I’ll never forget the day I scoured the scientific literature for information on the association between hypothyroidism and heart disease. Goosebumps rose on my arms.

THE THYROID’S PROFOUND IMPACT ON THE HEART

The American Heart Association AHA publishes a prestigious portfolio of scientific journals respected worldwide for their high scientific standards. If you wonder about the seriousness of the the cardiac manifestations of thyroid disease, here’s a powerful abstract written in 2007 in the AHA’s journal Circulation:[1]

The cardiovascular signs and symptoms of thyroid disease are some of the most profound and clinically relevant findings that accompany both hyperthyroidism and hypothyroidism. On the basis of the understanding of the cellular mechanisms of thyroid hormone action on the heart and cardiovascular system, it is possible to explain the changes in cardiac output, cardiac contractility, blood pressure, vascular resistance, and rhythm disturbances that result from thyroid dysfunction. The importance of the recognition of the effects of thyroid disease on the heart also derives from the observation that restoration of normal thyroid function most often reverses the abnormal cardiovascular hemodynamics.
~Irwin Klein and Sara Danzi, AHA Circulation, 2007

Yet, time and time again, I hear from Hypothyroid Mom readers that learn about the heart connection for the very first time on my website. They’ve been diagnosed with heart disease, they’ve been prescribed a drawer full of cardiac-related prescription medicines, they’ve been asked to wear heart tracking devices by their doctor, gone for heart stress tests, and they’ve been sent for referrals to a cardiologist – yet no one has ever mentioned the thyroid connection. I mean no one, not until they visit my Hypothyroid Mom website. I have even received social media comments and emails written by my followers to me while they sit right there in their hospital beds recuperating from a massive heart attack.

In a 2017 meta-analysis of 55 cohort studies involving 1,898,314 participants, researchers found hypothyroidism associated with higher risks of ischemic heart disease (narrowed heart arteries), myocardial infarction (medical term for heart attack), and cardiac mortality.[2] Yes, you read that correctly – nearly 2 million participants.

CARDIOVASCULAR RISKS ASSOCIATED WITH THYROID

• Slow heart rate (<60 bpm)
• Heart arrhythmia
• Atrial fibrillation
• High cholesterol
• High blood pressure
• Atherosclerosis
• Enlarged heart
• Coronary artery disease
• Ischemic heart disease
• Pericardial effusion
• Heart attack
• Heart failure
• Congestive heart failure

A list is just a list, until you see the scientific studies that back it. If you have any doubt, see the reference list at the bottom of this article for recent studies on this very topic.[3-13] Or read this guest article by a cardiologist where he lists the cardiac signs he sees every day in his office when thyroid patients walk through the door.

IN 1878, AN AUTOPSY REVEALED A HYPOTHYROID HEART

“There was edema of the skin… much serous effusion in the pericardium… the heart was large… the arteries were everywhere thickened, the larger ones atheromatous.”

~Dr. William Smith Greenfield, 1878

This autopsy finding of a 58-year old woman with myxedema was published in 1878 as an appendix to William Ord’s classic description of a syndrome he called myxedema, which today we call hypothyroidism. Then in 1883, E. Theodor Kocher made the first documented hypothesis of a causal relationship between atherosclerosis and hypothyroidism. He noted that atherosclerosis commonly occurred after thyroidectomy (surgical removal of the thyroid gland).[14]

GROWING ATTENTION TO A LONG-KNOWN CONNECTION

In an editorial article published in Frontiers in Endocrinology in 2022, researchers gave this connection its very own name because of is significance – the thyro-cardiac axis. This is what they wrote:[15]

Among the premier effects of thyroid hormones in vertebrates are actions on the cardiovascular system. Cardiovascular complications rank among the key causes of death in thyroid emergencies.

The number of publications meeting the search formula “thyroid AND heart” is approaching the mark of 10,000 results, and it is still exponentially growing. A considerable proportion of these publications covers cardiac arrhythmia.

~Dietrich, J.W., et al. Frontiers in Endocrinology, September 2022

Yearly number of publications meeting the search term “thyroid AND heart” from 1854 to August 2022 in PubMed.[15]

The impact of thyroid dysfunction on the cardiovascular system has been well documented since the 1800s, yet very little has been done in terms of practical medical interventions to save thyroid patients from cardiovascular disease that is so blazingly obvious yet somehow invisible to the doctors treating their patients. Researchers have leaned in on this topic for well over a hundred years and the body of research builds every single year to the present day. They see, just like I do, the crystal clear connection.

Despite the seriousness of this disease, the medical world has placed thyroid disease in a miscellaneous box of simple to treat diseases, not deserving of in-depth investigation. A seriously flawed model is in place that is so overly simplified that it boggles the mind. Medical schools continue to train their doctors with this same thyroid model that simply fails us as patients.

• If TSH is too high, treat with T4 levothyroxine medication.
• If TSH is too low, reduce T4 levothyroxine medication.

Here a doctor explains how symptoms, including cardiovascular symptoms, can persist even when our TSH is normal on levothyroxine treatment.

I wonder if we went around to all the cardiology offices all across the world right now and polled the patients in the waiting rooms – waiting to be seen for serious heart diseases – and asked them whether or not they also have hypothyroidism, or suspect they have it, I wonder just how many of them would say yes. Hmmm…..

Scientific References:

[1] Klein, I., et al. Thyroid Disease and the Heart. Circulation. 2007;116:1725–1735

[2] Ning, Y., et al. 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. 2017;15:21.

[3] Brussea, V., et al. Heart rate variability in hypothyroid patients: A systematic review and meta-analysis. PLoS One. 2022 Jun 3;17(6):e0269277.

[4] Kim, K., et al. Association between Thyroid Function and Heart Rate Monitored by Wearable Devices in Patients with Hypothyroidism. Endocrinology and Metabolism. 2021;36(5):1121-1130.

[5] Abbasova, L., et al. P-69 Beneficial outcomes of hypothyroidism treatment in atrial fibrillation patient. JCEM Case Reports. 2024 Jan 12;2(Supplement_1):luad146.065.

[6] Kowal, A., et al. Treatment of thyroid dysfunction and serum lipids: A systematic review and meta-analysis. J Clin Endocrinol Metab. 2020;105:dgaa672.

[7] Berta, E., et al. Hypertension in Thyroid Disorders. Frontiers in Endocrinology (Lausanne). 2019 Jul 17;10:482.

[8] Muneer, R., et al. Thyroid and Heart: Severe Thyroid Vessel Coronary Artery Disease in a Middle-Aged Female with Hypothyroidism. Cureus. 2019 Nov 8;11(11):e6095.

[9] Vaideeswar, P., et al. The thyroid in ischemic heart disease: An autopsy study. 2018 Dec;70(3):S489-S491.

[10] Karki, S., et al. Pericardial effusion in hypothyroidism: A case report. Annals of Medicine and Surgery. 2021 Dec;72:102999.

[11] Rasool, R., et al. A Role of Thyroid Hormones in Acute Myocardial Infarction: An Update. Curr Cardiol Rev. 2023 Jan 1;19(1):e280422204209.

[12] Kannan, L., et al. Thyroid Dysfunction in Heart Failure and Cardiovascular Outcomes. Circulation: Heart Failure. 2018 Dec 14;11(12).

[13] Lisco, G., et al. Endocrine system dysfunction and chronic heart failure: a clinical perspective. Endocrine. 2022;75;360-376.

[14] Cappola, A.R., et al. Hypothyroidism and Atherosclerosis. The Journal of Clinical Endocrinology & Metabolism. 2003 June 1;88(6):2438-2444.

[15] Dietrich, J.W., et al. Editorial: Thyroid hormones and cardiac arrhythmia. Front Endocrinol (Sec. Thyroid Endocrinology). 2022 September 05;13:2022.