Chronically sleep deprived? You can't make up for lost sleep

We’ve all experienced that occasional all-too-short night of sleep - staying out too late at a party on a weeknight, studying into the wee hours for a morning exam or being kept up during the night with a sick child. Our bodies try to catch up by making us sleep more and/or more deeply the following night.

It is well established that following an acute period of sleep loss, the body responds this way in order to maintain a homeostatic balance between sleep and wakefulness. Very little is known, however, about the health consequences of chronic partial sleep loss - losing a little bit of sleep over a period of days, months or even years.

Now sleep researchers at Northwestern University have discovered that when animals are partially sleep deprived over consecutive days they no longer attempt to catch up on sleep, despite an accumulating sleep deficit. Their study is the first to show that repeated partial sleep loss negatively affects an animal’s ability to compensate for lost sleep. The body responds differently to chronic sleep loss than it does to acute sleep loss.

The results, which shed light on a problem prevalent in industrialized nations with 24/7 societies such as the United States, where Americans get nearly an hour less sleep a night than they did 40 years ago, were published online recently by the Proceedings of the National Academy of Sciences (PNAS).

“We now know that chronic lack of sleep has an effect on how an animal sleeps,” said Fred W. Turek, professor of neurobiology and physiology and director of Northwestern’s Center for Sleep and Circadian Biology and an author of the paper. “The animals are getting by on less sleep but they do not try and catch up. The ability to compensate for lost sleep is itself lost, which is damaging both physically and mentally.”

In the study, the researchers kept animals awake for 20 hours per day followed by a four-hour sleep opportunity, over five consecutive days. The team monitored brain wave and muscle activity patterns in order to precisely quantify sleep-wake patterns.

After the first day of sleep loss, animals compensated by increasing their intensity, or depth, of sleep, which is indicative of a homeostatic response. However, on the subsequent days of sleep loss, the animals failed to generate this compensatory response and did not sleep any more deeply or any longer than they did under non-sleep deprived conditions (baseline measurements). At the end of the study, the animals were given three full days to sleep as much as they wanted. Amazingly, they recovered virtually none of the sleep that was lost during the five-day sleep deprivation period.

The findings support what other scientists have discovered in recent experimental studies in humans. Chronic partial sleep loss of even two to three hours per night was found to have detrimental effects on the body, leading to impairments in cognitive performance, as well as cardiovascular, immune and endocrine functions. Sleep-restricted people also reported not feeling sleepy even though their performance on tasks declined.