Welcome to Focus on Fatigue
Last month we looked at the short-term consequences of sleep deprivation and one of the sections compared not getting enough sleep with being drunk. This can be a tricky one to comprehend. After all, having one too many drinks feels completely different from being overtired. What does one really have to do with the other?
This month we will look more closely at what researchers mean when they say that being sleep deprived is comparable to being drunk?
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I’m not drunk, just tired
In most countries there is a clear, well-known legal limit for how much alcohol can be present in the bloodstream when a person is operating a vehicle or other machinery. This is known as the Blood Alcohol Concentration (BAC). Everyone knows that if you drive when you’re over the limit there is an increased risk of accident and injury because your performance is impaired. The drunker you are, the worse you will drive.
It is because we, as a community, understand how detrimental alcohol is to our performance that researchers find it useful to compare BAC levels with the performance detriments caused by sleep deprivation. After all, if we are told that being awake for 18 hours will cause our response speed on a particular task to drop by 50%, this may not feel very meaningful. However, being told that our driving performance after 18 hours of wakefulness will be comparable to someone who has BAC level of 0.05%, gives us something that we can relate too.
For this reason, researchers have spent a great deal of time over the past few decades trying to ascertain exactly where the similarities between BAC levels and sleep deprivation effects lie. Usually this involves testing participants on a wide range of skills under three different conditions, when they are sober and well-rested, when they are sleep deprived, and when they have consumed alcohol (usually at BAC levels of between 0.05% and 0.10%).
So, what has the research found?
Is being sleep deprived the same as being drunk?
Not exactly. Researchers actually believe that alcohol and sleep deprivation effect different areas of the brain. For example, acute alcohol intoxication has been shown to disrupt the functioning of the hippocampal memory systems, while fatigue is believed to have more of an effect on the prefrontal cortex. Also, there are some areas in which consuming alcohol and being sleep deprived will result in different outcomes. Alcohol will speed up your heart rate but sleep deprivation usually won’t. Sleep deprivation could increase your anxiety levels but alcohol will generally decrease anxiety.
However, there are enough similarities in how alcohol and sleep deprivation effect different types of performance levels to make the comparisons between them worthwhile. This is especially true when it comes to the kinds of skills necessary to do things like drive a car.
In what ways are BAC levels and sleep deprivation comparable?
The sorts of tests where researchers have found BAC levels to be comparable to sleep deprivation include skills such as:
- simple reaction times,
- detection times,
- dual tasks,
- vigilance and continuous attention tests,
- spatial memory,
- learning, and
- grammatical reasoning.
More complex cognitive tasks are effected sooner than simple cognitive tasks.
Often these studies use tests that are completed on a computer with a mouse and keyboard. However, a study conducted by Arnedt and colleagues used a driving simulation task to more directly compare the effects of alcohol and sleep deprivation on driving performance. This study looked at tracking and tracking variability (how far the vehicle deviated from the middle of the lane), speed deviation (from the speed limit), speed variability, and off-road incidents (the number of times the vehicle left the road). It was found that prolonging wakefulness by as little as 3 hours can produce decrements in the ability to maintain speed and road position comparable with BAC levels of 0.05%-0.08%.
When does sleep deprivation become a problem?
The culmination of the research suggests that the following meaningful comparisons can be made:
- 17-19 hours of sustained wakefulness = blood alcohol concentration of 0.05%
- 24 hours of sustained wakefulness = blood alcohol concentration of 0.10%
There are also some indications that having short sleeps of 4-5 hours repeated over a week will also make performance comparable with someone with a BAC of 0.05%-0.10%.
It’s important to note that if you do wake up at 6am and stay awake all day then you will reach 17 hours of sustained wakefulness at 11pm. This length of sustained wakefulness is not an uncommon occurrence for many of us, especially for shift workers.
The effects can be worsened when the increasing hours of wakefulness coincide with a natural dip in our circadian rhythm (the internal clock that tells our body when to be awake/asleep) or when we mix sleep deprivation with alcohol (e.g. having a couple of drinks at a late-night social gathering).
How can we use this information?
The purpose of these studies has been to highlight the effects of sleep deprivation on our ability to perform tasks such as driving a car, or operating machinery, in a practical way that we can easily understand. The comparisons can help us judge how our performance in certain areas will be effected by the number of hours we’ve been awake. It can also inform our behaviour when we are deciding how much alcohol is safe when we know we’ll be driving. It is not enough just to consider how many standard drinks we can safely consume, but how many hours we’ve been awake and the cumulative effect of mixing the two. The more information we have at our disposal when making these decisions, the safer we’ll be.
- Arnedt, J. T., Wilde, G. J. S., Munt, P. W. and MacLean, A. W. (2001) How do prolonged wakefulness and alcohol compare in the decrements they produce on a simulated driving task? Accident Analysis and Prevention, 33, 337-344.
- Falleti, M. G., Maruff, P., Collie, A., Darby, D. G. and McStephen, M. (2003) Qualitative similarities in cognitive impairment associated with 24h of sustained wakefulness and a blood alcohol concentration of 0.05%. Journal of Sleep Research, 12, 265-274.
- Fletcher, A., Lamond, N., van den Heuvel, C. J and Dawson, D. (2003) Prediction of performance during sleep deprivation and alcohol intoxication using a quantitative model of work-related fatigue. Sleep Research Online, 5(2), 67-75.
- Lamond, N. and Dawson, D. (1999) Quantifying the performance impairment associated with fatigue. Journal of Sleep Research, 8, 255-262.
- Orzel-Gryglewska, J. (2010) Consequences of Sleep Deprivation. International Journal of Occupational Medicine and Environmental Health, 22(1), 95-114.
- Williamson, A. M. and Feyer, A.-M. (2000) Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication. Occupational and Environmental Medicine, 57, 649-655.
In the News
There’s a reason why happy hour starts right after people typically get out of work. After a long, hard day at the office, it’s not uncommon for tired employees to hit the bar or even wait until they get home to have a few beers. Finnish researchers from the Finnish Institute of Occupational Health studied the health consequences of working long hours and overtime with how it affects a person’s alcohol consumption and published their findings in the British Medical Journal.
Having a drink before bedtime might make you fall asleep a little faster. But the sleep you get after imbibing may not be so restful, finds a new paper in the journal Alcoholism: Clinical & Experimental Research.
Video: Dangers of fatigued drivers
Falling asleep at the wheel is responsible for 30 per cent of all road deaths; a serious concern on our roads.
Video: Driving Tipsy-Sleep Deprived
When the MythBusters team took on the challenge of driving tipsy vs. driving sleep deprived they revealed some interesting individual differences in their drivers. They also found that driving while very tired (over 24 hours of sustained wakefulness) is extremely dangerous.
Article: How do prolonged wakefulness and alcohol compare in the decrements they produce on a simulated driving task?
The effects of alcohol ingestion were compared with those of prolonged wakefulness on a simulated driving task. Eighteen healthy, male subjects aged between 19 and 35 years drove for 30 min on a simulated driving task at blood alcohol concentrations of 0.00, 0.05 and 0.08%. Subjective sleepiness was assessed before and after the driving task. Driving performance was measured in terms of the mean and standard deviation (S.D.) of lane position (tracking); the mean and S.D. of speed deviation (the difference between the actual speed and the posted speed limit); and the number of off-road occurrences. Ratings of sleepiness increased with increasing blood alcohol concentration, and were higher following the driving task. With increasing blood alcohol concentration, tracking variability, speed variability, and off-road events increased, while speed deviation decreased, the result of subjects driving faster. The results were compared with a previous study examining simulated driving performance during one night of prolonged wakefulness [Arnedt, J.T., MacLean A.W., 1996. Effects of sleep loss on urban and motorway driving stimulation performance. Presented at the Drive Alert… Arrive Alive International Forum, Washington DC], using an approach adopted by Dawson and Reid [Dawson, D., Reid, K., 1997. Fatigue, alcohol and performance impairment. Nature 388, 23]. For mean tracking, tracking variability, and speed variability 18.5 and 21 h of wakefulness produced changes of the same magnitude as 0.05 and 0.08% blood alcohol concentration, respectively. Alcohol consumption produced changes in speed deviation and off-road occurrences of greater magnitude than the corresponding levels of prolonged wakefulness. While limited to situations in which there is no other traffic present, the findings suggest that impairments in simulated driving are evident even at relatively modest blood alcohol levels, and that wakefulness prolonged by as little as 3 h can produce decrements in the ability to maintain speed and road position as serious as those found at the legal limits of alcohol consumption.