows that the microbiota of patients with Hashimoto’s disease tends to be more diverse and may be harmful to an individual. Studies also showed that supplementation with Lactobacillus reuterii improved thyroid function in mice because it increased T4 levels. They also noticed that when given lactic acid-producing bacteria, chickens had higher T3 levels.

Estrogen levels play a profound role in Hashimoto’s disease. Estrogen dominance occurs when a women’s progesterone levels drop during perimenopause. This can negatively affect the microbiota. In turn, an imbalance in microbiota can negatively affect estrogen clearance and metabolism.

Medications for thyroid can also affect microbial growth since they may not absorb well when dysbiosis or small intestinal bacterial overgrowth is present. There is also a link between Helicobacter pylori infection and Hashimoto’s disease which can lower hydrochloric acid levels in the stomach.

The Roles of Iodine, Selenium, Zinc, and Iron in the Thyroid

Iodine

Iodine is a mineral found in foods like seaweed, dairy, tuna, shrimp, and eggs. Your body uses iodine to make thyroid hormones and is the microenvironment for thyroid cells to survive. Iodine excess can cause hypothyroidism and autoimmune thyroiditis. It can be inhibited by inflammation to be absorbed properly due to a variety of reasons including food sensitivities, dysbiosis, and H. pylori.

Selenium

Selenium is a mineral found in soil and acts as an antioxidant. It is found in water, brazil nuts, oysters, liver, canned tuna, sardines, eggs, and couscous. Selenium is essential for thyroid function for thyroid hormone metabolism, reproduction, DNA synthesis, and protecting against infection and oxidative stress damage. Selenium may affect the composition of intestinal microflora and the colonization of the gastrointestinal tract.

Zinc

Zinc is a mineral and an essential trace element as it is crucial for human health. Humans can not store zinc in their body and it must be regularly consumed. Deficiency of zinc can cause many consequences including stunting growth, acute diarrhea in children, slow healing of wounds, Wilson’s disease, and the inability of ovaries and testes to function normally. Zinc can be found in beef, lamb, pork, shellfish, legumes, seeds, nuts, dairy, eggs, whole grains, potatoes, green beans, kale, and dark chocolate. Zinc deficiency has been found to be associated with hypothyroidism and alopecia (hair loss).

Levels of zinc can affect thyroid function in the following ways:

• TSH or thyroid-stimulating hormone is not created if zinc levels are low
• Low levels of thyroid hormones T4 and T3 when zinc levels are low
• Converts T4 into functional T3

If zinc levels are low or missing,

• T3 cannot be made
• Increased levels of autoimmunity, high amounts of anti-thyroid antibodies when levels of zinc are low
• Zinc regulates gut epithelial walls and modifies the gut microbiome in humans. Deficiency of zinc can also alter your gut bacteria, cause imbalances, and change the diversity.

Iron

Iron is a mineral crucial to hemoglobin, a protein needed to transport oxygen in the blood. It also plays an important role in energy production, growth, development, and synthesis of hormones. Deficiency of iron can cause anemia and the development of hypothyroidism. Iron is crucial to the production of red blood cells and thyroid-stimulating hormone (TSH). Gut microbiota plays a role in iron absorption and research shows that gut bacteria actively compete with the human body for iron.

How to Improve Gut Microbiota

Your food should be diverse – a healthy gut microbiota is a diverse one.
Plant-based foods mostly – these are the best sources of nutrients for microbiota since they are high in fiber, contribute to diverse eating, stimulates the growth of certain bacteria. This includes:

• Chickpeas
• Artichokes
• Raspberries
• Lentils
• Kidney beans
• Pinto beans
• Whole grains
• Green peas
• Apples, Almonds
• Pistachios

Add fermented foods to your diet – these involve yeasts or bacteria that convert the sugars to organic acids or alcohols – many of these foods are rich in lactobacilli and have fewer Enterobacteriaceae (bacteria associated with inflammation and chronic disease):

• Yogurt
• Sauerkraut
• Kombucha
• Tempeh
• Kefir
• Kimchi

Stay away from artificial sweeteners – these can affect your gut microbiota and higher Clostridium and
Enterobacteriaceae.

Pre-biotic foods – these are happy food for your gut! They increase the growth of beneficial microbes in the gut. These are complex carbs and fiber that human cells cannot digest but they are fuel for your gut microbiota. These include:

• Jerusalem artichoke
• Garlic
• Onions
• Leeks
• Asparagus
• Bananas
• Barley
• Dandelion Greens
• Chicory root
• Oats
• Apples
• Konjac root
• Burdock root
• Cocoa
• Flax seeds
• Jicama root

Eat whole grains – These promote the growth of Bifidobacteria, lactobacilli, and Bacteroidetes

Foods rich in polyphenols – these are plant compounds can be digested by gut bacteria. In particular, polyphenols in cocoa increase Bifidobacteria and lactobacilli while decreasing clostridia. Sources include:

• Cocoa
• Dark chocolate
• Red wine
• Green tea
• Onions
• Blueberries
• Broccoli
• Almonds
• Grape skins
• Probiotics – can help improve gut microbiota