Medication for hypothyroidism may boost fracture risk

Elderly patients taking levothyroxine for hypothyroidism may be at an increased risk for bone fractures, according to a new report released by the University of Toronto.

A study published in the British Medical Journal found that individuals age 70 or older who were currently taking the synthetic form of the thyroid hormone thyroxine were 88 percent more likely to suffer a broken bone over a four-year period, compared to those who had terminated such treatment several years earlier.

Levothyroxine is commonly prescribed to replace the hormones of which an underactive thyroid gland produces too little. Though the National Institutes of Health (NIH) lists many possible side effects of such a drug regimen, until now increased fracture risk has not been one of them.

That said, the study's authors recommend that healthcare experts consider levothyroxine therapy as having the potential to weaken bones during treatment.

Researchers came to this conclusion after analyzing data on more than 213,000 patients given the prescription medication for hypothyroidism. All participants were at least 70 years old during the time of treatment.

Overall, slightly more than 10 percent of the group experienced at least one fracture during the four-year study. Not only were those currently on levothyroxine more likely to break a bone, but higher doses of the drug greatly increased the risk.

The team determined that a medium current dose - defined as between 0.044 and 0.093 milligrams per day (mg/day) - increased the risk of fracture 2.6 times, relative to a low, sub-0.044 mg/day dose.

Likewise, taking more than 0.093 mg/day of the medication boosted the risk of a broken bone by a factor of nearly 3.5, compared to the low dose.

By contrast, patients who had been off of levothyroxine for months or years displayed a much reduced tendency toward fractures of any kind. Researchers concluded that while the medication has many positive health benefits, it may confer a significant fracture risk on elderly individuals with hypothyroidism.

The NIH notes that women over the age of 50 have a particularly high likelihood of developing both hypothyroidism and osteoporosis.