A study to be presented at the Radiological Society of North America (RSNA) annual meeting found that levothyroxine use was associated with bone loss in older adults, even when thyroid levels measured within normal ranges. Levothyroxine, the second most commonly prescribed medication among older adults in the U.S., is used to treat hypothyroidism.
In a longitudinal analysis spanning 6.3 years, the data showed levothyroxine users experienced greater loss of total body bone mass and density compared to non-users, despite thyroid-stimulating hormone (TSH) levels within the standard reference range of 0.4-5.0 microunits per milliliter.
The study analyzed data from 445 participants aged 65 and older through the Baltimore Longitudinal Study of Aging (BLSA), comparing 81 euthyroid levothyroxine users (32 men, 49 women) with 364 non-users (148 men, 216 women). The median age was 73 years, with baseline TSH levels of 2.35.
Using propensity score matching and controlling for variables—including age, gender, body mass index, race, alcohol intake, smoking history, and medication use—the study found significantly greater longitudinal loss of total body bone mass (beta: -6.53; 95% CI: -10.39, -2.67; P < .001) and total body bone density (beta: -0.0014; 95% CI: -0.002, -0.0006; P < .001) among levothyroxine users. The findings suggest that higher free thyroxine (FT4) levels, even within the reference range, may exacerbate this effect.
Approximately 23 million Americans—about 7% of the U.S. population—take levothyroxine daily. The medication, marketed under various brand names including Synthroid, treats hypothyroidism, a condition where the thyroid gland doesn't produce sufficient hormones naturally.
“Our study suggests that even when following current guidelines, levothyroxine use appears to be associated with greater bone loss in older adults,” said Shadpour Demehri, MD, professor of radiology at Johns Hopkins and co-senior author of the study. Co-senior author Jennifer Mammen, MD, PhD, added, “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.”
Lead author Elena Ghotbi, MD, stated, “Data indicates that a significant proportion of thyroid hormone prescriptions may be given to older adults without hypothyroidism, raising concerns about subsequent relative excess of thyroid hormone even when treatment is targeted to reference range goals.”
The research team used dual-energy X-ray absorptiometry (DEXA) measurements at each study visit to track changes in bone density and mass over time. The BLSA dataset represented the longest-running study on aging conducted by the National Institute on Aging's Intramural Research Program.
This study was a collaboration between the Russell H. Morgan Department of Radiology and Radiological Science and the Endocrinology Department at Johns Hopkins Medical Institutions. Co-authors include Hamsa Ibad, MBBS, and Qian-Li Xue, PhD.
The study’s findings are subject to updates during the RSNA meeting as researchers refine their data.
