A recent study conducted by Johns Hopkins Medicine has established a correlation between elevated levels of thyroid hormone, known as thyrotoxicosis, and a heightened risk of cognitive disorders in older adults. The study delineates two sources of thyrotoxicosis: exogenous, resulting from the intake of thyroid medication, and endogenous, stemming from thyroid ailments such as hyperthyroidism and Graves’ disease, both of which have been identified as contributing factors to an increased likelihood of cognitive impairment. This research was made available online on October 23 by JAMA Internal Medicine.
Roy Adams, PhD, M.S., the study’s lead author and an assistant professor of psychiatry and behavioural sciences at the Johns Hopkins University School of Medicine, pointed out that while previous research hinted at a possible link between thyrotoxicosis and cognitive disorders, the findings were inconsistent, and studies often excluded cases of exogenous thyrotoxicosis. He highlighted the significance of understanding the impact of thyroid hormone levels on cognitive health, especially given that thyroid hormone prescriptions are among the most common in the United States. A prior investigation by Johns Hopkins Medicine revealed that as many as 20% of individuals taking thyroid hormone medication might be receiving doses too high, exposing them to the risk of exogenous thyrotoxicosis.
The aim of the study, as Adams explained, was to explore whether the aggressive treatment approaches that lead to exogenous thyrotoxicosis could also be causing cognitive damage. The importance of recognizing the adverse effects of overtreatment lies in guiding medical professionals in their prescription of thyroid hormone therapies more cautiously.
For their research, the team utilized a database of electronic health records from Johns Hopkins Medicine, selecting a cohort of 65,931 individuals aged 65 and above who had been under primary care within the Johns Hopkins Health System from January 1, 2014, to May 6, 2023. The initial primary care visit recorded for these participants showed an average age of 71, with each individual having attended at least two appointments spaced by a minimum of 30 days.
The findings revealed a 39% increase in the diagnosis of cognitive disorders among patients experiencing any form of thyrotoxicosis—whether endogenous or exogenous—across different age brackets. Specifically, by the age of 75, 11% of patients who had undergone thyrotoxicosis received a diagnosis of cognitive disorder, compared to 6.4% who hadn’t experienced thyrotoxicosis. This risk escalated with age; by 85, the figures rose to 34% for those with thyrotoxicosis versus 26% for those without. Even after adjusting for potential biases and alternative explanations through statistical models, the increased risk linked to thyrotoxicosis persisted.
Moreover, the study established a correlation between the severity of thyroid hormone excess and the risk of developing cognitive disorders. Patients with severe excess were found to have a 65% increased risk, whereas those with a moderate excess faced a 23% increased risk.
Jennifer Mammen, M.D., Ph.D., the senior author of the study and an assistant professor of medicine at the Johns Hopkins University School of Medicine, underscored the implication of their findings: an increased risk of cognitive disorders could be a consequence of excess thyroid hormone, a frequent outcome of thyroid hormone treatment. She advised clinicians to employ age-appropriate treatment strategies to mitigate the risk of cognitive disorders in older adults by preventing overtreatment.
More information: Roy Adams et al, Endogenous and Exogenous Thyrotoxicosis and Risk of Incident Cognitive Disorders in Older Adults, Johns Hopkins Medicine. DOI: 10.1001/jamainternmed.2023.5619
Journal information: Johns Hopkins Medicine
