People who have difficulty breathing while they sleep cause more car accidents than those who breathe normally, researchers from the University of Virginia Medical Center in Charlottesville have found.

Victims of sleep apnea, a condition that causes people to stop breathing intermittently while they sleep because their airways are too small, are seven times more likely to have an auto accident than normal people, "probably because they are falling asleep at the wheel," the researchers said. Nearly a quarter of the apnea sufferers interviewed reported falling asleep behind the wheel at least once a week.

Sleep apnea could contribute to thousands of the 2 million auto accidents in the United States each year, according to Dr. Larry J. Findley, who led the study. Findley's group compared the driving records of 29 sleep apnea patients to a group of 35 drivers without the condition. The apnea victims had a sevenfold greater auto crash rate than the group without apnea, and were involved in accidents 2 1/2 times more often than the average Virginia driver.

And the apnea suffers just weren't unlucky. They were eight times more likely to be at fault for the accident than normal drivers.

Most of the accidents could be prevented by treating the driver's apnea problems, Findley said. Apnea, a major cause of daytime sleepiness, may affect as many as 1 percent of all Americans. It can be successfully treated by having the individual lose weight or wear a device that aids breathing during sleep.

Unless the apnea is treated, Findley said, apnea patients should not drive.