RESEARCH · 1996
A nap or a coffee for sleepy drivers?
Horne JA, Reyner LA. Counteracting driver sleepiness: effects of napping, caffeine, and placebo. Psychophysiology. 1996;33(3):306–309.
At a glance
- Who
- 10 sleepy adults
- Setup
- Two monotonous one-hour afternoon drives in a car simulator, with a 30-minute break between them
- Compared
- A nap of under 15 minutes, 150 mg of caffeine in coffee, and decaf coffee as a placebo
- Finding
- The nap and the caffeine each reduced driving mistakes and sleepiness. A break on its own didn't help.
What they did
Sleep researchers at Loughborough University wanted to know what a sleepy driver should actually do during a break. Each volunteer came in several times. Every time they drove for an hour in the early afternoon, the time of day when sleepiness naturally peaks, then took a 30-minute break, then drove for another hour. During the break they either napped for under 15 minutes, drank coffee with 150 mg of caffeine, or drank decaf without knowing it. The order was random.
The researchers counted driving mistakes, asked how sleepy the drivers felt, and recorded their brain activity (EEG) to spot drowsiness.
What they found
- Both the short nap and the caffeine clearly reduced driving mistakes, felt sleepiness and the brain signs of drowsiness during the next hour.
- Caffeine worked more consistently. How much people actually slept during the nap varied from person to person.
- A break with decaf, so just a rest, didn't help.
- Drivers knew they were sleepy before they started making mistakes.
What it means for your coffee nap
This study tested the nap and the coffee separately, and both worked. That raised the obvious next question: what happens if you combine them? The same team answered it a year later, and the result became the coffee nap.
Limits
Ten people is a small group, the drives were in a simulator rather than on a real road, and the effects were measured for one hour after the break.