Thursday, 9 February 2012

Poor sleep and a large lunch increases risk of a car accident

There's a lot of anecdotal evidence that would suggest that if you've had a bad night's sleep and you've got an afternoon full of boring dual carriageway driving ahead of you, it's probably not the best idea to have a large lunch. Well now there is the scientific data to prove it.

Researchers at The Sleep Research Centre at Loughborough University have recently published their results looking at the effect of eating a large lunch on afternoon driving ability [1]. It is the first of it's kind to look at long montonous driving in the lab. Most studies have only analysed the first 20 minutes and others were limited by examining non-driving skills such as psychologocial performance tests, which have come up with confusing results.

Experienced drivers who normally sleep well were recruited to perform monotonous afternoon driving in a simulator. In the simulator the drivers had to stay in the left hand lane, at a steady speed and would occasionally have to overtake slow drivers, to avoid collision. They were asked to drive for 2 hours without taking a break, the maximum time advised by UK road safety organisations.
Monotonous afternoon driving on a dual carriageway was simulated to look for
incidents of sleep-related lane deviations (C) fras1977, 2009
The study aimed to find out when they were falling asleep at the wheel. This can happen for seconds without the driver knowing they are falling asleep. Whenever the driver drove onto the "rumble strip" on the hard shoulder an "incident" was recorded. EEG (brain activity) and eye movement were monitored to determine when this lack of concentration was due to sleep, as opposed to being distracted.

The drivers were required to sleep well for 3 days and then the night before the experiment to restrict their sleep to 5 hours. Coming into the lab they were given lasagne and a yogurt, either a calorific meal or a light lunch. Both looked the same, in the same packaging, but one was 922 calories with lots of fats and carbs whilst the other was only 305 calories, and the subject didn't know which one they were eating. Then they were then sat down to drive for 2 hours in the driving simulator.

After 30 minutes of driving there was no difference between the number of "incidents" (driving on to the rumble strip due to drifting off to sleep). However at all times between 30 min - 2 hours of driving those who'd had the heavy meal were drifting off the road more.

The number of "incidents" (driving out of lane due to sleep) is increased in those who have had
a heavy lunch, EEG also shows their increased sleepiness. Adapted from Reyner, 2012

So this confirms what common sense would dictate, eating a heavy lunch after a bad night's sleep damages your ability to drive safely for long montonous car journeys in the afternoon. However, this was still an important study to perform.

The results of this experiment will improve the advice given to road users. Further information about their research, advice and services can be found at here. And, if you were concerned about whether the drivers got home safely after falling asleep in the simulator, don't worry, they were all taken home in a taxi.

[1] Reyner, L.S., Wells, S.J., Mortlock, V., & Horne, J.A. (2012). “Post-lunch” sleepiness during prolonged, monotonous driving - Effects of meal size. Physiology & behavior, 105(4), 1088-91. Elsevier Inc. doi:10.1016/j.physbeh.2011.11.025


  1. "Both looked the same" How do you make yoghurt look like Lasagne! Or did they blend the Lasagne?

    1. Thanks for your comment. No blending, there was a high calorie lasagne and low calorie lasagne that looked the same, and a high calorie yogurt and low calorie yogurt that looked the same. Drivers were either given the high calorie or low calorie meal. Sorry if this wasn't clear.