Being sleepy behind the wheel is almost as bad as drinking and driving, suggests a new study from France.

The study, published as a letter in the Archives of Internal Medicine, found that drivers who were either drunk or sleepy were at least twice as likely to be responsible for a vehicle accident compared to their well-rested or sober counterparts.

Christopher Drake, an associate scientist at the Henry Ford Hospital Sleep Disorders and Research Center in Detroit, said the findings do not change what was already known, but the study is still "interesting."

"We know from experimental studies that just four hours of sleep loss will produce as much impairment as a six pack. If you have a whole night of sleep loss, that's equivalent to having a blood alcohol content of 0.19," Drake, who was not involved with the new research, told Reuters Health.

Under the direction of Dr. Nicholas Moore at the Centre Hospitalo-Universitaire de Bordeaux in France, researchers analyzed information from 679 drivers who were admitted to a hospital in southwest France for more than 24 hours because of a serious accident between 2007 and 2009.

The researchers used information from driver questionnaires and police reports to determine what may have contributed to the accidents. Drivers reported what medications they were on, their alcohol use and how sleepy they had been before the crash. Patient files provided information on blood alcohol levels.

The majority of the injured drivers were under 55 years old and men. Over half were on a motorcycle, about one-third of the drivers were in a car and 10 percent were peddling a bicycle at the time of the accident.

The police determined 355 of the drivers were responsible for their respective crash. From that, Moore and his colleagues found that being between the ages of 18 and 29 years old, driving a car, drinking alcohol and being sleepy were all tied to an increased risk of causing an accident.

Surprisingly, taking medications that carry warnings about affecting a driver's abilities -- one of the researchers' main focuses -- was tied to a lower risk of causing an accident.

Moore told Reuters Health that may be because people taking those medications are more aware of their side effects.

"Medicinal drugs might be an issue to keep an eye on and warn people about, but it's not the main issue," he said.


One way for people to reduce their accident risk is to take a nap before they hit the road, according to Moore.

"Don't hesitate if you're tired to take a short nap or drink a few cups of coffee. And if you drink coffee, it will take some time to take effect," he said.

Drake added, however, that coffee's effectiveness can wear off over time.

"Anytime you're feeling sleepy behind the wheel is a danger sign," he said.

The standard techniques of turning on the air conditioner or blasting the radio only mask the signs of sleepiness -- they don't make it go away. "They're good to get you to the next exit, but it's not going to get you home," Drake said.

There are some laws in the U.S. to punish sleepy drivers, but Drake told Reuters Health they are hard to enforce unless someone gets into an accident.

"It's very difficult. There is no breathalyzer for sleepiness," he said.

The study did have some limitations. Some of the questions are based on the patients' own reports, which may be subjective. Also, there is no way to know how many accidents sleepiness actually caused.

Overall, Moore said the best advice is, "don't drink and please sleep."

"There is no substitute for sleep," said Drake.