Efficacy of a functional energy drink in counteracting driver sleepiness

Transcription

1 Physiology & Behavior 75 (2002) Efficacy of a functional energy drink in counteracting driver sleepiness L.A. Reyner*, J.A. Horne Sleep Research Centre, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK Received 14 August 2001; received in revised form 1 November 2001; accepted 8 November 2001 Abstract Driver sleepiness is a major cause of serious road crashes. Coffee is often used as an effective countermeasure to driver sleepiness. However, the caffeine levels in coffee are variable, whereas certain proprietary functional energy drinks (FEDs) contain known levels of caffeine (and other ingredients). We investigated the effectiveness of a well-known FED in reducing sleepiness in drivers. Twelve healthy young adults drove an instrumented car simulator between 14:00 and 17:00 h. Their sleepiness was enhanced by sleep restriction to 5 h the night before. Following a pretreatment 30-min drive and at the beginning of a 30-min break, participants were given double-blind 250-ml FED (containing sucrose, glucose, 80-mg caffeine, taurine, glucuronolactone and vitamins) vs. a control drink with the same volume and same taste but without caffeine, taurine and glucuronolactone. Two hours of continuous driving ensued. Lane drifting, subjective sleepiness and the electroencephalogram (EEG) were monitored throughout. Compared with the control, the FED significantly reduced sleep-related driving incidents and subjective sleepiness for the first 90 min of the drive. There was a trend for the EEG to reflect less sleepiness during this period. It was concluded that the FED is beneficial in reducing sleepiness and sleep-related driving incidents under conditions of afternoon monotonous driving following sleep restriction the night before. D 2002 Elsevier Science Inc. All rights reserved. Keywords: Energy drink; Caffeine; Taurine; Sleepiness; Driving; EEG 1. Introduction Falling asleep at the wheel accounts for a significant number of road crashes, particularly on dull and monotonous roads [1,2]. Our laboratory has been investigating the effectiveness of various practical countermeasures that a sleepy driver could utilise during a short break from driving, including low doses of caffeine (as in one or two cups of coffee). Although this amount of caffeine is effective (see below), the caffeine content of a cup of coffee is variable. In contrast, certain proprietary functional energy drinks (FEDs) contain known amounts of caffeine as well as other active ingredients such as sucrose/glucose, taurine and glucuronolactone. Caffeine blocks brain adenosine receptors, and as adenosine is thought to be a potent sleep promoter [3,4], then caffeine may well have a direct inhibitory effect on this aspect of the sleep system. There are other routes by which * Corresponding author. Tel.: address: [email protected] (L.A. Reyner). caffeine can act on alertness, for example, through its effects on the synthesis and turnover of catecholamines [5]. Taurine has a variety of modulatory effects on the CNS [6 9]. Glucose (derived from the sucrose) can also have an alerting effect, and although this can be rapid following absorption, this is usually of short duration (about 10 min). Research outside the field of driving has shown that about mg caffeine significantly improves alertness in sleepy people [10 14]. Also, we have found that young adults, sleep restricted to 5-h sleep for one night and required to drive the subsequent morning or afternoon for 2 h continuously in a driving simulator under monotonous road conditions, experience levels of sleepiness that can be significantly reduced by this dose of caffeine given under double-blind conditions [15 17]. Significant improvements were found with impaired driving performance (lane drifting), subjective sleepiness and electroencephalographic (EEG) measures of sleepiness. The present study examined the effectiveness in alleviating driver sleepiness of 250 ml (one can equivalent see below for ingredients) of a well-known FED ( Red Bull /02/$ see front matter D 2002 Elsevier Science Inc. All rights reserved. PII: S (01)

2 332 L.A. Reyner, J.A. Horne / Physiology & Behavior 75 (2002) Energy Drink ) vs. a similar-tasting control drink without caffeine, taurine and glucuronolactone. 2. Method 2.1. Participants Drivers most likely to have sleep-related crashes are aged under 30 years [1]. We targeted this group for study, as we have done previously [15 18]. Twelve graduate students [7 men, 5 women; mean age 24 years (S.E. = 2 years)] were recruited by advert and screened by interview. They were healthy (medication free), of normal weight range for height, experienced drivers (having driven for more than 2 years and for more than 3 h/week), good sleepers, slept regular hours and took daytime naps less than once per month. They were moderate (2 4 cups daily) drinkers of caffeinated coffee. There is no evidence [5,19,20] that this level of daily intake would have led to any caffeine withdrawal effects for the control condition during the driving session. Participants had the procedures fully explained, signed consent forms and were paid for each session. They were informed that they would be consuming a variety of unspecified energy drinks Design and procedure On an initial baseline day, following a normal night s sleep, participants had a 2-h practice drive on the car simulator (see below). One week later, they underwent two experimental conditions (see below) at least a week apart in a counterbalanced design, with their afternoon sleepiness enhanced by sleep being restricted to 5 h (delayed bedtime) the night before. Participants slept at home, with sleep monitored by wrist actimeters [21]. These were downloaded and checked for participant compliance soon after each participant s arrival at the laboratory and before the drive commenced. All participants complied with their respective sleep regimens. There was nil consumption of alcohol for 36 h before each study and nil caffeinated drinks after 18:00 h the evening before. There is a bicircadian rhythm of sleepiness that has its second peak in the afternoon (cf. Ref. [2]). Impaired nighttime sleep leads to a potentiation of this afternoon trough. Sleep-related crashes also show such an afternoon peak [1,22 25]. Our driving task comprised an initial (pretreatment) 30-min simulated motorway-type, dull and tedious drive that commenced at 14:00 14:15 h. This was followed by a 30-min break (sitting at the wheel) then another 2-h posttreatment drive. During the break, participants consumed one of two drinks (given double blind) poured from prepacked plain glass bottles: FED ( Red Bull Energy Drink ): containing 21-g sucrose, 5-g glucose, 1-g taurine, 600-mg glucuronolactone, 80-mg caffeine, 50-mg inositol and vitamin B complex per 250 ml. Control drink: as above, but excluding caffeine, taurine and glucuronolactone. Drinks were given at the beginning of the break, thus allowing time for the absorption of the caffeine [26] and other ingredients. Participants consumed FEDs on an infrequent basis, and as the tastes of the two experimental drinks were almost identical, participants were unable to distinguish the two. The drinks were not given in proportion to body weight but as a fixed dose, as the typical driver would consume this drink by the can Car simulator This comprised an immobile car with an interactive fullsized, computer-generated bending, dull and monotonous roadway projected on to a m screen located 2.3 m from windscreen. There were two up and two down lanes, hard shoulder and simulated auditory rumble strips. Participants sat in the driving seat and drove at their normal cruising speed within white lane markings. Lane drifting is the usual manifestation of sleepy driving, which was automatically detected by the computer data logger from continuously recorded steering data. A car wheel crossing a lateral lane marking was the criterion for this detection and was identified as an incident. An unobtrusive infrared camera filmed the driver s face that was recorded with the roadway using a split-screen video display. The video data were further analysed by a skilled assistant blind to the experimental conditions, whereby all the incidents were checked to see whether these were due (1) to driver distraction (looking elsewhere), which were discounted, or (2) to episodes associated with sleepiness (i.e. eye rolling or vacant staring ahead). Additional quality checks on these video data were undertaken blind by a second trained assessor. Incident data tend to have large individual differences [16] Subjective sleepiness This was verbally reported by the driver every 200 s on the nine-point Karolinska Sleepiness Scale (KSS) [27] shown in Table 1. The scale and descriptors were printed Table 1 The KSS 1 = extremely alert 2 = very alert 3 = alert 4 = rather alert 5 = neither alert nor sleepy 6 = some signs of sleepiness 7 = sleepy, no effort to stay awake 8 = sleepy, some effort to stay awake 9 = very sleepy, great effort to keep awake

3 L.A. Reyner, J.A. Horne / Physiology & Behavior 75 (2002) hoc t tests were undertaken when appropriate, with findings of P <.05 reported. 3. Results 3.1. Sleep-related driving incidents Fig. 1. Driving incidents due to sleepiness. Group mean values (with standard error bars) for pretreatment 30-min period and consecutive 30-min periods after a 30-min break when 250 ml of FED or a control drink was consumed (at the beginning of this break). There was a significant difference between the conditions (see Results) for the first 90 min of the drive. There was no significant effect of time. on the car s dashboard, within easy view of the driver. Any alerting effect caused by this response was common to both conditions. It should be remembered that participants have already undergone a 2-h practice session and that the KSS response was part of a routine procedure that usually lasted less than 5 s (from the experimenter s brief request to the participant s response) EEG Drivers were comfortably seated and remained still, apart from steering. The EEG derivation A1-C3 was logged at 100 Hz and spectrally analysed in 4-s epochs. High and low band-pass filtering at above 15 Hz and below 4 Hz removed slow eye movements and muscle artefact. There was some unavoidable eye blink contamination on the EEG, which was mostly filtered out and does not bias the EEG outcome [15]. Increasing a (8 11 Hz) and q (4 7 Hz) EEG power indicates increasing sleepiness, and within the context of driving, the summation of these activities (i.e Hz) gives more consistent EEG findings than either alone [15]. Power was averaged in 1-min epochs and standardised by the transformation described by Horne and Reyner [15] before averaging across participants. Fig. 1 shows the rate of incidents to be similar for both conditions during the pretreatment period. Following consumption of the FED, incidents were reduced to about 25% of control levels during the 2-h drive. The ANOVA was significant for conditions [ F(1,11) = 24.45, P <.001; Huynh-Feldt e = 1.0]. Post hoc t tests were significant ( P <.05) for the 0 30, and min periods. There was an almost significant ( P <.073) effect of time Subjective sleepiness These changes can be seen in Fig. 2. Before treatments, self-reported sleepiness was slightly higher in the control drink condition but not significantly so. Posttreatment subjective sleepiness was appreciably lower following the FED and for much of the 2-h period. The ANOVA showed this effect to be significant [ F(1,11) = 19.39, P <.001; Huynh-Feldt e =1.0]. Post hoc t tests were significant ( P <.05) between the two conditions for the first three 30-min periods. There was an overall significant effect of time [ F(1.9,21) = 12.07, P <.001; Huynh-Feldt e =0.63]. There was a significant interaction between condition and time [ F(2.7,30) = 3.05, P <.05; Huynh-Feldt e =0.91], with post hoc tests being significant for the first three 30-min periods Statistical analysis For all indices, the pretreatment data should be the same for both conditions. To check this statistically, the 30 min of pretreatment data were averaged within groups and compared between conditions using a paired t test. If this was satisfactory, then posttreatment data were averaged in four 30-min blocks ( Time ) and analysed by a two-way (Conditions Time) repeated-measures ANOVA using the Huynh-Feldt e adjustment for degrees of freedom. Post Fig. 2. Subjective sleepiness. Group mean values every 200 s before and after treatment. There was a significant difference between the two conditions for the first 90 min following the treatment break (see Results). There was also a significant effect of time and a significant interaction between condition and time. See Table 1 for sleepiness scale descriptors.

4 334 L.A. Reyner, J.A. Horne / Physiology & Behavior 75 (2002) This study was conducted under double-blind counterbalanced conditions. We found that following a night of restricted sleep, 250 ml of the FED was beneficial in reducing sleep-related driving incidents and subjective sleepiness during the afternoon in young adults, particularly during the first 90 min of the drive. As the control drink did not contain caffeine, taurine or glucuronolactone, it is probable that the improved performance associated with the FED was due to these ingredients. Although caffeine was the important determinant in these respects, there is evidence that 1 g of taurine may also be beneficial in counteracting fatigue [28,29]. It is unlikely that the control drink had any reverse effect of enhancing sleepiness, as there is no evidence that these ingredients (see Method) have this property. Interestingly, the magnitude of the reductions in incidents and subjective sleepiness following the FED (containing only 80-mg caffeine) is similar to those we have previously found [16] with coffee containing higher amounts (200 mg) of caffeine in comparable participants and under identical testing conditions (same sleep restrictions, duration and timing of drive). Moreover, the control (nonactive treatment) conditions from these two studies (present and past) were similar with respect to incidents and subjective sleepiness. Together, these findings suggest that the FED, containing 80-mg caffeine and other ingredients such as taurine, is much more effective than coffee with the same amount of caffeine. Acknowledgments This project was funded by Red Bull. We thank Stuart Baulk for his help with the running of this study. References Fig. 3. EEG. Group mean values of a + q power in 1-min epochs before (00:00 00:30 h) and after (01:00 03:00 h) treatments. There was no significant difference between conditions, although there was some trend for power to be lower (i.e. less sleepy) with the FED during the middle hour (30 90-min period) of the drive EEG There were no significant findings, although it can be seen from Fig. 3 that there was a trend for a + q power to be reduced (less sleepy) following the FED during the middle hour of the drive. 4. Discussion [1] Horne JA, Reyner LA. Sleep related vehicle accidents. Br Med J 1995;310(6979): [2] Horne JA, Reyner LA. Vehicle accidents related to sleep: a review. Occup Environ Med 1999;56: [3] Radulovacki M. Pharmacology of the adenosine system. In: Kales A, editor. Handbook of experimental pharmacology the pharmacology of sleep. Berlin: Springer-Verlag, pp [4] Porkka-Heiskanen T, Strecker RE, Thakkar M, Bjorkum AA, Greene RW, McCarley RW. Adenosine: a mediator of the sleep-inducing effects of prolonged wakefulness. Science 1997;276: [5] Battig K, Welzl H. 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