0191 Combining Caffeine and a Nap to Improve Alertness During a Simulated Nightshift

Abstract

Introduction: Shiftwork is common in a 24/7 society. Shiftworkers experience circadian misalignment and disrupted daytime sleep and are more prone to errors and accidents than non-shiftworkers. Countermeasures such as caffeine and naps have been used to mitigate the attentional deficits associated with shiftwork, with inconsistent results. The aim of this study was to investigate the combined effects of 200mg of caffeine prior to a 30-minute nap opportunity during the circadian nadir on vigilant attention. Methods: Six healthy non-shiftworkers (aged 21-36y; 4 females) were recruited for a within-subjects counter-balanced double-blind crossover design study at the University of South Australia's Sleep and Chronobiology Laboratory. Participants completed two 36-hour laboratory visits, separated by one week, consisting of a simulated nightshift (1930-0900h); a 30-minute nap opportunity at 0330h; and, a 7-hour daytime recovery sleep opportunity (1000- 1700h). Participants were randomised to a «cafnap” or placebo condition: Cafnap=200mg of caffeine powder added to a 200ml decaffeinated coffee; or placebo=200ml of decaffeinated coffee. The drink was consumed 5-minutes prior to the nap. Participants undertook a 3-minute psychomotor vigilance task (PVT) at 1930, 2015, 0100, 0315, 0400, 0445, 0645, 0745 and 0845h. Linear mixed model ANOVAs with fixed effects of condition, time and condition∗ time interactions and random effect of participant ID were conducted for PVT lapses and mean reciprocal reaction time (MRRT). Results: The cafnap produced a significant reduction in the number of lapses F(1,105)=12.45, p=.001 and significant increase in MRRT F(1,105)=39.42, p≤.001 compared to placebo. PVT performance was maintained at or above 96% of baseline across the entire simulated nightshift post-cafnap. Conclusion: This combined countermeasure may be useful for improving shiftworker safety by limiting the physiological and behavioural decrements experienced by shiftworkers. Further investigation is needed to examine the cafnap's impact upon daytime recovery sleep, habitual caffeine users, actual shiftworkers and various chronotypes.