The thyroid and immune system have an interactive relationship. This means that thyroid issues can affect the immune system, and immune system issues can affect the thyroid.

Hyperthyroidism often occurs due to an autoimmune disease, but regardless of its cause, it may affect immune function. Researchers know that thyroid function may affect the immune system, but exactly how remains unclear.

Instead, the effects may be more subtle.

Emerging research also suggests that SARS-CoV-2, the virus that causes COVID-19, may affect thyroid function.

Read on to learn about the connection between hyperthyroidism and the immune system.

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The most common cause of hyperthyroidism is Graves’ disease. This is an autoimmune disease, which means that it causes the immune system to attack healthy tissue.

In the case of Graves’ disease, the body attacks tissue in the thyroid, causing an overproduction of thyroid hormone.

Researchers do not know exactly what triggers the immune system to attack the thyroid in Graves’ disease. 2017 evidence suggests immunodeficiency — a weak immune system — may contribute to the development of Graves’ disease.

This means that Graves’ disease may be a sign of, but not necessarily a cause of, a weak immune system.

Additionally, researchers believe that the thyroid and immune system communicate with each other, so an issue with one may cause an issue with the other. 2019 research on rats with hyperthyroidism suggests that dysregulated thyroid hormone may affect the immune system. However, this does not mean the same is true in humans.

Some doctors have observed that people who develop COVID-19 are more likely to experience thyroid disorders. This suggests that viruses or immune system issues could affect the thyroid, again suggesting that thyroid disease could be a sign of an underlying immune system issue.

More research is necessary to understand the precise effects hyperthyroidism has on the immune system.

While some studies suggest the thyroid affects the immune system, others undermine that claim. For example, in a 2017 study that followed a large cohort of women, researchers compared people with thyroid disease to those without thyroid disease.

While the study found a link between hyperthyroidism and an increased risk of death from breast cancer, it did not increase the risk of dying from infections. The study did not show a direct causal link between the two — this means it did not find that having hyperthyroidism caused death from breast cancer.

Environmental factors, including those that affect the immune system, sometimes trigger Graves’ disease.

They include:

Graves’ disease does not directly weaken the immune system. However, a 2017 review highlights research suggesting that it may develop because of immune system weakness. It claims that immunodeficiency may cause Graves’ disease.

A 2019 review highlights that people with Graves’ disease may have higher levels of a type of interleukin, an inflammatory chemical the immune system secretes. They may also have lower levels of certain immune system cells.

Researchers do not yet know the effects these changes may have, but data suggests that Graves’ disease correlates with changes in the immune system.

Hyperthyroidism tends to speed up many functions in the body. As a result, a person may have some or all of the following symptoms:

A person can have mild or no symptoms and still have hyperthyroidism. The only way to definitively diagnose it is to test for thyroid hormone levels in the blood.

Treatment for hyperthyroidism depends on the severity of the person’s symptoms. The primary treatment options include:

  • Symptom medication: Medications such as beta-blockers can control symptoms of hyperthyroidism.
  • Thyroid medication: Anti-thyroid drugs slow the overproduction of thyroid hormone. Some commonly prescribed options include methimazole and carbimazole.
  • Removing the thyroid: If symptoms are severe, doctors may recommend removing the thyroid. This usually means a person will have to take replacement thyroid hormone for the rest of their life.
  • Radioactive iodine: This targets the thyroid gland by damaging or destroying the cells that produce thyroid hormone. Treatment usually involves taking 1 dose only in the form of a small capsule.

The relationship between the thyroid and the immune system is complex, and experts do not fully understand it. People with thyroid disease may have weaker immune systems, but it is not clear that this results from having a thyroid condition.

Ongoing research may help doctors better understand thyroid disease, its impact on the immune system, and the relationship between the thyroid and immune function.