Levothyroxine is one of the most commonly prescribed drugs in the United States.
It’s a synthetic version of a thyroid hormone and is used to treat people with an underactive thyroid, a condition known as hypothyroidism.
The fact that it’s been in the top three most prescribed medications for years shows how common thyroid problems are.
At the same time, heart disease remains the number one cause of death in the U.S., affecting nearly half of adults over 20. A new study from the University of Michigan has found a troubling link between how thyroid hormone treatment is managed and the risk of dying from heart-related issues.
The study, led by Dr. Maria Papaleontiou and published in JAMA Network Open, looked at health data from over 705,000 U.S. veterans who received thyroid hormone therapy between 2004 and 2017. The researchers wanted to understand how the level of thyroid hormone in the body affects heart health.
Thyroid hormone therapy is important for treating low thyroid function. But if the dosage isn’t right, it can push a person’s TSH (thyrotropin) levels too low or too high. TSH is the hormone that tells the thyroid when to produce more hormones. When TSH levels are off balance, it can put stress on the heart.
In the study, up to half of the patients had TSH levels outside the normal range—either too low or too high. These people had a higher risk of dying from heart-related problems compared to those whose TSH levels were normal.
The risk was highest for people whose TSH levels were extremely low (under 0.1 mIU/L) or extremely high (over 20 mIU/L). Older adults were especially at risk.
The study left out patients with thyroid cancer, because doctors often purposely keep TSH levels low in these cases. It also excluded patients taking certain medications like lithium or amiodarone, which are known to affect thyroid function.
What this study tells us is that the intensity of thyroid hormone treatment matters. It’s something that can be changed to help reduce heart risks. Keeping TSH levels in a healthy range might lower the chance of heart-related deaths for people on thyroid medication.
This research shows how important it is to get the dose just right, especially for older adults. Too much or too little thyroid hormone can both be harmful.
People interested in heart health may also want to pay attention to other factors. For example, eating eggs has been linked to a lower risk of heart disease. Some herbal supplements may be bad for heart rhythm.
Research also shows that vitamin C (but not vitamin E) may help lower the risk of heart failure. And drinking espresso might affect cholesterol levels.
In short, the thyroid and the heart are closely connected. This study is a reminder that careful treatment and regular monitoring can make a big difference. By keeping thyroid hormone levels balanced, doctors can help protect patients from preventable heart problems.
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