Let’s Talk About the Causes of Hypothyroidism
From genetics to autoimmune conditions, there are many factors that increase your risk of getting this form of thyroid disease.
Who gets hypothyroidism, and why? This is a big question when it comes to this chronic condition, which affects about 5% of the U.S. population over age 12. There's a bunch of different potential reasons why someone may develop hypothyroidism, which is when your body doesn’t have enough thyroid hormone to function properly. In addition to learning what causes the condition to develop in the first place, researchers have also pinpointed a variety of risk factors that may make you more likely to get this disease. Learning about these causes and risk factors can help you detect hypothyroidism early, which means less chance of severe complications in the long run and a quicker return to better health overall.
Our Pro Panel
We went to some of the nation’s top hypothyroidism experts to bring you the most scientific and up-to-date information possible. Look who’s on your side:
Jennifer Mammen, M.D.
Assistant Professor of Medicine in the Division of Endocrinology, Diabetes, and Metabolism
Johns Hopkins University School of Medicine
Debbie Chen, M.D.
Clinical Lecturer in Endocrinology
Ann Arbor, MI
Thayer Idrees, M.D.
Assistant Professor of Medicine in the Division of Endocrinology, Metabolism, and Lipids
Emory University School of Medicine
Hashimoto’s is the most common type of hypothyroidism, in which your immune system mistakenly attacks your thyroid gland. Unfortunately, researchers aren’t quite sure why this happens in the first place, but it’s likely the result of a combination of genetic and environmental factors.
Other than autoimmune disease (Hashimoto’s), other causes of hypothyroidism can include surgery to remove the thyroid, radiation treatment to the thyroid or head and neck area, medications, pituitary gland problems, iodine deficiency, and congenital problems with the thyroid.
There’s no way to prevent hypothyroidism, but you can learn about your risk factors and the signs that you may be developing this condition. Arming yourself with this knowledge can help you get diagnosed and treated sooner to minimize symptoms and complications.
Anyone can develop hypothyroidism, but some of the most common risk factors are being a woman, being over age 60, having a family history of thyroid problems, or having other autoimmune conditions.
Remind Me, What Is Hypothyroidism?
Here’s a quick refresher: Remember the thyroid gland? It’s that butterfly-shaped organ on the lower part of your neck. Its job is to produce thyroid hormones, which help your body use energy to function properly. So when something happens to prevent your thyroid from making enough hormones, it’s called hypothyroidism—a.k.a. underactive thyroid. Without the hormones it needs to function, your organs start to slow down, causing a host of potential symptoms from fatigue to constipation.
Some people may not even notice their symptoms because they are so mild, whereas others can have symptoms such as fatigue, hair loss, and constipation that can become severe and get in the way of everyday life.
What Causes Hypothyroidism?
If you’ve been diagnosed with this condition or you’re worried you may be someday, this is probably one of the main questions on your mind: What causes an underactive thyroid, anyway? There are a few different scenarios that can lead to this condition.
Autoimmune Disease: Hashimoto’s
The majority of people with hypothyroidism develop the condition as a result of an autoimmune disease called Hashimoto’s disease (sometimes you’ll also see it called Hashimoto’s thyroiditis). Hashimoto’s affects 1% to 2% of people in the United States. In this condition, your body accidentally signals your immune system to attack your healthy thyroid gland cells and enzymes.
Here’s how it happens: Your immune system sends a bunch of white blood cells (called lymphocytes) to your thyroid gland. These cells make antibodies, which usually attack invaders that aren’t supposed to be in your body, like viruses or bacteria. But in this case, they attack the healthy thyroid. And the damage done in this mistaken attack can prevent your thyroid from producing enough thyroid hormone for your body, leading to hypothyroidism symptoms.
But why does your immune system make this mistake in the first place? The answer is a little murky, since scientists aren’t 100% sure why people develop autoimmune diseases like this. That said, current theories suggest a combo of genes and other environmental factors may play a role.
Sometimes, necessary treatments for other health conditions can result in hypothyroidism. For example, if you have Graves’ disease (a form of hyperthyroidism, a.k.a. overactive thyroid), thyroid nodules, or thyroid cancer, you may need to have all or part of your thyroid removed via surgery. This is called a thyroidectomy. When this happens, your body can no longer make enough (or any) of its own thyroid hormone, which means, ironically, you become hypothyroid.
The “good” news though is that your doctors anticipate you’ll develop hypothyroidism with these treatments, which means they can start monitoring your thyroid levels and treating you right away with thyroid hormone replacement to help you minimize any potential symptoms. In these cases, you’ll have to take replacement hormones for life.
Similarly, radiation treatments to the head or neck for certain health conditions can also lead to hypothyroidism. For example, some conditions that may require such treatment include:
Graves’ disease (a form of hyperthyroidism)
Other head and neck cancers
In these cases, your healthcare team may advise the use of radiation (either via radiation therapy or radioactive iodine) to treat your condition. These treatments can result in the loss of part or all of the function in your thyroid, meaning it can’t produce enough thyroid hormone. This is what leads to hypothyroidism.
In rare cases—about one in 2,000-4,000—babies can be born with hypothyroidism. This happens if they are born without a thyroid, with a thyroid that isn’t fully formed, or with a thyroid in the wrong location in their body (called ectopic thyroid). In these cases, the baby’s body may not have enough thyroid hormone to function properly, resulting in hypothyroidism.
Unfortunately, what causes problems with the formation of a healthy thyroid in a baby is typically unknown. There is a potential genetic link—2% to 5% of cases may be passed down genetically, according to the National Institutes of Health. In these cases, the baby may inherit a mutated form of a gene that plays a role in the development of the thyroid gland, resulting in the missing or abnormal gland.
Congenital hypothyroidism is treated in babies the same way as in adults—with replacement thyroid hormone medication called levothyroxine. It’s important for babies to get the proper dosage on a daily basis to ensure healthy development.
Certain drugs you might be taking for other health conditions may also contribute to hypothyroidism by interfering with the thyroid’s ability to make thyroid hormones. These drugs include:
Lithium. Lithium is a drug that may be prescribed to help stabilize mood in conditions like bipolar disorder.
Interferon alpha. This medication may be prescribed to treat a range of conditions, including certain types of cancer and hepatitis infections.
Amiodarone. This drug is used to treat certain types of abnormal heart rhythms.
Interleukin-2. This is a drug used to treat various cancers, including melanoma and kidney cancer.
When hypothyroidism does happen as a result of a medication, it’s usually in people who already have a genetic predisposition to develop autoimmune thyroid disease.
Iodine is a mineral your body needs to make thyroid hormone. But your body doesn’t make it on its own—you have to get it through food. Not getting enough iodine can contribute to hypothyroidism. In the United States, this cause is super uncommon these days, thanks to the fact that iodine is added to most table salt. In other parts of the world, though, iodine deficiency is a very-common cause of hypothyroidism.
Pituitary Gland Damage
The pituitary gland plays a key role in thyroid health: It’s the small gland in your brain that sends a message to your thyroid about how much thyroid hormone it should make for your body’s needs. But in rare cases, a tumor, surgery, or radiation can damage the pituitary gland, which stops it from doing its job. And without this important messenger, your thyroid stops making enough hormone, leading to the development of hypothyroidism.
Risk Factors for Hypothyroidism
Now that we have a better understanding of some of the potential root causes of hypothyroidism, let’s take a look at risk factors. Risk factors are things that raise your chances of developing a disease. With some health conditions, some of the risk factors are things you can change—but unfortunately, most of the risk factors for hypothyroidism are things you don’t have control over.
Still, learning about your specific risk factors is important because it can help you keep an eye out for changes in your body that may signal that something is up with your thyroid so you can get checked out by your doctor right away. Remember: With hypothyroidism, early detection and treatment is key in helping to reduce symptoms and prevent severe complications. Here are the risk factors you should be aware of.
Your age may increase your risk of developing hypothyroidism. People over age 60 are most likely to develop this condition, with women more likely to develop it after going through menopause.
Genetics and Family History
Another thing you can thank your family for: Hypothyroidism appears to run in families. If you’ve had a family member with this condition, you’re more likely to develop it as well. For example, one study in Clinical Thyroidology for the Public found that people with a parent, sibling, or child with hypothyroidism due to Hashimoto’s were nine times more likely than the general population to develop the condition as well.
Yep, that means that there may be something in your genes that may make you susceptible to hypothyroidism. For example, the most common form of hypothyroidism, Hashimoto’s disease, is believed to have a genetic component.
Researchers have identified that variations in a family of genes called human leukocyte antigen complex appear to contribute to Hashimoto’s risk. These genes are supposed to help the immune system tell the difference between the body’s own proteins and proteins from invaders like viruses. Plus, research shows that Hashimoto’s is more common in white people than Black people. That said, researchers are still working to understand just how much of a role these genes and others may play in whether someone develops hypothyroidism.
History of a Thyroid Problem
Have you had a thyroid problem in the past? That can increase your chances of developing hypothyroidism, too. For example, if you’ve had a goiter, if you’ve had surgery on your thyroid (like a partial thyroidectomy), or if you’ve had radiation therapy to the thyroid, neck, or chest area, your risk is heightened.
Other Medical Conditions
Having certain other health conditions—especially autoimmune diseases—can increase your risk of developing hypothyroidism. Some conditions that can up your risk include:
If you have been pregnant in the past six months, your risk of hypothyroidism is also increased. In fact, 5% to10% of women in the United States develop what’s called postpartum thyroiditis after giving birth. With this condition, your thyroid becomes inflamed, which can cause a temporary phase of hyperthyroidism followed by hypothyroidism.
In most cases, the hypothyroidism phase occurs about four to eight months after giving birth. During this time, you may need treatment with synthetic thyroid hormone replacement, depending on how severe your symptoms are. Thankfully, this form of hypothyroidism usually resolves on its own after about a year—but in some cases, it can last longer.
It’s completely unfair, but women are much more likely to develop hypothyroidism than men are. A study in Advances in Therapy reports that the condition is eight to nine times more likely to occur in women than in men. It’s not exactly clear why women get the raw end of this deal, but the fact that women are also twice as likely as men to develop autoimmune diseases (like Hashimoto’s) may be a factor.
The Bottom Line on Risk Factors
Even if you have some of these risk factors, you’re not guaranteed to develop hypothyroidism. And if you do get diagnosed with this condition, know that you’re not doomed to a sluggish existence for the rest of your days—available treatments are highly effective at managing hypo and can get you back to feeling healthy and energetic.
Hypothyroidism Statistics Study: Advances in Therapy. (2019.) “Hypothyroidism in Context: Where We’ve Been and Where We’re Going.” https://doi.org/10.1007/s12325-019-01080-8
Causes of Hypothyroidism: Mayo Clinic. (2020.) “Hypothyroidism (underactive thyroid).” https://www.mayoclinic.org/diseases-conditions/hypothyroidism/symptoms-causes/syc-20350284
Hashimoto’s Information: National Institutes of Health. (2020.) “Hashimoto thyroiditis.” https://medlineplus.gov/genetics/condition/hashimoto-thyroiditis/
Hashimoto’s FAQs: National Institute of Diabetes and Digestive and Kidney Diseases. (2017.) “Hashimoto’s Disease.” https://www.niddk.nih.gov/health-information/endocrine-diseases/hashimotos-disease
Atrophic Thyroiditis: Diagnostic Criteria in Autoimmune Diseases. “Atrophic Thyroiditis.” (2008.) https://link.springer.com/chapter/10.1007/978-1-60327-285-8_42
Congenital Hypothyroidism: National Institute of Health. (2015.) “Congenital hypothyroidism.” https://medlineplus.gov/genetics/condition/congenital-hypothyroidism/
Congenital Hypothyroidism Treatment: HealthyChildren.org. (2016.) “Congenital Hypothyroidism in Infants.” https://www.healthychildren.org/English/health-issues/conditions/Glands-Growth-Disorders/Pages/Congenital--Hypothyroidism-Infants.aspx
Autoimmune Disease Prevalence: Cureus. (2020.) “The Prevalence of Autoimmune Disorders in Women: A Narrative Review.” https://www.cureus.com/articles/31952-the-prevalence-of-autoimmune-disorders-in-women-a-narrative-review
Hashimoto’s and Family History Study: Clinical Thyroidology for the Public. (2017.) “First-degree family members of patients with hypothyroidism due to Hashimoto’s Thyroiditis have an increased risk of developing hypothyroidism.” http://www.thyroid.org/patient-thyroid-information/ct-for-patients/september-2017/vol-10-issue-9-p-8-9/
Hashimoto’s and Genetic Risk: National Institutes of Health Genetic and Rare Diseases Information Center. (2017.) “Hashimoto’s syndrome.” https://rarediseases.info.nih.gov/diseases/6570/hashimotos-syndrome
Hashimoto’s and Race Study: JAMA. (2014.) “Variation in Rates of Autoimmune Thyroid Disease by Race/Ethnicity in US Military Personnel.” https://jamanetwork.com/journals/jama/fullarticle/1860451
Postpartum Thyroiditis: American Thyroid Association. (2021.) “Postpartum Thyroiditis.” https://www.thyroid.org/postpartum-thyroiditis/
Hypothyroidism Information: National Institute of Diabetes and Digestive and Kidney Diseases. (2021.) “Hypothyroidism (Underactive thyroid).” https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism
Hypothyroidism FAQs: American Thyroid Association. (2021.) “Hypothyroidism FAQs.” http://www.thyroid.org/hypothyroidism/