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.