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How Thyroid Hormone Affects Your Heart

Content provided by the Faculty of the Harvard Medical School

High and low levels increase the potential for heart trouble.

A little gland in your neck can have a big effect on your heart.

The butterfly-shaped thyroid gland secretes hormones that regulate metabolism and energy levels. In most people, the thyroid produces just the right amount of hormone. But in some people, it produces too much or too little. When it does, the risk for heart problems grows.

Too little hormone

Too little thyroid hormone (a condition called hypothyroidism) makes the body slow down. The first clues are often fatigue and weight gain. As thyroid hormone levels continue to drop, these symptoms worsen, and additional symptoms may appear, including fatigue, feeling cold all the time, constipation, irritability, even trouble concentrating.

When thyroid hormone production wanes, the organs demand less oxygen, including the heart. As a result:

  • The heart does not contract as strongly. It pumps less blood with every beat and refills itself incompletely.

  • With less thyroid hormone to relax the cells that line the arteries, blood pressure in the arms and legs rises when the heart is resting between beats.

  • Cholesterol and blood pressure rise.

  • Heart disease may accelerate.

Hypothyroidism can be corrected by taking thyroid hormone to restore what is missing. Sometimes this will prevent heart disease from progressing; sometimes it won't.

"When hypothyroidism is severe enough to cause high blood pressure and elevated cholesterol levels, replacement therapy will normalize both and prevent further heart damage. But when hypothyroidism is mild, the impact on blood pressure and cholesterol is harder to predict, and the cardiac benefits are less certain," says Dr. Jeffrey Garber, an endocrinologist at Harvard-affiliated Beth Israel Deaconess Medical Center.

Too much hormone

Overproduction of thyroid hormone (hyperthyroidism) puts the body into overdrive. The heart pumps harder and beats faster, often racing, pounding, or beating rapidly and irregularly. Blood pressure rises. Women in particular may experience chest pain. The risk of developing heart failure may rise, even in people who did not have heart disease.

Treatment for an overactive thyroid depends on the underlying cause for the disorder. Fortunately, when palpitations are caused by hyperthyroidism, the symptoms will disappear when the thyroid disorder is treated. In some people, heart rhythm abnormalities resolve spontaneously.

Don't wait to seek help

So what should you do if you suspect a thyroid hormone problem might be at the root of your heart trouble?

"If your heart disease is getting worse, and you have symptoms suggestive of hypo- or hyperthyroidism, ask your cardiologist or primary care physician to check your thyroid function," says Dr. Douglas Ross, an endocrinologist at Harvard-affiliated Massachusetts General Hospital.

Last Annual Review Date: April 1, 2013 Copyright: 2013 Harvard Health Publications
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