January 14, 2010
Using The Weekend To Catch Up On Sleep Not Healthy
New research on chronic sleep loss revealed that simply catching up on lost sleep during the weekend is not the answer to maintaining adequate amounts of rest, The Associated Press reported.
After studying the effects of short- and long-term sleep loss, scientists found that the chronically sleep-deprived may function normally soon after waking up, but experience steadily slower reaction times as the day wears on, even if they had tried to catch up the previous night.
Lead researcher Dr. Daniel Cohen of Boston's Brigham and Women's Hospital said experts know that staying awake 24 hours in a row impairs performance to a level comparable to a blood-alcohol content beyond the legal limit to drive.
But Cohen said when the already chronically sleep-deprived pull an all-nighter, the deterioration is increased tenfold.
Adults need seven hours to nine hours of sleep for good health, according to the National Institutes of Health.
Regularly getting too little increases the risk of health problems, including memory impairment and a weakened immune system. Too little sleep also affects reaction times, as sleepiness is to blame for many car crashes and other accidents.
However, the new study shows that two different sleep-drives impact the brain, one during the normal waking hours and the other over days and weeks of sleep loss.
Shelby Freedman Harris, behavioral sleep-medicine director at New York's Montefiore Medical Center, who wasn't involved with the new research, said the study holds critically important ramifications for anyone who works "crazy hours" and thinks they're performing fine with a few hours of weeknight sleep.
Harris warned that people shouldn't think they can just bank up on extra sleep over the weekend, because it doesn't work that way.
In order to find out how both acute and chronic sleep loss interact with our bodies' natural circadian rhythms -- the 24-hour biological clock that signals when it's time to sleep and wake -- Cohen recruited nine young, healthy volunteers and messed up their normally good sleep habits for three weeks.
The test subjects stayed awake for 33-hour stretches with 10 hours of sleep in between, a radical enough schedule that their internal circadian clocks couldn't adjust.
Cohen said their sleep deprivation was comparable to that of someone who gets about 5 1/2 hours of sleep a night, but the extra-long wake-sleep schedule also allowed him to test the value of catch-up sleep.
Every few waking hours the subjects were given cognitive and motor skills tests that measured their ability to stay alert and attentive, with results compared to similar volunteers getting a normal amount of sleep.
The results showed that the well rested could catch up from the occasional all-nighter fairly easily. But Cohen reported Wednesday in the journal Science Translational Medicine that as the study wore on and the volunteers became more sleep-deprived, the rejuvenation they felt each time they awoke increasingly proved a facade.
He noted that while they functioned fairly normally during their first few waking hours, especially that first week, their reaction times steadily worsened with each hour they stayed awake, with a big drop in performance between the first and second weeks of sleep deprivation.
The study shows that their daytime decline was subtle, but their circadian rhythms provided a bit of rescue.
Just as most people get tired in the afternoon, even these sleep-deprived volunteers got an energy boost then, as their circadian rhythms kicked in.
However, Cohen's team found that if they stayed up past bedtime yet again, their performance suddenly plummeted just as their circadian rhythm reached its natural lowest point.
The drop was so sharp that he concluded these people were increasingly vulnerable to accidents and errors.
Cohen, who is also a neurologist at Beth Israel Deaconess Medical Center, said when exposed to the next all-nighter, the sleep deprived test subjects really fell apart much faster than they previously would.
Cohen also added that scientists don't yet know how quickly people can recover from chronic sleep loss once they resume a good bedtime.
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