Transport Research International Documentation (TRID)

Daily Caffeine Intake and the Effect of Caffeine on Pilots’ Performance After Extended Wakefulness

Mon, 23 Oct 2023 15:08:13 GMT

Fatigue is a major contributor to aviation accidents. Sufficient sleep may be difficult to achieve under operational conditions in military aviation. Countermeasures include caffeine, however, studies evaluating its effects often do not represent daily practice with regular caffeine consumption. This study aims to establish the effect of caffeine on psychomotor performance in a realistic scenario (i.e., after a limited period of extended wakefulness). This randomized, double-blind, crossover, placebo-controlled trial included 30 aeromedically fit subjects. On trial days, subjects followed their normal routine till 17:00, after which caffeine intake was stopped. At midnight, subjects were given 300 mg of caffeine or placebo and performed the Psychomotor Vigilance Test, Vigilance and Tracking Test, and the Stanford Sleepiness Scale hourly up to 04:00 and again at 06:00 and 08:00. Four blood samples were collected. Statistical analyses included repeated-measures ANOVA or Friedman tests, marginal models, and Wilcoxon Signed Rank tests. Median time awake at midnight was 17 h (IQR 16.5–17.5 h). Performance decreased significantly less during the night in the caffeine condition versus placebo. Neither habitual intake nor daytime caffeine consumption affected this. No statistically significant correlation was identified between blood concentrations of caffeine and performance. A single dose of 300 mg of caffeine has beneficial effects on performance during the night in a realistic scenario for military aviation. Daytime caffeine consumption does not affect the effects of caffeine at night. These findings could be relevant for all industries in which optimal performance is required during nighttime after a limited period of extended wakefulness.

Bright light alone or combined with caffeine improves sleepiness in chronically sleep-restricted young drivers

Tue, 07 Jun 2022 16:13:58 GMT

Young drivers are over-involved in sleepiness-related crashes. The alerting effects of bright light offer a potential countermeasure for driver sleepiness, either replacing or in conjunction with current countermeasures such as the use of caffeine. Thirty young (18-25) chronically sleep-restricted drivers drove in a simulator under randomized conditions of continuous bright light ('Light,' 500 nm, 230muw/cm2), caffeine ('Caffeine,' 100 mg caffeinated gum), or light and caffeine together ('Light + Caffeine'), after driving under a placebo condition ('Placebo,' decaffeinated gum, 555 nm light, 0.3 muW/cm2) on three consecutive days. Using mixed-effects linear models, the associations between these conditions and physiological outcomes (EEG alpha and theta power, heart rate, and beat-to-beat intervals), driving performance (lateral lane and steering-related outcomes and lateral acceleration), and subjective sleepiness was assessed. Relative to Placebo, all conditions improved driving performance outcomes (P < 0.0001), with effects of Light + Caffeine equal to Light but greater than Caffeine. Light + Caffeine reduced EEG alpha power more than Light or Caffeine (P < 0.0006), but ECG outcomes were generally worse under all conditions relative to Placebo. Subjective sleepiness improved under the Light + Caffeine condition only (P < 0.0001). Combining bright light and caffeine enhances their alerting effects on lateral lane variability and subjective sleepiness. A bright light could be a practical alternative to caffeine for sleepy drivers who avoid caffeine. The alerting effects of bright light could alleviate chronic community-level mild sleep restriction and provide on-road benefits to reduce severe injuries and fatal sleepiness-related crashes.

The Effect of Caffeine and Sleep Quality on Military Pilot Students’ Flight Performance-Related Cognitive Function

Tue, 24 May 2022 10:05:03 GMT

To assess the effect of caffeine and sleep quality on the flight performance-related cognitive function. High levels of cognitive performance in pilots is required for flight safety. Students at a military flight school in Thailand were invited to participate in this study. Exclusion criteria was positive screening for caffeine use disorder. The authors examined three cognitive functions required for flight performance: (1) vigilance (Mackworth Clock Test), (2) situational awareness, including memory (Corsi block-tapping test) and spatial reasoning (mental rotation test), and (3) reaction time (Deary-Liewald task). Neuropsychological tasks were performed before and 30 minutes after drinking a bottle of 220 ml coffee containing 143 mg of caffeine. Sleep quality was measured by the Thai-Pittsburgh Sleep Quality Index. Twenty-nine healthy males without caffeine use disorder with a mean age of 25.1 years were enrolled. After low-dose caffeine intake (<3 mg/kg body weight), cognitive performance improved significantly in vigilance, situation awareness, and reaction time. Baseline cognitive performance was not different between high (HSQ) and low sleep quality (LSQ) groups. After drinking coffee, however, participants with HSQ demonstrated improvements in vigilance and reaction time, while the LSQ group had improved vigilance only. Low dose caffeine improved vigilance, situational awareness, and reaction time which were cognitive functions required for flight performance. The cognitive-enhancing effect of caffeine was more obvious in student pilots with high-quality sleep.

Stimulant Use as a Fatigue Countermeasure in Aviation

Mon, 19 Apr 2021 17:20:42 GMT

Fatigue is a common problem in aviation. The identification of efficacious fatigue countermeasures is crucial for sustaining flight performance during fatigue-inducing operations. Stimulants are not recommended for consistent use, but are often implemented during flight operations with a high risk of fatigue. As such, it is important to evaluate the efficacy of approved stimulants for sustaining flight performance, alertness, and mood. Four electronic databases (PubMed, PsycInfo, SPORTDiscus, Web of Science) were systematically searched to identify research on the effects of caffeine, dextroamphetamine, and modafinil during simulated or in-flight operations. There were 12 studies identified that assessed the effects of at least 1 stimulant. Overall, dextroamphetamine and modafinil were effective for sustaining flight performance and pilot mood during extended wakefulness. Results with caffeine were inconsistent. Dextroamphetamine and modafinil appear to sustain flight performance and mood during extended wakefulness. However, most studies have used flight simulators and short operation durations. Additional research is needed in realistic settings and during longer duration operations. Caffeines effects were inconsistent across studies, possibly due to differences in study methodology or individual caffeine responses. Despite fatigue being a common problem in civilian aviation as well, only one study in this review included civil aviators. More research should be conducted on the effects of caffeine during civil operations. Dextroamphetamine and modafinil appear to be effective fatigue countermeasures but should be further evaluated in more ecologically valid settings. The effects of caffeine are unclear at this time and should continue to be evaluated.

The impact of sleep deprivation and alcohol on driving: a comparative study

Mon, 22 Feb 2021 10:21:50 GMT

BACKGROUND: There is concern about the detrimental effects of shift-workers’ increasing working hours particularly when driving sleep deprived. The approach to measuring the magnitude of driving impairment caused by sleep deprivation was by comparing it to alcohol. The study compared driving performance after 24-h of wakefulness to performance with a BrAC of just over 22 μg/100mls of breath which is equal to 50 mg of alcohol per 100mls of blood (Scottish drink-drive limit). The effectiveness of coffee as a countermeasure for driver fatigue and the association between subjective impairment and actual performance was also investigated. METHODS: A study of 30 participants (11 male and 19 female; mean age 21) was conducted. Subjects were tested under three conditions: fully rested, sleep deprived, and alcohol intoxicated – BrAC mean [SD] 25.95 μg [2.78]. Under each condition, subjects were tested before and after coffee ingestion. This involved driving simulation (Lane Change Task and Reaction Test) and subjective Likert scales (Karolinska Sleepiness Scale and driver impairment scale). Outcome measures included lane tracking adaptive mean deviation, reaction time, and subjective sleepiness and impairment ratings RESULTS: Compared to alcohol, sleep deprived mean reaction times were slower (2.86 s vs. 2.34 s) and lateral control of the vehicle was reduced (lane tracking adaptive mean deviation: 0.5 vs. 0.3). Coffee did not produce an improvement when sleep deprived, and instead, performance deteriorated. Females were less impaired following sleep deprivation than males. Following prolonged wakefulness, the correlation between subjective impairment and actual performance was significant. CONCLUSIONS: It was concluded that sleep deprivation has a greater impact on driving performance than a BrAC of 22 μg/100mls of breath, as measured by driving simulation. Coffee is not an effective countermeasure for sleep deprived driving and drivers’ ability to judge this impairment is suggested to be limited.

Impact of Caffeine Ingestion on the Driving Performance of Anesthesiology Residents After 6 Consecutive Overnight Work Shifts

Fri, 17 Jul 2020 10:24:22 GMT

The objective of this study was to determine the effects of ingesting a caffeinated energy drink on the driving performance of anesthesiology residents after they had worked six consecutive overnight shifts. Twenty-six residents were randomly chosen to consume a caffeinated or noncaffeinated energy drink sixty minutes prior to testing their driving performance in a high-fidelity, virtual reality driving simulator. The following week, residents completed the same driving session while consuming the opposite type of energy drink. It was found that after ingesting a caffeinated energy drink, the residents showed increased variability in driving for throttle, steering, and speed during the first ten minutes of open-road driving. However, during the final thirty minutes of driving, they displayed improved driving performance with fewer obstacle collisions, versus the residents who consumed a noncaffeinated energy drink. The mean reaction time for a caffeinated state was considerably faster than for a noncaffeinated state (279 versus 294 milliseconds) while the number of major and minor lapses was not significantly different (0.09 versus 0.27 and 1.05 vs. 2.05, respectively). It is concluded that caffeine may assist with improved driving performance for fatigued residents working night shifts, although it should be noted that caffeine is not a substitute for adequate rest and sleep.

Three consecutive nights of sleep loss: Effects of morning caffeine consumption on subjective sleepiness/alertness, reaction time and simulated driving performance

Thu, 23 Apr 2020 15:55:00 GMT

Caffeinated products are often consumed as a popular countermeasure to the effects of sleep loss. However, the efficacy of caffeine to exert these effects after consecutive nights of sleep loss is poorly understood. The aim of this study was to investigate the effects of three consecutive nights of restricted sleep and morning caffeine consumption on subjective ratings of sleepiness/alertness, reaction time, and simulated driving performance. Twenty healthy, habitual caffeine consumers (11 females; age: 23.3 ± 5.7 y; BMI: 22.3 ± 3.5 kg⋅m−²; caffeine intake: 204 ± 89 mg⋅day−¹; Mean ± SD) who had normal sleeping patterns (≥8 h⋅night−¹) participated in this double-blind, placebo-controlled, randomised study. Following one night of normal sleep (≥8 h time in bed (TIB)), participants underwent three consecutive nights of restricted sleep (5 h TIB). Participants received caffeine (200 mg; n = 10) or placebo (n = 10) capsules each morning and all participants received caffeine (100 mg) capsules each afternoon. Subjective ratings of alertness, concentration and tiredness were measured before and 1 h after morning capsule administration. Choice Reaction Time (CRT) was examined 1 h after morning capsule administration, with response speed and accuracy as outcome variables. Driving performance was assessed using a 30 min simulated driving task, with lateral (standard deviation of lane position [SDLP]; total number of line crossings [LC]) and longitudinal (standard deviation of speed [SDSP]) measures of vehicle control as outcome variables. Alertness and concentration significantly decreased, and tiredness increased across the three days of sleep loss. Caffeine only marginally alleviated these effects. No differences were observed between treatments or across trial days for response speed and accuracy on the CRT task. Likewise, no significant differences were observed between groups or across trial days for any measures of simulated driving performance. Overall, results from this study indicate that three consecutive days of sleep loss influence subjective ratings of alertness, concentration and tiredness, but does not alter CRT or simulated driving performance. Caffeine may alleviate some of the negative subjective effects imposed by restricted sleep, but the efficacy of caffeine to attenuate performance changes in CRT and driving performance were unable to be observed.

Associations Between High Caffeine Consumption, Driving Safety Indicators, Sleep and Health Behaviours in Truck Drivers

Tue, 24 Mar 2020 10:51:32 GMT

Truck drivers are vulnerable to driver sleepiness due to pressures of shift work and prolonged driving hours; this is a safety concern as sleepiness more than doubles crash risk. Caffeine is a commonly used countermeasure to driver sleepiness. Previous research with truck drivers has demonstrated a positive impact of caffeine consumption on crash risk. However, habitual use of caffeine has the potential to impair night time sleep resulting in increased sleepiness and safety risk. One group that may be particularly vulnerable to the potential negative impacts of high caffeine consumption are those truck drivers who consume ≥ 5 caffeinated drinks per day (≥90th percentile American average daily caffeine consumption). 1,653 self-reported low (1 caffeinated drink per day) and 1,354 high (≥5 caffeinated drinks per day) caffeine consumers were compared across a range of driving safety indicators, health and sleep variables. All drivers completed an initial background questionnaire including the Epworth Sleepiness Scale (ESS), Berlin Questionnaire (BQ) and Dula Dangerous Driving Index (DDDI). Crashes and driving violations were monitored for up to 3 years (depending on enrolment date). Medical Examination Reports were available for 83.0% of the 3,007 participants. High caffeine consumers were more likely to report poor sleep outcomes: shorter average sleep time, (7.08 h compared to 7.41 h), higher prevalence of excessive daytime sleepiness (7.5% compared to 5.7%) and higher proportion at high risk of obstructive sleep apnea (OSA) on the BQ (13.1% compared with 9.4%). The higher caffeine consumers were more likely to report negative health behaviors: smoking, alcohol consumption, poor diet and infrequent exercise. Poorer driving safety indicators (negative emotions and aggressive driving on the DDDI) and previous crashes (27.8% compared to 21.6%) were also more common in high than low caffeine consumers. Caffeine is an effective countermeasure to driver sleepiness, however, high caffeine consumers do not exhibit any benefit to driving safety indicators. In fact, there is some evidence for safety concern because high caffeine consumers self-report more crashes and worse driving safety indicators than low caffeine consumers. High caffeine consumption was associated with poor health behaviors. Further research is needed to fully understand the implications of high caffeine use. Interventions aiming to reduce truck driver sleepiness should be cautious in promotion of caffeine in isolation; a wholistic approach to improve driver health would likely be more effective than focusing on sleep health alone.

High-Risk Driving Behaviors Among 12th Grade Students: Differences Between Alcohol-Only and Alcohol Mixed with Energy Drink Users

Tue, 28 May 2019 09:46:21 GMT

This article reports on a study that compared high-risk driving behaviors among high school students who use alcohol mixed with energy drinks (AmED) and those use consumed alcohol only. The authors measured risky driving behaviors by conducting secondary analyses of nationally-representative data from the Monitoring the Future Study (n = 1305 students). The authors found that 12th graders who drank AmED were significantly more likely to be in a motor vehicle accident (p < .001) and receive a ticket for a traffic violation (p<.05), compared to those using alcohol alone. Other results found that the 12th graders who used AmED were less like to use seat belts (as either passenger or driver). The authors conclude with a discussion of the implications of these findings for teenage health, including a review of the relevant literature. They voice concern over the possible interplay between this high-risk driving behavior and the already-established higher risk of automobile fatalities in teenage drivers.

Driving under the Influence Behaviours among High School Students Who Mix Alcohol with Energy Drinks

Tue, 19 Feb 2019 11:54:08 GMT

Alcohol and energy drinks are commonly used substances by youth in Canada, and are often mixed (AmED). While several studies have shown that AmED can have dangerous effects, less well understood is how AmED is associated with driving under the influence of either alcohol or drugs. This study sought to determine whether youth who use AmED were more likely to engage in driving, or being a passenger of a driver, under the influence of alcohol or cannabis compared to youth who use either alcohol or energy drinks alone.This study used data from grade 10–12 students who took part in the 2014/2015 Canadian Student Tobacco, Alcohol and Drugs Survey (N=17,450). The association of past-year AmED use with past-30day: driving under the influence of alcohol or cannabis, and riding with an alcohol- or cannabis-influenced driver, was assessed using logistic regression. One in four youth had consumed AmED in the previous 12 months. AmED users were more likely to engage in all risk behaviors except riding with a drinking driver, relative to youth who only consumed alcohol. No association was observed for youth who consumed alcohol and energy drinks on separate occasions. Youth who use AmED demonstrate a higher risk profile for driving under the influence of alcohol or cannabis, than youth who use alcohol alone. Future research should explore the biopsychosocial pathways that may explain why using energy drinks enhances the already heightened risk posed by alcohol on other health-related behaviors such as driving under the influence.

Caffeine Reduces the Impact of Drowsiness on Driving Errors

Mon, 09 Apr 2018 11:43:29 GMT

The study examined the moderating effect of repeat-dose, chewing gum-administered caffeine on the well-established relationship between drowsiness and driving performance, under the conditions of accumulating sleep loss. 50-h sleep deprivation protocol with a double-blind, placebo-controlled design. Eleven volunteers (6 male), aged 18–28 years were screened for pre-existing medical conditions (including sleep disturbances), tobacco and recreational drug use, recent time-zone travel and shift-work. They were randomly allocated to placebo or caffeine group and administered 4 oral doses of either caffeinated gum pellets (200mg/dose) or non-caffeinated placebo gum every two hours (01:00, 03:00, 05:00, 07:00) on the first and second nights of the protocol. Participants were constantly monitored and remained awake for 50h, while performing 15 identical, evenly-spaced 40-min monotonous driving tasks in a medium-fidelity moving-base driving simulator. Their drowsiness was monitored with a spectacle frame-mounted infra-red sensor registering ocular parameters and converting them into a Johns Drowsiness Scale (JDS) score every 60s. Lane keeping and speed variability measures were used to assess driving performance. Driving performance declined and drowsiness increased from the first simulated drive to the last. When driving performance was examined in one-minute epochs synchronized with JDS scores, both lateral lane positioning and speed variability were found to be associated with drowsiness. The strength of this association was significantly weaker in the caffeine group, compared to placebo. Placebo group replicated the linear relationship between drowsiness and driving errors across the full range of JDS scores. This pattern was significantly weaker under the caffeine condition, and was even reversed at the upper range of JDS, with higher JDS scores not resulting in further degradation of driving performance. This dissociation between drowsiness and driving errors persisted across the 24-h cycle under the caffeine condition, despite caffeine being administered only during early morning hours. Strategically timed, repeat 200mg doses of caffeine administered via chewing gum can mitigate fatigue-induced impairments in driving performance by not only reducing drowsiness but also by significantly weakening its impact on driving errors. This dual effect of sustained drowsiness reduction and the dissociation between drowsiness levels and driving errors seems worth further investigation as it might offer an effective emergency countermeasure against driver drowsiness and its subsequent conversion into potentially fatal driving errors.

Drivers' Attitude towards Caffeine Chewing Gum as Countermeasure to Driver Task-Related Fatigue

Fri, 26 May 2017 11:30:40 GMT

Driver fatigue is one of the major contributors to road accidents. In this study, the authors refer to task-related fatigue, in contrast to sleep-related fatigue. Sleep-related fatigue decrements in driving performance are related to the circadian rhythm, sleep disorders, and sleep deprivation or restriction. Task-related fatigue depends on driving conditions: active and passive task-related fatigue may arise according to the combination of driving task and driving environment. Active task-related fatigue is related to overload driving conditions, and passive task-related fatigue with underload ones. Several countermeasures have been proposed to face the problem of driver fatigue, such as taking a nap or caffeine beverages. The intake of caffeine has shown the enhancement of vigilance and choice reaction time. Those enhancements have an effect within 5-10 min in a caffeine chewing gum compared with 30 to 45 min in coffee. The enhancement in alertness within 5 min is crucial and potentially can reduce sleep related car accidents. Recent study showed that the caffeine effect is directly related to driving performance in monotonous conditions. In this study, two groups of drivers were asked to provide their preferences on several products that might positively affect their driving performance on long and monotonous conditions. The first group composed of participants that drove a driving simulator and actually consumed the products. The second group was composed of questionnaire responders that were presented with animations replicating the first group's actual driving. Both groups’ participants preferred to consume coffee or regular chewing-gum over caffeine chewing gum when asked at the beginning of the experiment (or survey). Drivers that actually consumed the products changed their attitude in favour of caffeine chewing-gum. On the other hand, the drivers that participated in the survey did not change their attitude, but rather changed their attitude with regards to the safety in using caffeine chewing-gum.

Causes, Consequences and Countermeasures to Driver Fatigue in the Rail Industry: The Train Driver Perspective

Mon, 27 Feb 2017 09:38:34 GMT

Fatigue is an important workplace risk management issue. Within the rail industry, the passing of a stop signal (signal passed at danger; SPAD) is considered to be one of the most major safety breaches which can occur. Train drivers are very aware of the negative consequences associated with a SPAD. Therefore, SPADs provide a practical and applied safety relevant context within which to structure a discussion on fatigue. Focus groups discussing contributing factors to SPADs were undertaken at eight passenger rail organisations across Australia and New Zealand (n = 28 drivers). Data relating to fatigue was extracted and inductively analysed identifying three themes: causes, consequences, and countermeasures (to fatigue). Drivers experienced negative consequences of fatigue, despite existing countermeasures to mitigate it. Organisational culture was a barrier to effective fatigue management. A fatigue assessment tool consistently informed rostering, however, shift swapping was commonplace and often unregulated, reducing any potential positive impact. In discussing fatigue countermeasure strategies, drivers talked interchangeably about mitigating task related fatigue (e.g. increasing cognitive load) and sleepiness (e.g. caffeine). Ensuring the concepts of fatigue and sleepiness are properly understood has the potential to maximise safety.

Caffeinated Chewing Gum as Countermeasure to Drivers’ Passive Task-Related Fatigue Caused by Monotonous Roadway

Mon, 06 Feb 2017 13:28:20 GMT

This study analyzed driver passive task-related fatigue caused by a monotonous environment and the effectiveness of caffeinated chewing gum as a countermeasure. Data collected by a driving simulator in the laboratory were used to measure changes in driving performance. A self-perceived measure of fatigue was also analyzed. Seventy-two subjects were asked to drive for 70 min along a straight road after receiving one of the following substances (treatments): caffeinated chewing gum, a cup of coffee, or placebo chewing gum. The 72 subjects were subdivided into three groups of 24 each, and all participants were asked to take part in two driving sessions: one control drive without administration (no treatment) and one with administration (one of the treatments). The negative effects on driving performance of prolonged driving and the effectiveness of the standard deviation of the lateral position in representing worsening driving performance were demonstrated. This analysis indicated that intake of caffeine in the form of caffeinated chewing gum (100 mg caffeine) improved driving performance in less than 10 min. Drinking an ordinary cup of coffee (with the same caffeine content) did not improve driving performance in the same short time interval.

The effects of caffeine use on driving safety among truck drivers who are habitual caffeine users

Tue, 24 Nov 2015 09:29:37 GMT

In this study, the authors seek to describe caffeine use among truck drivers both on- and off-duty. They also examine the association between truck drivers’ caffeine use and safety-critical events (SCEs) using real-time naturalistic observation in the work setting. A secondary analysis of 2007 data originally gathered for the Naturalistic Truck Driving Study is conducted, with comparisons also made between sleep and caffeine consumption by duty status and by age. Findings reveal differences in caffeine use by duty status, but no differences in sleep time by duty status and no differences between sleep time and caffeine use regardless of consumption time. The rate of SCEs per eight ounces of caffeinated beverage is found to decrease by 6% based on the data. Caffeine use among habitual users such as truck drivers is determined to offer a protective effect for safety-critical driving events. The authors suggest that this information may be used by occupational health nurses to counsel workers on caffeine use to improve driving safety.