Multiple studies have linked driving drowsy and sleep disorders with an increased risk of having a car crash. However, the first study into the severity of those crashes has found that sleep apnea patients are much more likely than other drivers to have a serious crash involving personal injury.

The study, which was presented last month at the American Thoracic Society 2007 International Conference in San Francisco, compared 800 people with sleep apnea with 800 people that had normal nighttime breathing. It found that those 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 3 years, compared with 123 crashes in the group without sleep apnea.

In addition, the study found that while in the general population men have more vehicle crashes than women, among sleep apnea patients, men and women crash at a similar rate.

“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,” said Alan Mulgrew, MD, of the UBC Sleep Disorders Program in Vancouver, British Columbia, Canada.

The findings of the study—one of the largest to combine validated sleep apnea diagnosis through overnight polysomnography with data from insurance records—have implications for all involved in sleep apnea diagnosis, not just those who work to certify professional drivers, such as truckers.

Mulgrew said that those with sleep apnea may be unaware that driving could be dangerous as their self-reported feelings of sleepiness were not linked with an increased risk of having a car crash. “Based on these findings, I now consider driving risk when deciding on treatment for patients with mild sleep apnea,” he said.