The Cost of Fatigue Is Great and a Short Nap May Just Help Pay the Debt

Mark R. Rosekind, Ph.D., is President and Chief Scientist of Alertness Solutions, a scientific consulting firm that works with corporations to maximize alertness, productivity and safety. He formerly led the Fatigue Countermeasures Program at the NASA Ames Research Center.

How sleep-deprived are we as a society?


Dr. Rosekind: We know from data that most people get probably about an hour and a half less sleep than they actually need, so even though we may physiologically need eight hours of sleep every single night, most of us are operating on maybe six and a half hours of sleep.

That's an issue because when you lose sleep it doesn't just disappear. You actually build what's called a cumulative sleep debt. You can think about it like a bank account. If you're getting an hour and a half less sleep than you need over five days of the work week, then you're going into the weekend basically seven-and-a-half hours in the red; it's as if you stayed up one full night going into the weekend.

What does that sleep debt mean to us on a daily basis?

Dr. Rosekind: Well, we know that getting about two hours less sleep than you need is enough to significantly reduce or even impair your performance and productivity the next day. So if you need eight hours and you're only getting six or less, then we know the next day you're going to pay for that. If you need eight hours of sleep and you got seven, you're only an hour in the red, it's not a big deal.

But over two nights it just became a big deal. If you're seven-and-a-half hours in the red by the end of the week, you should watch yourself driving home on that Friday afternoon. So we're individually paying a cost, but that also obviously puts people around us in our society at risk as well.

Can we buy back that sleep?

Dr. Rosekind: The good news is that you actually recover from sleep debt by sleeping deeper, not necessarily a lot longer. So typically when you're very tired you get more deep sleep when you do sleep, so it might only take you one to two nights to recover.


The Cost of Fatigue Is Great (<i>cont'd</i>)

How many motor vehicle accidents are due to sleepiness?

Dr. Rosekind: Just recently a group of scientists got together, and we estimated that fatigue plays a role in ten to twenty percent of all accidents in all modes of transportation.


Most of the published official Government estimates underestimate fatigue. And the reason for that is that we don't have a blood test the way we do alcohol or drugs to be able to say that's what caused the accident. You would have to know how long they'd slept, how long were they awake, what time of day was it—and without that we typically underestimate whether fatigue played a role or not.

I think people are looking for a way to measure fatigue, either by measuring our blood or testing how we might use technology to figure out whether people are too tired to drive, to fly, or to perform a safety-sensitive job.

We know that it's a big issue, because even the official estimates suggest that there are at least a 100,000 accidents in the United States every year, 71,000 injuries and probably 1,500 fatalities due to people falling asleep at the wheel. In fact, in the most recent National Sleep Foundation poll, fifty-one percent of the people said that they had driven while drowsy during the last year. And 17 percent, that's almost one out of five, said they'd actually nodded off at the wheel. So we know it's a big issue, not just in commercial truck-driving, but even just for passengers and people in passenger vehicles as well.

What mechanisms control our internal "clock"?

Dr. Rosekind: Every human has a clock in the brain. It's made up of several thousand cells in our brain stem, in a place called the suprachiasmatic nucleus. Basically it's just like a timer you would have at home that would control the lights if you're on vacation or the sprinklers on your lawn, and that clock pretty much times every single thing that goes on in your body.

That twenty-four hour clock, called a circadian clock, basically programs your sleep-wakefulness, when your hormones are secreted, when you get hungry, when you go to the bathroom, your mood, your alertness—pretty much everything you do.

That internal clock is actually programmed to have two periods during the day when we are maximally sleepy. Our most important sleep period is programmed for about three to five a.m. That's the point in our cycle where we are the sleepiest and everything in our body is at its lowest: our slowest breathing, our slowest heart rate, our lowest temperature, our lowest alertness, all those happen in the middle of the night.

If you're trying to work during that time, like on an all-night flight or on an all-night shift, then basically you're trying to work at a time when biologically you're programmed to be asleep. So you have to override that natural programming to actually stay awake to do the job, but clearly you're still at risk.

The clock also has an afternoon period during which we're programmed for sleepiness, about three to five p.m. or siesta time. So we're actually biologically programmed to have a siesta or sleepy time in the afternoon. Most people think that the afternoon feeling of the head dropping is due to the big lunch they had. But what we know is whether you eat or not, you're going to get sleepy in the afternoon.


The Cost of Fatigue Is Great (<i>cont'd</i>)

It's kind of interesting to actually see how different cultures have responded to that. In some cultures you have a siesta where literally things are shut down, people go home, go take a nap, then come back later to work. Think about high tea in the United Kingdom. It's giving you caffeine at four o'clock in the afternoon to help. In the United States its the macho thing to push through that period, when really people's heads are nodding...

As humans we're horrible at knowing how alert we are. So our tendency is to say "Oh, I'm wide awake and alert," but if we measured it physiologically we'd actually find out you could be ready to nod off in just a moment.


Part of the problem [in recognizing sleep deprivation] is that we don't realize how bad off we are. Only after getting a good night's sleep does the fog lift and you suddenly realize how bad off you were.

What are the symptoms of sleepiness?

Dr. Rosekind: You know, I tell everybody that if you're walking around noticing that you're having to read that paragraph for the third time, or somebody just gave you a phone number and you can't remember the last couple of digits, or that you were a little more edgy in that conversation, a little moodier and angrier and more upset than you needed to be, or you're in a big business deal and all of a sudden your decision-making is way off—all of these are signs and symptoms that you need to get some sleep, whether that's a full night's sleep or a strategy like taking a nap if you need to.

How effective is napping in combating the effects of fatigue?

Dr. Rosekind: One of the most effective strategies to improve alertness is a short nap. When I was at NASA we conducted a study in which we gave pilots planned, controlled 40-minute naps in the cockpit to see how they affected their alertness and performance. What we found was that performance was improved 34 percent and their alertness was improved 54 percent. I always challenge people to name another productivity tool that's as simple and straightforward to help improve performance, productivity and safety as a quick nap.

The guidelines for napping are that if you are going to take a short nap, make it up to about forty-five minutes. The reason for that is that a slightly longer nap will put you into deep sleep. If you awaken somebody in deep sleep they can be sleepy and groggy and disoriented for a period of time, that's called sleep inertia. So a short nap up to forty-five minutes helps you avoid that by awakening you before you enter the deep sleep phase.

If you're going to take a longer nap, you want to make it about two hours or so to get you through a full sleep cycle. And that's how simple it is to get that kind of performance and safety benefit by having a short nap.