An Underactive Thyroid Has Ties to Dementia

Do you have an underactive thyroid? If yes, you may have an elevated risk of developing dementia as you age, particularly if you’re taking thyroid hormone replacement therapy, according to a study published in an online edition of Neurology. The study is observational, which means researchers didn’t find that low thyroid levels caused dementia, just that they were linked.

How Does the Thyroid Function?

The thyroid is a small, butterfly-shaped gland located in front and below of the larynx. It produces triiodothyronine (T3) and thyroxine (T4), hormones that work together to regulate your body’s energy use and help control metabolism, body temperature, muscle strength, weight and nervous system. 

“Like other organs, the thyroid is susceptible to disease,” says Bernard Kaminetsky, MD, medical director, MDVIP. “Thyroid disease is divided into two umbrellas -- hypothyroidism or underactive thyroid and hyperthyroidism or overactive thyroid.”

Hypothyroidism vs. Hyperthyriodism: What's the Difference?

Let’s focus on hypothyroidism. This includes thyroiditis, Hashimoto’s disease, postpartum thyroiditis, iodine deficiency and non-functioning thyroid. Hypothyroidism is a common condition that affects nearly 5 in every 100 Americans, according to the National Institute of Diabetes and Digestive and Kidney Disease. 

It can develop in men and women at any age but tends to occur in women over age 60. With an underactive thyroid, not enough T3 or T4 is released into the bloodstream, causing symptoms such as fatigue, weight gain and poor ability to tolerate cold temperatures. Hypothyroidism also is linked with heart health issues including a slower heart rate, higher bad cholesterol level, constricted blood vessels, raised blood pressure, fluid retention and heart failure. And dementia-like symptoms have been reported in some patients. There’s a connection between heart health and brain health issues like dementia. 

Researchers from Brown University reviewed health records of two groups of people consisting of close to 7,800 Taiwanese people with an average age 75. One group was recently diagnosed with dementia, while the other group didn’t have dementia. Researchers looked for histories of hypothyroidism and hyperthyroidism. 

Researchers found a link between hypothyroidism and dementia but not between hyperthyroidism and dementia. In the study:

• 68 people with dementia also had hypothyroidism (0.9 percent)
• 34 people without dementia had hypothyroidism (0.4 percent)
• After adjusting data for factors such as gender, age, blood pressure and diabetes status, researchers found people over 65 with hypothyroidism had an 80 percent greater chance of developing dementia compared to those without thyroid disease. 
• People younger than 65 with hypothyroidism didn’t seem to have a higher risk for dementia. 
• People taking medication for hypothyroidism were three times more likely to develop dementia compared to those not taking drugs.

“This is an observational study -- researchers weren’t able to find a causal relationship between hypothyroidism and dementia – just an observational one,” says Kaminetsky. “However, this study should serve as encouragement to work closely with your primary care doctor to manage thyroid conditions and other issues associated with brain health like cardiovascular disease.”  

Looking for a primary care physician? Consider partnering with an MDVIP-affiliated physician. An MDVIP-affiliated doctor can customize a wellness plan for you that focuses on a thyroid-friendly lifestyle. Find an MDVIP affiliate near you and begin your partnership in health »