THURSDAY, May 9, 2002 (HealthDayNews) -- We all know that sleepy drivers and automobiles don't mix, but new research details just how bad the combination is.
Researchers in New Zealand have found that sleepy drivers are eight times more likely to crash than alert ones, that drivers who report five hours or less of sleep in the past 24 hours are three times more likely to crash, and that people who drive between 2 a.m. and 5 a.m. are five times more likely to crash.
"If all these behaviors were eliminated, about 19 percent of serious injury crashes could be avoided," says Dr. Jennie Connor, lead author of the study and a senior lecturer in epidemiology in the Division of Community Health at the University of Auckland. "The difference is that most crashes have several causes, and if you eliminate any one of them you may be able to prevent the crash. Usually sleepiness combines with other causes to produce crashes."
The findings, appearing in the May 11 issue of the British Medical Journal, come as no surprise to sleep expert Dr. Alon Avidan.
"When we change to daylight savings, we see an increased risk in the overall incidence of motor vehicle accidents and the number of injuries and fatalities, so it's known that whenever we interfere with the circadian clock and with total sleep time and sleep quality, people are more likely to be sleepy and more likely to be involved in motor vehicle accidents," says Avidan, clinical assistant professor of neurology at the University of Michigan's Michael S. Aldrich Sleep Disorders Laboratory.
The researchers profiled 571 car drivers or passengers who were admitted to a hospital or who died as a result of a car crash in greater Auckland, which with 1 million residents is the largest metropolitan area in New Zealand. (Loved ones of those who died were interviewed.) An additional 588 people, randomly selected from drivers who were using the same roads during the same time period, were used as controls.
The researchers found that acute sleepiness contributed significantly to the risk of a serious crash. Acute sleepiness refers to sleepiness that is associated with the time of driving (that day or the day before), not a long-term condition.
"People who reported symptoms of sleep disorders -- which generally increase usual sleepiness levels -- and people who regularly sleep less at night didn't have an increased risk of a crash unless they had one of the other acute characteristics as well," Connor says. "That is, unless they were sleep-deprived that day, felt sleepy while driving, or were driving in the early hours of the morning [their risk was not increased]."
The observations regarding chronic vs. acute sleepiness have not been seen before, Avidan says.
The findings could help authorities to fashion safety messages more specifically geared to at-risk drivers. Connor states that the only "cures" known to be effective are sleep (even a 15-minute nap will help for a short period) and caffeine (again, effective in the short term). Possible public-service messages include: "Avoid driving after less than five hours' sleep, even if you don't feel sleepy," and "Avoid driving between 2 a.m. and 5 a.m. when your body wants to be asleep, even if you aren't."
Previous estimates of the risk of crashing in this population have varied from region to region. Connor says that almost all her individual findings can be extrapolated to other populations.
What To Do: For more information on driving safely, visit the Partnership for Safe Driving or the Insurance Institute for Highway Safety.
