Short sleepers -- even when they feel well-rested -- are more likely to be drowsy drivers than people who get more shuteye each night, according to a new study.
Researchers from the University of Pennsylvania's Perelman School of Medicine found that people who sleep an average of fewer than six hours each night are three times more likely to report having driven while drowsy in the last month, compared with people who get seven hours a night.
Plus, people who sleep five or fewer hours a night, on average, are four times as likely to report drowsy driving in the last month, compared with those getting seven hours.
"Falling asleep at the wheel is a major cause of road accidents. It might even be more of a problem than drunk driving, since it is responsible for more serious crashes per year," study researcher Michael Grandner, Ph.D., a psychiatry instructor and member of the Center for Sleep and Circadian Neurobiology at the university, said in a statement. "We already know that people who are sleep-deprived in the laboratory have impaired driving performance, but we haven't been able to better define what sleep profiles and patterns put drivers in the general population at the highest risk."
Indeed, a recent study in the Archives of Internal Medicine did show that the risk of car accidents is the same with drunk driving and drowsy driving -- both double car accident risk.
The new study, which is published in the journal Accident Analysis and Prevention, is based on data from the Center for Disease Control and Prevention's 2009 Behavioral Risk Factor Surveillance System, which had information from 31,522 people.
Even though it may not be surprising that people who get less sleep are more likely to report drowsy driving, what is notable is that researchers found that short sleepers who report getting enough sleep each night are still at a three times higher risk for driving drowsy.
While the amount of sleep each person requires is different, with some needing more than others, the National Sleep Foundation notes that adults should generally get somewhere between seven and nine hours a night.
Just this year, a CDC study showed that one in 24 adults in the U.S. has reported falling asleep while at the wheel, with officials worried that the number could actually be even higher since nodding off while driving can happen so quickly.