Millions of people take a daily pill for thyroid problems without thinking much about it. One of the most common of these medicines is levothyroxine, a man‑made version of a natural thyroid hormone.
It has been one of the most prescribed drugs in the United States for many years because thyroid disorders are very common, especially in women and older adults. The medicine helps people whose thyroid gland does not produce enough hormone, a condition called hypothyroidism.
Without enough thyroid hormone, the body slows down, causing tiredness, weight gain, feeling cold, dry skin, and memory problems. Treatment aims to bring hormone levels back to normal so the body can function properly again.
At the same time, heart disease continues to be the leading cause of death in the United States and many other countries. The heart and thyroid are closely connected because thyroid hormones affect heart rate, blood pressure, and how strongly the heart pumps.
When thyroid hormone levels are too low or too high, the heart can suffer. A new large study has now shown that the strength of thyroid treatment itself may affect the risk of dying from heart problems.
The research was carried out by scientists at the University of Michigan and examined medical records from more than 700,000 U.S. veterans who were treated with thyroid hormone between 2004 and 2017. This makes it one of the largest studies ever done on this topic.
The results were published in a medical journal called JAMA Network Open. The scientists wanted to see whether patients whose hormone levels were not well controlled had a higher risk of heart‑related death.
Doctors measure thyroid treatment using a blood test that checks a hormone called TSH. This hormone acts like a signal from the brain telling the thyroid how much hormone to produce. When TSH is within a normal range, it usually means the body has the right balance of thyroid hormone.
If TSH is too low, it can mean the patient is getting too much hormone from medication, which can speed up the heart and strain it over time. If TSH is too high, it can mean the patient is not getting enough treatment, leaving the body in a low‑hormone state that also increases heart risks.
The study found that about half of the patients had TSH levels outside the normal range at some point during treatment. Those with very low or very high levels faced a greater risk of dying from heart disease than patients whose levels stayed normal.
The danger was especially high for people at the extreme ends, such as those with very low TSH or very high TSH. Older adults were the most vulnerable, possibly because their hearts are already weaker or they have other health problems.
To make sure the results were accurate, the researchers removed patients with thyroid cancer, since those patients sometimes need intentionally low TSH levels. They also excluded people taking certain medications that affect thyroid function. This helped the scientists focus on patients receiving standard treatment for common thyroid problems.
The findings show that the way thyroid hormone therapy is managed can be changed to reduce heart risks. Regular blood tests are important to make sure TSH stays in a healthy range. Doctors may need to adjust the medication dose over time, especially as people age or develop new health conditions.
Patients should also tell their doctor about symptoms such as rapid heartbeat, chest discomfort, unusual tiredness, or sudden weight changes, as these may signal that hormone levels are off balance.
This research adds to growing evidence that many parts of the body are connected. The thyroid gland may be small, but it influences almost every organ, including the heart.
Careful treatment that avoids both too much and too little hormone can help protect long‑term health. For people taking levothyroxine or similar drugs, staying in touch with a healthcare provider and having regular checkups can make a life‑saving difference.
If you care about heart health, please read studies about how eating eggs can help reduce heart disease risk, and herbal supplements could harm your heart rhythm.
For more health information, please see recent studies about how drinking milk affects risks of heart disease and cancer, and results showing strawberries could help prevent Alzheimer’s disease.
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