Thyroid Health: Hypothyroidism, Hyperthyroidism and Autoimmunity Linked to the Gut Microbiome

The thyroid gland is a small organ with a big impact. Through its hormones, it regulates our metabolism, influencing energy levels, digestion, weight, mood, and immune system. When it gets out of balance, it can affect many areas of the body—often in nonspecific ways and not always easy to attribute.

Our gut, and especially our gut microbiome (also known as gut flora), plays a crucial role in our health. You can learn more about this connection in this blog article: Thyroid & Gut Health: The Underrated Connection You Should Know About

Thyroid disorders are widespread. The most common are hypothyroidism and hyperthyroidism, as well as the autoimmune diseases Hashimoto’s thyroiditis and Graves’ disease. In this article, you will get an easy-to-understand overview of how these conditions differ, which symptoms commonly occur, and why the gut microbiome may be involved in their development.

What happens in the case of an underactive or overactive thyroid?

When thyroid hormone production becomes unbalanced, many bodily functions run either too fast or too slowly. Causes can include autoimmune diseases, but also, for example, iodine deficiency or excess, certain medications, congenital thyroid malformation, or inflammation after viral infections (1).

Hypothyroidism (underactive thyroid)

➡️ The thyroid gland produces too few hormones.
Typical signs include:

• fatigue and lack of energy
• feeling cold
• weight gain
• constipation
• dry, pale skin
• brittle hair

A common cause is the autoimmune disease Hashimoto's thyroiditis.

Overactive thyroid (hyperthyroidism)

➡️ The thyroid gland produces too many hormones.
Possible symptoms include:

• nervousness and inner restlessness
• heart palpitations
• weight loss
• diarrhea
• sweating

A common cause is Graves' disease, which is also an autoimmune condition.

Autoimmune thyroid diseases: Hashimoto's thyroiditis and Graves' disease

Autoimmune diseases develop when the immune system mistakenly attacks the body's own tissues. Instead of fighting pathogens, the immune system targets the body's own tissues, such as the thyroid gland. This can lead to chronic inflammation, dysfunction, and long-term damage.

Furthermore, these diseases often occur together with celiac disease (CD), gluten sensitivity or non-celiac wheat sensitivity and an imbalance in the microbiome (dysbiosis) - highlighting the close connection with gut health (2).

Autoimmune diseases of the thyroid gland often develop gradually and frequently go unnoticed for a long time.

Hashimoto's thyroiditis – when the immune system slows down the thyroid

Hashimoto's thyroiditis is the most common autoimmune thyroid disease, affecting up to 10% of the general population, predominantly women.

What happens in the body?

• The immune system produces antibodies against thyroid tissue (e.g., TPO antibodies).
• The thyroid gland becomes inflamed and is gradually damaged more and more.
• As a result, it can produce fewer and fewer thyroid hormones.

Initially, hormone production may be normal or even elevated (hyperthyroidism). Over time, however, hypothyroidism usually develops. Treatment typically consists of taking thyroid hormones to compensate for the deficiency and minimizing iodine intake (3,4).

Graves' disease – when the immune system stimulates the thyroid gland

Graves' disease is also an autoimmune disease, but it works in exactly the opposite way - it causes the thyroid gland to produce more and more hormones.

What happens in the body?

• The immune system produces stimulatory antibodies (TRAK).
• These antibodies permanently activate the thyroid gland.
• The thyroid gland produces too many hormones - this results in hyperthyroidism.

The disease may occur in episodes and is usually treated with medication, less commonly with radioactive iodine or surgery. In advanced cases, it can lead to thyroid enlargement (goiter) and eye changes such as bulging eyes (exophthalmos) (3,5).

Why the gut microbiome can trigger autoimmune diseases

The reasons why autoimmune diseases develop are not always clear. In addition to genetic predisposition, the gut is increasingly becoming the focus of research.

The intestinal mucosa, a crucial protective barrier, likely plays a significant role in this process: If the intestinal barrier is weakened and more permeable ("leaky gut"), substances from the intestines can enter the bloodstream that don't belong there. These include, for example, bacterial components, toxins, and poorly digested food residues. This constantly alerts the immune system and throws it off balance.

In this constant state of alert, it can happen that the immune system loses its bearings and suddenly attacks the body's own structures – such as components of the thyroid gland (3).

A healthy gut microbiome supports the barrier function of the intestinal lining – among other things, by producing important substances such as short-chain fatty acids (SCFAs). Learn how you can support your microbiome here: 5 steps to a healthy gut microbiome

If you would now like to understand the state of your individual microbiome, whether there are indications of a leaky gut, and whether your gut bacteria are effectively supporting your thyroid, the myBioma microbiome tests may provide valuable insights for you. 

Want to know how to support both your gut and thyroid? You'll find tips in this blog post: Thyroid & Gut Health: The Underestimated Connection You Should Know About

Important note at the end

Understanding how the thyroid, gut, and immune system interact can empower you to better understand your body and take the right steps early on. If you experience persistent symptoms or suspect a thyroid disorder, you should always seek medical advice.

Carina Gurtner BSc, BA

Nutritionist

As a nutritionist and media & communication scientist, Carina uses her expertise to communicate complex health topics in an understandable way. Her aim is to inspire others to lead a conscious, healthy and sustainable lifestyle.

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