CHICAGO - The most popular pills for depression might substantially raise the risk for bone breaks in older people, a drawback that should be considered when the drugs are prescribed, Canadian researchers say.

People aged 50 and older who took antidepressants, including Zoloft, Prozac and other top-sellers, faced double the risk of broken bones during five years of follow-up, compared with those who didn't use the drugs, the study found.

Still, few of 5,008 people studied used the drugs and had fractures. While more rigorous research is needed to prove the link, the study provides the strongest evidence yet tying these drugs to fracture risks, said Dr. David Goltzman, an endocrinologist at McGill University in Montreal and one of the study authors. The study was part of ongoing osteoporosis research funded partly by the Canadian Institutes of Health Research and makers of osteoporosis drugs.

Antidepressants have been linked with low blood pressure and dizziness leading to falls, which can increase risks for broken bones, but the researchers said they found fracture risks independent of those factors.

Pills may sap strength of bones
Research in animals suggests that the pills might have a direct effect on bone cells, decreasing bone strength and size, Goltzman and colleagues said.

The results have important public health implications since millions of people worldwide use the drugs and because osteoporosis, a bone-thinning disease that can lead to broken bones, can be so debilitating for older adults, Goltzman said.

Still, the researchers said potential fracture risks should be balanced against the drugs' effectiveness at treating depression, which also can be debilitating.

Depression affects about 10 percent of U.S. adults, or nearly 30 million people, including about 7 million aged 65 and older. Depression in older adults is often missed and untreated.

"If patients need these drugs, they should not be advised against taking them because of the fracture risk. They should however be warned about the risks," Goltzman said.

The study appears in Monday's Archives of Internal Medicine.

Some previous studies found similar results but did not adequately consider other factors, the researchers said.

Depression itself a possible cause
Dr. Gregory Asnis, director of an anxiety and depression clinic at Montefiore Medical Center in New York, said depression itself has been linked with low bone density, and it's possible the disease rather than the drugs could explain the findings. He said more rigorous research is needed.

The drugs in question are called SSRIs or selective serotonin reuptake inhibitors. These are generally the favored treatment for depression in many patients and their combined U.S. sales jumped 32 percent from 2000 to 2004, to more than $10.9 billion, the researchers said.

The study tracked 5,008 Canadians aged 50 and older for five years. They included 137 people who reported using SSRI antidepressants daily. In this smaller group, 18 people or 13.5 percent had bone fractures during the follow-up, compared with 317 people with fractures or 6.5 percent among the 4,871 who didn't take the pills.

Broken forearms, ankles, feet, hips and ribs were the most common fractures.

Amy Sousa, a spokeswoman for Prozac maker Eli Lilly and Co., said the drug's label lists osteoporosis as a potential but rare side effect. Still, she said the new study was too small to establish any proof that SSRIs might cause fractures.

Pfizer Inc., maker of Zoloft, issued a statement responding to the study and calling depression "a serious problem in the elderly that is under-diagnosed and under-treated."

"SSRIs are an important option for the treatment of depression in this population. As the authors note, the risks must be balanced against the benefits gained by the treatment of depression," Pfizer said.

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