New research suggests that a thyroid medication often prescribed to older Americans may be linked to a common problem in old age — bone loss.

Levothyroxine is a synthetic hormone often prescribed to treat hypothyroidism. People with the condition don't make enough thyroxine on their own, which can cause weight gain, fatigue, hair loss and eventually lead to serious, even deadly, complications.

An estimated 23 million Americans take levothyroxine daily. Some take it for so long that it's no longer clear why it was prescribed to begin with or even if it is still needed, researchers said.

"Data indicates that a significant proportion of thyroid hormone prescriptions may be given to older adults without hypothyroidism," said study leader Dr. Elena Ghotbi, a postdoctoral research fellow at Johns Hopkins University School of Medicine in Baltimore.

A normal range for thyroid-stimulating hormone (TSH) in the blood is between 0.4 to 5.0 microunits per milliliter. Excess TSH has been tied to increased risk of broken bones.

For this study, Ghotbi's team wanted to learn whether using levothyroxine and having hormone levels on the high end of that range might cause more bone loss over time in older adults with normal thyroid function.

They drew on data from 445 participants in a Baltimore-based study of older adults with normal thyroid levels. Participants included 49 women and 32 men taking levothyroxine and 364 who were not. They were followed for a median of 6.3 years, meaning half were followed longer, half for less time.

After accounting for such factors as height, weight, race, alcohol, and tobacco history and other medications, researchers found those taking levothyroxine had greater loss of total bone mass and bone density.

The findings were presented Sunday at a meeting of the Radiological Society of America in Chicago.

"Our study suggests that even when following current guidelines, levothyroxine use appears to be associated with greater bone loss in older adults," said co-senior study author Dr. Shadpour Demehri, a professor of radiology at Johns Hopkins.

Co-senior study author Dr. Jennifer Mammen, an assistant professor of endocrinology at Johns Hopkins, urged adults taking levothyroxine to discuss their treatment with their doctor and have regular thyroid function tests.

"A risk-benefit assessment should be conducted, weighing the strength of the indications for treatment against the potential adverse effect of levothyroxine in this population," she said in a meeting news release.

Research presented at meetings is typically considered preliminary until published in a peer-reviewed journal.