A class of drugs commonly prescribed to women with Type 2 diabetes appears to double their risk of bone fractures, says a study published Wednesday in the Canadian Medical Association Journal.

Earlier studies of the drugs — sold as Avandia and Actos — not only hinted at the risk of increased fractures, but also found an increased risk of heart failure. The study published in CMAJ is the first to quantify the effect of the drugs on the incidence of fractures in women.

Researchers looked at 10 randomized controlled trials lasting at least one year and involving more than 13,000 diabetes patients taking the class of drugs known as thiazolidinediones, and those not taking the therapy.

In absolute terms, they found that if the drugs are used by elderly, postmenopausal women (around 70 years) with Type 2 diabetes for one year, one additional fracture would occur among every 21 women. Among younger women (around 56 years), use of the drugs for one year or longer would result in one additional fracture for every 55 women, said Dr. Sonal Singh, an internal medicine specialist at Wake Forest University Baptist Medical Center.

"This is a substantial risk of fracture. We're talking about a doubling. There's very few agents that would carry this risk of fractures," said Singh, who wrote the study with colleagues from Wake Forest University, in Winston-Salem, N.C., and from the University of East Anglia, in Norwich, England.

The study found no increase in bone fractures in men using the drugs. In addition to doubling the risk of fractures in women, use of the drugs was linked to significant decline in bone mineral density at the lumbar spine and the hip among women.

In 2006, there were nearly four million patients in the United States taking this class of drugs, half of whom were likely women, Singh said.

Dr. Lorraine Lipscombe, an endocrinologist with the Toronto-based Institute for Clinical Evaluative Sciences, suggested in a commentary written for the journal that other drugs should be tried first.

"These drugs are very effective about lowering blood sugar and that's important, but we do have other drugs that can also lower blood sugars that are not associated with the same adverse effects," she said.