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Introduction
Long distance drivers of commercial motor vehicles routinely experience monotonous and extended driving periods in a sedentary position; this, combined with the disruption to circadian rhythms linked to the common requirement of night driving, has been associated with wake time drowsiness. 1 2 Alertness is critical to safety for the driver and other road users as lapses of vigilance in relation to the task of driving can increase the likelihood of crashing. 3 4 Many strategies are available to long distance drivers to maintain their alertness, and studies have identified positive benefits from the use of stimulants such as caffeine. 5 6 We investigated the effects of use of caffeinated substances on the likelihood of a crash among long distance drivers of commercial motor vehicles.
Caffeine is a psychostimulant that works by suppressing the innate adenosine mediated drive to sleep while activating arousal 7 8 and is one of the most commonly consumed stimulants worldwide. 9 It has been shown to increase alertness in shift workers 10 and improve the capacity for task performance. 5 When used in excess, however, caffeine can also affect the quantity and quality of sleep, as sleep latency is prolonged and slow wave sleep is reduced. 11 The effectiveness of caffeine for enhancing alertness in the performance of monotonous tasks has previously been shown in laboratory and driving simulator settings. 5 12 Some authors have raised concerns about the methods used in these studies-namely, that the effects seen in comparisons of caffeine and placebo groups are simply an exaggerated response to caffeine withdrawal because of caffeine deprivation before the test and not caused by the substance alone. 13 In contrast, a recent study used a field setting and found that a combination of caffeine and naps improved performance and alertness for night workers, 14 and Mets and colleagues 15 16 have described both driving improvement and increased alertness in a simulator setting while adjustment for average daily caffeine consumption to prevent withdrawal effects after administration of coffee.
A recent systematic review examined the influence of caffeine in the prevention of injuries caused by impaired alertness in shift workers. While the use of caffeine was recognised as an effective strategy for improving alertness, the findings were inconclusive in relation to...