Levothyroxine is one of the most commonly prescribed medicines in the world. It is used to treat hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormone.
The thyroid is a small butterfly-shaped gland in the front of the neck, but it has a very important job. It helps control how fast the body uses energy, regulates body temperature, and supports the normal function of the heart, brain, muscles, and many other organs.
When the thyroid does not make enough hormone, people may feel tired, gain weight, feel cold, have dry skin, or develop slow thinking and depression. Levothyroxine replaces the missing hormone and helps the body return to normal.
Although levothyroxine is generally safe and highly effective, a new study suggests that taking the correct dose is extremely important.
Researchers from the University of Michigan found that thyroid hormone levels that are too high or too low during treatment may increase the risk of dying from heart disease. Their findings were published in JAMA Network Open.
The research was led by Dr. Maria Papaleontiou and examined medical records from more than 705,000 U.S. veterans who received thyroid hormone treatment between 2004 and 2017. This large study gave researchers an opportunity to better understand how thyroid hormone levels affect long-term heart health.
The researchers focused on a blood test called thyroid-stimulating hormone, or TSH. TSH is produced by the brain and tells the thyroid gland how much hormone to make. Doctors regularly measure TSH because it is one of the best ways to determine whether a person is receiving the right amount of levothyroxine.
If TSH levels are very low, it usually means the body has too much thyroid hormone. This often happens when the levothyroxine dose is too high. Doctors call this exogenous hyperthyroidism because the extra hormone comes from medication rather than from the thyroid gland itself.
If TSH levels are very high, it usually means the body is not getting enough thyroid hormone, often because the medicine dose is too low.
Both situations can place extra stress on the heart. Too much thyroid hormone can make the heart beat too quickly, trigger abnormal heart rhythms, and increase strain on the heart.
Too little thyroid hormone can slow the heart, raise cholesterol levels, and make it more difficult for the heart to pump efficiently. Over time, either condition may increase the risk of serious cardiovascular problems.
The study found that as many as half of the patients did not have their thyroid hormone levels well controlled. The greatest danger was seen in people whose TSH levels were extremely low, below 0.1, or extremely high, above 20.
These patients had the highest risk of dying from heart-related causes. Older adults were especially vulnerable because they are more sensitive to changes in thyroid hormone levels.
To improve the accuracy of the research, the scientists excluded people with conditions that could strongly affect thyroid hormone levels, including thyroid cancer and the use of medicines such as lithium or amiodarone. This helped ensure that the results reflected the effects of levothyroxine treatment as accurately as possible.
The findings highlight an important message. Treating hypothyroidism is not simply a matter of taking a daily pill. The medicine must be adjusted to each person’s needs, and the correct dose may change over time because of age, weight, pregnancy, other illnesses, or interactions with different medications.
The good news is that these risks can often be reduced. Regular blood tests allow doctors to monitor TSH levels and adjust the dose when necessary. Even people who feel well should continue having routine check-ups because thyroid hormone levels can change without causing obvious symptoms.
This study also reminds us that the thyroid and the heart are closely connected. Careful monitoring, personalized treatment, and regular follow-up appointments can help people receive the full benefits of levothyroxine while reducing the chance of heart complications.
With the right dose and ongoing medical care, most people with hypothyroidism can successfully manage their condition and enjoy healthy, active lives.
If you care about heart health, please read studies about how eating eggs can help reduce heart disease risk, and Vitamin K2 could help reduce heart disease risk.
For more information about heart health, please see recent studies about how to remove plaques that cause heart attacks, and results showing a new way to prevent heart attacks, strokes.
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