SUNDAY, May 20 (HealthDay News) -- People with sleep apnea -- a nighttime breathing disorder that disrupts sleep -- are at double the risk of being in a serious car crash, a Canadian study finds.

"We were surprised not only about how many of the sleep apnea patients' crashes involved personal injury, but that some patients had fairly mild sleep apnea and were still having serious crashes," study author Dr. Alan Mulgrew, of the University of British Columbia Sleep Disorders Program, said in a prepared statement.

Researchers studied 800 people with sleep apnea and 800 people without the condition.

They found that those with sleep apnea were twice as likely to be in a car crash, and three to five times more likely to be in a serious crash involving personal injury.

Over three years, the people with sleep apnea had a total of 250 crashes, compared with 123 crashes among those without sleep apnea. Previous studies have identified a link between sleep apnea and increased risk for crashes, but this is the first study to examine the severity of such crashes.

The sleep apnea patients' self-reported feelings of sleepiness were not linked with an increased risk of crashes, which suggests that the patients weren't aware of the potential driving hazards caused by sleep apnea.

In the general population, men have more vehicle crashes than women. Among the sleep apnea patients in this study, men and women had similar crash rates.

The study was expected to be presented Sunday at the American Thoracic Society's international conference in San Francisco.