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This thyroid condition may boost the risk of dementia in older adults

A study by researchers in U.S. and Taiwan says having too little of a thyroid hormone could increase the risk of cognitive impairment

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In this Monday, Feb. 6, 2012, file photo, Alexis McKenzie, the executive director of The Methodist Home of the District of Columbia Forest Side, an Alzheimer’s assisted-living facility in Washington, puts her hand on the arm of a resident.

Charles Dharapak, Associated Press

Older adults who have an underactive thyroid may face an increased risk of dementia, according to a new study by researchers in the United States and Taiwan just published online in the journal Neurology.

They found the risk was higher for those who needed medication to replace their missing thyroid hormone.

The condition, called hypothyroidism, occurs when the thyroid gland doesn’t produce enough hormones, which can slow metabolism, as a report on Science Daily explains.

Gaining weight, feeling tired and being sensitive to cold are among the symptoms of an underactive thyroid.

“In some cases, thyroid disorders have been associated with dementia symptoms that can be reversible with treatment,” said lead author Dr. Chien-Hsiang Weng, a Brown University researcher. “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, researchers compared the health records of 7,843 people in Taiwan, average age 75, who had just been diagnosed with dementia against the same number who didn’t have dementia. They also checked to see who had been diagnosed with an underactive or overactive thyroid.

While the comparison didn’t show a link with dementia for those with an overactive thyroid, researchers did find such a connection in those who had underactive thyroids.

Twice as many people with dementia had hypothyroidism compared to those without dementia. It was still, however, a very low percentage. When researchers adjusted for other factors that could impact risk of dementia — sex, age, high blood pressure, diabetes, hearing problems and heart disease — “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,” according to a news release from the American Academy of Neurology.

Those who had hypothyroidism severe enough to require medication were three times more likely to develop dementia than those who did not take medication.

“We don’t think the medication itself if causing the risk. We think it’s the severity of the disease to the point where medication is needed,” Weng told United Press International. He noted that people with underactive thyroid “don’t have to be panicky,” but said they should get proper medical care and not ignore their thyroid problem.

The study shows correlation, not causation. And the researchers noted a limitation in that they could not include information about how severe the hypothyroidism was.

Other experts say they hope the study will spark more research on a possible link between thyroid function and cognitive decline.

“Research has found links between having multiple health conditions and an increased risk of dementia, but we need to know more about the causes of these links,” Dr. Sara Imarisio, head of research at Alzheimer’s Research UK, said in the organization’s report on the study. She said that while the study found high correlation between too-little thyroid hormone production and dementia, it didn’t look at why that might happen.

“If you are worried about your thyroid, it is best to arrange an appointment with your doctor who can do some simple test to check that it is working properly,” she said, noting that in the United Kingdom, 2% of people have an underactive thyroid.

The new study is not the first to find a correlation between thyroid function and cognition. For example, a 2020 study in The Egyptian Journal of Internal Medicine said that “thyroid dysfunction is associated with many neuropsychiatric disorders, mainly cognitive impairment.”

That’s similar to findings of a Danish nationwide register-based study published in 2021 in the journal Clinical Endocrinology. That research noted, as well, that the length of time someone had hypothyroidism also influenced the risk of dementia.