Older people with underactive thyroid, which is formally called hypothyroidism, may be at increased risk of developing dementia, according to a new research study published in the July 6, 2022, online issue of Neurology, the medical journal of the American Academy of Neurology. According to the findings, the risk of developing dementia was even higher for people whose thyroid condition was serious enough to require thyroid hormone replacement medication.
Simply stated, hypothyroidism occurs when the thyroid gland doesn’t make enough thyroid hormones. This can slow metabolism. Symptoms include feeling tired, dry skin, weight gain, puffy face, and sensitivity to cold.
“In some cases, thyroid disorders have been associated with dementia symptoms that can be reversible with treatment,” said study author Chien-Hsiang Weng, MD, MPH, of Brown University in Providence, Rhode Island. “While more studies are needed to confirm these findings, people should be aware of thyroid problems as a possible risk factor for dementia and therapies that could prevent or slow irreversible cognitive decline.”
For the study, scientists analyzed the health records of 7,843 people newly diagnosed with dementia in Taiwan and compared them to the same number of people who did not have dementia. The average age of study participants was 75. Researchers examined the data to see who had a history of either hypothyroidism or hyperthyroidism. Hyperthyroidism, which is also called overactive thyroid, is when the thyroid produces too much hormone. This can increase metabolism. Symptoms include unintended weight loss, rapid or irregular heartbeat, and nervousness or anxiety.
The prefixes hypo- and hyper- are opposites. Hypo means low, under, down, or below normal. Hyper means high, over, up, or above normal.
A total of 102 people had hypothyroidism and 133 had hyperthyroidism.
The researchers found no link between hyperthyroidism and dementia.
Of the people with dementia, 68 people, or 0.9%, had hypothyroidism, compared to 34 of the people without dementia, or 0.4%. When researchers adjusted for other factors that could affect the risk of dementia, such as sex, age, high blood pressure, and diabetes, they found that people over age 65 with hypothyroidism were 80% more likely to develop dementia than people the same age who did not have thyroid problems. For people younger than 65, having a history of hypothyroidism was not associated with an increased risk of dementia.
When researchers looked only at people who took medication for hypothyroidism, they found they were three times more likely to develop dementia than those who did not take medication. “One explanation for this could be that these people are more likely to experience greater symptoms from hypothyroidism where treatment was needed,” Weng said.
Weng noted that the observational study does not prove that hypothyroidism is a cause of dementia; it only shows an association.
A limitation of the study was that researchers were not able to include information about how severe the hypothyroidism was for participants.
Reference: “Thyroid Disorders and Dementia Risk: A Nationwide Population-Based Case-Control Study” by Daniel R Wieland, Julia R Wieland, Han Wang, Yi-Huei Chen, Ching-Heng Lin, Jing-Jie Wang and Chien-Hsiang Weng, 6 July 2022, Neurology.