Long-distance commercial drivers regularly experience monotonous, sedentary drives, as well as frequent night-time driving, and often report drowsiness. But “their alertness is critical to safety for the driver and other road users,” said researcher Lisa Sharwood, Ph.D., of the University of Sydney, Australia, and colleagues in the British Medical Journal.
Her team investigated the link between use of substances containing caffeine and the risk of a crash. They recruited 530 long-distance drivers of commercial vehicles who were involved in a crash between 2008 and 2011 in New South Wales and Western Australia, and compared their caffeine use against 517 similar drivers who had not had a crash in the previous year.
Overall, 43 percent of the drivers said they used substances containing caffeine such as tea, coffee, caffeine tablets, or energy drinks for the express purpose of staying awake. In addition, three percent said they took illegal stimulants such as amphetamine (“speed”), MDMA (ecstasy), and cocaine.
Once several risk factors including age, health, sleep patterns, distance driven, and breaks were taken into account, the drivers who used caffeine to stay alert had a 63 percent reduced risk of crashing.
Caffeine is a psychostimulant that suppresses the urge to sleep and increases mental arousal. It has been found to increase alertness in shift workers as well as boosting performance on tasks. But it can also decrease sleep quality and create caffeine withdrawal with habitual use.
The experts conclude, “Caffeinated substances are associated with a reduced risk of crashing for long-distance commercial motor vehicle drivers.” They point out that “comprehensive mandated strategies for fatigue management” are necessary, but meanwhile the use of caffeinated substances “could be a useful adjunct strategy” to such strategies.
Sharwood commented that these drivers are making a behavioral adaptation in order to manage their fatigue.
“This may seem effective in enhancing their alertness, but it should be considered carefully in the context of a safe and healthy fatigue management strategy; energy drinks and coffee certainly don’t replace the need for sleep,” she said.
She added the benefit of caffeine is only useful for a short time and that having regular breaks, napping, and appropriate work schedules are strongly recommended.
Caffeine is one of the most commonly used stimulants worldwide. It stimulates the central nervous system, resulting in increased alertness and wakefulness, faster and clearer flow of thought, increased focus, and better general body coordination.
Its speed of metabolism varies widely among individuals according to age, liver function, pregnancy, medications, and the level of necessary enzymes in the liver. In healthy adults, caffeine’s half-life is about five hours.
The substance suppresses the adenosine-mediated drive to sleep, but when used in excess, it can also cause daytime sleepiness. It also affects both the quantity and quality of night-time sleep, with the time taken to fall asleep being prolonged and slow wave sleep being reduced.
Research on the use of other stimulants, including nicotine and illegal substances such as amphetamine drugs, among long-distance drivers is limited.
But various findings suggest that their use is still occurring. The self-reported rate of illegal stimulant use among Australian long-distance drivers has varied from 19 percent to 32 percent in different surveys.
“Efforts to reduce the use of illegal stimulant substances in these drivers would need to be introduced at the same time as equally effective countermeasures to maintain alertness on the road to prevent an increase in the incidence of crashes,” warned the Australian researchers.
In their study, use of illegal stimulants was not significantly linked to the risk of crashing, but this could be because of the low reported usage rate, of just three percent. The team suggests that the low reported use of illegal substances in the study “could merely reflect a reticence by drivers to admit their drug use, despite being assured confidentiality for interview responses.”
Napping during breaks when tired is strongly recommended for long-distance drivers, but in the study, only 70 percent of drivers reported stopping for a nap when tired.
“Although we did not probe in detail,” the researchers said, “the numbers suggest that it is not a strategy considered as favorable as others for the management of fatigue.”
Other fatigue-beating strategies that have been investigated include opening the vehicle window, stopping and resting quietly while seated, or stopping and going for a walk, but these do not appear to be as effective as caffeine or napping.
Sharwood, L. N., Elkington, J., Meuleners, L., Ivers, R., Boufous, S., Stevenson, M. Use of caffeinated substances and risk of crashes in long distance drivers of commercial vehicles: case-control study. BMJ 2013;346:f1140