What Causes Thyroid Disease?

Your thyroid—a small butterfly-shaped gland in your neck—is responsible for many of your body’s vital functions. The thyroid produces triiodothyronine (T-3) and thyroxine (T-4), which are two hormones that regulate your metabolism, heart rate, body temperature, mood, and weight.

Thyroid disease occurs when the thyroid produces too little or too much thyroid hormone. The two most common types of thyroid disease are hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid). 

The causes and risk factors of hypothyroidism and hyperthyroidism can vary. However, certain diseases, pregnancy, and other lifestyle factors can increase your risk of developing symptoms. 

Hashimoto’s Disease

Hashimoto’s disease is an autoimmune condition that causes hypothyroidism. The cause of Hashimoto’s disease—like most other autoimmune conditions—is unknown. But, researchers do know that having the condition increases your risk of developing an underactive thyroid.

When you have Hashimoto’s disease, your immune system makes antibodies that attack and damage the thyroid by mistake. As a result, your thyroid loses its ability to make enough hormone that your body needs. This can decrease your metabolism and slow down other vital functions of your body, leading to symptoms like fatigue, a slow heart rate, and weight gain. 

Graves’ Disease

Graves’ disease is also an autoimmune condition, but the most cause of hyperthyroidism. When your immune system is functioning properly, your body is able to fight infection. However, Graves’ disease causes a dysfunction in your immune system, causing your thyroid gland to produce too much hormone.

As a result of this attack, the thyroid produces more thyroid hormones than the body needs, which causes several body functions to speed up. If you have Graves’ disease or hyperthyroidism, you may notice symptoms such as weight loss, frequent bowel movements, shaky hands, a rapid heartbeat, and sweating due to difficulty tolerating heat. 

Thyroiditis

Thyroiditis is an umbrella term for the inflammation of the thyroid. There are several types of thyroiditis that may cause your thyroid to become inflamed.

The most common types of thyroiditis are a result of autoimmune diseases like Hashimoto’s disease and Graves’ disease. However, a variety of viral, fungal, and bacterial infections, radiation treatment in your neck, pregnancy, trauma, and taking certain medications can also trigger thyroid inflammation.

Thyrotoxicosis

Thyrotoxicosis occurs when your thyroid produces too much hormone throughout your body and in your bloodstream. This may sound similar to hyperthyroidism, but there is a subtle difference: hyperthyroidism occurs due to an overactive thyroid, while thyrotoxicosis happens when you have too much thyroid hormone, even if it’s not directly coming from your thyroid gland. 

However, symptoms of thyrotoxicosis can mimic symptoms of hyperthyroidism, including weight loss, irregular heartbeat, and diarrhea. Thyrotoxicosis is not very common—occurring in 2% of people assigned female at birth and 0.2% of people assigned male at birth. But, in people who do have thyrotoxicosis, causes may include taking too much thyroid medication, goiter (an enlarged thyroid), and thyroiditis.

Thyroid Storm

Thyroid storm is a rare, but sudden onset of hyperthyroidism that can be life-threatening. The condition occurs when your thyroid gland produces extremely high levels of thyroid hormone. 

Generally, people who experience thyroid storm have a pre-existing diagnosis of hyperthyroidism and a combination of other risk factors. These risk factors include:

• Suddenly stopping thyroid medication
• Having a lung or throat infection
• Getting thyroid or neck surgery 
• Experiencing severe conditions such as heart failure, diabetic ketoacidosis, or COVID-19
• Giving birth
• Going through severe emotional stress 

Pregnancy and Postpartum

The thyroid plays an important role in the development of the fetus during pregnancy. If you become pregnant and have a thyroid condition (or are at risk for thyroid disease), it’s important to talk to your healthcare provider to figure out how to keep your thyroid levels stable during pregnancy. 

Keep in mind: you don’t need to have a thyroid condition for pregnancy to affect your thyroid health. When you’re pregnant, your body experiences several changes which can lead to hyperthyroidism. Pregnant people who experience hyperemesis gravidarum (excessive nausea and vomiting) or molar pregnancy (noncancerous tumor in the uterus) may have a higher risk of developing hyperthyroidism.

Some people may experience thyroid-related symptoms postpartum (after pregnancy). Postpartum thyroiditis—thyroid inflammation caused by pregnancy—may lead to temporary symptoms of hypothyroidism or hyperthyroidism.

Congenital Hypothyroidism

In rare cases, you can develop a thyroid condition at birth. Typically, about 1 in every 2000 to 4000 babies are born with congenital (or, present at birth) hypothyroidism. 

The condition occurs when a baby’s thyroid gland doesn’t fully develop during pregnancy or is located in the wrong place when they are born. Usually, congenital hypothyroidism occurs randomly, meaning the condition is not inherited.

Don’t worry: babies who receive treatment for hypothyroidism soon after birth generally respond very well and live healthy lives. 

Is Thyroid Disease Hereditary? 

Researchers are still investigating the exact likelihood of someone inheriting thyroid disease from a parent. 

Here’s what they know so far: about 20% of congenital hypothyroidism cases are caused by genetic factors and people who have a family history of thyroid disease are 15 times more likely to develop a thyroid condition than people without.

However, like many other conditions, genetics don’t guarantee that you will develop a thyroid condition. Scientists agree that your genes increase your risk of getting thyroid disease, but environmental factors can also trigger the onset of symptoms. 

Who Gets Thyroid Disease?

Some people are more likely to develop thyroid disease than others. Demographic risk factors of thyroid disease include: 

• Sex: People assigned female at birth have a higher risk of developing both hypothyroidism and hyperthyroidism.
• Age: People over the age of 60 are more likely to experience a thyroid condition.
• Ethnicity: There is limited data on how ethnicity affects the likelihood of developing thyroid disease. However, white people appear to experience hyperthyroidism more than other ethnicities.

Environmental Risk Factors

In addition to having certain health conditions and infections, some environmental and lifestyle can increase your risk of developing thyroid disease. These factors include:

• Thyroid surgery: Any surgery that removes a part of the thyroid gland increases the risk of getting hypothyroidism.
• Smoking: Smoking cigarettes raises your likelihood of developing Graves’ disease and hyperthyroidism. 
• Radiation exposure: People who receive radiation treatment on their thyroid, neck, or chest may be more likely to develop hypothyroidism.
• Foods with too much iodine: People who eat large amounts of food containing iodine (e.g., kelp, shellfish, iodized salts) are more at risk for hyperthyroidism and thyroiditis. Examples of high-iodine foods include kelp, shellfish, and iodized salts.

A Quick Review 

Thyroid disease is a common condition that occurs when the thyroid either produces too much hormone (hyperthyroidism) or not enough hormone (hypothyroidism). The exact cause of your condition will depend on the type of thyroid disease you have. 

Generally, an underlying autoimmune condition can cause your immune system to attack the hormone production in your thyroid gland by mistake—leading to symptoms of either hypothyroidism or hyperthyroidism. However, other infections, being pregnant, having thyroid surgery, and certain lifestyle factors can increase your risk of developing a thyroid condition. 

If you begin to notice symptoms of a thyroid condition or may be at risk of developing thyroid disease, it’s good practice to visit your healthcare provider for proper testing and diagnosis.