Hyperthyroidism is a condition in which your thyroid gland is overactive, producing more hormones than your body needs. Both high and low thyroid hormone levels can cause exercise intolerance.

Your thyroid gland releases the hormones triiodothyronine (T3) and thyroxine (T4). These hormones regulate your metabolism by influencing the rate at which your body uses calories. They are also involved in most body functions, including heart rate.

Hyperthyroidism may lead to cardiovascular changes and arrhythmias (abnormal heart rhythms) that could make exercise even more challenging. In some people with severe hyperthyroidism, the heart may not be able to pump enough blood to meet the demands of exercise, especially during intense physical activity.

Thyroid hormones influence practically every cell in your body. Disruptions in your thyroid hormone levels can affect many of your bodily functions.

Hyperthyroidism is thought to affect a little over 1% of people in the United States. It can range from subclinical (meaning it doesn’t cause noticeable symptoms) to severe.

Hyperthyroidism may cause you to have trouble with exercise because your heart may be less able to meet the demands of physical activity. You might also have an exaggerated heart rate response during exercise. For example, your heart rate might jump up very high very quickly, even during moderate activity.

One of the major effects thyroid hormones have on your body is on your heart rate. Both high and low thyroid hormone levels are associated with a greater chance of developing heart problems.

Hyperthyroidism may increase your risk of:

Additionally, hyperthyroidism has been associated with several factors that might contribute to exercise intolerance, such as:

Atrial fibrillation is an abnormal heart rhythm that’s found in up to 28% of people who have received a hyperthyroidism diagnosis.

Even subclinical hyperthyroidism is a risk factor for atrial fibrillation, and peak exercise intolerance is common in people with this condition. With peak exercise intolerance, your heart cannot pump enough blood to meet your body’s oxygen demands during intense activity.

Regular exercise and physical activity can benefit people with hyperthyroidism, and most people can exercise without a risk of serious complications.

The benefits of exercising may include:

  • improving your overall cardiovascular health
  • regulating your sleep cycles
  • boosting your energy levels
  • strengthening your muscles and bones

If you have a heart condition such as atrial fibrillation, it’s a good idea to talk with a healthcare professional before starting an exercise program. They can perform an electrocardiogram or an exercise stress test to examine your heart rhythm and help you establish safe limits.

Some people with severe hyperthyroidism may be at an increased risk of sudden cardiac death during intense activity due to an inability to meet cardiovascular demands. But this is preventable in many cases.

Regular exercise is important for everyone, including people with hyperthyroidism. Here are some tips for exercising safely if you have hyperthyroidism:

Talk with a doctor

A healthcare professional can help you determine safe limits for physical activity. They can also screen you for any potential abnormal heart rhythms that may increase your risk of heart-related complications.

Listen to your body

If you have hyperthyroidism, notice low tolerance to physical activity, and haven’t had any heart tests performed, it may be best to avoid overexerting yourself.

Light to moderate physical activity can also benefit your cardiovascular health. For example, instead of running at maximum speed, you could try walking for up to 30 minutes per day. A healthcare professional can tailor recommendations to your case.

Progress slowly

If you aren’t currently physically active, it’s best to start building up intensity over time instead of jumping to intense activity right away. Sudden increases in exercise intensity might overload your heart before it has time to adapt to stress and may increase your risk of complications.

Include resistance training

Hyperthyroidism — especially untreated severe hyperthyroidism — can increase the breakdown of bone and increase your risk of osteoporosis. Including some type of resistance training in your exercise routine, such as Pilates or weightlifting, can help you keep your bones strong.

Stick to exercise you enjoy

Many types of exercise can contribute to your overall health, so you don’t need to restrict yourself to activities you dislike. For example, dancing, swimming, or skating can offer heart-health benefits.

If you have hyperthyroidism, it’s important to talk with a doctor before starting a new exercise program. It’s especially important to consult with them if you develop symptoms such as:

  • shortness of breath while at rest or while performing light or moderate physical activity
  • unintentional and significant weight loss
  • a feeling as if your heart is pounding, fluttering, or beating irregularly
  • chest discomfort or pain
  • severe fatigue and muscle weakness
  • dizziness

Both high and low thyroid hormone levels can increase your chances of developing heart problems. Severe hyperthyroidism may cause reduced exercise tolerance because your heart may not be able to pump enough blood to match the oxygen demands of intense activity.

It’s important to talk with a doctor about safe exercise limits if you have hyperthyroidism. They may want to run tests to measure your heart function and rule out abnormal heart rhythms and other complications.