It may not be an intuitive leap to consider that your digestive system and your thyroid gland are intimately connected, and that the optimal function of one feeds back on the optimal function of another.
Yet, this is exactly the case. The body is an interconnected web, not a conglomeration of isolated linear systems that operate independently of each other. When one strand of the web is pulled, there are reverberations through the entirety.
I consider the digestive system to be the foundation of health – I tend to agree with Hippocrates when he said ?all disease begins in the gut?. The gut is Central Station of the body, interacting and interweaving with all other systems and cells of the body, all day every day. Not just the avenue through which we absorb nutrition, the gut plays roles in defense, the cycling, activation and recycling of hormones; is one of the Big 5 organs of detoxification; houses the immune system; holds the microbiome, the colony of beneficial bacteria that does innumerable functions for us and even impacts our mood.
When it comes to the gut-thyroid connection, it gets interesting.
The Gut in the Rise of Autoimmune Thyroid Disease: One of the most important things to know about thyroid function and the gut is that autoimmune thyroid disease – Hashimoto?s and Graves disease – is strongly driven, created and exacerbated through gastrointestinal dysfunction. There is a thorough explanation here, but in a nutshell autoimmune activity arises from unchecked intestinal irritation leading to increased permeability and a provocation of the immune system. The end game is loss of the immune system?s ability to tolerate food particles, friendly bacteria and your own human cells. Ina process known as molecular mimicry, the switch is flipped and autoimmune thyroid disease manifests. Treatment of autoimmune thyroid disease (and any autoimmune dysfunction) begins in the gut.
Thyroid Hormones Maintain the Integrity of the Small Intestine: The lining of the small intestine is the interface between the immune system and the foods that you eat and everything else that comes through the digestive system. Appropriate integrity is key for a balanced, non-reactive immune system. Both T3 and T4 help maintain the integrity of the lining by ensuring that the desmosomes – the button-like structures that keep the cells that line the small intestine – intact. When desmosomes become unbuttoned, the immune system can become provoked and irritated and set the stage for leaky gut and autoimmunity.
Thyroid Hormones Help Develop the Immune System: The lion?s share of the immune system is found within the digestive system, about two thirds to three quarters of it. Primarily is is found in specialized tissue called GALT (gut associated lymphoid tissue) and MALT (mucosa associated lymphoid tissue). Two hormones – TSH (thyroid stimulating hormone) and TRH (thyrotropin releasing hormone) help with the building up and fortification of excellent immune function. The levels for great function are on a bell curve – you want neither too much nor too little, but just right amounts. This is partly why those with abnormal numbers of TSH can have immune perturbations.
Thyroid Hormones Help Balance the Immune System: There are many, many different types of immune cells that have a variety of different functions in the body. One in particular, called an IEL (intraepithelial lymphocyte) is one that is on a rather short, reactive leash. When activated, they rapidly create inflammation in the gut. Inflammation which if left unchecked increases the permeability of the small intestine and thus flirts with the development of autoimmune disease. T4 helps blunt IEL activation, which confers an overall anti-inflammatory effect on the gut and immune system.
The Microbiome Helps with Thyroid Hormone Conversion: There are 2 main thyroid hormones, T3 and T4, both of which have metabolic activity and function. Thyroid hormones help set the pace for your metabolism and the rate at which you burn fuel for specific activities. Those with low thyroid hormone burn much less fuel. T3 is much more metabolically active than T4, has a much shorter half-life than T4 and is found at much lower levels in the body than T4. It also has to be converted from T4 to do its thing, continuously. This conversion happens at multiple sites in the body. The microbiome – the hundred-trillion cell strong colony of beneficial bacteria that resides in your gut – converts a whopping 20% of thyroid hormone into active form.
Dysbiosis and Thyroid Function: Our healthy, good bacteria do a lot of converting of thyroid hormone into the active form, and imbalance in the microbiome slows it down. An imbalance in the ratio of good bacteria to bad or less-than-good bacteria, frank infection with pathogenic bacteria, yeast or parasites, small intestinal bacterial overgrowth (SIBO) are all forms of dysbiosis and can slow down conversion big-time. Many people with dysbiosis and dysbiotic conditions, including IBS, IBD, Celiac Disease and SIBO have low thyroid symptoms, but their lab numbers tend to look ?perfect?. This is a direct consequences of reduced functional power of the microbiome.
To add insult to injury, a dysbiotic microbiome pumps out a lot of LPS. LPS (lipopolysaccharides) are compounds found within the walls of bacterial bad guys. As these guys die and replace themselves, LPS is released. LPS has been shown to decrease thyroid function by impairing thyroid hormone receptor sites. LPS is also provocative to the immune system and stimulates the release of inflammatory compounds and immune cells that are responsible for autoimmune activity.
Inflammation Blunts Thyroid Hormone Activity: Increased inflammation, from elevated LPS and dysbiosis in general, when left unchecked over time, increases cortisol. High levels of cortisol, over time, increase TSH and depress levels of T3, active thyroid hormone.
Constipation and Thyroid Function: The large intestine is one of the Big 5 organs of detoxification, along with the skin, lungs, kidneys and liver. The major avenue through which the hormone estrogen is cleared from the body is through the large intestine – you poop it out. When you are constipated, you don?t poop out as much estrogen. Your hormonal clearance is compromised, which leads to increased hormones circulating in your blood. Estrogen elevates a protein called thyroid binding globulin (TBG). TBG grabs up thyroid hormone, rendering it useless to the body. Not what you want!
Constipation and slow transit time promote dysbiosis, which blunts thyroid hormone conversion and leads to less active thyroid hormone being produced and lower thyroid function. Lower thyroid function in turn slows down bile flow, and ironically it is bile that is used by the body to bind estrogen before it is sent to the large intestine to be pooped out.
The see-saw of gut and thyroid function and dysfunction can be optimized and healed through taking care of the many facets of the gut and by supporting thyroid function. In no place is this more powerful than in autoimmune thyroid disease, which can be greatly helped and mitigated through taking a strategic approach to restoring the health and process of the gastrointestinal tract.