Study Links Automobile Accidents and Sleep Apnea

May 28, 1997

People with undiagnosed sleep apnea may be at greater risk for automobile accidents, researchers at UW Medical School have found.

In a study of 913 adults, researchers found that people with mild sleep apnea, including habitual snorers, were three times more likely to be involved in a motor vehicle accident than people who didn't have the problem. People with moderate sleep apnea were seven times more likely to experience accidents.

The findings were presented May 21 at the annual meeting of the American Thoracic Society in San Francisco.

"Our data show for the first time that there is a link between sleep-disordered breathing in the general population and objectively measured motor vehicle accidents," said study director Terry Young, Ph.D., professor of preventive medicine. "Additional research is needed to more accurately assess the magnitude of the risk."

Sleep apnea consists of episodes of breathing pauses during sleep that may be linked to severe daytime sleepiness and significant cardiovascular problems.

UW researchers are studying sleep apnea in some 1,200 randomly selected Wisconsin state employees participating in the Wisconsin Sleep Cohort Study. The volunteers have been examined in an overnight stay at the General Clinical Research Center of the UW Hospital and Clinics.

The Wisconsin study has already revealed that the prevalence of sleep apnea is much greater than previously expected, many more women than previously noted experience breathing disorders related to sleep apnea and women have the same standard symptoms as men. The investigators now are determining the adverse health effects of the disorder.

Previous studies by other groups have hinted at an association between sleep apnea and car accidents, but the studies were methodologically limited. Some were based on small samples, relied on patients' recall of accident history or involved simulated driving tests. Most studies also were based on sleep clinic patients, who may have sought help because they worried about their driving performance or, on the other hand, may have been afraid to admit to any accidents for fear of having their licenses revoked.

In the current study, researchers determined the presence of sleep disorders and the five-year accident history of 913 employed adults randomly selected from the general population. Sleep characteristics of each volunteer were established using standard measures in an overnight stay.

The UW researchers found that, compared to people who didn't have sleep apnea, men who were habitual snorers or who had more than five breathing pauses per hour while they slept were three times more likely to have at least one driving accident in five years. Both men and women with a moderate degree of sleep apnea were seven times as likely to have multiple accidents in the study period.

"Surprisingly, we found that people with sleep apnea who said they were chronically sleepy during the day were not most likely to have a history of accidents, compared to those who denied sleepiness during the day," said Young. "Therefore, a general warning to sleep apnea patients about 'driving while sleepy' may not be effective."

Young said untreated sleep apnea patients should be warned about the possible risks of driving, regardless of whether or not they feel sleepy.

CONTACT: Dian Land, 608-263-9893, dianland@macc.wisc.edu