Bharti Jayshankar
December 3, 2024: A study conducted by researchers at Johns Hopkins University revealed concerning links between levothyroxineâa commonly prescribed medication for hypothyroidismâand bone loss in older adults. Levothyroxine, the second most frequently prescribed medication among this demographic, may contribute to greater reductions in total body bone mass and density, even among patients whose thyroid-stimulating hormone (TSH) levels fall within the normal range.
The study analyzed data from the Baltimore Longitudinal Study of Aging (BLSA), focusing on participants aged 65 and older. The study included 81 levothyroxine users and 364 non-users, with a median follow-up period of 6.3 years.
The results showed that levothyroxine use was associated with a significant loss of total body bone mass and density. Specifically, participants taking levothyroxine experienced greater reductions compared to those not using the medication, regardless of their TSH levels being within the normal reference range (0.4 â 5.0 microunits per milliliter) .
Lead author Dr. Elena Ghotbi emphasized that a considerable number of prescriptions may be issued to older adults without hypothyroidism, raising concerns about excess thyroid hormone levels and their potential adverse effects on bone health. Co-senior author Dr. Shad Demehri noted that even adherence to current treatment guidelines does not eliminate the risk of bone loss associated with levothyroxine use.
Previously, the authors had shown that the use of levothyroxine in people with higher thyroid hormone levels harmed leg mass in older adults, in a study whose results appeared in Frontiers in Aging.
Levothyroxine and hypothyroidism
Levothyroxine is a synthetic version of the thyroid hormone thyroxine (T4) and is primarily prescribed to treat hypothyroidismâa condition where the thyroid gland fails to produce adequate hormones, leading to symptoms such as fatigue, weight gain, and hair loss. Approximately 23 million Americans, or about 7% of the U.S. population, take levothyroxine daily.
The global levothyroxine market is projected to reach approximately USD 3.95 billion by 2024. North America leads the market with over 40% share, followed by Europe at 30% and Asia-Pacific at around 23%.
While levothyroxine is crucial for managing hypothyroidism, long-term use raises questions about its necessity and potential risks in older adults.
Overdiagnosing of hypothyroidism in older adults is an ongoing debate. A letter published in Clinical Chemistry in 2023 suggested that hypothyroidism was overdiagnosed in many people.
It cited research showing that TSH levels vary significantly throughout the year, peaking in the winter and dropping in the summer months. The letter alleged that by not taking normal seasonal variation in TSH levels into consideration, many people were being prescribed drugs that might not help them, and they may even experience negative, avoidable side effects.
Recommendations for patients
Given these findings, healthcare providers are advised to conduct regular assessments of patients on levothyroxine therapy. Dr. Jennifer Mammen, another co-senior author, recommends that patients discuss their treatment plans with their healthcare providers and consider regular monitoring of thyroid function tests. A thorough risk-benefit analysis should be performed to weigh the necessity of treatment against potential adverse effects on bone health.
The implications of this study are particularly relevant as osteoporosisâa condition characterized by weakened bonesâis a significant health concern among older adults, especially postmenopausal women. Bone density loss is a natural part of aging but can be exacerbated by medications like levothyroxine.
With millions relying on levothyroxine for hypothyroidism management, understanding its potential impact on bone health is crucial for ensuring safe and effective treatment strategies.
The research was presented at the  Annual Meeting of the Radiological Society of North America session in late November and is yet to be peer-reviewed.