Thyroid conditions are usually talked about in terms of hormones, antibodies, and nutrient deficiencies. The focus is on limiting the overproduction of thyroid hormone or supplementing it if levels are too low. That is still the foundation. However, research is now considering another part of the picture: the gut microbiome.

The gut and thyroid appear to communicate through immune signalling, nutrient absorption, inflammation, and thyroid hormone metabolism. This connection is called the gut-thyroid axis, and it’s one of the most fascinating discoveries of recent years.

What Is the Gut-Thyroid Axis?

The gut-thyroid axis is a two-way relationship between the digestive system, gut bacteria, and thyroid function. Changes in either system can influence and alter how the other organ functions.

There isn’t a single mechanism.

Instead, gut bacteria can regulate nutrients needed for thyroid hormone functions, influence bodily inflammation, and even digest thyroid hormones itself. In contrast, thyroid hormones alter gut motility, gut barrier function, and much more.

This complex connection isn’t fully understood, nor is it always the reason behind every thyroid condition. But it may point to additional ways to support thyroid health alongside standard medical treatment.

Why the Gut May Matter for Hashimoto’s

Hashimoto’s thyroiditis is an autoimmune condition where the immune system attacks the thyroid gland. Autoimmune diseases have long been linked to genetic aspects. But the specific trigger that causes the immune system to turn against the body has remained elusive.

Gut bacteria could provide a potential solution.

Patients with Hashimoto’s have an altered gut microbiome. One 2018 study found that certain bacteria were elevated and others decreased compared to people with normal thyroid function. This suggests the microbiome composition could contribute to Hashimoto’s.

Gut Bacteria and Thyroid Nutrients

Gut bacteria are literally the gatekeepers to the body. The thyroid depends on several nutrients, including iodine, selenium, iron, zinc, and vitamin D, to produce thyroid hormones.

Gut health can influence how well some of these nutrients are absorbed. If levels are unbalanced, it can lead to malabsorption, gut inflammation, and other issues, which indirectly alter thyroid function.

That doesn’t mean everyone needs to start supplementing with specific nutrients. But it could be a beneficial treatment in individuals with gut dysbiosis and thyroid problems.

Can Gut Bacteria Affect Thyroid Hormones?

Thyroid hormones are partly processed by the liver and excreted into bile. Gut bacteria can then metabolise these bile components, allowing a portion to be reabsorbed. That means gut bacteria can directly influence levels of thyroid hormones.

Indirectly, gut bacteria can support bile acid metabolism and inflammation. These two processes are connected to wider hormone and metabolic signalling. In short, it determines how thyroid hormones are processed, recycled, and made available to the body.

Gut Health, Hypothyroidism, and Medication Absorption

People with hypothyroidism (low levels of thyroid hormone) often take levothyroxine. The medication is given orally, so it has to be absorbed via the gut.

This can be a problem if a patient has gut dysbiosis.

Factors like bacterial overgrowth, gut inflammation, or altered motility can reduce absorption, preventing the medication from doing its job. Doctors may need to increase the dose or advise lifestyle changes to support the microbiome.

What Can You Do to Support the Gut-Thyroid Connection?

Treating problems with your gut microbiome isn’t as simple as just taking thyroid hormones. Your gut microbiome needs constant support, reducing stressors, and helping to restore a healthy balance.

Follow these recommendations:

• Build meals around fibre. Include vegetables, fruits, oats, legumes, nuts, seeds, and wholegrains to support a more diverse gut microbiome.

• Check key nutrient levels. Low iron, vitamin D, B12, zinc, selenium, or iodine can affect thyroid health, so testing may be useful if symptoms suggest a deficiency.

• Investigate ongoing gut symptoms. Persistent bloating, diarrhoea, constipation, reflux, or suspected SIBO may need proper assessment.

• Be careful with thyroid supplements. Iodine-heavy products can be risky for some people, especially with autoimmune thyroid disease.

• Take thyroid medication consistently. Follow medical advice around timing, food, coffee, calcium, iron, and other interactions.

Understand Your Gut Health More Clearly

If you have a thyroid condition, it’s sensible to pay attention to your gut. The two are linked, after all. This may involve monitoring gut symptoms, eating a healthy, high-fibre diet, or getting your gut microbiome checked.

The Functional Gut Clinic offers specialist gut testing, including microbiome testing and SIBO breath testing, to help identify digestive factors that may be affecting your wider health. We provide expert analysis, helping you understand the results and develop a personalised plan to support your gut health.

Explore our gut microbiome testing and begin your journey to a healthier gut.

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