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Sleep deficiency linked (yet again) to an increased risk of being in a motor vehicle crash

“We found that chronically sleep-deprived individuals don’t perceive themselves as being excessively sleepy and thus don’t perceive themselves as impaired,” said lead author Dr. Daniel Gottlieb.

Millions of people are driving daily on U.S. roads while under the influence of a sleep deficiency, putting their lives and the lives of others at great risk.

Among public health officials, sleep deficiency is a well-recognized cause of motor vehicle crashes — and deaths. Experts now attribute as many as one in five deaths in crashes on U.S. roads to drowsy driving.

Being behind the wheel while sleepy makes drivers less able to pay attention to the road, slower to react should there be a sudden need to brake or steer, and less likely to make good decisions.

The public, however, has been slow to connect sleep deficiency with unsafe driving. That lack of awareness is troubling, given that at least one in four American adults gets six or fewer hours of sleep on most nights — below the minimum seven hours per night considered necessary for most people to feel truly rested. 

That means millions of people are driving daily on U.S. roads while under the influence of a sleep deficiency, putting their lives and the lives of others at great risk. 

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A recent study in the journal BMC Medicine, underscores the seriousness of the problem. It found that sleep deficiency due to either sleep apnea or not sleeping long enough at night is strongly associated with motor vehicle crashes — whether or not people are aware that they are sleepy.

“We found that chronically sleep-deprived individuals don’t perceive themselves as being excessively sleepy and thus don’t perceive themselves as impaired,” said Dr. Daniel Gottlieb, the study’s lead author and a physician specializing in sleep disorders at the Harvard University-affiliated Brigham and Women’s Hospital, in a released statement. “This resulted in an increased risk of motor vehicle crashes in sleep-deprived individuals.”

Collecting the data

For the study, Gottlieb and his colleagues analyzed data from 1,745 men and 1,456 women between ages of 40 and 89 who were participating in the Sleep Heart Health Study, a community-based study of the health consequences of sleep apnea.

Obstructive sleep apnea is a disorder that occurs when tissue in the back of a person’s throat narrows or blocks the airways, causing breathing to stop briefly during sleep. The pauses typically last for only a few seconds, but they can, in severe cases, occur 30 times or more a minute. The sleeper may not wake up, but the pauses will prevent deep, restful sleep. Daytime symptoms of sleep apnea include intense fatigue, depression, difficulty concentrating and excessive sleepiness.

When they entered the study, the participants filled out questionnaires about their health and sleep habits, including questions designed to measure their daytime sleepiness. They also underwent overnight polysomnography, a test that tracks and measures specific activities of the brain and the body during sleep. The test is used to diagnose sleep disorders, including sleep apnea.

Two years later, the participants filled out another set of questionnaires about their general health and sleep habits. This time they also answered questions related to their driving habits and their history of motor vehicle crashes. About 7 percent of the respondents reported that they had been involved in at least one motor vehicle crash during the previous year.

Key findings

The researchers compared the motor vehicle crash risk of the people with sleep apnea with those without the condition. They found that severe sleep apnea was associated with a 123 percent increased risk of motor vehicle crashes, while mild to moderate sleep apnea was linked to a 13 percent increased risk. 

Next, the researchers looked at the link between hours slept at night and motor vehicle crash risk. They found that sleeping six hours a night was associated with a 33 percent increase in crash risk when compared to sleeping seven or eight hours per night.

That risk was also found to be independent of whether the person reported being sleepy during the day.

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“It remains to be determined why many people with severe sleep apnea or short sleep duration in this study did not report excessive sleepiness, even though their elevated crash risk suggests that their driving performance was impaired,” Gottlieb and his co-authors write in their paper.

It might be, the researchers point out, because sleep deficiency makes people less vigilant — and impairs their driving — even if they don’t necessarily feel sleepy. Or the drivers may not feel sleepy because they are able to mask the symptoms with caffeine or other stimulants.

Also, research has shown that people’s subjective measures of their own sleepiness tend to plateau after several days of not getting enough sleep — even though objective measures of their performance show they aren’t as vigilant as they were when they were rested.

Avoiding drowsy driving

This study comes with several caveats, of course. It shows only a correlation between sleep deficiency and an increased risk of motor vehicle crashes, rather than a direct causal link. In addition, the study relied on self-reports of both daytime sleepiness and motor vehicle crashes, both of which the participants may have been reluctant to acknowledge, even though they knew the information would be kept confidential.

Still, the study supports plenty of other research on this topic and should therefore serve as yet another wake-up call to all of us who get behind the wheel: Drowsy driving can be as dangerous as drunk driving.

As the National Highway Traffic Safety Association (NHTSA) stresses, the only true preventive measure against the risks of drowsy driving is to make sure you get seven to eight hours of sleep on a daily basis. Here are the agency’s additional tips:

  • Before the start of a long family car trip, get a good night’s sleep, or you could put your entire family and others at risk.
  • Many teens do not get enough sleep at the same time that their biological need for sleep increases, thereby increasing the risk of drowsy-driving crashes, especially on longer trips.
  • Avoid drinking any alcohol before driving. Consumption of alcohol interacts with sleepiness to increase drowsiness and impairment.
  • If you take medications that could cause drowsiness as a side effect, use public transportation when possible. If you drive, avoid driving during the peak sleepiness periods (midnight – 6 a.m. and late afternoon).
  • If you must drive during the peak sleepiness periods, stay vigilant for signs of drowsiness, such as crossing over roadway lines or hitting a rumble strip, especially if you’re driving alone.

And don’t rely on caffeine to keep you alert. “The effects last only a short time,” the NHSTA points out, “and you might not be as alert as you think you are. If you drink coffee and are seriously sleep-deprived, you still may have ‘micro sleeps’ or brief losses of consciousness that can last for four or five seconds. This means that at 55 miles per hour, you’ve traveled more than 100 yards down the road while asleep. That’s plenty of time to cause a crash.” 

FMI: You can read the new study on the BMC Medicine website.