Epilepsy is a brain disorder that causes recurrent seizures. According to the World Health Organization, it affects about 50 million people worldwide.

There is no cure for the condition. Medications can control seizures for most people, but the drugs have at least some negative side effects, which can include memory loss, reduced fertility, and birth defects.

Dr. Alison Pack, an assistant professor of clinical neurology at Columbia University, led a study to look at another potential health risk: bone loss.

The study included 93 women between the ages of 18 and 40, who did not have any other conditions that might weaken their bones. All the women had epilepsy and were taking one of four common anti-seizure medications.

The women were given blood tests, urine tests, and bone density scans when they first enrolled in the study, and then again, after one year.

Prior research had suggested that at least one of the medications - phenytoin - might have a negative effect on bone health. "And indeed," explains Pack, "what we found was significant loss at one site, the femoral neck of the hip - loss of 2.6 percent - in women taking phenytoin."

The research did not measure significant bone mass loss in the women taking any of the other three medications tested.

To put a loss of 2.6 percent in perspective, Pack says that in a previous study done in pre-menopausal women who did not have epilepsy and were not taking medication, researchers observed a loss in hip bone mass of only 0.3 percent. In other words, the women taking phenytoin lost eight times more bone in a year than the women who were not taking any epilepsy medication.

Pack notes that like many older medications that are available in generic form, phenytoin is relatively inexpensive and is used in developing countries, where the choice of anti-seizure drugs is limited.

She adds that people should also be concerned about another epilepsy medication: phenobarbital. "There are older studies suggesting that it can affect bone health in the same way that phenytoin can," she explains, "and that medication is very commonly used in developing countries."

Dr. Pack's current study was funded by the National Institutes of Health and GlaxoSmithKline, a company that produces one of the alternatives to phenytoin included in this study. Her research was published in the April 29 issue of Neurology.