The sleep deficit puzzle: Is it not enough sleep or too much being awake?

We know lack of sleep produces a range of cognitive and health problems. But is the problem not enough sleep, too much wakefulness — or both? A clever experiment answers the question by shortening the day.

A clever experiment answers the question by shortening the day

We know lack of sleep produces a range of cognitive and health problems. But is the problem not enough sleep, or too much wakefulness? (Getty Images)
Listen7:23

Not enough sleep or too much wakefulness?

Here's a puzzle: we know lack of sleep produces a range of cognitive and health problems. But is the problem not enough sleep, too much wakefulness — or both?

The scary part is that when somebody decides they can drive because they feel alert or that they're not sleepy. These results show that they're not really accurate.- Elizabeth Klerman

These seem like the same thing, but they aren't. In a new study, Dr. Elizabeth Klerman, a sleep researcher at Brigham and Women's Hospital in Boston, devised a way to separate the two, and found that not enough sleep is indeed a problem.

The experiment

A normal wake-sleep cycle is about 16 hours awake and eight hours sleeping in a 24-hour day. That's a ratio of 1:2 of sleep to wake time.  

"We wanted to know to what extent extended wake is important, and to what extent shortened sleep is important," says Klerman.

Dr. Elizabeth Klerman is a sleep researcher at Brigham and Women's Hospital in Boston. (Harvard Medical School )

To find out which is doing the real damage, Klerman and her group changed the length of the day. They took about 20 volunteers and put them in a controlled environment for a month where they changed the day length to 20 hours.  

This allowed them to create a situation where people would be awake for a "normal" amount of time (15.33 hours), but asleep for a short amount of time (4.67 hours). That was a ratio of sleep to wake of about 1:3.3.  

They also had a control group that was in a "normal" sleep ratio of 1:2 (6.6 hours of sleep and 13.3 hours of wakefulness).

By keeping the amount of wake time "normal" while sleep time on the short side for the first group, it allowed researchers to isolate the effects that restricted sleep has on cognitive abilities.

The findings

After testing the volunteers on this protocol using standard cognitive evaluations, they found pretty much the same things found under other sleep studies: reflexes were shot — half as fast. Alertness and focus were similarly compromised, and it got worse through the 32 days of the experiment.

Sleep is good for you, but most of us don't let ourselves sleep as much as our body wants to. You should give yourself permission to sleep more. ​- Elizabeth Klerman

Perhaps most interesting, and most sinister, was that people were unaware of how compromised they were.

"The scary part is that when somebody decides they can drive because they feel alert or that they're not sleepy," says Klerman. "These results show that they're not really accurate."

The good news is there's a simple solution to avoid that: make sure you get enough sleep.

"Sleep is good for you, but most of us don't let ourselves sleep as much as our body wants to," says Klerman. "You should give yourself permission to sleep more."