A new study from Johns Hopkins Medicine has found that having too much thyroid hormone in the body may increase the risk of memory and thinking problems in older adults.
The condition, known as thyrotoxicosis, can happen when the thyroid gland produces too much hormone naturally or when a person takes a thyroid medication dose that is too high.
The findings are important because thyroid problems are very common, especially in older adults. Millions of people around the world take thyroid hormone medications every day to treat low thyroid function.
The new research suggests that while thyroid hormones are essential for health, having too much may be harmful to the aging brain.
The study was published in the medical journal JAMA Internal Medicine and adds to growing evidence that hormone balance plays an important role in brain health as people get older.
The thyroid is a small butterfly-shaped gland located in the front of the neck. Even though it is small, it has a powerful effect on the body.
The thyroid produces hormones that help control metabolism, which is how the body uses energy. These hormones affect many body functions, including heart rate, body temperature, digestion, sleep, mood, and brain activity.
When thyroid hormone levels are too low, people may feel tired, cold, depressed, or gain weight. When thyroid hormone levels are too high, symptoms can include a racing heart, anxiety, sweating, shakiness, weight loss, trouble sleeping, and muscle weakness.
In older adults, thyroid hormone imbalance can sometimes be difficult to recognize because the symptoms may appear slowly or look similar to normal aging. This is one reason why thyroid problems may go unnoticed for a long time.
Researchers have suspected for years that too much thyroid hormone might affect the brain and increase the risk of cognitive decline. Cognitive disorders include problems with memory, thinking, learning, attention, and decision-making. In severe cases, these problems may progress to dementia.
However, earlier studies on this topic produced mixed results. Some only looked at people with diagnosed thyroid disease and did not include people taking thyroid hormone medications. Others involved smaller groups of patients, making it difficult to draw strong conclusions.
To better understand the connection, researchers at Johns Hopkins Medicine studied the health records of nearly 66,000 adults aged 65 and older. The patients received medical care between 2014 and 2023, and the average age at the beginning of the study was 71 years old.
The researchers carefully followed the participants over time. Each person had at least two doctor visits separated by more than one month so the researchers could track health changes and thyroid hormone levels more accurately.
The results showed a clear pattern. Older adults with thyrotoxicosis had a 39% higher risk of being diagnosed with a cognitive disorder compared with people whose thyroid hormone levels were normal.
The increased risk was seen in both groups of patients. It affected people whose thyroid glands naturally produced too much hormone and people who developed high hormone levels because they were taking thyroid medication.
The study also showed that the severity of hormone imbalance mattered. The higher the thyroid hormone levels, the greater the risk of cognitive problems.
People with very high thyroid hormone levels had a 65% higher risk of cognitive disorders. Those with moderately high levels still had a 23% greater risk compared with people whose thyroid hormone levels stayed in a healthy range.
The researchers also examined how the risk changed as people aged. By age 75, about 11 out of every 100 people with thyrotoxicosis had developed a cognitive disorder, compared with just over 6 out of 100 people without the condition.
By age 85, the numbers became even more concerning. About one-third of people with too much thyroid hormone had cognitive problems, compared with about one-fourth of those without excess hormone levels.
These findings may have important implications for doctors who prescribe thyroid hormone replacement therapy. Many older adults take medications to treat hypothyroidism, which is a condition where the thyroid does not make enough hormone.
Thyroid replacement therapy can greatly improve health and quality of life when properly managed. However, if the dose becomes too high, patients may accidentally develop thyrotoxicosis. This study suggests that over-treatment may carry serious risks for brain health in older adults.
The researchers emphasized the importance of regular blood tests and medical check-ups to make sure thyroid hormone levels stay within a safe range. Older adults may be more sensitive to hormone changes than younger people, so doctors may need to adjust treatment carefully as patients age.
The study does not prove that excess thyroid hormone directly causes dementia or memory loss. It only shows a strong link between high hormone levels and higher rates of cognitive disorders. More research will be needed to understand exactly how thyroid hormones may affect the brain.
Scientists believe several possible explanations may exist. Excess thyroid hormone may affect blood flow in the brain, increase inflammation, place stress on nerve cells, or worsen other health problems linked to cognitive decline. Future studies may help explain these biological effects more clearly.
The findings are another reminder that balance in the body is extremely important for healthy aging. Hormones that are necessary for life can become harmful when levels become too high or too low.
For patients and families, the study highlights the importance of paying attention to thyroid health, especially in later life. Regular monitoring, careful treatment, and open communication with healthcare providers may help lower the risk of complications and protect long-term brain health.
Experts also advise patients not to stop or change thyroid medications without medical guidance. Proper treatment of thyroid disease remains very important. The goal is not to avoid treatment, but to keep hormone levels carefully balanced and monitored over time.
As researchers continue learning more about aging and brain health, studies like this may help doctors develop safer treatment plans for older adults and reduce the risk of memory and thinking problems later in life.
If you care about brain health, please read studies about low choline intake linked to higher dementia risk, and how eating nuts can affect your cognitive ability.
For more health information, please see recent studies that blueberry supplements may prevent cognitive decline, and results showing higher magnesium intake could help benefit brain health.
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