Higher Thyroid Hormone Levels Increase Older Adult Cognitive Disorder Risk

According to a new study from Johns Hopkins Medicine, thyrotoxicosis (excess thyroid hormone levels in the body) is associated with an elevated risk of cognitive impairments in older persons. Exogenous thyrotoxicosis (induced by taking thyroid medication) and endogenous thyrotoxicosis (produced by thyroid illnesses such as hyperthyroidism and Graves’ disease) were both linked to an increased risk of having a cognitive problem. JAMA Internal Medicine published the findings online on October 23.

“Some previous studies suggested that thyrotoxicosis was associated with an increased risk of cognitive disorders,” says Roy Adams, Ph.D., M.S., the study’s first author and assistant professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine. “But results have been mixed, and exogenous thyrotoxicosis was mostly excluded from those studies.”

Thyroid hormone is one of the most commonly prescribed drugs in the United States, according to GoodRx. A recent Johns Hopkins Medicine study discovered that up to 20% of persons prescribed thyroid hormone may be overtreated, putting them at risk for exogenous thyrotoxicosis.

“Our goal was to investigate whether aggressive treatment practices, which can cause exogenous thyrotoxicosis, can also possibly cause cognitive harm,” Adams adds. “Understanding the negative effects of overtreatment is critical to help guide clinicians in how they prescribe thyroid hormone therapy.”

The study’s subjects were chosen from a database of computerized health records at Johns Hopkins Medicine. The researchers identified 65,931 suitable patients aged 65 and older who received primary care at the Johns Hopkins Health System between January 1, 2014, and May 6, 2023. The average age at the time of the first recorded primary care visit was 71, and all patients had at least two visits that were 30 days or more apart.

All-cause thyrotoxicosis — endogenous and exogenous thyrotoxicosis combined — was related with a 39% increase in the likelihood of cognitive disorder diagnosis across age groups. By the age of 75, 11% of patients who had thyrotoxicosis had a cognitive problem, compared to 6.4% of patients who did not have thyrotoxicosis. By the age of 85, 34% of patients with thyrotoxicosis had a cognitive problem, compared to 26% of those who did not have thyrotoxicosis. An examination utilizing statistical models that addressed various sources of bias and alternative explanations for the correlations found that the elevated risk linked with thyrotoxicosis maintained.

The study also discovered that among people prescribed thyroid hormone, the level of thyroid hormone exposure associated with the degree of risk for a cognitive problem. Patients with a higher level of excess thyroid hormone had a 65% increased risk of cognitive dysfunction, while those with a lower level of excess thyroid hormone had a 23% increased risk.

“Our findings suggest that an increased risk of cognitive disorders is one of the potential negative consequences of thyroid hormone excess, which is a common side effect of thyroid hormone therapy,” says Jennifer Mammen, M.D., Ph.D., senior author of the study and assistant professor of medicine at the Johns Hopkins University School of Medicine. “Clinicians considering thyroid hormone therapy in older adults should avoid overtreatment by using age-appropriate treatment strategies.”

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