Hypothyroidism may increase dementia risk, new study reports 

Depending on the type of thyroid disease you have, you may be at a higher risk of developing memory loss and cognitive decline. 

A new study published in the American Academy of Neurology found that older people with hypothyroidism, also known as an underactive thyroid, were at an increased risk of developing dementia. 

However, the risk was even higher for people whose condition required thyroid hormone replacement medication, said Chien-Hsiang Weng, MD, MPH, corresponding author and clinical associate professor of Family Medicine at Alpert Medical School of Brown University. 

What else did the study find? 

Weng and his colleagues analyzed health records from more than 7,800 Taiwanese residents who were newly diagnosed with dementia and compared them to the same number of participants who did not have dementia. They also looked to see who had a history of either hypothyroidism or hyperthyroidism. 

The researchers found: 

• People over age 65 with hypothyroidism were 80% more likely to develop dementia compared to people of the same age who did not have any thyroid problems. 
• Patients 65 and older with hypothyroidism who received medication for the condition were three times more likely to develop dementia than those who did not take the medication. 
• People under 65 with a history of hypothyroidism were not associated with an increased risk of dementia. 
• Patients 65 and older who had hyperthyroidism and received treatment for the condition but later developed hypothyroidism did not have an increased risk for dementia. 
• There was no link between hyperthyroidism and dementia. 

Weng noted this observational study only shows an association between hypothyroidism and dementia but does not prove it’s a direct cause. 

Why is hypothyroidism linked to a higher risk of dementia? 

According to David Merrill, MD, PhD, director of the Pacific Neuroscience Institute’s Pacific Brain Health Center at Providence Saint John’s Center in Santa Monica, California, a more severe thyroid condition necessitates a longer treatment duration—increasing the likelihood patients will experience greater symptoms and potentially higher damage from the condition. 

“When you have to go through treatment for a longer period of time, that just shows that they [participants] had dysregulation of the thyroid function and that was stressing both the brain, the skin, the heart, the bones, and other parts of the body out,” he said. 

Merrill added if medication is needed to treat the thyroid, it could be an indicator that participants in the study had more problematic or more severe thyroid dysfunction and that, in general, affects organ function and other parts of the body like the brain, bones and skin. 

However, Weng said taking medication for the condition is not related to a higher risk of dementia. 

“People are more likely to experience greater symptoms from hypothyroidism where treatment was needed,” he said. “We don’t think it’s related to the medication itself. The medication use for patients with hypothyroidism is likely reflecting the severity of hypothyroidism or being symptomatic.” 

What to do if you’re showing symptoms or have an active thyroid 

Because the researchers found an association between an underactive thyroid and dementia, Weng said patients should seek medical attention if they feel tired/cold, experience hair loss, dry skin, or any other symptoms associated with hypothyroidism. 

He added that people who have an active thyroid or 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. 

“Once somebody recognizes that their thyroid is underactive and they start getting it treated, know that you’ve done what you can to reduce your risk of later problems, not just for the brain, but also for the heart, bones, muscles, hair and skin,” he said. 

Furthermore, patients who may not be showing symptoms or have an active thyroid can still speak with their primary care doctor to run screening tests to make sure their thyroid function is at an optimal level as early in life as possible. 

“It’s a good thing to get your thyroid checked as part of health maintenance, and it’s something patients can ask their doctors about if they’re worried about their thyroid function and or their risk for memory loss,” Merrill added. 

How is hypothyroidism treated? 

In most cases, hypothyroidism is treated using hormone replacement therapy, which involves taking medication that replaces the amount of hormones your thyroid is no longer making. Patients will often have to take the medication continuously for the rest of their life to normalize thyroid hormones in the body. 

If a thyroid is not treated, it can lead to more severe symptoms, including trouble breathing, mental health problems, nerve injury, heart problems and enlargement of the thyroid gland. In severe cases, an untreated hypothyroid can lead to a serious condition called myxedema coma or even death.