Can A Little Alcohol Impair A Tired Driver That Isn't Drunk?

By Bryan Le 08/21/17

A recent study examined the impact of moderate drinking and sleep deprivation. 

Man sleeping behind the steering wheel of a car.
Don't drink, not sleep and drive.

If you are under the legal alcohol limit and sleep-deprived, you may be as impaired as a drunk driver, a study finds.

Using 16 healthy young men as subjects, researchers exposed the men to varying levels of sleep deprivation and drunkenness, including both impairments at once. The researchers observed that even with moderate levels of alcohol consumed and blood alcohol content within legal limits, having five hours of sleep caused subjects to become drowsier and more inattentive than either impairment by itself.

The effect could last up to two to three hours.

“No amount of alcohol intake has been deemed safe when under the influence of sleepiness through either poor or inadequate sleep, or being awake when the body (should be) asleep at night,” said Clare Anderson, a study co-author and researcher at the Institute of Cognitive and Clinical Neuroscience at Monash University in Australia. “Our take-home message would therefore be to avoid alcohol when feeling sleepy and to have a short nap before attempting to drive or undertaking any other safety critical task.”

While the negative effects of alcohol and lack of sleep on motor coordination and decision-making have been well-documented separately, the combined effects of alcohol and sleep deprivation have not.

In this experiment, the subjects, aged 18 to 27, were tested four separate times. They were asked to self-report their level of drowsiness and then had their eye movements measured during a test of their response to visual stimuli. Researchers timed their button press when an image appeared on a screen.

A baseline measurement was set with sober, well-rested subjects before adding alcohol and sleep deprivation to the mix. Researchers found that the subjects were most impaired about 90 minutes after drinking alcohol while lacking sleep. Considering the experiment was done on healthy young men, the effects may vary in female or elderly populations.

Most deceptively, people who drink while sleep-deprived may not feel the buzz and figure they are safe getting behind the wheel. “So while you may feel fine driving home when you leave that party, that feeling can make a turn for the worse on the drive home, particularly since alcohol increases the feeling and effects of sleep deprivation,” said Russell Griffin, a University of Alabama researcher not involved in this particular experiment.

“The body is only able to metabolize, or remove, a little bit of alcohol at a time, so the more alcohol a person drinks, the more alcohol is circulating through their system and the higher the impairment.”

Astronauts in space, while they don’t drink, get an average of 5.96 hours of sleep a night and use a bevy of sleeping pills to keep awake.

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Bryan Le grew up in the 90's, so the Internet is practically his third parent. This combined with a love for journalism led him to The Fix. When he isn't fulfilling his duties as Editorial Coordinator, he's obsessing over fancy keyboards he can't justify buying. Find Bryan on LinkedIn or Twitter