A recent study presented at the Radiological Society of North America (RSNA) annual meeting reveals that the use of levothyroxine, a medication commonly prescribed to treat hypothyroidism, may contribute to bone density loss in older adults. This study sheds light on the potential risks of long-term levothyroxine use, particularly among individuals with normal thyroid function.
Levothyroxine, which is marketed under various brand names including Synthroid, is a synthetic form of the thyroid hormone thyroxine. It is primarily prescribed to treat hypothyroidism, a condition in which the thyroid does not produce enough of this hormone, leading to symptoms like fatigue, weight gain, and hair loss. If left untreated, hypothyroidism can cause serious health complications.
Currently, about 23 million Americans—roughly 7% of the population—take levothyroxine, with many users being older adults. While the medication is essential for those with hypothyroidism, the study raises concerns about its use in individuals without the condition, particularly as thyroid hormone prescriptions are sometimes given to older adults who may no longer require the medication.
Bone Loss and Levothyroxine Use in Older Adults
Dr. Elena Ghotbi, the study’s lead author and a postdoctoral fellow at Johns Hopkins University School of Medicine, explains that excess thyroid hormone—whether from an overactive thyroid or from taking levothyroxine—has been linked to an increased risk of bone fractures. This is because thyroid hormone excess can accelerate bone loss, especially in older individuals.
For this study, Dr. Ghotbi and her team focused on a group of older adults with normal thyroid function, known as euthyroid adults, to see whether levothyroxine use was associated with accelerated bone loss over time. They used data from the Baltimore Longitudinal Study of Aging (BLSA), a long-running research project examining aging in community-dwelling older adults. The participants in the study were aged 65 and older, and their thyroid function was consistently within the normal reference range.
Research Methods and Key Findings
The study included 81 euthyroid participants using levothyroxine (32 men, 49 women) and 364 non-users (148 men, 216 women), with a median age of 73. Over a median follow-up period of 6.3 years, the researchers measured bone density changes using DEXA scans, which are commonly used to assess bone health.
The results revealed that those using levothyroxine experienced greater bone loss, even when their thyroid-stimulating hormone (TSH) levels were within the normal reference range. This association remained after accounting for other factors that can affect bone health, such as age, gender, and lifestyle factors like smoking and alcohol consumption.
“Our findings suggest that levothyroxine use, even with normal TSH levels, is linked to greater bone density loss in older adults,” said Dr. Shadpour Demehri, co-senior author and professor of radiology at Johns Hopkins.
Implications for Levothyroxine Users
These findings have important implications for older adults taking levothyroxine, particularly those who may not have a current need for the medication. Dr. Jennifer Mammen, another co-senior author and associate professor of endocrinology at Johns Hopkins, advises that individuals taking levothyroxine regularly monitor their thyroid function tests and discuss their treatment options with their healthcare provider. A thorough risk-benefit assessment should be conducted to ensure that the benefits of levothyroxine outweigh the potential risks, such as bone density loss.
Given the widespread use of levothyroxine, especially among older adults, this study provides valuable insight into the long-term effects of the medication. For those using levothyroxine without clear indications for its use, it may be worth reassessing treatment plans with the guidance of a healthcare professional.
Looking Ahead
The study highlights a need for more research into the long-term effects of levothyroxine, particularly its impact on bone health in older adults. As levothyroxine remains one of the most prescribed medications in the U.S., further studies will be important in understanding the full scope of its effects on aging and bone health.
The research was conducted in collaboration with Johns Hopkins University’s Russell H. Morgan Department of Radiology and Radiological Science, along with the Department of Endocrinology. Other contributors to the study include Dr. Hamsa Ibad, Dr. Qian-Li Xue, and Dr. Eleanor Simonsick from the National Institute on Aging.