Hypothyroidism (an underactive thyroid) can affect anyone, presenting a slew of unpleasant symptoms like weight gain, fatigue, depression, and hair loss, among other symptoms. When left untreated, it can cause serious and life-threatening conditions. Thankfully, there is medication to treat the condition, with the most common approach being hormone replacement therapy like levothyroxine (better known by brand names like Synthroid). However, new research suggests that this treatment may actually have unexpected consequences in the form of bone loss.
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The new study examined the potential connection between levothyroxine use and bone loss in older adults. According to a press release outlining findings, roughly 23 million Americans, or 7 percent of the population, take this prescription daily. Researchers also pointed out that some people have been taking this medication for years, and it’s not always clear why it was first prescribed or whether they still need to take it.
Researchers used data from the Baltimore Longitudinal Study of Aging (BLSA), which included information on “community-dwelling older adults.” For the present study, investigators included participants who were 65 and older with at least two visits and thyroid tests that fell within the normal reference range for thyroid-stimulating hormone (TSH), defined as roughly 0.4 to 5.0 microunits per milliliter. (The press release notes that “excess thyroid hormone,” otherwise known as hyperthyroidism, can lead to weaker bones. The condition is formally called osteoporosis.)
In total, the study included 81 older adults taking levothyroxine and 364 who were not. Participants had a mean age of 73, and all had TSH levels in the normal range of 2.35 at the initial visit.
Patients included in the BLSA had multiple bone-density scans, providing “valuable insight into the progression of bone density and bone mass changes over time, offering a more comprehensive understanding of aging-related osteoporosis,” study co-author Eleanor Simonsick, PhD, epidemiologist, and BLSA co-director, said in the press release.
After an average follow-up period of 6.3 years, older adults on levothyroxine had a greater loss of both total body bone mass and bone density.
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“Our study suggests that even when following current guidelines, levothyroxine use appears to be associated with greater bone loss in older adults,” Shadpour Demehri, MD, co-senior author and professor of radiology at Johns Hopkins, said in the release. The new data is set to be presented at the annual meeting of the Radiological Society of North America (RSNA) next week in Chicago.
Additional recent studies have also looked at levothyroxine, with Yale School of Medicine estimating that as many as 90 percent of those taking the medication may not even need it. Overuse of the treatment in adults over the age of 80 can also have “potentially severe side effects,” including death, Joe El-Khoury, PhD, associate professor of laboratory medicine, in a 2023 letter published in Clinical Chemistry.
Jennifer Mammen, MD, PhD, co-senior author of the recent study and associate professor of endocrinology at Johns Hopkins, recommended that older adults on levothyroxine talk to their doctor about their medication and actively check thyroid levels.
“A risk-benefit assessment should be conducted, weighing the strength of the indications for treatment against the potential adverse effects of levothyroxine in this population,” Mammen said in the release.