A new study from Johns Hopkins Medicine shows that having too much thyroid hormone—a condition called thyrotoxicosis—may raise the risk of memory and thinking problems in older adults.
This includes both cases where people take too much thyroid medicine (called exogenous thyrotoxicosis) and where the body makes too much hormone due to thyroid diseases like hyperthyroidism or Graves’ disease (called endogenous thyrotoxicosis).
Thyroid hormone is important for the body. It helps control how fast we burn energy, how warm we feel, and how our organs work. But when there is too much of it in the body, things can go wrong.
Past studies have suggested a possible link between too much thyroid hormone and cognitive decline—like memory loss or dementia—but these studies did not include people who were taking thyroid medication. The new research fills this gap.
The team studied medical records of 65,931 people aged 65 and older who visited doctors within the Johns Hopkins Health System between 2014 and 2023. The average age was 71, and each person had at least two visits over time, giving researchers enough information to track health changes.
The results were clear: people with thyrotoxicosis were more likely to develop cognitive problems than those without it. In fact, the risk was 39% higher in people with any kind of thyrotoxicosis. By age 75, about 11 out of every 100 people with too much thyroid hormone had been diagnosed with a cognitive disorder like dementia.
For those without the condition, only about 6 out of 100 had such a diagnosis. By age 85, the numbers were even more concerning—34% of those with thyrotoxicosis had cognitive issues, compared to 26% of those without it.
The study also found that how much extra thyroid hormone a person had mattered. Among people taking thyroid medicine, those with very high levels of hormone had a 65% higher risk of developing cognitive problems. Even those with only moderately high levels still had a 23% higher risk than people with normal levels.
This means that too much thyroid hormone—whether from the body or from medicine—may harm the brain over time, especially in older people. Since thyroid problems are common and many older adults take thyroid hormone as part of their treatment, this finding is important.
Doctors should be careful when treating older patients with thyroid hormone. Giving too much can do more harm than good. Treatments should be tailored to the patient’s age and health condition to avoid unnecessary risks.
This research shows how important it is to watch thyroid hormone levels closely, especially in older adults. The brain can be affected by many things, and hormones are one of them. More studies are needed to better understand how this works and how doctors can safely treat thyroid problems without increasing the risk of memory loss or confusion in their patients.
The full research was published in JAMA Internal Medicine.
If you care about brain health, please read studies about how the Mediterranean diet could protect your brain health, and blueberry supplements may prevent cognitive decline.
For more information about brain health, please see recent studies about antioxidants that could help reduce dementia risk, and Coconut oil could help improve cognitive function in Alzheimer’s.
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