The study compared 800 people with sleep apnea and 800 without the nighttime breathing disorder and found that patients with sleep apnea were twice as likely as people without sleep apnea to have a car crash, and three to five times as likely to have a serious crash involving personal injury.

Overall, the sleep-apnea group had a total of 250 crashes over three years, compared with 123 crashes in the group without sleep apnea, according to a study presented at the American Thoracic Society International Conference in San Francisco.

"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," Dr. Alan Mulgrew of the University of British Columbia Sleep Disorders Program in Vancouver said in a statement.