Modifying the diet to promote a healthy gut may help relieve symptoms of thyroid dysfunction. The gut microbiota digests our food and keeps our cells supplied with important micronutrients such as selenium, zinc, and iron. Each of these are particularly important to healthy thyroid function. Probiotics can promote diversity and balance of gut microbiota, ensuring we get enough of these nutrients.
Thyroid hormone synthesis is a very complex process.
Several micronutrients like selenium, zinc, and iron are essential to this process.
Prebiotics and probiotics are important to keep the gut microbiota balanced.
Probiotics may also help stabilize thyroid hormone production.
Certain mineral supplements may also help with thyroid hormone synthesis.
What is the gut microbiota?
The microbiome is the collection of trillions of bacteria, fungi, and viruses (and all of their genes) that coexist with us, on and in our bodies. These healthy commensal microbes also live on our skin where they help break down lipids which keep our skin moist. This prevents the skin from cracking and stops pathogens from getting into our blood. Helpful microbes also live in our mouths and in the urogenital tract.
The trillions of microbes living in our gut are an organ system as important as any other organ. These microbes (the microbiota) help break down food, but they also compete for resources so that it is harder for invading, disease-causing pathogens to multiply and thrive.
The gut microbiota is determined partly by genetics, early environmental exposures (such as breastfeeding), and our diet and medication. The microbiota is critically important to digestion, but it also interacts with the immune system as well. This is the connection that influences the development and management of thyroid dysfunction.
A damaged intestinal barrier
Two types of thyroid dysfunction, Graves’ disease (over-active thyroid) and Hashimoto’s thyroiditis (under-active thyroid) are the most common autoimmune thyroid diseases (AITD). They are often accompanied by other intestinal ailments such as Celiac Disease and Non-celiac wheat sensitivity.
A damaged intestinal barrier is more leaky, allowing immune-stimulating antigens to pass out of the intestinal tract more easily. When the immune system is over-stimulated, it can generate the production of antibodies which attack other organs, such as the thyroid.
People with thyroid dysfunction may have an altered gut microbiota. A recent study found that the microbiota was just as abundant and diverse in people with thyroid dysfunction compared to those with a healthy thyroid, but the particular makeup of the microbiota was different.
More carcinogenic and inflammatory bacterial strains may explain the onset of Graves’ disease and Hashimoto’s thyroiditis, but this insight might also point the way forward to treating the two conditions.
The composition of gut microbes can influence mineral absorption
The microbiota in the gut help break down food into important nutrients. The thyroid needs iodine, selenium, zinc and iron for proper functioning. Two bacteria (Lactobacillaceae and Bifidobacterium spp.) have a direct influence on iron, selenium and zinc.
People affected by Graves’ disease and Hashimoto’s thyroiditis have fewer of these two bacteria, suggesting a possible avenue for modifying the gut bacteria composition to improve mineral uptake for the thyroid.
To reverse these mineral deficiencies, it may be helpful to supplement the diet with probiotics. These “good” microbes are the actual bugs which reach your colon alive and join the microbiota already in residence.
The two probiotics mentioned earlier, Lactobacillaceae and Bifidobacterium spp, are the most studied groups of bacteria. They are often found in yogurt, kefir, fermented products. Kombucha is also packed with probiotics.
Are prebiotics the same as probiotics?
No, they are not the same. “Prebiotics” are not living microorganisms but rather the foods which the probiotics need to survive. Prebiotics include carbohydrates and fibers.
Carbohydrate prebiotics include cereals and whole grains, nuts, and seeds.
The soluble fibers include oats, barley, and apples. These foods dissolve in water and are highly fermentable by the gut microbiota.
Other fibers, called inulin-type fructans, are found in agave, artichokes, asparagus, bananas, chicory root, garlic, onions, leeks and wheat. The research on these inulins is limited in humans, but rodent models suggest that they can help reduce body weight, cholesterol, and blood glucose.
A mutually symbiotic relationship
The prebiotics feed the microbiota, which, in turn help digest complex plant products which we lack the enzymes to break down. However, our ability to digest these foods depends on having the right balance of gut microbiota.
By eating a well-balanced diet enriched with whole foods containing prebiotics and probiotics, we promote good thyroid hormone levels.
Most of the research on the connection between diet and thyroid hormone synthesis has been done in animal models. Obviously, animal models are poor proxies for humans but this is where exploratory research starts. In two separate studies of broiler chickens, levels of T3 and T4 were increased after probiotic supplementation.
For those with Hashimoto’s thyroiditis, another study showed that probiotics can help stabilize thyroid hormone levels.
In this experiment, the group which received probiotic supplementation with Lactobacillaceae and Bifidobacterium spp. needed less adjustment for T4 levels than the control group. The inference from this finding is that modifying the microbiota stabilizes thyroid function by increasing levothyroxine availability.
Stable thyroid hormone levels depend on selenium, zinc, and iron
The probiotics may lower serum (blood) hormone fluctuations by gathering up the trace micronutrients needed by the thyroid: selenium, zinc and copper.
Selenium in particular is needed to help manage the complex and volatile process of thyroid hormone synthesis.
During thyroid hormone production, a series of chemical reactions occur. One of the byproducts is hydrogen peroxide (H2O2), a powerful germ killer often found in first-aid kits. If too much hydrogen peroxide accumulates during thyroid hormone synthesis, though, it can directly damage the tissues of the thyroid gland and cause dysfunction.
The two antioxidant enzymes that help the thyroid protect itself are dependent on selenium to convert hydrogen peroxide (H2O2) to water (H2O).
The thyroid gland is the largest reservoir of selenium in the body. Given the importance of selenium to the process of thyroid hormone synthesis, it may be helpful to measure selenium levels and talk about supplementation with your health care professional. The recommended daily intake is 55 mcg for adults. Natural sources are Brazil nuts, seafood, and organic meats.
Zinc is also essential for proper thyroid function. A zinc deficiency can affect the translation of thyroid genes and the conversion of T4 to T3. The recommended daily intake is between 8 and 13 mg, depending on age and sex. Excellent high-zinc foods are oysters, meat, fish, poultry, crab and lobsters, beans, nuts, whole grains, eggs, and dairy products.
Iron deficiency is a common problem for women of childbearing age. Low iron levels impair thyroid hormone synthesis, storage, and secretion. Important thyroid enzymes such as thyroid iodine peroxidase (TPO) depend on iron to synthesize thyroid hormones. The recommended daily intake of iron is 8 to 27 mg, depending on age and sex. Dietary sources are lean meats, seafood, poultry, fortified breakfast cereals and bread, white beans, lentils, spinach, kidney beans, peas, nuts, and raisins.
Vitamin D helps regulate the immune system
The hormone vitamin D is either ingested in the diet or synthesized in the skin during sun exposure. Most people are low in vitamin D during the winter and would benefit from supplementation. This important hormone plays a role in modulating the immune response, and studies have shown low vitamin D levels in people with hypothyroidism.
However, given that many people are low in vitamin D, it is uncertain whether the deficiency contributes to the development of hypothyroidism or is simply a coincidental finding. Given the ease of supplementing with vitamin D, this may be one way to help regulate the immune system and buffer against the development of autoimmunity.
A good diet feeds our microbiota
Busy people often eat rather robotically on the go, or while working. However, learning more about how the micronutrients in our diet can fortify us at a cellular level and may make going to the market a bit more meaningful.
Our bodies are host to trillions of microscopic creatures which also need to be fed properly in order to keep our cellular supply chains moving.
For those who have already been diagnosed with a thyroid condition, it is important to talk to your doctor before starting a serious supplement regimen so that you can monitor thyroid hormone levels as appropriate.
For those with normal thyroid hormone levels but typical symptoms of thyroid dysfunction, it may be worth modifying your diet a bit. Pay attention to your digestive symptoms as you seek out more pre-and probiotics. Animal models suggest that shifting your diet toward healthy pre- and probiotics can have an immediate effect within a day or two.
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- Nutrients. Thyroid-Gut-Axis: How Does the Microbiota Influence Thyroid Function?
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- National Center for Complementary and Integrative Health. Probiotics: What You Need To Know.
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- Poultry Science. Alleviation of cyclic heat stress in broilers by dietary supplementation of mannan-oligosaccharide and lactobacillus-based probiotic: Dynamics of cortisol, thyroid hormones, cholesterol, C-reactive protein, and humoral immunity.
- Bulgarian Journal of Agricultural Science. Effect of probiotics and avotan on the level of thyroid hormones in the blood plasma of broiler chickens.
- National Institutes of Health. Selenium.
- National Institutes of Health. Zinc.
- National Institutes of Health. Iron.