You might think of thyroid issues and stomach complications as independent problems. But have you considered the actual close connection between gut health and your thyroid?
It’s not intuitive to consider that your digestive system and your thyroid gland are intimately connected, and that the function of one feeds back on the function of the other. But the thyroid-gut connection runs deeper than you may expect.
Rather than a set of linear, isolated systems acting independently of one another, the body is an interconnected web. When one strand of the web is pulled, reverberations are created throughout the body.
Hippocrates said “all disease begins in the gut.” Indeed, gut health is foundational for the health and well-being of the rest of the body and its systems, including the hormonal system.
Your digestive system is not only the avenue through which you absorb nutrition, the gut: plays roles in the cycling, activation and recycling of hormones; is one of the Big 5 organs of detoxification; houses the immune system and is a key player in defense; holds the microbiome, the colony of beneficial bacteria that does innumerable functions for us; and even impacts our mood.
When discussing the gut-thyroid connection, things get interesting.
The Rise of Autoimmune Thyroid Disease and the Gut
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. 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. In a process known as molecular mimicry, the switch is flipped—your immune system makes antibodies against your thyroid cells and autoimmune thyroid disease manifests. Treatment of autoimmune thyroid disease (and any autoimmune dysfunction) begins in the gut.
Thyroid Hormones Protect the Small Intestine
The lining of the small intestine is the interface between the immune system, 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. Thyroid hormones 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 inappropriately provoked and set the stage for leaky gut and autoimmunity.
Thyroid Hormones Hone and Mature the Immune System
The vast majority of the immune system is found within the digestive system—about two thirds to three quarters of it. It is primarily 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 issues.
Thyroid Hormones Help Keep the Immune System Balanced
There are many different types of immune cells in the body, all of which have a variety of different functions and jobs. One in particular, called an IEL (intraepithelial lymphocyte), is one that is on a rather short, reactive leash. When activated, IELs rapidly create inflammation in the gut. Inflammation, left unchecked, increases the permeability of the small intestine and can thus contribute to the development of autoimmune disease. T4 helps blunt IEL activation, which confers an overall anti-inflammatory effect on the gut and immune system.
Thyroid Hormone Activation and Your Gut Flora
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 hormones burn much less fuel at a slower pace, often resulting in weight gain. T3 is more metabolically active than T4, has a shorter half-life than T4, and is found at 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 action of your microbiome—the one-trillion-to-hundred-trillion-cell strong colony of beneficial bacteria that resides in your gut—converts a whopping 20% of thyroid hormone into active form.
Thyroid Function and Dysbiosis
Since your healthy, good bacteria do a lot of converting of thyroid hormone into its active form, an imbalance in the microbiome can slow 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, and 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 consequence of the reduced functional power of the microbiome.
Even more disconcerting, a dysbiotic microbiome releases 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 blunt thyroid function by impairing thyroid hormone receptor sites. LPS is also provocative to the immune system and stimulates the release of the inflammatory molecules and immune cells that are responsible for autoimmune activity.
Thyroid Hormone Activity is Depressed from Inflammation
Increased inflammation, from elevated LPS and dysbiosis in general, over time and unmanaged, will increase cortisol. High levels of cortisol, over time, increase TSH and depress levels of T3, the active thyroid hormone. This confers a pseudo hypothyroid state on the body. Folks who need ever-increasing amounts of medication or who do not respond well to medication would be prudent to have their salivary cortisol checked throughout the day (an adrenal stress index/ASI test).
Thyroid Function and Constipation
The large intestine is one of the Big Five organs of detoxification, in addition to the skin, lungs, kidneys and liver. The hormone estrogen is cleared from the body 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 reduces thyroid hormone conversion and leads to less active thyroid hormone being produced, as well as lower thyroid function. Lower thyroid function, in turn, slows down bile flow; 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. Constipation and thyroid dysfunction often go hand in hand in a self-perpetuating cycle that impacts many other organs and systems of your body.
The push and pull of thyroid and digestive system function and dysfunction can be greatly improved through taking care of the many aspects that promote gut health and supporting thyroid function. Those with thyroid disease or symptoms would do well to embrace gut health and restoration, for this is a pivotal step towards feeling better.
(Read This Next: 7 Signs Your Gut Bacteria Are Out of Whack)