• Posted November 30, 2023

Could an Overactive Thyroid Harm the Aging Brain?

Elevated levels of thyroid hormone appear to harm the aging brain, increasing seniors' risk of dementia or other cognitive disorders, a new study finds.

High levels of thyroid hormone -- a condition called thyrotoxicosis -- was associated with thinking problems whether they came from an overactive thyroid gland or from taking thyroid medication, researchers found.

“Our results suggest that an increased risk of cognitive disorders is among the potential negative consequences of thyroid hormone excess, a common consequence of thyroid hormone therapy,” said senior researcher Dr. Jennifer Mammen, an assistant professor of medicine at Johns Hopkins University School of Medicine in Baltimore.

“Clinicians considering thyroid hormone therapy in older adults should avoid over-treatment by using age-appropriate treatment strategies,” Mammen added in a university news release.

Some prior studies have suggested that high thyroid levels were associated with an increased risk of cognitive disorder, but those results have been mixed, researchers said. Additionally, those earlier studies didn't include excess thyroid hormone caused by taking medication.

Thyroid hormone is among the most common prescriptions in the United States, researchers said. As many as 20% of people prescribed thyroid hormone might be taking too much, putting them at risk for thyrotoxicosis.

“Our goal was to investigate whether aggressive treatment practices … can also possibly cause cognitive harm,” said lead researcher Roy Adams, an assistant professor of psychiatry and behavioral sciences at Hopkins.

For their study, researchers analyzed the health records of nearly 66,000 seniors who received primary care from the Johns Hopkins Health System between January 2014 and May 2023.

Overall, elevated thyroid levels were associated with a 39% increase in the risk of a cognitive disorder diagnosis, researchers found.

About 11% of patients with thyrotoxicosis wound up diagnosed with a thinking problem by age 75, compared with around 6% of those who never had high thyroid levels, researchers found.

By age 85, 34% of patients with thyrotoxicosis had been diagnosed with a thinking problem, compared with 26% of patients without high thyroid.

Among people prescribed thyroid hormone, the amount they took was associated with their risk of cognitive disorders.

Patients whose meds caused severely high thyroid hormone levels had a 65% increased risk of cognitive problems, compared with a 23% increased risk for those whose meds caused a more moderate degree of excess thyroid.

The new study was published recently in the journal JAMA Internal Medicine.

“Understanding the negative effects of over-treatment is critical to help guide clinicians in how they prescribe thyroid hormone therapy,” Adams said.

More information

The Cleveland Clinic has more about thyrotoxicosis.

SOURCE: Johns Hopkins Medicine, news release, Nov. 28, 2023