Your thyroid and heart health

Your thyroid gland may only be small, but it’s mighty. The butterfly-shaped gland in your neck has a huge responsibility, releasing hormones that affect every organ in your body — including your heart. 

Did you know, for example, that an underactive thyroid can increase your risk of developing fatty plaques in the arteries? Or that an overactive thyroid may cause an abnormal heart rhythm?

We look at how your thyroid function can directly impact your heart health.

How your thyroid and heart are connected

Your thyroid makes two hormones that it releases into the blood — triiodothyronine (T3) and thyroxine (T4). T3 is the more potent form. We say it is more biologically active as it exerts a bigger effect on the organs and tissues it binds to. Together, T3 and T4 influence the activity of all the cells in the body, regulating the body’s metabolic rate. 

T3 has a particularly prominent effect on the heart. Each heart cell has receptors on its surface. When T3 binds to it, it triggers a cascade of events that affect heart rate, rhythm, and how much the heart contracts. 

Too much or too little of these thyroid hormones can affect the heart in different ways. 

Underactive thyroid (hypothyroidism)

An underactive thyroid (hypothyroidism) affects about one in 50 people in the UK and is up to ten times more likely to affect women than men. You’re also more likely to develop hypothyroidism as you get older [1]. 

The most common cause is an autoimmune condition called Hashimoto’s thyroiditis. This is where the immune system attacks the thyroid gland causing it to swell. 

If you have an underactive thyroid, and it’s not well controlled, it can make you more prone to heart problems. Or, if you already have a heart condition, it may make it worse. 

Having an underactive thyroid can [2]:

• Slow your heart rate — Your heart rate may be slower than usual with an underactive thyroid.
• Raise your blood pressure — An underactive thyroid can cause arteries to stiffen, causing a rise in blood pressure. This typically affects diastolic blood pressure more than systolic blood pressure. High blood pressure (hypertension) increases your risk of conditions like stroke and heart attacks.
• Increase your cholesterol levels — One of the essential roles of thyroid hormones is to support the liver in removing excess bad cholesterol from the blood. Without enough T3, your levels of bad cholesterol can increase. 
• Increase your risk of coronary heart disease — As a result of raised cholesterol, an underactive thyroid can increase your risk of coronary heart disease. This is when your heart’s blood supply is interrupted by a build-up of cholesterol and fatty substances in the artery walls. People with hypothyroidism are more at risk of a fatal cardiac event than someone who had normal thyroid function [3]. 

Subclinical hypothyroidism 

Subclinical hypothyroidism is when thyroid-stimulating hormone (TSH) levels are raised but T3 and T4 levels are within normal range. This condition affects up to one in five people, and is often detected by chance as most people don’t develop symptoms [1]. It will likely resolve by itself but may develop into overt hypothyroidism.

Subclinical hypothyroidism can also increase the risk of heart disease, particularly for people aged over 65 [1, 3, 4]. However, there is conflicting evidence as to whether treatment can reverse these negative effects on the heart [5].

Overactive thyroid (hyperthyroidism)

An overactive thyroid (hyperthyroidism) is about as common as an underactive thyroid in the UK, affecting about one in 50 people [1]. The most common form is Graves’ disease, where the immune system attacks the thyroid cells. 

An excess of thyroid hormones can cause problems with the heart’s rate and rhythm. This can be even more problematic if you already have an underlying heart condition.

An overactive thyroid can:

• Increase your heart rate — Your heart rate may be higher than usual and perhaps more than 100 beats per minute (known as tachycardia). 
• Raise your blood pressure — Typically, an overactive thyroid affects systolic blood pressure more than diastolic blood pressure. This can put increased strain on the heart [6].
• Cause palpitations — Palpitations are noticeable rapid, strong, or irregular heartbeats. They may be harmless, but some may be a symptom of an underlying of your heart rhythm. 
• Trigger abnormal heart rhythms — People with an underactive thyroid are more likely to develop rhythm problems. One of the most common is atrial fibrillation (AF). AF is an irregular and often abnormally fast heart rate that increases the risk of blood clots in the heart. The risk of atrial fibrillation increases with age and whether you have underlying coronary heart disease [7]. 
• Lead to heart failure if not treated — An increased heart rate and blood pressure, as well as possible rhythm disturbances, can put enormous strain on the heart over time. Ultimately, it may lead to heart failure [7, 8]. This is rare, however, as most people with hyperthyroidism are now promptly treated.

Subclinical hyperthyroidism 

Subclinical hyperthyroidism describes a lowered thyroid-stimulating hormone (TSH) level but normal T3 and T4 levels. Usually, results are repeated a few months later to confirm the result.

There’s evidence to suggest an association between subclinical hyperthyroidism and cardiac conditions, like heart failure and atrial fibrillation, especially for people over 65 [7, 9]. Treatment for subclinical hyperthyroidism will depend on your age, symptoms, and how low your TSH levels are.

Keeping your heart healthy with a thyroid condition 

The good news is that in most cases, your risk of heart problems is reduced when the underlying thyroid condition is recognised and treated [6]. That’s why it’s important to take your treatment as prescribed and attend all your appointments. 

It is possible to under-or overtreat a thyroid condition which can be just as harmful — regular blood testing helps your doctor tailor your treatment dose. With time, your blood tests may not need to be as frequent. You can keep an eye on your thyroid function at home with our Thyroid Function Blood Test. 

Even once your thyroid function is stable and correct, it’s still important to look after your heart. You may still be at risk of heart disease, especially if your cholesterol levels and blood pressure remain high. 

Look after your heart by: 

• Keeping active — Visit our blog which has tips to keep active with a thyroid condition. It details how you can exercise safely and effectively with an over-or underactive thyroid. 
• Eat a healthy, well-balanced diet — Make sure you eat plenty of fresh fruit and veg and limit your salt intake to no more than 6g per day. The Mediterranean diet has been proven to benefit heart health and lower cholesterol levels. 
• Check your blood pressure — It’s worth checking your blood pressure at least every year to make sure it’s not raised. Find out how to take your blood pressure at home. 
• Quit smoking — Smoking is very harmful to your heart and seriously increases your risk of a heart attack. 
• Manage stress — Chronic stress can put excessive strain on your heart by raising your blood pressure. See our top ten ways to de-stress. 

Find out more about thyroid health

For all things thyroid, head to our thyroid health hub. We detail the ins and outs of thyroid disease and how you can best manage your condition, including thyroid-friendly diets, lifestyle advice, and a thyroid buying guide to make sure you’re buying the right test for you. 

References

1. NICE. 2019. Context | Thyroid disease: assessment and management. [online] Available at: <https://www.nice.org.uk/guidance/ng145/chapter/Context> [Accessed 20 April 2022].
2. Grais, I. M., & Sowers, J. R. (2014). Thyroid and the heart. The American journal of medicine, 127(8), 691–698.
3. Ning et al., 2017. What is the association of hypothyroidism with risks of cardiovascular events and mortality? A meta-analysis of 55 cohort studies involving 1,898,314 participants. BMC Medicine, 15(1).
4. Udovcic, M., Pena, R. H., Patham, B., Tabatabai, L., & Kansara, A. 2017. Hypothyroidism and the Heart. Methodist DeBakey cardiovascular journal, 13(2), 55–59.
5. Simon, C., Weidman-Evans, E. and Allen, S., 2020. Subclinical hypothyroidism. Journal of the American Academy of Physician Assistants, 33(5), pp.21-26.
6. Klein, I. and Danzi, S., 2007. Thyroid Disease and the Heart. Circulation, 116(15), pp.1725-1735.
7. Osuna, P. M., Udovcic, M., & Sharma, M. D. 2017. Hyperthyroidism and the Heart. Methodist DeBakey cardiovascular journal, 13(2), 60–63.
8. Riaz, K., Forker, A. D., Isley, W. L., Hamburg, M. S., & McCullough, P. A. 2003. Hyperthyroidism: a "curable" cause of congestive heart failure--three case reports and a review of the literature. Congestive heart failure (Greenwich, Conn.), 9(1), 40–46.
9. Biondi, B., Bartalena, L., Cooper, D. S., Hegedüs, L., Laurberg, P., & Kahaly, G. J. (2015). The 2015 European Thyroid Association Guidelines on Diagnosis and Treatment of Endogenous Subclinical Hyperthyroidism. European thyroid journal, 4(3), 149–163.