"The take-home message is this: Don't rely on your own sense of whether or not you're getting enough sleep. You may very well be chronically sleep-deprived and consider that normal," he tells WebMD. "In some ways, it's similar to people in chronic pain -- they don't realize how much pain they have until it's relieved."
This self-denial may play a key role in many of the 100,000 car crashes each year in the U.S. that result from sleep deprivation. "Another study showed that 50% of the people who caused car crashes did not perceive that they were sleepy immediately prior to the crash," says Mark Mahowald, MD, director of the Minnesota Regional Sleep Disorders Center and a spokesman for the National Sleep Foundation. "So if you talk to people who are sleep-deprived, half of the time they will be driving impaired but do not perceive themselves to be."
Mahowald, professor of neurology at the University of Minnesota Medical School who was not involved in Van Dongen's study, considers these new findings on sleep deprivation very important. "This study clearly shows that mild but chronic sleep deprivation has very serious adverse performance consequences," he tells WebMD. "How many people are sleep-deprived? Just about everybody. Anyone who uses an alarm clock to wake up is sleep-deprived by definition. Their brains would have awakened spontaneously if they have accumulated the amount of sleep they need."
While some people can function fine on fewer than eight hours of sleep, most need to average that amount over time to keep mind and body healthy.
"These findings don't surprise me in the least," adds sleep researcher Teri J. Bowman, MD, assistant professor of medicine at the Nebraska Medical Center and spokeswoman for the American Academy of Sleep Medicine. "Most Americans think they can beat the odds and cram more time into their schedule. In fact, they cannot."
While she and other experts recommend following "good sleep hygiene" -- maintaining a consistent sleep schedule averaging about eight hours nightly -- the fact is, slightly more than half of all Americans sleep less than that. But the good news is that you can actually make up for lost time. If you've missed out on some precious sleep during the week, Van Dongen suggests that you try to catch up over the weekend or whenever time permits.