Focus on Fatigue

Focus on Fatigue, Issue 37: The coffee bean – Friend or foe?

By November 1, 2015 No Comments

Welcome to Focus on Fatigue.

Caffeine. Many of us greet it in the morning like an old friend. Some swear they just can’t function until they’ve had their first cup of coffee in the morning. Amongst shift workers, caffeine consumption is a popular strategy for maintaining alertness through the long hours of the night shift.

This month’s Focus on Fatigue will take a closer look at our favourite bean. Is it really as helpful as we think it is? And just how much caffeine is too much?

The FRMS Team

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Views expressed in articles and links provided are those of the individual authors, and do not necessarily represent the views of InterDynamics (except where directly attributed).

Feature Articles

The Coffee Bean: Friend or Foe?

Drinking a cup of coffee is, for many of us, an easy way to perk up when we’re feeling low on energy. Along with the increase in alertness, caffeine can also have many other benefits, including: enhanced physical and cognitive performance, faster reaction times, enhanced short-term memory, greater ability to concentrate and focus attention, greater accuracy, and it tastes great too. With so many advantages to caffeine consumption, it would easy to assume that we should all be drinking way more coffee. Unfortunately, this is not the case.

Consuming too much caffeine also comes with a long list of side effects, including: a rise in body temperature, dizziness, headaches, greater fatigue following the energy burst, heart palpitations, restlessness, anxiety, irritability, impaired fine motor control, trembling hands, sleeplessness, and withdrawal symptoms.

So, caffeine does give us some great benefits, but only if we don’t consume too much of it.

How much is too much?

There is no agreed upon level of safe caffeine usage, and some people are more sensitive to caffeine than others. However, an expert working group overseen by the Australia New Zealand Food Authority published a paper on the safety aspects of dietary caffeine. This group classed anything up to 400mg of caffeine per day as a low dosage. This is about 4-5 cups of instant coffee or two espresso coffees. A google search can generally provide information on the caffeine content of different products and it is a good idea to find out how many serving of your favourite caffeinated foods and drinks you can have each day to ensure you are not exceeding these low dosage levels.

Caffeine and shift work

In 2010, Ker and colleagues reviewed studies that investigated the use of caffeine for the prevention of injuries and errors in shift workers. It was concluded that “there is no reason for healthy shift workers who already use caffeine within recommended levels to improve their alertness, to stop doing so.” However, it is important to understand what caffeine does and doesn’t do within the shift work context.

Caffeine will…

  • Wake you up – Caffeine does reverse the effects of drowsiness and make you more alert.
  • Help you maintain your performance – Caffeine can help you maintain your performance on cognitive tasks, psychomotor tasks and many executive functions.
  • Help your attention span and focus – Caffeine can make you more vigilant in your work.
  • Improve your driving – Caffeine has been found to significantly reduce line crossing errors in simulated night driving performance.

However, caffeine will also…

  • Make you overconfident – Caffeinated people are more likely to feel confident about their work performance, even when that performance has suffered. This may have serious consequences in real-life situations where accurate self-perception is crucial for avoiding risks.

Caffeine will not…

  • Help you make complex decisions in the face of changing information – While the effects of caffeine consumption on complex decision making have not been well researched, one study did find that a moderate dose of caffeine did nothing to reverse the effects of sleep deprivation in this sort of context. In other words, drinking coffee may make you feel alert, but it may not help you think more clearly in complex situations.
  • Replace sleep – Sleep gives your brain time to conduct a whole host of basic maintenance jobs that it simply cannot do when you’re awake. Caffeine can help you get the job done temporarily, but eventually sleep is your only safe option.

Caffeine and sleep: The catch-22

You sleep poorly one night, so in the morning you have a nice strong cup of coffee to get you going. A few more throughout the day keep your energy levels up until you get home. That night you have trouble falling asleep because of the extra caffeine you’ve consumed. Sometime after midnight you drift off and when the alarm sounds you stumble out of bed, bleary-eyed and searching for the coffee pot. Obviously this is an extreme version of the story, but most of us are guilty of falling into this cycle from time to time.

Caffeine consumption may impair many of our sleep habits, including the quality of our sleep, sleep duration, and how much time we spend in the important slow-wave and REM stages of sleep. Therefore, it is important to keep in mind not just how much caffeine we are consuming, but when we are consuming it. It is recommended that, whenever possible, caffeine consumption should stop at least six hours before sleep is due to begin.

What about the non-coffee drinkers?

Not everyone enjoys a cup of coffee or tea. Indeed, some people consume very little caffeine at all on a regular basis. Are these people missing out on some advantage that all the coffee drinkers are getting?

Not necessarily. One study (Rogers, et al) compared alertness between high-caffeine consumers and those who usually consume little to no caffeine. They found that giving caffeine to people who were not regular consumers did not make them more alert. Meanwhile, giving caffeine to people who usually consume of lot of it did make them more alert, but not more alert than the non-consumers. In other words, this study found that “we don’t gain an advantage from consuming caffeine – although we feel alerted by it, this is caffeine just bringing us back to normal.”

The verdict

So far, researchers have generally concluded that low dosages of caffeine can be used as a safe, effective way to manipulate your mental state. It is beneficial in restoring low levels of wakefulness and maintaining task performance. However, it may have a detrimental effect on subsequence sleep, which can result in increased sleepiness and fatigue the following day.

If you are not a coffee drinker there is no compelling reason to start drinking it. However, if you do enjoy coffee, or another caffeinated food or beverage, go right ahead and enjoy – in moderation.


  • Dagan, Y. and Doljansky, J. T. (2006) Cognitive performance during sustained wakefulness: A low dose of caffeine is equally effective as modafinil in alleviating the nocturnal decline. Chronobiology International, 23(5), 973-983.
  • Glade, M. J. (2010) Caffeine: Not just a stimulant. Nutrition, 26(10), 932-938.
  • Ker, K., Edwards, P. J., Felix, L. M., Blackhall, K., and Roberts, I. (2010). Caffeine for the prevention of injuries and errors in shift workers. Cochrane Database of Systematic Reviews, 5, CD008508.
  • Killgore, W. D. S., Lipizzi, E. L., Kamimori, G. H. and Balkin, T. J. (2007) Caffeine effects on risky decision making after 75 hours of sleep deprivation. Aviation, Space and Environmental Medicine, 78, 957-962.
  • Rogers, P. J., Hohoff, C., Heatherley, S. V., Mullings, E. L., Maxfield, P. J., Evershed, R. P., Deckert, J. and Nutt, D. J. (2010) Association of the anxiogenic and alerting effects of caffeine with ADORA2S and ADORA1 Polymorphisms and habitual level of caffeine consumption. Journal of the American Medical Association, 35, 1973-1983.
  • Smith, A. (2002) Effects of caffeine on human behaviour. Food and Chemical Toxicology, 40(9), 1243-1255.
  • Smith, P. F., Smith, A., Miners, J., McNeil, J. and Proudfoot, A. (2000) The safety aspects of dietary caffeine. Expert Working Group on Caffeine. Australia New Zealand Food Authority. Canberra, Australia.
  • Snel, J. and Lorist, M. M. (2011) Effects of caffeine on sleep and cognition. Progress in Brain Research, 190, 105-117.
  • Victorian Government (2013) Caffeine. Better Health Channel. Accessed on: 11/11/2015.

InterDynamics News

Conferences and Presentations

This section outlines recent and upcoming InterDynamics speaking engagements and/or conferences that we recommend and will be attending.

Human Factors for Transport Safety Investigators, Australian Transport Safety Bureau (ATSB), Canberra, 2nd-6th November 2015

Earlier this month, InterDynamics attended the Human Factors for Transport Safety Investigators course, run by the Australian Transport Safety Bureau (ATSB) in Canberra.

The Course Objectives were to provide participants with an awareness of:

  • the key terms and concepts used in human factors;
  • basic human performance capabilities and limitations;
  • the factors that influence human performance;
  • the importance of human factors in transport safety;
  • how human factors issues can be considered during an investigation; and
  • where to find expertise on more complex human factors issues.

The ATSB Human Factors course provides participants with a general overview of human factors in safety-critical systems, including the aviation, marine, and rail industries.

Human Factors is the multi-disciplinary science that applies knowledge about the capabilities and limitations of human performance to all aspects of the design, manufacture, operation, and maintenance of products and systems.

After any accident or incident, a thorough operational and technical investigation is essential to determine what happened during the occurrence. However, very often, it is only by investigating the possible role of human factors, at both the individual and organisational level, that it can be determined how and why the events occurred. Only then can appropriate safety action be taken.

The ATSB is a leader in the application of human factors to transport safety investigations, and has developed a highly regarded Human Factors for Transport Safety Investigators course. While the course is intended primarily for ATSB personnel, a limited number of places are available to industry participants from the aviation, marine and rail industries.

InterDynamics would like to encourage all of our Focus on Fatigue Newsletter readers to attend such a course as part of your FRMS operation and development. Please check with your local investigation board or regulator for international readers.

In the News

Provided below are a selection of articles and videos from around the web on the issues associated with fatigue. We hope you find them useful and interesting.

Article: Caffeine can disrupt sleep hours later

by Catharine Paddock, Medical News Today (15 November 2013)

Drinking coffee might be a nice way to round off the evening meal or perk you up in the late afternoon, but it may well disrupt your sleep hours later when you retire for the night, according to a new study.

Video: Your brain on coffee

by ASAPScience (28 August 2014)

How does the world’s favourite drug actually work? This short video will explain what caffeine does to your brain to make you feel more alert.


Article: Caffeine for the prevention of injury and errors in shift workers

Ker, K., Edwards, P. J., Felix, L. M., Blackhall, K. and Roberts I. (2010) Caffeine for the prevention of injuries and errors in shift workers. Cochrane Database of Systematic Reviews 2010, Issue 5. Art. No.: CD008508. DOI: 10.1002/14651858.CD008508.

Plain Language Summary

Sleepiness leads to a deterioration in performance and is associated with an increased risk of error and injury. Shift work is an major cause of sleepiness as it requires workers to be awake at times which are different to those dictated by their ’body clock’. This in turn can compromise the safety of themselves and of others – sleepiness is a risk factor for events such as traffic crashes, occupational injuries and medical errors.

The identification of interventions which can reduce the risk of error and injury is necessary to help ensure that those who are required to work through the night, can do so safely. Caffeine has been proposed as one such intervention, although how effective it is in shift workers is unknown.

For this systematic review, the authors searched for randomised controlled trials which investigated the effects of caffeine on injury, error and cognitive performance in shift workers. They found 13 trials – none of the trials looked at the effect on injury, two trials measured error, while the remaining trials used neuropsychological tests to assess cognitive performance.

The results of the trials suggest that compared to no intervention, caffeine can reduce the number of errors and improve cognitive performance in shift workers. No difference in effect was found by the trials comparing caffeine with other interventions (such as nap, bright light and modafinil). However, due to some methodological weaknesses of the trials, some caution is required when interpreting the results.

The authors of the systematic review conclude that caffeine may be an effective intervention for improving performance in shift workers however, there are no trials from which they could assess its effect on injuries. Based on the current evidence, the review authors judge that there is no reason for healthy shift workers who already use caffeine within recommended levels to improve their alertness, to stop doing so. They go on to suggest that it would be useful for further trials to be undertaken to assess the effects of caffeine against other potential countermeasures.

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