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Meta-Analysis
. 2010 May 12;2010(5):CD008508.
doi: 10.1002/14651858.CD008508.

Caffeine for the prevention of injuries and errors in shift workers

Katharine Ker  1 , Philip James Edwards, Lambert M Felix, Karen Blackhall, Ian Roberts
Affiliations
Meta-Analysis

Caffeine for the prevention of injuries and errors in shift workers

Katharine Ker et al. Cochrane Database Syst Rev. .

Abstract

Background: Sleepiness leads to a deterioration in performance and attention, and is associated with an increased risk of injury. Jet lag and shift work disorder are circadian rhythm sleep disorders which result in sleepiness and can elevate injury risk. They create a need for individuals to operate at times which are different to those dictated by their circadian rhythms. Consequently there is also a need for interventions to help ensure that these persons can do so safely. Caffeine has a potential role in promoting alertness during times of desired wakefulness in persons with jet lag or shift work disorder, however its effects on injury and error are unclear.

Objectives: To assess the effects of caffeine for preventing injuries caused by impaired alertness in persons with jet lag or shift work disorder.

Search strategy: We searched the Cochrane Injuries Group Specialised Register, CENTRAL (The Cochrane Library), MEDLINE, EMBASE, PsycINFO, CINAHL, TRANSPORT (to July 2008); and PubMed databases (to April 2010). We also searched the Internet and checked reference lists of relevant papers.

Selection criteria: Randomised controlled trials investigating the effects of caffeine on injury, error or cognitive performance in people with jet lag or shift work disorder.

Data collection and analysis: Two authors independently screened search results and assessed full texts for inclusion. Data were extracted and risk of bias was assessed. Estimates of treatment effect (odds ratio and standardised mean difference (SMD)) and 95% confidence intervals (CI) were calculated and pooled using the fixed-effect model.

Main results: Thirteen trials were included. None measured an injury outcome. Two trials measured error, and the remaining trials used neuropsychological tests to assess cognitive performance. The trials assessing the impact on errors found that caffeine significantly reduced the number of errors compared to placebo. The pooled effect estimates on performance by cognitive domain suggest that, when compared to placebo, caffeine improved concept formation and reasoning (SMD -0.41; 95% CI -1.04 to 0.23), memory (SMD -1.08; 95% CI -2.07 to -0.09), orientation and attention (SMD -0.55; 95% CI -0.83 to -0.27) and perception (SMD -0.77; 95% CI -1.73 to 0.20); although there was no beneficial effect on verbal functioning and language skills (SMD 0.18; 95% CI -0.50 to 0.87). One trial comparing the effects of caffeine with a nap found that there were significantly less errors made in the caffeine group. Other trials comparing caffeine with other active interventions (for example nap, bright light, modafinil) found no significant differences. There is a high risk of bias for the adequacy of allocation concealment and presence of selective outcome reporting amongst the trials.

Authors' conclusions: Caffeine may be an effective intervention for improving performance in shift workers however, there are no trials from which we can assess its effect on injuries. The results largely originate from studies involving young participants under simulated conditions, and the extent to which the findings are generalisable to older workers and real world shift work is unclear. Based on the current evidence, there is no reason for healthy individuals who already use caffeine within recommended levels to improve their alertness to stop doing so. The assessment of the relative effects of caffeine to other potential countermeasures should be a focus of future research.

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Conflict of interest statement

None known

Figures

Figure 1
Figure 1
Methodological quality summary: review authors' judgements about each methodological quality item for each included study.
Analysis 1.1
Analysis 1.1
Comparison 1 Caffeine versus placebo, Outcome 1 Error.
Analysis 1.2
Analysis 1.2
Comparison 1 Caffeine versus placebo, Outcome 2 Error.
Analysis 1.3
Analysis 1.3
Comparison 1 Caffeine versus placebo, Outcome 3 Cognitive performance.
Analysis 2.1
Analysis 2.1
Comparison 2 Caffeine versus nap, Outcome 1 Error.
Analysis 2.2
Analysis 2.2
Comparison 2 Caffeine versus nap, Outcome 2 Cognitive performance.
Analysis 3.1
Analysis 3.1
Comparison 3 Caffeine versus modafinil, Outcome 1 Error.
Analysis 4.1
Analysis 4.1
Comparison 4 Caffeine versus chewing intervention, Outcome 1 Cognitive performance.
Analysis 5.1
Analysis 5.1
Comparison 5 Caffeine+nap versus placebo, Outcome 1 Cognitive performance.
Analysis 6.1
Analysis 6.1
Comparison 6 Caffeine+dim light versus placebo+dim light, Outcome 1 Cognitive performance.
Analysis 7.1
Analysis 7.1
Comparison 7 Caffeine+bright light versus placebo+bright light, Outcome 1 Cognitive performance.
See this image and copyright information in PMC

References

References to studies included in this review

    1. Babkoff H, French J, Whitmore J, Sutherlin R. Single‐dose bright light and/or caffeine effect on nocturnal performance. Aviation, Space, and Environmental Medicine 2002;73(4):341‐50. - PubMed
    1. Beaumont M, Batejat D, Pierard C, Beers P, Denis JB, et al. Caffeine or melatonin effects on sleep and sleepiness after rapid eastward transmeridian travel. Journal of Applied Physiology 2004;96(1):50‐8. - PubMed
    2. Lagarde D, Beaumont M. How to alleviate jet lag / the chronobiotic substances [Comment réduire les effets du décalage horaire: les substances chronobiotiques]. Defense Technical Information Center2002; Vol. ADP013770.
    3. Lagarde D, Chappuis B, Billaud PF, Ramont L, Chauffard F, French J. Evaluation of pharmacological aids on physical performance after a transmeridian flight. Medicine and Science in Sports and Exercise 2001;33(4):628‐34. - PubMed
    4. Piérard C, Beaumont M, Enslen M, Chauffard F, Tan DX, Reiter RJ, et al. Resynchronization of hormonal rhythms after an eastbound flight in humans: effects of slow‐release caffeine and melatonin. European Journal of Applied Physiology 2001;85:144‐50. - PubMed
    1. Childs E, Wit H. Enhanced mood and psychomotor performance by a caffeine‐containing energy capsule in fatigued individuals. Experimental and Clinical Psychopharmacology 2008;16(1):13‐21. - PubMed
    1. Dagan Y, Doljansky JT. Cognitive performance during sustained wakefulness: a low dose of caffeine is equally effective as modafinil in alleviating the nocturnal decline. Chronobiology International 2006;23(5):973‐83. - PubMed
    2. Lemberg H, Rigbi A, Green A, Ashkenazi IE, Dagan Y. The effect of stimulant drugs on cognitive performance: relevance to pilot tasks at night flight under conditions of sleep deprivation. Journal of Sleep Research 2002;11 Suppl 1:136.
    1. Doan BK, Hickey PA, Lieberman HR, Fischer JR. Caffeinated tube food effect on pilot performance during a 9‐hour, simulated nighttime U‐2 mission. Aviation, Space, and Environmental Medicine 2006;77(10):1034‐40. - PubMed

References to studies awaiting assessment

    1. Bonnet MH, Arand DL. The use of prophylactic naps and caffeine to maintain performance during a continuous operation. Ergonomics 1994;37(6):1009‐1020. - PubMed

Additional references

    1. American Academy of Sleep Medicine. The International Classification of Sleep Disorders, revised. http://www.absm.org/PDF/ICSD.pdf2001.
    1. Akerstedt T. Consensus statement: fatigue and accidents in transports operations. Journal of Sleep Research 2000;9:395. - PubMed
    1. Anderson C, Horne JA. Sleepiness enhances distraction during a monotonous task. Sleep 2006;29(4):573. - PubMed
    1. Ayas NT, Barger LK, Cade BE, Hashimoto DM, Rosner B, Cronin JW, Speizer FE, Czeisler CA. Extended work duration and the risk of self‐reported percutaneous injuries in interns. JAMA 2006;296(9):1055‐62. - PubMed
    1. Beers TM. Flexible schedules and shift work: replacing the '9‐to‐5' workday?. Monthly Labor Review 2000;June:33‐40.

MeSH terms