Levothyroxine—a synthetic thyroid hormone—has consistently ranked among the top three most prescribed medications in the United States for over a decade, reflecting how common thyroid disorders are.
At the same time, heart disease remains the nation’s leading cause of death, affecting nearly half of U.S. adults over 20. Now, a large study from the University of Michigan has revealed a worrying connection: the intensity of thyroid hormone treatment may influence the risk of dying from heart-related causes.
The Thyroid–Heart Connection
Thyroid hormone therapy is often prescribed for hypothyroidism, a condition where the thyroid gland doesn’t produce enough hormones. Treatment aims to restore normal hormone balance, but sometimes therapy can overshoot or undershoot the target.
Thyrotropin (TSH)—a hormone that regulates thyroid function—is the key measure:
– Too little TSH (below normal) can indicate exogenous hyperthyroidism from overtreatment, which strains the heart.
– Too much TSH (above normal) signals undertreatment, leaving hypothyroidism unmanaged—also a cardiovascular risk.
The Study
Led by Dr. Maria Papaleontiou and published in JAMA Network Open, researchers analyzed health records from over 705,000 U.S. veterans who received thyroid hormone therapy between 2004 and 2017.
The study find up to half of patients had abnormal TSH levels—either too low or too high—while on therapy. hese patients faced higher risks of heart-related death compared to those with normal TSH (euthyroidism). The greatest risk occurred at extremes: TSH below 0.1 mIU/L or above 20 mIU/L. Older adults were particularly vulnerable.
To ensure accuracy, the study excluded patients with thyroid cancer (where low TSH is intentionally maintained to prevent recurrence) and patients taking lithium or amiodarone, which affect thyroid function.
Why This Matters
The research shows that thyroid hormone treatment intensity is a modifiable risk factor for heart disease. Keeping TSH within a healthy range could significantly reduce the risk of heart-related deaths.
This underscores the importance of regular blood tests to monitor TSH, personalized treatment plans, especially for older patients, and avoiding both over- and undertreatment.
A Bigger Picture in Heart Health
This study joins other research highlighting ways to protect heart health. For example: Eating eggs may lower heart disease risk. Some herbal supplements can disrupt heart rhythm. Vitamin C (but not Vitamin E) may reduce heart failure risk. Drinking espresso coffee may affect cholesterol levels.
Bottom line: The thyroid and heart are deeply connected. Careful, individualized management of thyroid hormone therapy—aimed at maintaining stable TSH levels—can help prevent avoidable heart complications.
If you care about heart health, please read studies about heart disease hidden and essential vitamins for heart health: a guide to a healthy heart.
If you care about heart health, please read studies about the stuff in your mouth that can increase heart attack risk and statin alternative lowers risk of heart disease as well as cholesterol levels.
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