How Does Thyroid Disease Affect the Heart?

One of the most important reasons to diagnose and treat thyroid disease is to prevent the cardiac conditions that can result from it.

Thyroid disease can worsen cardiac symptoms in people with heart disease and accelerate underlying cardiac problems. It can even produce new heart problems in people with otherwise healthy hearts.

This article explains what the thyroid gland does and how it affects the heart. It also covers the difference in symptoms and treatment between an underactive and an overactive thyroid.

how thyroid conditions affect the heart

Verywell / Emily Roberts

The Thyroid Gland

By producing just the right amount of thyroid hormone, the thyroid gland helps regulate your body's metabolism—most importantly, how much oxygen and energy your body uses—as well as your digestive function, muscle function, and skin tone.

The thyroid has at least some effect on every organ in the body, including the heart.

Too little thyroid hormone (a condition known as hypothyroidism) or too much thyroid hormone (called hyperthyroidism) can affect the heart id different ways.

Hypothyroidism

Known as an underactive thyroid, hypothyroidism can be a subtle condition. It typically starts gradually, so its symptoms can easily sneak up on someone.

Furthermore, hypothyroidism often occurs without the typical group of "textbook" symptoms, especially in older people.

When there is not enough thyroid hormone, neither the heart nor the blood vessels can function normally.

The reduced level of thyroid hormone causes the heart muscle to pump less vigorously and eventually become weak.

In addition, the heart muscle cannot fully relax after each heartbeat. This failure to relax can produce diastolic dysfunction, or stiffening of the heart's pumping chambers—a condition that can lead to heart failure.

Hypothyroidism also causes blood vessels to stiffen, which can cause high blood pressure (hypertension).

If you have any symptoms of hypothyroidism that your healthcare provider can't explain, such as fatigue or weight gain, ask them to measure your thyroid hormone levels. This is particularly important if you already have heart disease.

Cardiac Symptoms

Cardiac symptoms can occur in anybody with hypothyroidism, but they are especially likely in people who already have underlying heart disease.

Common cardiac problems associated with hypothyroidism include:

  • Swelling (edema): Edema can occur as a result of worsening heart failure. In addition, hypothyroidism itself can produce a type of edema called myxedema, which is caused by an accumulation of abnormal proteins and other molecules in the fluid that surrounds the body's cells.
  • Heart arrhythmias: Hypothyroidism may also worsen the tendency for premature beats and irregular, quivering heartbeats (atrial fibrillation).
  • Heart failure (new or worsening): Hypothyroidism can cause heart failure for the first time in patients with relatively mild underlying heart disease.
  • High diastolic blood pressure (diastolic hypertension): The arteries can grow stiff with hypothyroidism, which causes diastolic blood pressure to increase.
  • Shortness of breath (dyspnea): Shortness of breath on exertion and poor exercise tolerance in hypothyroidism is usually due to weakness in the skeletal muscles. In people who also have heart disease, it may be due to worsening heart failure.
  • Slow heart rate (bradycardia): Your heart rate is modulated by thyroid hormone. In people with hypothyroidism, the heart rate is typically 10 to 20 beats per minute slower than normal, especially in patients who also have heart disease.
  • Worsening of coronary artery disease (CAD): The reduction in thyroid hormone can actually make angina (chest discomfort associated with CAD) less frequent. But the increase in LDL cholesterol ("bad cholesterol") and C-reactive protein (an inflammatory protein) seen with hypothyroidism may accelerate any underlying CAD.

Hypothyroidism Treatments

Physicians often prescribe Synthroid (levothyroxine( to treat an underactive thyroid.

Taken once a day, this replacement hormone mimics thyroxine, the hormone that the thyroid gland produces naturally.

If you start taking thyroid medication, expect to stay on it for life. The effects of hypothyroidism are irreversible.

Hyperthyroidism

Hyperthyroidism is caused by the overproduction of thyroid hormone. When there is too much thyroid hormone, the heart muscle must work harder. For a person with heart disease, having an overactive thyroid can take a big physical toll.

Excess thyroid hormone increases the force of contraction of the heart muscle and increases the amount of oxygen demanded by the heart. It also increases the heart rate. As a result, the work of the heart is greatly increased.

As with hypothyroidism, hyperthyroidism may be present without producing the classic textbook symptoms. So if you have cardiac symptoms that cannot otherwise be readily explained, have your thyroid function measured. The sooner, the better.

Cardiac Symptoms

Cardiac symptoms can occur in anybody with hyperthyroidism but can be particularly dangerous in people with underlying heart disease.

Common symptoms include:

  • Fast heart rate (tachycardia) and palpitations: Undetected hyperthyroidism is a common cause of an increased heart rate at rest and with mild exertion. Hyperthyroidism should always be ruled out with blood tests before making the diagnosis of inappropriate sinus tachycardia.
  • Heart arrhythmias: Particularly in patients with underlying heart disease, hyperthyroidism can also produce a host of other arrhythmias, such as premature ventricular complexes (PVCs), ventricular tachycardia, and especially atrial fibrillation.
  • Heart failure: Hyperthyroidism itself can produce heart failure, but only rarely. On the other hand, if pre-existing heart disease is present, greater risk of heart failure with hyperthyroidism is common. This can be difficult to treat.
  • High systolic blood pressure (systolic hypertension): The forceful cardiac contraction increases systolic blood pressure, or the pressure within blood vessels during cardiac contraction.
  • Shortness of breath: Shortness of breath with exertion can be due to the skeletal muscle weakness associated with hyperthyroidism or to worsening heart failure.
  • Worsening angina: Patients with coronary artery disease often experience a worsening of symptoms with hyperthyroidism. These can include an increase in angina or even a heart attack.
Hyperthyroidism can cause increased heart rate at rest.

Hyperthyroidism Treatments

Physicians often prescribe Tapazole (methimazole) or Propylthiouracil (PTU) to treat hyperthyroidism. It's important to remember that these treatments are not a cure.

If a tablet treatment is unsuccessful, surgery to remove all or part of the thyroid gland is an alternative. So is a radioactive iodine treatment to slow the production of thyroid hormones.

Summary

The thyroid gland, a small, butterfly-shaped gland at the back of your throat, performs many vital functions. Thyroid disease—resulting in too little thyroid hormone (hypothyroidism) or too much (hyperthyroidism)—can, therefore, have several consequences.

Heart issues tops the list. Among them? Spikes in blood pressure, irregular heartbeats, slow or fast heart rate, heart failure, and more.

Managing thyroid disease can have far more benefit than just reducing symptoms like fatigue. That includes reducing your risk of some of these concerns. Be sure to get tested for thyroid disease if you exhibit any signs, or if you are experiencing new or worsening cardiac health problems.

Frequently Asked Questions

  • Who is most at risk for thyroid problems?

    You are more likely to get thyroid disease if you were born female, are white and age 60 or older, have a family history of thyroid conditions, or have a history of diabetes, rheumatoid arthritis, or radiation treatment.

  • How can you prevent thyroid disease?

    To reduce your risk, ask for a thyroid collar before getting X-rays taken, quit smoking, self-check your neck for lumps and swelling, limit your soy intake, consider a selenium dietary supplement, and see your healthcare provider regularly.

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6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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