Share on PinterestCould a commonly prescribed thyroid drug lead to bone loss? Image credit. Willie B. Thomas/Getty Images.

• Levothyroxine is a frequently prescribed drug in the United States, particularly for older people, as lower thyroid function can be associated with aging.
• Questions remain over how appropriately it is prescribed, however, as side effects can cause problems.
• A recent abstract presented at the annual meeting of the Radiological Society of North America suggested that levothyroxine use in people with typical hormone ranges could lead to lower bone mass and density in older people, over time.

Levothyroxine, a drug used to treat hypothyroidism, can lead to reduced bone mass and density in older adults with normal thyroid levels, a small cohort study has shown.

Researchers from Johns Hopkins University School of Medicine in Baltimore, MD, showed that total body bone mass and density both decreased in adults over the age of 65 who received levothyroxine over a 6-year follow-up period.

They presented the results at the Annual Meeting of the Radiological Society of North America on November 25, 2024. These results are yet to appear in a peer-reviewed journal.

The results came from a small study comprising 81 participants who had typical thyrotropin levels, which are used to indicate thyroid function, and who were taking levothyroxine.

The study authors point out that levothyroxine is one of the most commonly prescribed drugs in the United States, particularly among older adults.

Sean Ormond, MD, of Atlas Pain Specialists, dual board-certified in anesthesiology and interventional pain management, who was not involved in this research, told Medical News Today that:

“Levothyroxine is a very common medication because thyroid problems become more likely as we age. Older adults are more prone to hypothyroidism, where the thyroid slows down and doesn’t make enough hormones to keep the body running smoothly.“

“When the thyroid underperforms, people often feel tired, gain weight, get cold easily, or even feel depressed. These symptoms can make life tough, so doctors often prescribe levothyroxine to restore hormone levels and help people feel like themselves again. It’s especially important in cases where untreated thyroid issues could harm the heart or other organs,” he further explained.

Why is the thyroid gland important?

The thyroid is found in the neck, and is responsible for producing hormones that in turn play a role in metabolism, growth and development in children, temperature regulation and in the functioning of the heart and digestive system.

Thyroid stimulating hormone (TSH) is produced by the pituitary gland, another hormone-producing organ in the head. This in turn causes the thyroid to produce T3 and T4, which play a role in the aforementioned processes.

Low levels of thyroid hormones can lead to symptoms including fatigue, weight gain, cold intolerance, dry, flakey skin, loss of hair and inability to concentrate.

Conversely, hyperthyroidism — where thyroid levels are too high — is associated with weight loss and muscle weakness, high heart rate and blood pressure, feeling anxious and irritable.

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Levothyroxine: Can it raise osteoporosis risk?

The team behind the recent study had previously shown that levothyroxine use, particularly in people it is used in unnecessarily, can have an array of unwanted side effects.

Previously, the authors had shown that the use of levothyroxine in people with higher thyroid hormone levels had a negative effect on leg mass in older adults, in a study whose results appeared in Frontiers in Aging.

That study included an analysis of the Baltimore Longitudinal Study of Aging, as does their latest research.

To look at the impact of levothyroxine use on a similar cohort of adults, in their latest research, the authors studied 32 males and 49 females who were aged 65 or over at the start of the study, with a mean age of 73.

They matched these participants to five other members of the cohort by biological sex, body mass index (BMI), age, race, history of alcohol consumption, history of smoking, other treatments they were undertaking, and TSH levels to create a quasi-control group.

The analysis of this cohort occurred following two visits where they had their bone mass and density measured using Dual-Energy X-ray Absorptiometry.

Researchers showed that over the course of the study, those who had typical thyroid hormone levels and were on levothyroxine demonstrated a lower bone mass and density.

The results suggest that bone loss could be an effect of levothyroxine use in older adults, even when used at the appropriate dosage, which could be a concern in terms of osteoporosis risk.

Is levothyroxine overprescribed?

Questions have been asked for sometime whether levothyroxine is overprescribed for older adults, with a letter published in Clinical Chemistry in 2023 suggesting 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.

Hypothyroidism is diagnosed by looking at the free thyroxine (T4) levels in people with elevated TSH levels, and comparing the ratio between them.

People with high TSH and low T4 get a diagnosis of hypothyroidism. Those with slightly elevated TSH and slightly low T4 get a diagnosis of subclinical hypothyroidism, which might be treated with levothyroxine.

The letter proposed that by not taking normal seasonal variation in TSH levels into account, many people were being prescribed drugs that might not help them, and they may even experience negative, avoidable side effects.

Deprescribing is an option for patients who experience unpleasant side effects, said Sue Clenton, MD, a consultant clinical oncologist at Weston Park Cancer Centre in Sheffield, U.K.

She told MNT that:

“Indications for prescribing levothyroxine include elevated TSH levels (indicating an underactive thyroid), fatigue, weight gain, and cognitive slowing. However, deprescribing may be considered if a patient experiences side effects like rapid heart rate, anxiety, or bone loss, or if their thyroid function tests normalize.”

She said the study highlighted “the importance of careful monitoring and individualized treatment plans, especially in older adults.”

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