A popular thyroid medication taken by 23 million Americans may be associated with bone loss, a startling new study finds.
Levothyroxine — marketed under brand names such as Synthroid — is the second-most commonly prescribed medication among older adults in the US. It’s consumed by about 7% of the US population.
The drug addresses hypothyroidism, also known as an underactive thyroid, by replacing or providing more of a thyroid hormone naturally produced by the body.
The study authors, from Johns Hopkins Medicine, linked levothyroxine use to a greater loss of bone mass and bone density over six years — even in older adults with normal thyroid function.
The preliminary research compared the bone health of 81 levothyroxine users and 364 nonusers, who were mostly in their early 70s.
“Our study suggests that even when following current guidelines, levothyroxine use appears to be associated with greater bone loss in older adults,” said Dr. Shadpour Demehri, co-senior study author and professor of radiology at Johns Hopkins.
For their part, the makers of Synthroid acknowledge that taking too much levothyroxine can lead to increased bone loss — especially in postmenopausal women.
The loss of bone mineral density and bone mass is called