Why should your dose of thyroid medication be reviewed every year?

A recent study found that patients who take too much of certain thyroid medications are at a higher risk of dementia. Scientists say it was previously known that cognitive decline occurs in people whose bodies produce too much thyroid hormone, but new research links it to the risk of dementia. levothyroxinea drug that supplements thyroid hormone in people with too low levels.

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

Here’s what experts want you to know about the link between thyroid medications and dementia, and when you should talk to your provider about your dosage if you’re taking levothyroxine.

The importance of thyroid hormones

The thyroid gland is located in the front of the neck and produces thyroid hormone, which affects almost every organ in your body. The hormone helps control weight, body temperature, muscle strength and even mood, David Cooper, M.D., chief of the Thyroid Clinic at Johns Hopkins Medicine in Baltimore, told Verywell. Cooper was not involved in 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 gland produces more TSH to tell the thyroid gland to work harder. If thyroid hormone levels are too high, the pituitary gland produces little or no TSH.

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

TSH levels and the brain

In the new study, researchers looked at the records of nearly 65,000 patients in the Johns Hopkins Community Physician Network who were age 65 and older between 2014 and 2022. None of the patients had cognitive decline or low TSH within six months of visiting their first provider.

Because previous research has shown that people whose bodies produce too much thyroid hormone have a higher risk of dementia, the scientists wanted to find out whether people who take too much thyroid medication also have a higher risk.

In the study, some patients taking thyroid hormone supplements had lower TSH levels. During the follow-up period, 7.2% (4,779) of patients taking an extremely high dose of levothyroxine received a new diagnosis of cognitive impairment.

The study had limitations. for example, the population was predominantly white and female. But the researchers say the findings add to growing evidence that there may be cognitive risks for older adults taking thyroid medication who may not even need to be taking it.

Who is at risk?

Based on the findings, Mammen recommends checking TSH levels annually, especially in older patients, to see if their thyroid medication dose needs to be changed or stopped.

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

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

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

A commentary by endocrinologists at the University of Michigan and the Mayo Clinic, published alongside the study, explains that levothyroxine is one of the top three prescription drugs in the United States, with 24 million people receiving a prescription in 2020. The authors emphasized that with so many people taking the medication, the results of a new study examining the risks are important.

The commentary also notes that levothyroxine is generally prescribed more often to elderly patients and that several studies have shown that the medication is sometimes prescribed without medical evidence of need.

In response to the study, the authors of the commentary wrote that “increased awareness of the risks associated with levothyroxine use should encourage more cautious prescribing,” such as not giving levothyroxine to older people with mildly low thyroid levels.