A widely prescribed thyroid medication called levothyroxine may cause bone loss and increase the risk of the bone disease osteoporosis, according to new research—but this does not mean Americans should stop taking it.
Levothyroxine is the second most commonly prescribed medication among adults in the U.S., taken by approximately 23 million Americans—equivalent to 7 percent of the population—under several different names, including Synthroid.
However, new research has found that taking this medication is associated with an increased risk of bone loss.
Levothyroxine is prescribed to treat hypothyroidism—where the thyroid doesn't produce enough of the hormone thyroxine—and works by topping up thyroid hormone levels.
The study followed older adults with healthy ranges of thyroid hormones, 81 of whom were taking levothyroxine and 364 of whom were not.
After about six years, those taking the thyroid medication were more likely to have lost more bone mass than those not taking it.
Lead author Dr. Elena Ghotbi, postdoctoral research fellow at Johns Hopkins University School of Medicine, Maryland, told Newsweek: "In individuals with reduced thyroid function, hypothyroidism, the production of thyroid hormone is disrupted, and the goal of treatment is to restore them to the reference range.
"But in some of these people, this could be correcting a true deficit and in others it could be supplementing above a natural set point," Ghotbi said.
What Is Thyroid Medication Like Levothyroxine For?
The thyroid is a butterfly-shaped organ that sits inside the neck and releases hormones, affecting metabolism, energy, heart rate, digestion, muscle function, brain development and bone density.
In the case of hypothyroidism, the thyroid doesn't produce enough of these hormones. Symptoms can include fatigue, depression, weight gain, hair loss, constipation, face puffiness, constipation, dry skin and muscle weakness. Hypothyroidism particularly affects postmenopausal women.
Too much thyroid hormone is called hyperthyroidism, and may present as heart palpitations, high blood pressure, shakiness, anxiety, weight loss, diarrhea, persistent thirst and itchiness. Hyperthyroidism also increases the risk of losing bone density.
Individuals who are prescribed too much medication for hypothyroidism may end up with too much replacement thyroid hormone, leading to symptoms of hyperthyroidism—and this may explain why levothyroxine was associated with bone loss in the recent study.
"An interesting possible implication of these results is that thyroid hormone is being incorrectly prescribed in some cases, even when it looks like the levels are in the correct range," said Ghotbi.
Levothyroxine Side Effects: Can Thyroid Medication Cause Bone Loss?
Bone loss doesn't mean losing bones, but a loss of bone density. The inside of bones looks a bit like a sponge, full of air pockets that keep bones light.
When people lose bone mass, these air pockets get bigger and the bones get more delicate, leading to an increased risk of fracture.
Mild loss of bone mass—called osteopenia—is a normal part of the aging process, but in some cases, osteopenia can develop into osteoporosis, a bone disease where the bones are so fragile that even a sneeze could break a rib.
Osteoporosis is a known potential risk of having too much thyroid hormone or taking too much hormone-replacement medication.
But the new study found that even people taking the medication to bring their thyroid hormone to normal levels were at increased risk of losing bone density, compared to people who did not have any thyroid problems.
What To Do About Levothyroxine and Bone Loss
Ghotbi told Newsweek that people taking thyroid medication to treat genuine hypothyroidism shouldn't worry about or stop taking it.
However, she said in a statement that "a significant proportion of thyroid hormone prescriptions may be given to older adults without hypothyroidism."
So, individuals taking levothyroxine without a clear diagnosis of hypothyroidism may wish to discuss the risks and benefits of the medication with their doctor.
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