Our thyroid is a butterfly-shaped gland that's located at the base of our neck (right under the Adam's apple), and plays a major role in metabolic function throughout the body. It produces hormones that have an influence on our heart rate, body temperature, weight, cholesterol levels, digestive function, and more.
The thyroid produces hormones T3 and T4, which are respectively the active and inactive forms, that play a role in our metabolism, energy, mood, digestive function, etc.
There are some pretty common illnesses and issues associated with the thyroid: things like hypothyroidism, hyperthyroidism, and autoimmune conditions like Hashimoto's thyroiditis, and even Graves disease.
As you might've guessed from the title of this article, our thyroid gland does have an impact on our digestive health, and vice versa.
Let's explore what that relationship looks like.
Gut-associated immunity and leaky gut
One of the major ways that our gut can impact our thyroid function, is through our immune system. Upwards of 70% of our immune system is actually located in the gut, through specific tissue called "gut-associated lymphoid tissue" that lives throughout our intestinal lining.
If there is an imbalance in the microbiome, whether it's dysbiosis where pathogenic species are overgrown, or a lack of beneficial flora to provide us with health benefits, our intestinal lining can become impacted. This can lead to intestinal permeability, otherwise known as "leaky gut."
When leaky gut is present, and we have substances landing in the bloodstream from the gut that aren't supposed to be there, the immune system is activated to respond accordingly. This can play a role in the development of autoimmune thyroid disorders, like Hashimotos.
Stress and the Gut
Stress can impact our thyroid function. How does this relate back to the gut, you ask? The state of our gut can lead to chemical stress on our body — in the form of infection, dysbiosis, overgrowth, inflammation, leaky gut, and serious gastrointestinal disease.
These imbalances can cause stress on the body, leading to the initiation of the stress response, which involves the release of our anti-inflammatory stress hormone: cortisol.
Cortisol (especially chronically heightened levels), might actually impact the body's ability to convert T4 to T3, which can impact our thyroid function.
Constipation and Low Thyroid Function
Low thyroid function can contribute to slowed motility, and constipation. As the thyroid main function is to influence metabolic processes in the body, when this gland becomes underactive, it can slow down processes in the body. Including digestive processes, like motility and peristalsis, which can leave people struggling with constipation.
Constipation can lead to a whole host of further digestive issues. Uncomfortable associated symptoms like bloating, distention and abdominal pain, but also things like hemorrhoids, fissures, and even things like dysbiosis (an imbalance in the gut microbiome), and SIBO.
Key Nutrients and Maldigestion
Another way our gut can impact thyroid function is through maldigestion. Our thyroid needs key nutrients to be able to function optimally, including iodine, selenium, zinc, iron, copper, and more.
If your intestinal lining is compromised (due to an imbalance or overgrowth of pathogenic species, a deficiency of beneficial flora in the gut, excessive use of medications, inflammation, stealth infection, etc.), the body might not be able to properly absorb these nutrients from food, so that the thyroid can use them to make its hormones.
Our gut microbes can also impact iodine, selenium, and iron uptake (the cell's ability to use these nutrients), which can impact their availability to the thyroid.
If you have a known thyroid disorder or suspect that your thyroid may be under-functioning, it could be worthwhile to investigate your gut further, to address anything that could be impacting your thyroid function.
Likewise, if you're struggling with digestive imbalances (especially constipation), and have done everything you can to address your gut specifically — then it could be time to look deeper into your thyroid function.