What is the relationship between hyperthyroidism and high blood pressure?

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When a person has too much thyroid hormone, it tends to speed up many bodily functions, including metabolism and heart rate. This can lead to high blood pressure.

Hyperthyroidism can increase cardiac output. This may elevate a person’s heart rate and systolic blood pressure. Systolic blood pressure is the top number in a blood pressure reading and records the pressure when the heart contracts.

Hyperthyroidism also relaxes the blood vessels. This can lower diastolic blood pressure, the bottom number in a blood pressure reading. Diastolic blood pressure is a measure of blood pressure between heartbeats.

Hypothyroidism — an underactive thyroid — can also increase the risk of hypertension. A 2019 review estimates that 30% of people with hypothyroidism have diastolic high blood pressure.

Learn more about blood pressure readings.

The thyroid is a butterfly-shaped gland in the neck. It produces thyroid hormone, which plays an important role in metabolism, including how the body uses nutrients such as sodium. Thyroid hormone levels can also affect heart function.

Untreated hyperthyroidism is not usually immediately dangerous. However, over time, it can damage the heart. It can also cause a life threatening complication called thyroid storm.

The autoimmune condition Graves’ disease is the most common cause of hyperthyroidism in the United States. People who take too much thyroid hormone to treat hypothyroidism may also have hyperthyroid symptoms. Doctors call this factitious hyperthyroidism.

High blood pressure often causes no obvious symptoms, especially in the early stages. This is why people should monitor their blood pressure regularly, especially if they have an underlying thyroid disease.

Additionally, a person may not have any initial symptoms of hyperthyroidism. Symptoms tend to appear over time. These include:

• an increased appetite while losing weight
• rapid heart rate
• feeling jittery, anxious, or on edge
• often feeling hot
• excessive sweating
• frequent bowel movements or diarrhea
• difficulty sleeping
• muscle weakness
• shaking hands
• irregular heartbeat
• high systolic and low diastolic blood pressure

Risks for hyperthyroidism include:

• Graves’ disease
• taking too much thyroid medication
• a growth on the thyroid
• too much iodine in the diet
• inflammation in the thyroid

Some people with hyperthyroidism develop a growth in the neck due to an enlarged thyroid gland, known as a goiter.

Hyperthyroidism is a risk factor for high blood pressure. However, having high blood pressure with hyperthyroidism does not necessarily mean thyroid disease is causing hypertension.

Some other risk factors for high blood pressure include:

• diabetes
• a high sodium diet
• drinking excess alcohol
• being physically inactive
• smoking
• older age
• a family history of high blood pressure

Treating hyperthyroidism often, but not always, cures high blood pressure. Treatment depends on the cause of hyperthyroidism, but the ultimate goal is to reduce the amount of thyroid hormone in the bloodstream.

Some treatment options include:

• reducing thyroid hormone medication or eliminating it until numbers stabilize
• using drugs to control anxiety, high blood pressure, and heart palpitations, such as beta-blockers
• ongoing monitoring if a person has a temporary form of hyperthyroidism

After giving birth, some people may develop thyroiditis, which can cause hyperthyroidism. Temporary forms of hyperthyroidism do not usually require treatment. Instead, a doctor may recommend treatments to manage symptoms. For example, a doctor might prescribe a beta-blocker to help with anxiety.

If treatment to manage symptoms does not work, if a person’s symptoms are very severe, or their thyroid levels are very high, a doctor may recommend treatment to prevent the thyroid from continuing to secrete high thyroid hormone levels. Options include:

• radioactive iodine therapy
• surgery to remove the thyroid, called a thyroidectomy
• thionamide therapy

These treatments may cause a person to develop hypothyroidism. This means they will need to take supplemental thyroid hormone. A doctor will need to monitor their thyroid levels to ensure they are neither too high nor too low.

If blood pressure does not improve, a person may need additional treatment. This may include beta-blockers or other medications. Lifestyle changes such as a low sodium diet may also help.

Learn what foods to eat and avoid when following a low sodium diet.

A person should contact a doctor if they have consistently high blood pressure readings or a sudden unexplained change in blood pressure. It is also important to contact a doctor when an individual:

• is undergoing therapy for hypothyroidism and develops symptoms of hyperthyroidism
• develops new hyperthyroidism symptoms
• feels chronically anxious, restless, or unable to sleep
• has a rapid heart rate
• develops hypothyroidism symptoms, such as low energy and feeling chronically cold, following treatment for hyperthyroidism

Untreated thyroid disease is a risk factor for heart disease. People with hyperthyroidism may develop high blood pressure, especially elevated systolic blood pressure. However, as high blood pressure is common, not all cases are due to thyroid disease.

People with high blood pressure and hyperthyroidism should consult a doctor to explore treatment options. Even after treating hyperthyroidism, they may still need to treat high blood pressure.