Women who smoke may have a higher risk of developing seizures than non-smokers do, a new study suggests.

Researchers found that among more than 100,000 U.S. women in a long-running health study, current smokers were between two and three times more likely than non-smokers to suffer a seizure over 16 years.

Current smokers did not clearly show a higher risk of developing epilepsy, a disorder marked by recurrent seizures that are not provoked by a specific cause, such as a reaction to a drug.

However, epilepsy risk was somewhat elevated among former smokers, who had a 46 percent higher risk than women who had never smoked.

Dr. Barbara Dworetzky and colleagues at Harvard Medical School and Brigham & Women's Hospital in Boston report the findings in the journal Epilepsia.

Seizures arise from an episode of abnormal electrical activity in the brain -- with symptoms ranging from a brief staring spell or change in vision or sensations in the skin to convulsions and loss of consciousness. Epilepsy is diagnosed when a person suffers at least two unprovoked seizures.

In some cases, seizures and epilepsy have an identifiable cause, such as head trauma or brain damage from a stroke. But more often, no specific cause can be found.

Little is known about how seizures can be prevented, according to Dworetzky's team, but if the current findings are correct, avoiding smoking may be one way.

The idea that smoking could be a risk factor does have physiological evidence to back it up, the researchers point out. High levels of nicotine, for instance, have been found to trigger convulsions in both animals and humans.

Smoking also diminishes the oxygen supply to body tissues and, via the stimulating effects of nicotine, can trigger sleep problems, both of which may contribute to seizures.

Dworetzky and her colleagues based their findings on data from the Nurses' Health Study II, which began following more than 116,000 U.S. nurses between the ages of 25 and 42 in 1989. Over 16 years, 95 women suffered a seizure, and 151 were newly diagnosed with epilepsy.

Smokers were at greater risk of having an isolated seizure than non-smokers, even when other risk factors, including history of stroke, were taken into account.

Research has suggested that, as with nicotine, high alcohol or caffeine intake may also contribute to seizures. But in this study, women's drinking and caffeine habits were unrelated to the risks of seizure or epilepsy.

Because there is little knowledge of modifiable risk factors for seizures or epilepsy, Dworetzky and her colleagues conclude, more prospective studies are needed to find ways to possibly prevent their occurrence.

SOURCE: Epilepsia, online November 18, 2009.