A Good Night's Slumber Won't Reverse Chronic Sleep Loss
WEDNESDAY Jan. 13, 2010 -- Chronic sleep deprivation and the impact "sleep debt" has on functioning and thinking cannot be reversed by one good night's sleep, new research suggests.
While a night of good sleep can make you feel and operate better in the short run, the ill effects of long-term sleep loss linger much longer.
In fact, "chronic sleep loss from six hours of sleep per night for two weeks causes a similar level of impairment as staying awake for 24 hours," said the study's lead author, Dr. Daniel A. Cohen, a neurologist and sleep medicine specialist affiliated with Brigham and Women's Hospital and Beth Israel Deaconess Medical Center, both in Boston.
Chronically sleep-deprived people are "vulnerable to sudden sleepiness, errors and accidents," Cohen added, describing the vulnerability as something that won't disappear after a full night of "catch-up" sleep.
Cohen and his colleagues report their findings in the Jan. 13 issue of Science Translational Medicine.
They note that 16 percent of Americans are believed to routinely sleep six hours a day or less.
Such chronic sleep deprivation is thought to be most prevalent in professions that involve shift work and overtime, such as trucking and transportation, the military, the health-care industry and emergency-response organizations. Many such workers try to cope with long stretches of insufficient sleep -- and the safety hazards such sleep debt poses -- by sleeping for longer periods whenever they can.
But does this type of catch-up strategy help restore alertness? To find out, the researchers tracked the behavior of nine healthy men and women, 21 to 34 years old. Participants were put on a three-week sleep-wake schedule that involved staying awake for 33 hours, followed by 10 hours of sleep.
This chronic sleep deprivation routine -- which they said mimicked, for example, the typical on-call schedule of a resident physician -- meant that the participants slept just 5.6 hours for every 24-hour period.
Data on a second group of participants, who slept a more normal eight hours in every 24-hour period, were used as a point of comparison.
The team found that in the immediate aftermath of a 10-hour sleep period, the sleep-deprived participants did perform within normal parameters on cognitive function and reaction-time testing.
However, as the study progressed, the now chronically sleep-deprived participants' ability to recover full function after each 10-hour sleep began to fade. Their motor skills, as well as their ability to focus, pay attention and remain alert, all weakened over the ensuring 33-hour wake period.
Relatively normal reaction times for the sleep-deprived also dissipated significantly as day turned to night. The researchers attributed this to the interplay between chronic sleep deprivation and the body's circadian rhythms.
The bottom line: People who build up a "chronic sleep debt" during the week in the hope that they can then "pay it back" with a full night or two of sleep on the weekend are in for a disappointment.
"A long night of sleep can largely hide the effects of chronic sleep loss," Cohen said. But he said the sense of regaining full function is illusory.
"At this point," Cohen noted, "we still do not know how many normal sleep-wake cycles it takes to catch up on chronic sleep loss."
Gregg D. Jacobs, a sleep specialist with the Sleep Disorders Center at University of Massachusetts Memorial Medical Center in Boston, said that "sleep loss is not a one-size-fits-all phenomenon" and cautioned against generalizing too much from the findings.
"The sleep schedule they studied is similar to what residency physicians would experience," he noted. "However, very few people other than resident physicians ever undergo a sleep schedule like this. Sleep loss in daily life is much more modest for most people."
Jacobs also noted that the participants were relatively young and that older adults often need less sleep. And he added that sleep loss and an individual's related performance can often depend on how motivated a person is to execute a task, which can be different depending on whether sleep loss and performance is job-related or not.
"The problem with lab studies on sleep loss," he stressed, is that "they do not generalize well to daily life."
The U.S. National Center on Sleep Disorders Research has more on the science of sleep.
Posted: January 2010