Caffeine for the prevention of injuries and errors in shift workers.
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.


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


METHODS
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.


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


METHODS
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.


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.


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.
Ker
Katharine
K
Cochrane Injuries Group, London School of Hygiene & Tropical Medicine, Room 280, North Courtyard, Keppel Street, London, UK, WC1E 7HT.
Edwards
Philip James
PJ
Felix
Lambert M
LM
Blackhall
Karen
K
Roberts
Ian
I
D000062:Accidents, Occupational / Q000517:prevention & control*; D002110:Caffeine / Q000627:therapeutic use*; D000697:Central Nervous System Stimulants / Q000627:therapeutic use*; D003072:Cognition Disorders / Q000517:prevention & control*; D006801:Humans; D009483:Neuropsychological Tests; D011597:Psychomotor Performance / Q000187:drug effects / Q000502:physiology; D016032:Randomized Controlled Trials as Topic; D020178:Sleep Disorders, Circadian Rhythm / Q000188:drug therapy; D014940:Work Schedule Tolerance / Q000502:physiology*
D000697:Central Nervous System Stimulants; D002110:Caffeine
Ann Intern Med. 2005 May 17;142(10):877-80
15897548
J Exp Psychol Appl. 2000 Sep;6(3):236-49
11014055
Cochrane Database Syst Rev. 2009 Apr 15;(2):
25267894
Evid Rep Technol Assess (Summ). 2001;(43):i-x, 1-668
11510252
J Appl Physiol (1985). 2004 Jan;96(1):50-8
12959951
Inj Prev. 2008 Feb;14(1):51-8
18245316
Aviat Space Environ Med. 2002 Apr;73(4):341-50
11952054
Ind Health. 2004 Jan;42(1):1-14
14964612
J Sleep Res. 2000 Dec;9(4):395
11123524
Sleep. 1995 Jan;18(1):22-9
7761739
Sleep. 1988 Dec;11(6):528-36
3238256
J Sleep Res. 2000 Dec;9(4):335-52
11123521
Aviat Space Environ Med. 2006 Oct;77(10):1034-40
17042248
Ergonomics. 1989 Oct;32(10):1193-205
2598905
Sleep. 1988 Feb;11(1):100-9
3283909
Sleep. 1989 Feb;12(1):68-87
2648533
J Gen Intern Med. 2001 May;16(5):325-34
11359552
Sleep. 2006 Jan;29(1):39-50
16453980
BMJ. 2006 Jul 8;333(7558):75
16798754
Exp Clin Psychopharmacol. 2008 Feb;16(1):13-21
18266548
Nature. 1997 Jul 17;388(6639):235
9230429
J Sleep Res. 2008 Mar;17(1):34-41
18275553
Ann Intern Med. 2006 Jun 6;144(11):785-91
16754920
Physiol Behav. 2006 May 30;87(5):925-31
16574171
Sleep. 2005 Nov;28(11):1392-402
16335329
Sleep. 1997 Oct;20(10):871-7
9415947
BMJ. 2002 May 11;324(7346):1125
12003884
JAMA. 1995 Feb 1;273(5):408-12
7823387
N Engl J Med. 2002 Oct 17;347(16):1249-55
12393823
Accid Anal Prev. 2003 May;35(3):321-31
12643949
Sleep. 2007 Nov;30(11):1460-83
18041480
Int J Epidemiol. 2002 Feb;31(1):140-9
11914310
Sleep. 2006 Apr;29(4):573-6
16676792
Sleep. 1996 May;19(4):318-26
8776790
Sleep. 1983;6(2):102-7
6878979
Am J Surg. 2003 Aug;186(2):169-74
12885613
Pediatr Emerg Care. 2007 Jul;23(7):498-503; quiz 504-5
17666938
Sleep. 2004 Dec 15;27(8):1453-62
15683134
J Occup Health. 2004 Jul;46(4):272-80
15308826
Physiol Behav. 1998 Jul;64(5):599-604
9817569
Sleep. 2004 Sep 15;27(6):1181-94
15532213
Sleep. 2004 May 1;27(3):374-81
15164887
J Fam Pract. 2010 Jan;59(1 Suppl):S3-S11
20074508
Aviat Space Environ Med. 2009 Jan;80(1):29-59
19180856
Eur J Appl Physiol. 2001 Jul;85(1-2):144-50
11513308
Sleep Med Rev. 2008 Aug;12(4):257-73
18359253
Ergonomics. 1994 Jun;37(6):1009-20
8026448
Lancet. 2007 Mar 31;369(9567):1117-29
17398311
Chronobiol Int. 2006;23(5):973-83
17050212
Med Sci Sports Exerc. 2001 Apr;33(4):628-34
11283440
JAMA. 2006 Sep 6;296(9):1055-62
16954484
Occup Environ Med. 2003 Jun;60 Suppl 1:i88-92
12782753
Sleep Med Rev. 2008 Apr;12(2):153-62
17950009
Organ Behav Hum Decis Process. 1999 May;78(2):128-45
10329298
J Sleep Res. 2006 Dec;15(4):358-68
17118092
J Sleep Res. 2006 Mar;15(1):7-13
16489997
BMJ. 2001 Nov 24;323(7323):1222-3
11719413