The surprisingly common health issue that can affect your gut microbiome

When it comes to dealing with gut health issues, it can feel like a really confusing puzzle that comes with a million pieces (like examining your diet, stress levels, and exercise habits). One factor impacting the gut that may not have crossed your mind yet? Your thyroid.

In case you haven’t heard, your thyroid is a pretty important gland that helps regulate your metabolism, heart and digestive function, and muscle control. It can also play a role with mood, making its functioning crucial for mental as well as physical health.

Thyroid issues are also super common; per the American Thyroid Association, an estimated 12 percent of the U.S. population will develop some kind of thyroid disorder during their lives, and 20 million Americans have a type of thyroid disease. Yet roughly 60 percent of people with thyroid issues don’t even know they have a problem. Yasmin Akhunji, MD, an Arizona-based endocrinologist with Paloma Health, says that thyroid disorder symptoms can overlap with a lot of other health problems, making them easy to overlook.

Oftentimes those overlapping symptoms include those that affect your gut. “Thyroid hormones have effects on virtually all bodily tissues,” said Will Bulsiewicz, MD, a gastroenterologist and author of Fiber Fueled. “Make no mistake, changes in thyroid function will certainly have an effect on our gut.”

What you need to know about the thyroid-gut connection

Dr. Akhunji says the thyroid affects the gut mainly because of the hormones that the thyroid produces directly impact how your digestive system functions. So when the hormones are not produced at the right levels, it means bad news for your gut.

For example, hypothyroidism, one of the most common thyroid issues, occurs when the thyroid isn’t producing enough hormones. Given that thyroid hormones impact digestive function, it should then be no surprise that slow motility (aka constipation) is one of the early warning signs of thyroid problems (specifically, hypothyroidism).

“Without enough thyroid hormones, many of the body’s functions slow down,” says Dr. Akhunji. “In a normal digestive tract, the muscles lining the small intestine and large intestine contract, which helps to move digested food down the intestines. In the case of hypothyroidism, the contraction is slowed down. In addition to the slow digestive process, the elimination of stool also slows down.”

A person could also have hyperthyroidism, which is when the thyroid is overactive or produces too much hormone. This can also cause digestive issues, says Dr. Bulsiewicz. “Excessive thyroid function, or hyperthyroid, can be associated with diarrhea, hyper-defecation, and malabsorption. It can also include trouble swallowing due to an enlarged thyroid gland and abnormal liver function tests,” he says.

In case it wasn’t already abundantly clear, here’s why the health of your gut is so important: 

Thyroid issues, because of how they can impact digestion, can also be hugely disrupting to your gut microbiome—the community of bacteria that lives inside your gut. “Alterations in gut motility have been associated with overgrowth of bacteria in the small intestine, causing gas, bloating, and abdominal discomfort,” Dr. Bulsiewicz says. “Hypothyroidism causes more than just constipation—it can actually disrupt the gut microbiome and lead to SIBO.”

The gut is also responsible for the metabolism of thyroid hormone, which relies on a healthy microbiome. “It turns out that about 20 percent of the enzyme that converts thyroid hormone into its active form comes from our gut microbes,” says Dr. Bulsiewicz.

This means that poor gut health can then also impact thyroid health. Again, your gut is one of the places where your body converts T4 hormone (one of the two types of thyroid hormones) into the “active” form of thyroid hormone known as T3, says Dr. Akhunji. “So if our gut health is off for whatever reason—like IBS, celiac disease, or chronic constipation for example—any of those things can make you not get as much of the active conversion of T4 to T3 as you need.”

The result can be a perpetual cycle as one issue exacerbates another, and vice-versa. “The gut-thyroid connection can be a vicious circle as hypothyroidism causes poor digestive health, and poor digestive health may cause the treatment of hypothyroidism to not be as effective,” says Dr. Akhunji.

What to do if you’re concerned about your thyroid and gut health

One very important thing that everyone reading this should keep in mind: just because you have a gut issue like SIBO doesn’t automatically mean you also have a thyroid issue.

However, if you’re struggling with digestive symptoms, or symptoms of thyroid disorders, be sure to ask your doctor to run a routine thyroid test (as well as other tests) to get to the bottom of the issue. You can also purchase thyroid hormone tests yourself, such as Paloma Health Complete Thyroid Blood Test Kit ($99) or EverlyWell Thyroid Test ($159) to get some preliminary insights. Of course, those should then be followed up with a doctor’s visit to help you analyze the results and come up with a treatment plan (if necessary) that’s right for you and your unique needs.

“We are finding that the gut microbiome affects every aspect of our life,” says Dr. Bulsiewicz. And that, apparently, includes your thyroid health—along with practically everything else. 

One thing that can be helpful for thyroid issues: selenium. And these are some of the most surprising things we learned about gut health this past year.