Summary: Levothyroxine, a common thyroid medication, may contribute to bone loss in older adults, even within normal thyroid function levels, according to a Johns Hopkins study presented at the Radiological Society of North America (RSNA) annual meeting.

Key Takeaways

  • Levothyroxine and Bone Loss: Levothyroxine, a widely prescribed medication for hypothyroidism, may contribute to bone mass and density loss in older adults, even when thyroid hormone levels are within the normal range.
  • Research Findings: A Johns Hopkins study using data from the Baltimore Longitudinal Study of Aging (BLSA) found that levothyroxine users aged 65 and older experienced greater bone loss over 6.3 years compared to non-users, despite normal thyroid function tests.
  • Clinical Implications: The study highlights the need for regular monitoring of thyroid function and reassessment of levothyroxine use in older adults, with careful consideration of the risks and benefits to prevent potential bone health complications.

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Levothyroxine, the second most prescribed medication among older adults in the U.S., may contribute to bone loss, according to a study being presented at the upcoming annual meeting of the Radiological Society of North America (RSNA).

Levothyroxine May Weaken Bones

Marketed under brands like Synthroid, levothyroxine is a synthetic form of thyroxine, commonly prescribed to treat hypothyroidism—a condition where the thyroid gland underproduces hormones, leading to symptoms such as fatigue, weight gain, and hair loss. Left untreated, hypothyroidism can cause serious complications. About 23 million Americans, or 7% of the U.S. population, take levothyroxine daily, often for years, sometimes without reevaluating the necessity of the prescription.

“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,” says Elena Ghotbi, MD, lead author and postdoctoral research fellow at Johns Hopkins University School of Medicine.

Excess thyroid hormone, even within the normal thyroid-stimulating hormone (TSH) range of 0.4–5.0 microunits per milliliter, has been linked to higher fracture risk. Dr. Ghotbi’s study, a collaboration between Johns Hopkins University and the Baltimore Longitudinal Study of Aging (BLSA), investigated whether levothyroxine use is associated with increased bone loss in euthyroid older adults (those with normal thyroid function).

Risks in Thyroid Medication Use

The study analyzed data from BLSA, the longest-running aging study conducted by the National Institute on Aging. It included 81 euthyroid levothyroxine users and 364 non-users, all aged 65 or older. Participants had consistent thyroid function tests within the normal range and at least two study visits. “The BLSA’s extensive data, including repeated DEXA measurements, provided valuable insight into aging-related changes in bone density and mass,” says Eleanor Simonsick, PhD, epidemiologist and BLSA co-director.

Results showed that levothyroxine users experienced greater total body bone mass and density loss over a median follow-up of 6.3 years, even with normal TSH levels. This association persisted after accounting for factors like age, gender, weight, and other risk factors.

“Our study suggests that even within guideline-recommended use, levothyroxine is associated with greater bone loss in older adults,” said co-senior author Shadpour Demehri, MD, professor of radiology at Johns Hopkins.

Co-senior author Jennifer Mammen, MD, PhD, associate professor of endocrinology, advises that patients regularly monitor thyroid function and discuss their treatment with healthcare providers. “A risk-benefit assessment is essential, weighing treatment indications against potential adverse effects in this population,” Mammen says.