Lost Sleep Can't Be Made Up, Study Suggests

Wednesday, January 13, 2010 - 4:32pm

If you think staying in bed on the weekends will make up for a weeks' worth of sleep deprivation, think again. A new study finds that going long periods without sleep can lead to a sort of "sleep debt" that cannot simply be undone with a little extra snoozing from time to time.

The study involved a small number of participants, however, so further research would be needed to verify the results.

Such chronic sleep loss may eventually interfere with a person's performance on tasks that require focus, becoming particularly noticeable at nighttime when the body's natural sleep-wake cycle isn't giving you an extra boost.

Anyone who's ever pulled an all-nighter knows how debilitating sleep loss can be in the short term. Indeed, studies show that after 24 hours without sleep, a person's performance can drop to the level of someone who is legally drunk.

But what about if those all-nighters turned into all-weekers? The authors of the current study turned their attention to long-term sleep loss, and examined whether the effects of such constant sleep deprivation could be erased with an extended resting period.

Studying sleep

The researchers put nine young adults on a sleep schedule that a doctor or medical resident might experience on an on-call shift - about 33 hours spent awake followed by 10 hours sleeping, a cycle that is equivalent to about 5.6 hours of sleep every 24 hours. The participants continued on this grueling schedule for three weeks, at which time they were considered chronically sleep deprived. The study also had a control group of eight young adults who were not sleep deprived.

The subjects needed to periodically complete a performance task designed to test their ability to pay attention and their reaction time.

The sleep-deprived subjects generally performed the same as those who had sufficient sleep if the test was given early on in the "day," just two hours after the subjects had awakened from their long rest. This finding held true across all three weeks of the study, suggesting that a long period of shut-eye could temporarily make up for the chronic sleep loss.

However, the subjects performed significantly worse on tests that were given later in the "day," after 30 hours spent awake, as the study progressed in weeks. For instance, the subjects faired poorly on the last test of the day they took during week three as compared with that same test during week 1. While they had a median reaction time of 667 milliseconds in testing during week 1, that increased to 2,013 milliseconds by week 3. The subjects appeared to have developed a sleep debt - all that lost sleep really was catching up with them.

Here's how the results might play out in the real world: An individual who is constantly sleep deprived during weekdays might try to catch up during weekends. While that individual might feel recovered after their sleeping spell, the study suggests the next time they try to go without shut-eye, their performance may start to deteriorate.

The findings also suggest that short-term and long-term sleep loss may actually act on the brain in two different ways.

The sun makes a difference

The sleep debt was also found to be most noticeable during the subject's nighttime. This could be due to the effects of our natural sleep-wake cycle, or circadian rhythm, the researchers suggest.

This cycle goes hand-in-hand with the periods of light/dark we experiences as the sun rises and sets. Our natural tendency to want to be awake during the day may mask signs of sleep debt when it's light out. But this protective effect may go away as darkness arrives, the researchers say.

The findings are particularly applicable to people who work odd-hour jobs that may have them going without sleep for extended periods, such as health workers, truckers and emergency responders. Chronic sleep loss could leave these individuals "vulnerable to accidents and errors," the researchers say. They advise public health campaigns to emphasize the "potentially covert consequences of chronic sleep loss."

The study was conducted by Daniel Cohen, of Brigham and Women's Hospital in Boston, Mass., and colleagues. The findings will be published in the Jan. 13 issue of the journal Science Translational Medicine.