Did you know that approximately 20 million Americans¹ have some form of thyroid disease? And about 60% aren't aware of their condition. Given the high prevalence of thyroid disorders among Americans, it's essential to understand how the thyroid functions and how the body reacts when it’s not functioning properly.
A thyroid gland can be overactive (hyperthyroidism) or underactive (hypothyroidism). Each condition has unique symptoms. Here's what you need to know about the thyroid gland, hyperthyroidism, and hypothyroidism.
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The thyroid is a butterfly-shaped gland located toward the front of the neck. It forms part of the endocrine system that oversees hormone production and activity within your body.
The gland secretes thyroid hormones that regulate your metabolism. The hormones also influence growth, skin maintenance, body temperature, and digestion. In addition, adequate levels of thyroid hormones are vital for brain and organ development during infancy.
Abnormal thyroid functioning is linked to other conditions, including:
Suboptimal bone density
Muscle weakness and disease
Thyroid disease is not uncommon. According to the American Thyroid Association, more than 12% of Americans will develop a thyroid disorder in their lifetime.
Additionally, approximately 20 million Americans are currently living with thyroid disease — most of them are women. Alarmingly, around 60% of people with hyperthyroidism or hypothyroidism aren't aware of their illness.
Hyperthyroidism (elevated levels of thyroid hormones) is characterized by hypermetabolism, typically due to overproduction by the thyroid gland.
In contrast, hypothyroidism is a deficiency of thyroid hormones, usually caused by an underactive thyroid gland that doesn't produce enough thyroid hormones.
For the most part, these two thyroid conditions have unique symptoms, but some symptoms are present in both. Additionally, the causes and treatments differ between the two. To illustrate the differences, we’ll look at the causes, symptoms, diagnostic tests, and treatments for each condition.
Hyperthyroidism and hypothyroidism have different causes:
You have hyperthyroidism when your thyroid gland produces too much thyroid hormone. Various factors can contribute to hyperthyroidism, but the most common cause in developed countries is Graves' disease, which is responsible for about 80% of all cases in the US.
Graves’ disease is an autoimmune disorder. In Graves’, hyperthyroidism is triggered by the immune system’s attack on the thyroid gland, which causes an increase in hormone production. Graves’ disease has a genetic component and is more common in women than in men.
Other causes of hyperthyroidism include:
Thyroiditis is inflammation of the thyroid. It can be painful (De Quervain) or painless (subacute lymphocytic thyroiditis). In some cases, it’s triggered by giving birth. Thyroiditis can also cause hypothyroidism.
Thyroid nodules are lumps in the thyroid gland. They’re common and typically not cancerous, but they can become overactive and stimulate hormone production, leading to hyperthyroidism.
While only 10 to 15 percent² of thyroid nodules are cancerous, your doctor will check the lumps to be sure. If they’re benign (not cancerous) and not causing symptoms, your doctor may recommend leaving them. However, when they trigger hyperthyroidism, nodules need to be treated or removed (more on that below).
Iodine is an essential component of thyroid hormones. If you consume too much iodine — which is found in large amounts in certain medications and seaweed (nori, wakame) — you may develop hyperthyroidism.
Hypothyroidism most often develops when the thyroid is underactive and doesn't produce enough hormones. Many factors and conditions can cause hypothyroidism, including:
Like overactive thyroid, underactive thyroid may result from inflammation of the thyroid gland. Some thyroiditis is associated with initial hyperthyroidism due to ongoing glandular damage, followed by hypothyroidism after sufficient damage to the thyroid gland has been sustained.
Hashimoto’s disease (chronic immune thyroiditis) is the most common cause of hypothyroidism in developed countries and affects about 2% of Americans.
Hashimoto’s disease is an autoimmune condition. When a person has Hashimoto’s, their immune cells attack and damage the thyroid. When too much damage is sustained, the thyroid cannot produce normal amounts of thyroid hormones, and the person develops hypothyroidism.
There’s a genetic basis for Hashimoto’s, and it affects women more often than men.
Some children are born with hypothyroidism (congenital hypothyroidism). Thyroid hormones are crucial for growth and development; and left untreated, congenital hypothyroidism can slow growth and lead to intellectual disabilities. In the US and most other countries, newborns are tested for hypothyroidism so it can be treated early to reduce the risk of complications.
If doctors need to remove part of the thyroid due to nodules, cancer, or hyperthyroidism — or if they need to use radiation therapy to treat neck cancer, head cancer, or hyperthyroidism — they may induce hypothyroidism through inevitable thyroid damage.
It’s worth noting that medications, including those used to treat thyroid conditions, can trigger hyperthyroidism or hypothyroidism.
Anyone can develop a thyroid condition, but certain factors increase your risk. Many risk factors for hypothyroidism and hyperthyroidism overlap.
Hyperthyroidism has fewer known risk factors than hypothyroidism. Family history is a significant concern, especially for Graves’ disease. Other risk factors include:
Being biologically female
Being older than 60
Having pernicious anemia — a condition where an autoimmune-mediated decline in vitamin B12 absorption causes anemia
Having diabetes (type 1 or type 2)
Another disorder that’s characterized by insufficient hormone production
Eating too much iodine (or getting too much through medications or supplements)
Using products with nicotine
Having had a pregnancy within the past six months
Like in hyperthyroidism, family history drastically affects a person’s chances of developing hypothyroidism. Similarly, diabetes, recent pregnancy, and pernicious anemia are risk factors for both. Other factors that may increase a person's risk include:
Being biologically female
Being older than 60
Having previous treatment for a thyroid issue
Having a genetic disorder called Turner syndrome — a chromosomal condition that affects females exclusively and hinders growth
Having certain autoimmune diseases, including rheumatoid arthritis, lupus, and Sjogren’s syndrome
If you've been treated with certain medications, such as lithium
Not enough iodine in your diet
The symptoms of hyperthyroidism and hypothyroidism vary. Some signs are more pronounced, while others are subtle and hard to spot.
Symptoms of hyperthyroidism are triggered by the overproduction of thyroid hormones and include:
Rapid heartbeat (palpitations)
Nervousness, irritability, and anxiety
Frequent bowel movements
Goiter (an enlarged thyroid), depending on the cause
Heat intolerance and excessive sweating
Changes in menstrual patterns, including amenorrhea³ (periods stopping entirely)
As with hyperthyroidism, symptoms of hypothyroidism are caused by abnormal thyroid hormone levels. The underproduction of hormones associated with hypothyroidism may lead to:
Changes in menstrual patterns
Muscle or joint pain
Doctors use a variety of tools to diagnose thyroid disorders. If your doctor suspects you may have hyperthyroidism or hypothyroidism (based on your symptoms), they’ll check for physical signs (thyroid enlargement and an abnormal heart rhythm, for example) and assess hormone levels in your blood. If they suspect you have hyperthyroidism, they may also order imaging tests.
Because its symptoms overlap with other conditions, doctors can’t diagnose hyperthyroidism based on symptoms alone. If your symptoms align with a hyperthyroidism diagnosis, they’ll use physical, blood, and imaging tests to confirm.
A physical exam is often the first step toward a hyperthyroidism diagnosis. Your doctor will examine your thyroid, checking for enlargement, tenderness, or unusual firmness. Beyond that, they’ll check:
Your heart for a beat that’s unusually slow, fast, or irregular
Your eyes for signs of Graves’, including swelling, redness, and bulging
Your skin for moisture, cracks, and scaly patches
Your doctor will order blood tests to check your thyroid hormones. In particular, they’ll look at your T3, T4, and thyroid-stimulating hormone (TSH) levels.
Abnormal TSH levels can be an early warning sign of thyroid dysfunction, as changes in TSH are often detectable before changes in T3 and T4 hormones. High TSH levels indicate that the thyroid isn’t making enough hormones, and the body is trying to compensate by overproducing TSH (which, as its name suggests, stimulates the thyroid and its production of hormones).
Less commonly, low TSH may be linked to hypothyroidism caused by issues with the pituitary gland, so your doctor will test your T3 and T4 levels, as well.
Low TSH with high T3 and T4 hormones indicates hyperthyroidism, though in some cases of hyperthyroidism, the TSH may be high as well
Low TSH with low T4 indicates hypothyroidism with a problem in the pituitary gland
High TSH with low T4 indicates hypothyroidism
High or low TSH with normal levels of T3 and T4 typically indicates an earlier diagnosis
Your doctor may also request a thyroid antibody test to check for autoimmune diseases.
Your healthcare provider may request imaging tests to diagnose your hyperthyroidism, including:
An ultrasound to check for and assess thyroid nodules
A thyroid scan (radioactive iodine uptake (RAIU) to assess the size, shape, and location of the thyroid and to find the cause of your hyperthyroidism
A thyroid isotope scan to see which parts of the thyroid take up the iodine administered (from the bloodstream) — this test may be done alongside a thyroid scan
If you have a thyroid nodule, your doctor will also perform a biopsy to confirm it’s not cancerous.
Like hyperthyroidism, hypothyroidism is diagnosed based on symptoms, physical examination, and blood tests. Imaging tests aren’t used to diagnose hypothyroidism. If your doctor believes you may have hypothyroidism, they’ll perform the same types of physical examinations and blood tests used for diagnosing hyperthyroidism.
Thyroid disorders are treatable. However, treatment will vary depending on whether your thyroid is under or overactive and what’s causing your thyroid to malfunction.
When recommending a hyperthyroidism treatment, your doctor will consider your age, other conditions like heart diseases, and possible allergies or side effects. They’ll also consider what’s causing your hyperthyroidism.
Treatment options for hyperthyroidism include:
Your doctor may prescribe one or more medications to treat your hyperthyroidism.
Beta-blockers can help with symptoms, such as tremors and nervousness, but they don’t affect the root cause of the symptoms — excess thyroid hormones. They work quickly and are sometimes used temporarily until other drugs start to work.
Antithyroid drugs reduce the thyroid’s ability to produce hormones. They are considered the simplest way to treat hyperthyroidism, but it may take some time for hormone levels to reach a normal range.
In this effective treatment, a person with hyperthyroidism takes radioactive iodine orally. It selectively destroys cells in the thyroid that produce thyroid hormones and doesn’t affect other parts of the body.
Almost everyone who uses radioiodine therapy eventually develops hypothyroidism, but an underactive thyroid is easier to treat and associated with fewer long-term health problems.
In some cases, a doctor will recommend surgically removing part or all of the thyroid gland. It’s less common than other treatments but may be the best option for people with large goiters or those who can’t take medication.
When part of the thyroid is removed, a person may develop hypothyroidism. If all of it is removed, the person will need to take thyroid hormone medications forever.
The standard treatment for hypothyroidism is a hormone replacement medication (levothyroxine) taken daily.
When your doctor prescribes a hormone replacement medicine for your hypothyroidism, they’ll use regular blood tests to optimize your levels. They’ll start with an estimated dose and gradually adjust the amount based on your body's response.
Remember, there’s no known cure for hypothyroidism, so you’ll need to continue taking levothyroxine, even when you feel well. Fortunately, levothyroxine is typically well-tolerated when taken correctly.
Many Americans with thyroid disorders are not aware of their condition. Naturally, if someone is feeling well, they don’t seek diagnosis or treatment. The early signs of thyroid disorders can be subtle, so if you believe you may have one, it’s essential to see your doctor, even if your symptoms are mild.
Once you’re diagnosed, your primary healthcare provider may refer you to other providers or specialist doctors if necessary. In most cases, when you achieve balance and your condition is well-managed, you won’t need to spend much time at your doctor’s office, except for routine checkups.
Your thyroid gland is an organ that sits in the front part of your neck and controls various activities within your body. When it functions properly, the thyroid produces optimal levels of thyroid hormones, which are important for many of the body’s processes.
However, the thyroid can be over (hyperthyroidism) or underactive (hypothyroidism). In those cases, a person will need treatment to achieve normal levels of thyroid hormones.
General information/press room | American Thyroid Association
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Amenorrhea | Johns Hopkins Medicine
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Hyperthyroidism (Overactive thyroid) | NIH: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Hypothyroidism (Underactive thyroid) | NIH: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Symptoms-underactive thyroid (hypothyroidism) | NIH: National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Thyroid exam | Stanford Medicine
Thyroid disease: A checklist of skin, hair, and nail changes | American Academy of Dermatology Association
Thyroid function tests | American Thyroid Association
Thyroid tests | NIH: National Institute of Diabetes and Digestive and Kidney Diseases
Q and A: Can thyroid disease be cured? | American Thyroid Association