The suitability of a caffeinated energy drink for night-shift workers. The effects of caffeine on simulated night-shift work and subsequent daytime sleep. Laboratory and field studies of naps and caffeine as practical countermeasures for sleep-wake problems associated with night work. Enhanced mood and psychomotor performance by a caffeine-containing energy capsule in fatigued individuals. Low-dose repeated caffeine administration for circadian-phase-dependent performance degradation during extended wakefulness. Cognitive performance during sustained wakefulness: A low dose of caffeine is equally effective as modafinil in alleviating the nocturnal decline. Caffeinated tube food effect on pilot performance during a 9-hour, simulated nighttime U-2 mission. Single-dose bright light and/or caffeine effect on nocturnal performance. The effects of chewing versus caffeine on alertness, cognitive performance and cardiac autonomic activity during sleep deprivation.
Past research has indicated that caffeinated 'functional energy drinks' (FEDs) are effective in counteracting sleepiness. It is not known however, what impact FEDs have on sleep itself. FEDs contain several active ingredients, including caffeine. They may therefore impact negatively on sleep and hence subsequent performance, deeming their use counterproductive. In a randomised cross-over design, 15 young adults participated in a simulated first night-shift protocol with 2 conditions, Functional Energy Drink (FED) and Non Functional Energy Drink (NonFED). Both involved a period of extended wakefulness (0700-0730 h-24.5 h) followed by an 8-h daytime 'recovery' sleep (0730-1530 h). During the FED condition, a commercially available FED was administered twice during the night. Sleepiness was assessed during the period of extended wakefulness and for a further 6h after waking. Sleep periods were recorded using a standard 5 channel polysomnogram. Comparison of the sleep periods showed that sleep onset latency remained unchanged as did stage 2 and slow wave sleep. Total sleep time however, was 29.1 min shorter (p<.05) in the FED condition. Sleep efficiency was also significantly reduced from 91.8+/-.9% to 84.7+/-2.7% (p<.05). It is evident that the residual effects of the FED's active ingredients impact on some aspects of daytime sleep following a simulated night-shift. Subsequent performance however was unaffected. The results deem FEDs to be effective for a single night-shift and warrant investigation into their use over successive night-shifts. Thirty healthy volunteers were randomly assigned to either a caffeine or a placebo group to investigate the alerting effects of caffeine at night. Subjects adhered to a simulated night-shift schedule for 5 consecutive nights. On the first 3 nights, 2 mg/kg caffeine was added to decaffeinated coffee at 2220 and 0120 hours for the caffeine group. On nights 4 and 5 both groups received placebo. Each night, subjects completed five 60-minute sessions of a computerized simulated assembly line performance task (SALT), a multiple sleep latency test (MSLT) and questionnaires. Daytime sleep was recorded in the laboratory between 0900 and 1700 hours each day following nighttime testing. Caffeine decreased physiological sleep tendency on the night shift compared with placebo; however, the two groups performed at equivalent levels on the SALT. On nights 4 and 5, when both groups received placebo, there were no differences between the groups on the MSLT, suggesting the absence of a discontinuation effect. There were no differences on daytime polysomnograms between the groups. To evaluate the effects of napping, caffeine, and napping plus caffeine on performance and alertness in both laboratory and field settings.
                (1) Laboratory Study: parallel-groups design with random assignment to 1 of 4 experimental conditions. (2) Field Study: crossover design.
                Sleep laboratory and field settings.
                (1) Laboratory Study: 68 healthy individuals; (2) Field Study: 53 shiftworkers who worked nights or rotating shifts.
                (1) Laboratory Study: an evening nap opportunity before the first 2 of 4 consecutive simulated night shifts plus placebo taken all 4 nights, caffeine taken nightly, the combination of the nap and caffeine conditions, or placebo. (2) Field Study: an evening nap on the first 2 of 4 consecutive night shifts plus caffeine taken nightly versus placebo taken nightly without naps.
                (1) Laboratory Study: Napping, caffeine, and their combination all improved alertness and performance as measured by Maintenance of Wakefulness Test and Psychomotor Vigilance Task, but the combination of napping and caffeine was best in improving alertness. (2) Field Study: Napping plus caffeine improved performance as measured by Psychomotor Vigilance Test and decreased subjective sleepiness in individuals working the night shift.
                Napping plus caffeine helps improve performance and alertness of night-shift workers. Caffeine produces mild psychostimulant effects that may be particularly evident in individuals whose mood or performance is impaired by sleep restriction or caffeine withdrawal. Caffeinated energy drinks have been shown to improve energy and cognition but expectancy effects cannot be ruled out in these studies. Very few studies have examined the effects of caffeine-containing energy capsules upon behavioral and subjective measures. This study compared the effects of a caffeine-containing (200 mg) supplement (CAF) or placebo in capsule form after prolonged wakefulness, in participants who varied in their level of habitual caffeine use. Thirty-five healthy volunteers (16 male, 19 female) participated in two experimental sessions in which they remained awake between 5 p.m. and 5 a.m. At 3:30 a.m. they consumed CAF or placebo in random order under double-blind conditions. Participants completed subjective effects questionnaires and performed computerized attention tasks before and after consuming capsules. Heart rate and blood pressure were monitored at regular intervals. Compared to measures at 5 p.m., participants reported more tiredness and mood disturbance at 3 a.m., and exhibited longer reaction times and more attentional lapses. Heavier caffeine consumers exhibited the greatest decreases in Profile of Mood States (POMS) Vigor. CAF produced stimulant-like effects and significantly improved mood and reaction times upon the tasks. These effects did not vary with level of habitual caffeine consumption. These findings indicate that consumption of a caffeine-containing food supplement improves subjective state and cognitive performance in fatigued individuals that is likely a result of its caffeine content.
                2008 APA To investigate whether the effectiveness of a novel high-frequency low-dose caffeine regimen in counteracting the deterioration of performance during extended wakefulness is related to its interaction with homeostatic or circadian signals modulating performance and sleep propensity.
                Double-blind, placebo-controlled, parallel-group design in a 29-day forced desynchrony paradigm in which the period of the sleep-wake cycle was scheduled to be 42.85 hours, i.e., far removed from the circadian range. This design allowed for separate estimation of the sleep homeostatic, circadian, and caffeine contributions to performance deficits or improvements.
                Private suite of a general clinical research center, in the absence of time of day information.
                Sixteen healthy normal-sleeping men (aged 18-30 years)
                Caffeine (0.3 mg per kg per hour) or placebo was administered hourly during the 28.57-hour wake episodes.
                Plasma caffeine concentrations rose in an exponential saturating manner during wakefulness. Rising caffeine levels markedly attenuated wake-dependent deterioration of a number of measures of cognitive performance, particularly at the circadian performance nadir. Moreover, caffeine enhanced the ability of subjects to remain consistently awake for extended periods, holding subjects back from completing the full transition to sleep, but at the expense of increasing subjective sleepiness.
                High-frequency low-dose caffeine administration is effective in countering the detrimental performance effects of extended wakefulness. These data are in accordance with the hypothesis that adenosine is a mediator of performance decrements associated with extended wakefulness and may lead to new strategies to use caffeine in situations in which neurobehavioral functioning is affected by sleep loss. Cognitive performance at night exhibits a substantial drop, typically before dawn. One of the means of dealing with this phenomenon, as well as with the accompanying sleepiness during sustained wakefulness, is the administration of stimulants. The most widely used and well-documented stimulants are caffeine, amphetamines, and modafinil. Of these, amphetamines are the least recommended, as they may severely affect behavior. Caffeine and modafinil seem to produce relatively milder side effects and usually only at high doses. Previous comparison studies have revealed equal efficacy of both the stimulants in maintaining alertness and performance during sustained wakefulness. However, these studies used relatively high, and thus not completely safe, doses of these drugs (600 mg caffeine and 400 mg modafinil). Therefore, the aim of the present study was to assess the efficacy of a low and medically safe dose of caffeine (200 mg) and modafinil (200 mg) in maintaining cognitive performance during sustained wakefulness. A flight simulation task was chosen for the assessment of the stimulants in a counter-balanced, within-subject design under four different conditions: baseline (no drugs), placebo, caffeine (200 mg), and modafinil (200 mg). The equal effectiveness of both drugs in abolishing the nocturnal drop in cognitive performance, as well as of oral temperature and blood pressure, supported the use of low doses of caffeine and modafinil for the maintenance of alertness in healthy subjects during sustained wakefulness. Interventions to maintain performance are necessary to meet demanding mission requirements during sustained and surge aviation operations. Tube foods are the only foods that can be consumed during a U-2 mission due to the confining and encapsulating nature of required support equipment. Caffeine is a safe and effective strategy to enhance cognitive performance and is an ingredient in some tube foods. The objective of this study was to determine whether moderate doses of caffeinated tube foods would enhance performance in a simulated U-2 mission.
                Volunteers were 12 healthy USAF male pilots. The study used a double blind, placebo-controlled, two-factor, repeated-measures (five iterations per night) design. Caffeinated (200 mg each) or placebo tube food was consumed at 00:00 and 04:00. Dependent measures assessed included standardized tests of cognitive performance, vigilance, and mood designed to simulate the demands of a nighttime U-2 mission.
                Statistically significant (p < 0.05) improvements in performance due to caffeine administration compared with placebo were present in all five cognitive tasks either as main effects, interactions, or absence of significant degradation in the caffeine treatment condition compared with the placebo condition. A majority of sleep deprivation-induced performance decrements were attenuated by 200 mg of caffeine in tube food consumed every 4 h, and in some cases, performance was improved beyond baseline levels.
                Caffeinated tube food maintained cognitive performance representative of U-2 long-duration mission tasks at or near baseline levels for a 9-h overnight period in qualified USAF pilots. Side effects were minor and did not differ between placebo and caffeine conditions. The impact of the separate and combined effects of a 1-h exposure to bright light (approximately 3000 lx) and a 200-mg dose of caffeine on nocturnal performance was studied during a simulated shift-work schedule beginning 1730 in the evening and ending 1000 the next morning.
                Light and caffeine exposure were expected to improve nocturnal fatigue degradation.
                There were 11 subjects tested under 4 treatment conditions: 1) 1 h Dim Light-Placebo; 2) 1 h Bright Light-Placebo; 3) 1 h Dim Light-Caffeine; 4) 1 h Bright Light-Caffeine. Exposure to the light occurred between 0130 and 0230 hours. Caffeine or placebo was administered at 0140 hours.
                Choice Reaction Time (RT) recorded during the four post-treatment sessions were shorter for the Bright Light-Caffeine, Bright Light-Placebo, and Dim Light-Caffeine conditions than for the Dim Light-Placebo condition. During the sessions beginning 0430 and 0830 hours, the shortest RT was recorded for the Bright Light-Caffeine treatment. The largest number of trials without false alarms per session for the working memory task (letter cancellation) was found for the Bright Light-Caffeine condition. Exposure for 1 h to 3000 lx reduced melatonin concentration between 42-47% from 0230 to 0410 hours. A 200-mg dose of caffeine also reduced melatonin levels, although to a lesser degree than 1 h exposure to 3000 lx.
                Although 1 h exposure to bright light at 0130 hours combined with a 200-mg dose of caffeine maintains performance throughout the remainder of the night/early morning, a 1-h exposure to bright light without the caffeine may actually degrade performance. Chewing has been shown to alleviate feelings of sleepiness and improve cognitive performance during the day. This study investigated the effect of chewing on alertness and cognitive performance across one night without sleep as well as the possible mediating role of cardiac autonomic activity. Fourteen adults participated in a randomized, counterbalanced protocol employing a chewing, placebo and caffeine condition. Participants completed tasks assessing psychomotor vigilance, tracking, grammatical reasoning, alertness and sleepiness each hour across the night. All participants received either placebo or caffeine (200 mg), while the chewing condition also chewed on a tasteless and odorless substance for 15 min each hour. Heart rate (HR), root mean square of the successive differences in R-R intervals on the ECG (RMSSD), and preejection period (PEP) were simultaneously recorded. Alertness and cognitive performance amongst the chewing condition did not differ or were in fact worse when compared with placebo. Similarly, measures of HR and RMSSD remained the same between these two conditions; however, PEP was reduced in the later part of the night in the chewing condition compared with a relative increase for placebo. Caffeine led to improved speed and accuracy on cognitive tasks and increased alertness when compared with chewing. Relative increases in RMSSD and reductions in HR were demonstrated following caffeine; however, no change in PEP was seen. Strong associations between cardiac parasympathetic activity and complex cognitive tasks, as well as between subjective alertness and simpler cognitive tasks, suggest a differential process mediating complex versus simple cognitive performance during sleep deprivation.
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.