Levothyroxine is one of the most prescribed medications in the United States, showing just how common thyroid problems are.
It’s used to treat hypothyroidism, a condition where the thyroid gland doesn’t make enough hormones.
But a new study from the University of Michigan warns that too much or too little thyroid hormone therapy might increase the risk of dying from heart-related problems.
Heart disease is already the number one cause of death in the U.S., affecting nearly half of adults over age 20. This new research suggests that thyroid hormone levels may play a bigger role in heart health than previously believed.
The study, led by Dr. Maria Papaleontiou and published in JAMA Network Open, looked at data from more than 705,000 U.S. veterans who received thyroid hormone therapy between 2004 and 2017. The researchers focused on their levels of TSH, or thyrotropin, a hormone that helps regulate thyroid function.
They found that up to half of the patients had abnormal TSH levels—either too high or too low. This was a major concern because these patients had a higher risk of dying from heart-related issues compared to those with normal TSH levels.
When TSH levels are too low, patients may experience something called exogenous hyperthyroidism, a condition caused by taking too much thyroid hormone. When TSH levels are too high, it indicates that the hormone dose may be too low, leading to ongoing hypothyroidism. Both extremes can put extra strain on the heart.
The most alarming results were seen in patients whose TSH levels were extremely low (below 0.1 mIU/L) or extremely high (above 20 mIU/L). These patients had the greatest risk of heart-related deaths. Older adults were particularly vulnerable, making close monitoring even more important for this group.
To make sure their results were accurate, the researchers excluded people with thyroid cancer, since they are sometimes kept at low TSH levels on purpose to prevent cancer from returning. They also excluded people taking certain medications like lithium or amiodarone, which are known to affect thyroid hormone levels.
The study’s findings suggest that the way we manage thyroid hormone therapy could directly affect heart health. Fortunately, this is a risk factor that can be changed. By adjusting doses and checking TSH levels regularly, doctors can help reduce the risk of serious heart problems.
This study also highlights the need for personalized care. What works for one person might not be right for another, especially when it comes to older adults who may be more sensitive to hormone changes.
The link between thyroid function and heart health is clear. Taking too much or too little thyroid hormone can be dangerous, so it’s important for patients and healthcare providers to work together to find the right balance.
In related research, lifestyle and nutrition also play important roles in heart health. For example, eating eggs may help reduce the risk of heart disease, while some herbal supplements could affect heart rhythm. Vitamin C, but not Vitamin E, has been linked to a lower risk of heart failure, and even drinking espresso might influence cholesterol levels.
Together, these studies remind us that heart health depends on many factors—from medication to diet. Managing thyroid treatment carefully is one more way to protect your heart.
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