Thyroid hormone: How it affects your heart

Three-dimensional illustration of the thyroid gland in the neck, highlighted in glowing orange against a black background with the body outlined in blue.

Located at the base your throat, the butterfly-shaped thyroid gland releases hormones that affect every organ in your body - especially your heart. Thyroid hormone influences the force and speed of your heartbeat, your blood pressure, and your cholesterol level. As a result, a malfunctioning thyroid gland can cause problems that masquerade as heart disease or make existing heart disease worse.

An estimated 12% of people in the United States have thyroid disease. Most of them - about 90% - have an underactive thyroid, or hypothyroidism. When thyroid levels drop, all the systems in the body slow down, triggering a range of symptoms that include fatigue, weight gain, cold intolerance, constipation, and dry skin. But these symptoms also are very common in older people, including those with normal thyroid levels.

More than half of people with normal thyroid function have symptoms of hypothyroidism. In addition, some people over age 60 with low thyroid levels don't have the classic symptoms. That's why recognizing hypothyroidism can be particularly tricky.

Hypothyroidism: The cardiac connection

Hypothyroidism can affect the heart and circulatory system in several ways. Insufficient thyroid hormone slows your heart rate and makes the arteries less elastic, so blood pressure rises to circulate blood around the body. Low thyroid levels also slow liver function and metabolism. This can increase the amount of cholesterol in the blood, contributing to narrower, hardened arteries.

Another noncardiac symptom - muscle aches - may also be relevant. Muscle aches can be a symptom of hypothyroidism as well as a side effect of cholesterol-lowering statin medications, a condition known as statin-related myalgia. In fact, research suggests that hypothyroidism is more common in people who can't tolerate statins. Sometimes treating hypothyroidism helps relieve statin-related myalgia.

Hyperthyroidism: Excess thyroid hormone

The opposite problem, hyperthyroidism, or too much thyroid hormone, is far less common, affecting only about 1% of the population. But it, too, can harm the heart.

Classic symptoms include sleeplessness, heat intolerance, excess sweating, weight loss, extreme hunger, and loose bowels. Excess thyroid hormone also causes the heart to beat harder and faster. It may trigger abnormal heart rhythms such as atrial fibrillation, a disorganized rhythm in the heart's upper chambers. Some people may experience heart palpitations: sensations of a racing, skipping, or fluttering heartbeat. People with hyperthyroidism may also have high blood pressure.

In a person with clogged, stiff heart arteries, the combination of a forceful heartbeat and elevated blood pressure may lead to chest pain or angina.

Who's at risk for thyroid problems?

The following factors affect your odds of having a thyroid problem:

Family history. People whose first-degree relatives (parents or siblings) have an underactive or overactive thyroid face a higher risk of a similar problem.
Gender. Women are five to eight times more likely to have thyroid problems than men.
Age. The prevalence of hypothyroidism rises with age, especially after age 60.
Health history. Thyroid problems are more likely among people with a personal or family history that includes type 1 diabetes, Addison's disease, pernicious anemia, rheumatoid arthritis, premature gray hair, radiation treatments to the head and neck, or vitiligo.

Image: 3dMediSphere/Getty Images

About the Reviewer

Mallika Marshall, MD, Contributing Editor

Mallika Marshall, MD, is an Emmy-award winning journalist and physician who serves as Medical Director at WBZ-TV in Boston. A practicing physician who is Board Certified in both internal medicine and pediatrics, Marshall serves on staff … See Full Bio

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