Why Your Thyroid Medication Dose Should Be Rechecked Every Year

Fact checked by Nick Blackmer

Key Takeaways

• Hyperthyroidism—an overactive thyroid—is associated with a slightly increased risk of dementia in older adults.

• New research suggests that overmedication with levothyroxine, a medication for an underactive thyroid, may also be linked to dementia.

• Endocrinologists are calling for more research about when and how often levothyroxine is prescribed in older adults.

A recent study found that patients who get too much of a particular thyroid medication are at higher risk of dementia. The researchers said that cognitive decline was previously known to occur in people whose bodies made too much thyroid hormone, but the new study links dementia risk to levothyroxine, a medication that supplements thyroid hormone in people with levels that are too low.

The findings are especially important because millions of people take supplemental thyroid hormone medication, study author Jennifer Mammen, MD, PhD, an assistant professor of medicine at Johns Hopkins Medicine, told Verywell.

Here’s what experts want you to know about the link between thyroid medication and dementia and when you should talk to your provider about your dose if you take levothyroxine.

Related: Levothyroxine: Brand Name vs. Generic

The Importance of Thyroid Hormones

The thyroid gland is in the front of the neck and makes thyroid hormone, which affects nearly every organ in your body. The hormone helps control weight, body temperature, muscle strength, and even mood, David Cooper, MD, head of the thyroid clinic at Johns Hopkins Medicine in Baltimore, told Verywell. Cooper was not involved with the new study.

“Without enough thyroid hormones in your blood, many body functions slow down,” Cooper said.

The pituitary gland in the brain produces thyroid-stimulating hormone (TSH). If thyroid hormone levels in the blood are too low, the pituitary makes more TSH to tell the thyroid it needs to work harder. If thyroid hormone levels are too high, the pituitary makes little to no TSH.

Your provider can do a blood test to indirectly check your thyroid hormone levels by measuring your TSH levels. If your TSH levels are high, you might need to take supplemental thyroid hormone. If your TSH is low, you might have too much thyroid hormone. These blood tests can also help your provider tell if your thyroid medication needs to be adjusted or stopped.

Related: How Your Thyroid Gland Works

TSH Levels and the Brain

In the new study, the researchers looked at the records of around 65,000 patients in the Johns Hopkins Community Physicians Network between 2014 and 2022 who were aged 65 and older. None of the patients had a diagnosis of cognitive decline or a low TSH level within six months of their first provider visit.

Since previous research had shown that people whose bodies make too much thyroid hormone have a higher risk for dementia, the researchers wanted to find out if the risk was also higher in people taking too much thyroid medication.

During the study, some of the patients taking supplemental thyroid hormone medication had low TSH levels. In the follow-up period, 7.2% (4,779) of patients who were taking an excessively high dose of levothyroxine got a new cognitive disorder diagnosis.

The study had limitations—for example, the population was mostly White and female. But the researchers think the findings add to a growing body of evidence that there could be cognitive risks for older adults who are taking thyroid medication—and who may not even need to be taking it.

Who Is At Risk?

Based on the findings, Mammen recommends that TSH levels be checked every year, especially in older patients, to see if their dose of thyroid medication should be changed or stopped.

“People are often put on a certain dose of thyroid hormone when they are in their 40s and 50s, or even younger, but the dose can often be lowered when people grow older,” Mammen said.

The study also showed that patients who were women were more likely to have low TSH levels and be overtreated.

In addition to cognitive decline, too much thyroid hormone is linked to other health risks, including atrial fibrillation (AFib)—an irregular heartbeat that can lead to blood clots and stroke—and a risk of fractures (especially in older women), according to Cooper.

A commentary by endocrinologists from the University of Michigan and the Mayo Clinic published along with the study explained that levothyroxine is one of the top three most commonly prescribed medications in the United States, with 24 million people getting a prescription for the drug in 2020. The authors emphasized that with so many people taking the medication, the findings of the new study that explore the risks are important.

The commentary also noted that levothyroxine tends to be prescribed more frequently to older patients and that several studies have suggested the medication is sometimes prescribed without medical evidence that it’s needed.

In response to the research, the commentary authors wrote that “the increasing awareness of the risks associated with levothyroxine usage should promote more cautious prescribing practices,” such as not giving levothyroxine to older adults whose thyroid levels are only a little bit low.

What This Means For You

Thyroid hormone is one of the most commonly prescribed medications, but taking too much comes with health risks and might even be linked to an increased risk of dementia. If you take thyroid medication, talk to your provider at least once a year about your dose. You should have your TSH levels checked to see if your dose needs to be adjusted.

Read Next: Hypothyroidism vs. Hyperthyroidism: What's the Difference?

Read the original article on Verywell Health.