Mental and physical reaction times, accuracy, coordination and attention span were tested using a range of manual and cognitive tasks in 39 people in their 30s and 40s. The tests were carried out over a period of 28 hours during which the volunteers were given alcohol up to a maximum of 100 mg/dL. After a night's sleep the tests were repeated over the same time frame without alcohol. All those assessed worked in transport.
The results showed that after staying awake for 17 to 19 hours, a normal working day for many people, performance of some tasks was the same or worse than after 50 mg/dL of alcohol, and accuracy was significantly poorer. The longer the volunteers stayed awake, the worse they performed, reaching levels normally expected from alcohol intake above the legally accepted limit in Scandinavia and the UK.
Reaction times slow up to 50% after 17-19 h awake.
Dr Andrew Wilson and colleagues, from Sydney, Australia, note that lowest performance levels did not parallel the sleep-wake cycle that occurs as a result of the body's natural biorhythms (circadian rhythms). And they suggest that this is because it is sleep deprivation, rather than dips in the natural cycles, that most strongly impair performance, but that the effects are likely to be exaggerated by these rhythms.
The effects of fatigue are thought to play a part in almost two-thirds of the road accidents in the United States, say the authors. Extended working hours, shift work and lifestyle choices are likely to decrease the amounts of sleep we have, and the effects, which are likely to be cumulative, pose a serious risk to safety, they conclude.
Moderate sleep deprivation produces impairments in cognitive and motor performance equivalent to legally prescribed levels of alcohol intoxication.