What Causes Hashimoto’s Disease?

Hashimoto’s disease is an autoimmune disorder that occurs when your immune system attacks your thyroid, causing it to produce too little thyroid hormone. It is sometimes referred to as chronic autoimmune thyroiditis or Hashimoto’s thyroiditis.

The thyroid gland is a butterfly-shaped organ in your neck that produces hormones used by your body to control your metabolism (the process your body uses to burn energy).

The immune system is meant to protect your organs, but in Hashimoto’s disease, the immune system attacks the thyroid gland, causing permanent damage that can lower hormone production.

Many people with Hashimoto’s disease lose the majority of their thyroid gland to scarring and hardening.

Hashimoto’s disease is one of a few thyroid autoimmune disorders. Graves’ disease is another common thyroid autoimmune condition that causes the thyroid to produce too much hormone.

People with Hashimoto’s disease have a similar life expectancy to the general population, and highly-effective medications can treat the condition. But what causes Hashimoto’s, and are you at increased risk?

What causes Hashimoto’s disease?

The exact cause of Hashimoto’s disease is poorly understood. Most people with the condition develop thyroid antigens which cause the body to attack the thyroid. Up to 15%¹ of people never develop these antibodies, despite having clinical symptoms.

There is no link between the level of thyroid antigens in your blood and the severity of the disease. However, a positive thyroid antigen blood test is a common first sign of Hashimoto’s and often precedes the disease’s clinical course.

Researchers think there’s a link between Hashimoto’s and other autoimmune disorders,² including pernicious anemia, celiac disease, Graves’ disease, rheumatoid arthritis, and multiple sclerosis.

Several other factors may put you at increased risk of developing Hashimoto’s. Research suggests that around 80%¹ of Hashimoto’s cases are caused by genetic factors, with an additional 20%¹ caused by environmental factors.

Genetic risk factors for Hashimoto’s disease

Many studies have taken place to understand the link between Hashimoto’s disease and genetics, including:

Population-based studies

Researchers look at how diseases are dispersed throughout populations.

Hashimoto’s disease is ten times¹ more common in women than in men. Most population studies also suggest white people are more likely to get Hashimoto’s disease,³ and most people who develop thyroid disorders are aged 30–50.⁴

Family studies

These studies look at families of people with a disease to see if close relatives also develop it. The condition is thought to be genetic if they do.

There is up to a 50%⁵ chance your siblings or parents will also have Hashimoto’s if you have it.

Twin studies

One of the most reliable ways to tell if a disease or disorder is genetic is to study identical twins (or monozygotic twins).

If your twin has it, you have a 50–70%⁶ chance of developing Hashimoto’s disease.

Genetic studies

Gene clusters in DNA are studied to work out if any relevant genes are shared between people with diseases. Hashimoto’s disease shares common genes, suggesting the condition is genetic.

These studies all suggest Hashimoto’s disease is genetic, so you are at increased risk if a family member has it. However, most people with Hashimoto’s genetics never develop the disease.

Genetic risk factors for Hashimoto’s include:

• Being over 30

• Being female

• Having a close family member with Hashimoto’s disease

• Having other autoimmune conditions

Environmental risk factors for Hashimoto’s disease

Researchers believe almost everyone with Hashimoto’s has a genetic predisposition to the disease, but some environmental factors can trigger it.

Environmental triggers thought to contribute to the development of Hashimoto’s disease include:

Iodine intake

Consuming too much iodine increases your chance of developing Hashimoto’s disease.

Salt is iodized in most countries to prevent iodine deficiencies, but taking dietary iodine while also consuming significant amounts of table salt as part of your regular diet can lead to overconsumption.

Diseases

Certain viruses may cause Hashimoto’s disease, such as mumps, Epstein-Barr,⁷ and possibly even COVID-19.⁸

Toxins

Several heavy metals and carcinogenic chemicals have been shown to increase your risk of developing Hashimoto’s disease.

Vitamin D

Many people with Hashimoto’s disease are deficient in vitamin D. Researchers⁹ believe too little vitamin D may trigger Hashimoto’s, but a link between the two hasn’t yet been proven.

Anti-cancer drugs

Cytotoxic chemotherapy treatments (e.g., R-CHOP, ICE, DHAP, and FOLFOX) used to treat a variety of cancers can damage the thyroid and increase your risk of Hashimoto’s disease.

High-dose chemotherapy combined with stem cell transplants and some newer immunotherapy drugs¹⁰ (such as tyrosine kinase inhibitors, lenalidomide, and alemtuzumab) can also increase your risk of developing Hashimoto’s disease.

Does smoking increase your risk of Hashimoto’s disease?

The link between smoking, alcohol, stress, or recreational drug use and Hashimoto’s disease isn’t clear.

Some population-based studies (2007¹¹ and 2017¹²) suggest smoking may lower your risk of developing Hashimoto’s disease, but it significantly increases your risk of developing Graves’ disease.

With that said, smoking, drinking alcohol, stress, and recreational drug use all negatively affect your health, so it’s best to avoid them.

How is Hashimoto’s disease diagnosed?

Most people with Hashimoto’s disease have symptoms such as fatigue, temperature sensitivity, and difficulty concentrating.

Your doctor may order thyroid function tests if they suspect your thyroid gland is causing these symptoms.

Tests to diagnose Hashimoto’s disease can assess the following hormone levels:

Thyroid-stimulating hormone (TSH) levels

The pituitary gland in your brain produces thyroid-stimulating hormone, which tells your thyroid to produce its own hormones. Abnormal TSH levels might suggest you have an underactive thyroid.

T4 or T3 levels

T3 and T4 are thyroid hormones that help almost every cell in your body to function. Abnormal T3 or T4 levels suggest you might have a thyroid disorder like Hashimoto’s disease.

Your doctor can order an antibody test to determine what’s causing your abnormal hormone levels.

Hashimoto’s disease is usually diagnosed through antibody blood tests which look for thyroid antigens in your blood. If you have these antigens, you may be at increased risk of developing Hashimoto’s, but you might not be symptomatic.

How is Hashimoto’s disease treated?

Most Hashimoto’s disease cases are treated with synthetic thyroid hormones. These synthetic hormones (also called levothyroxine sodium) mimic the T4 hormone your thyroid would normally produce naturally. Common brand names include Synthroid, Unithroid, Levoxyl Tirosint, and Levo-T.

Your doctor will prescribe the correct dosage for maintaining optimal hormone levels. Most people take the medication once per day, but dosages vary based on age, height, weight, and gender.

People used to take thyroid extract from farm animals like cows and pigs, but most doctors now prescribe synthetic hormones. Modern synthetic hormones are carefully created to mimic human hormone levels, which are different from animal hormone levels.

While you can still purchase powdered animal thyroid extract, its use has decreased since modern synthetic hormone medications were introduced.

When to talk to your doctor

Contact your doctor if you suspect you have Hashimoto’s disease.

Your doctor will start by taking a complete medical history and performing a physical examination. Hashimoto’s disease symptoms can mimic several other illnesses, so your doctor will also test you for other illnesses to rule them out.

You might not be diagnosed with a thyroid disorder immediately; instead, your doctor may carry out several tests and prescribe different treatments before your thyroid issues are finally identified.

They may refer you to an endocrinologist (a hormone specialist) to help you get a diagnosis.

The lowdown

Hashimoto’s disease is an autoimmune disorder where your immune system mistakenly attacks your thyroid, causing its hormone production to slow down.

Genetics and environmental factors can increase your risk of developing Hashimoto’s disease. Genetic risks include gender, age, and ethnicity, while environmental factors include toxins, vitamin D levels, diseases, iodine intake, and certain medications.

Speak to your doctor if you suspect you have Hashimoto’s disease. They can order a thyroid function or antigen test to make a diagnosis.

Hashimoto’s disease symptoms overlap with many other common health conditions, so it’s not uncommon for thyroid disorders to go undiagnosed for many years.