THURSDAY, April 28 (HealthDay News) -- Many seniors may be at increased risk for fractures because they take "excessive" doses of drugs used to treat thyroid problems, a new study says.

The findings suggest that treatment targets may have to be modified in elderly patients with thyroid problems and that regular dose monitoring of thyroid drugs is essential into older age, the researchers said.

Reporting in the online April 28 edition of the BMJ, they examined the link between fractures and levothyroxine, a synthetic form of thyroid hormone, which is widely used to treat an underactive thyroid gland (hypothyroidism).

Many patients with hypothyroidism are diagnosed in early or middle adulthood. Even though their treatment requirements change as they age, many patients remain on the same drug dose. This can lead to excess levels of thyroid hormone, which increases the risk of fractures, especially in older women, the study authors explained.

They analyzed data from over 213,500 patients, aged 70 or older, in the province of Ontario, Canada, who filled at least one prescription for levothyroxine between April 1, 2002 and March 31, 2007. During the study period, more than 22,000 (10.4 percent) of the patients suffered at least one fracture.

Current and recent past users (who had discontinued the drug 15 to 180 days before the start of the study) had a significantly higher fracture risk than "remote" users (who had discontinued use of the drug more than 180 days before the start of the study).

Among current users, those who took high or medium doses of the drug were much more likely to suffer a fracture than those who took a low dose.

"Our findings provide evidence that levothyroxine treatment may increase the risk of fragility fractures in older people even at conventional dosages, suggesting that closer monitoring and modification of treatment targets may be warranted in this vulnerable population," concluded Lorraine Lipscombe, a scientist at the Women's College Research Institute in Toronto, and colleagues.

One expert wasn't surprised by the findings.

"It has long been known that high or excessive doses of levothyroxine usage predispose [people] to increases in osteoporosis and the risk of fracture," said Dr. Irwin Klein, director of the thyroid unit and associate chairman of the department of medicine at the North Shore-LIJ Health System in Manhasset, N.Y. "This study further confirms this finding in an elderly population of women who are inherently at risk for this occurrence."

Klein also noted that the study underscores the need for preventive action.

"As the authors conclude, it is important to monitor thyroid blood tests -- especially TSH levels -- to prevent this potential adverse health burden," he said.

More information

The Hormone Foundation has more about thyroid disorders.