July 6 (UPI) -- An underactive thyroid in older people may dramatically increase their risk of developing dementia, new research says.
After adjusting for age, sex, and other risk factors, a Brown University-led team of researchers found that people over age 65 with hypothyroidism, or underactive thyroid, were 81% more likely to develop dementia than people of the same age without thyroid problems.
And investigators found more than a three-fold increase in dementia risk for older people whose thyroid conditions required thyroid hormone replacement medication.
"We don't think the medication itself is causing the risk. We think it's the severity of the disease," to the point where medication is needed," said Dr. Chien-Hsiang Weng, the study's lead author.
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Roughly 12% of the U.S. population may develop a thyroid disorder in their lifetime, Weng , an clinical assistant professor of family medicine at the Warren Alpert Medical School of Brown University in Providence, R.I., told UPI in a phone interview.
In their paper, which was published Wednesday in Neurology, the medical journal of the American Academy of Neurology, researchers said they hope these findings will "better inform physicians and patients alike of the risk factors of dementia and possible therapies to prevent or slow irreversible cognitive decline."
Weng said primary care doctors probably should test patients' thyroid function as consider it as one of the risk factors for dementia if patients suggest that their memory or thinking seems impaired.
He added that people with thyroid problems "don't have to be panicky" about dementia risk, but they should stay on top of their illness with proper medical care instead of taking a wait-and-see approach if they have any concerns.
The investigators found that a history of hypothyroidism was not associated with an increased risk of dementia for younger individuals, ages 50 through 64. And they found no potential link between hyperthyroidism, or overactive thyroid, and dementia.
The latter finding is likely due to the fact that an overactive thyroid produces too much thyroid hormone that stimulates the brain, Weng said.
Weng said it's not possible from this study's design to determine whether an overactive thyroid may cause other brain issues aside from dementia.
He cautioned that these findings arise from research that does not prove a causal relationship between hypothyroidism and dementia.
"This is an observational study. It's not a clinical trial ... so we can say that we do see these associations [between underactive thyroid and dementia], but we can't say that this is causing dementia," Weng said.
"We can only say we do see this association and it's a risk factor," he said.
However, he added, "It still shows significant, increased risk, and this is one of the larger studies looking at this problem."
The study involved nearly 15,700 individuals in Taiwan's National Health Insurance Research Database, who either were newly diagnosed (between 2006 and 2013) with dementia or had no dementia.
After matching cases and controls 1:1 by age and sex, the researchers then determined whether the study participants had a history of thyroid disorders.
