Effects of caffeine on performance and mood depend on the level of caffeine abstinence

Effects of gypenoside L-containing Gynostemma pentaphyllum extract on fatigue and physical performance: A double-blind, placebo-controlled, randomized trial

This study was conducted to investigate the effect of Gynostemma pentaphyllum extract containing gypenoside L (GPE) on improving the cognitive aspects of fatigue and performance of the motor system. One hundred healthy Korean adults aged 19-60 years were randomized to the treatment (GPE for 12 weeks) and control groups, and efficacy and safety-related parameters were compared between the two groups. Maximal oxygen consumption (VO₂ max) and O₂ pulse were significantly higher in the treatment group than in the control group (p = 0.007 and p = 0.047, respectively). After 12 weeks, the treatment group showed significant changes such as decreases in the levels of free fatty acids (p = 0.042). In addition, there were significant differences in the rating of perceived exertion (RPE) (p < 0.05) and value of temporal fatigue between the treatment and control groups on the multidimensional fatigue scale (p < 0.05). Moreover, the level of endothelial nitric oxide synthase (eNOS) in the blood was significantly higher in the treatment group than in the control group (p = 0.047). In summary, oral administration of GPE has a positive effect on resistance to exercise-induced physical and mental fatigue.

Caffeine and attentional control: improved and impaired performance in healthy older adults and Parkinson's disease according to task demands

INTRODUCTION

Caffeine is frequently consumed to boost goal-directed attention. These procognitive effects may occur due to the adenosine-mediated enhancement of monoamines, such as dopamine, after caffeine administration. As such, caffeine's beneficial effects may be altered in conditions such as Parkinson's disease (PD). However, whether caffeine improves cognition, and at what cost, has not been experimentally established in patients with neurodegenerative disease.

METHODS

Single-dose trials to probe cognitive effects of caffeine are often confounded by short-term caffeine abstinence which conflates caffeine's effects with treatment of withdrawal. Using a placebo controlled, blinded, randomised trial design, we assessed the effect of 100 mg of caffeine across well-established tasks (Choice reaction time, Stroop Task and Rapid Serial Visual Presentation Task; RSVP) that probe different aspects of attention in PD patients (n = 24) and controls (n = 44). Critically, participants withdrew from caffeine for a week prior to testing to eliminate the possibility that withdrawal reversal explained any cognitive benefit.

RESULTS

Caffeine administration was found to reduce the overall number of errors in patients and controls on the Stroop (p = .018, η²_p = .086) and Choice reaction time (p < . 0001, η²_p = .588) tasks, but there was no specific effect of caffeine on ignoring irrelevant information in the Stroop task. On the RSVP task, caffeine improved dual item accuracy (p = .037) but impaired single item accuracy (p = .044). Across all tasks, there was little evidence that caffeine has different effects in PD participants and controls.

CONCLUSION

When removing withdrawal effects as a factor, we demonstrate caffeine has beneficial effects on selective attention but is a double-edge sword for visual temporal attention and would need careful targeting to be clinically useful.

Oxytocin-induced facilitation of learning in a probabilistic task is associated with reduced feedback- and error-related negativity potentials

BACKGROUND

Feedback evaluation of actions and error response detection are critical for optimizing behavioral adaptation. Oxytocin can facilitate learning following social feedback but whether its effects vary as a function of feedback valence remains unclear.

AIMS

The present study aimed to investigate whether oxytocin would influence responses to positive and negative feedback differentially or equivalently.

METHODS

The present study employed a randomized, double-blind, placebo controlled within-subject design to investigate whether intranasal oxytocin (24 IU) influenced behavioral and evoked electrophysiological potential responses to positive or negative feedback in a probabilistic learning task.

RESULTS

Results showed that oxytocin facilitated learning and this effect was maintained in the absence of feedback. Using novel stimulus pairings, we found that oxytocin abolished bias towards learning more from negative feedback under placebo by increasing accuracy for positively reinforced stimuli. Oxytocin also decreased the feedback-related negativity difference (negative minus positive feedback) during learning, further suggesting that it rendered the evaluation of positive and negative feedback more equivalent. Additionally, post-learning oxytocin attenuated error-related negativity amplitudes but increased the late error positivity, suggesting that it may lower conflict detection between actual errors and expected correct responses at an early stage of processing but at a later stage increase error awareness and motivation for avoiding them.

CONCLUSIONS

Oxytocin facilitates learning and subsequent performance by rendering the impact of positive relative to negative feedback more equivalent and also by reducing conflict detection and increasing error awareness, which may be beneficial for behavioral adaption.

Effects of Caffeine and Acute Aerobic Exercise on Working Memory and Caffeine Withdrawal

Studies show that a single bout of exercise confers cognitive benefits. However, many individuals use psychoactive substances such as caffeine to enhance cognitive performance. The effects of acute exercise in comparison to caffeine on cognition remain unknown. Furthermore, caffeine use is associated with withdrawal symptoms upon cessation. Whether acute exercise can reduce withdrawal symptoms also remains unknown. The objectives of this study were to compare the effects of acute moderate intensity aerobic exercise to caffeine on working memory (WM) and caffeine withdrawal symptoms (CWS). In Phase I, non-caffeine (n = 29) and caffeine consumers (n = 30) completed a WM assessment, followed by acute exercise and caffeine. In Phase II, caffeine consumers (n = 25) from Phase I underwent the WM assessment and reported CWS following a 12-hour deprivation period. Acute moderate intensity aerobic exercise and caffeine (1.2 mg/kg) significantly improved WM accuracy and reduced CWS comparably. WM performance was not reduced following caffeine deprivation.

Effects of acute caffeine, theanine and tyrosine supplementation on mental and physical performance in athletes

BACKGROUND

A limited amount of research has demonstrated beneficial effects of caffeine and theanine supplementation for enhancement of mental performance. The purpose of this investigation was to determine whether the acute ingestion of a supplement containing caffeine, theanine and tyrosine improves mental and physical performance in athletes.

METHODS

Twenty current or former male collegiate athletes (age: 20.5 ± 1.4 y; height: 1.82 ± 0.08 m; weight: 83.9 ± 12.6 kg; body fat: 13.8 ± 5.6%) completed this randomized, double-blind, placebo-controlled crossover trial. After familiarization, each participant completed two identical testing sessions with provision of a proprietary dietary supplement (SUP) containing caffeine theanine and tyrosine or a placebo (PL). Within each testing session, participants completed assessments of mental and physical performance before and after provision of SUP or PL, as well as after two rounds of exercise. Assessments were performed using a performance testing device (Makoto Arena) that evaluated multiple aspects of mental and physical performance in response to auditory and visual stimuli. Testing was performed both with the body in a static position and during dynamic movement. General linear models were used to evaluate the effects of SUP and PL on performance.

RESULTS

Changes in movement accuracy during performance assessment were greater following SUP ingestion as compared to PL for both static and dynamic testing (SUP: + 0.4 to 7.5%; PL: - 1.4 to 1.4% on average; p < 0.05). For dynamic testing, the change in number of targets hit was higher and the change in average hit time was lower with SUP as compared to PL (p < 0.05). However, there were no differences between conditions for the changes in number of targets hit or average hit time during static testing. There were no differences in changes of subjective variables during either condition, and performance measures during the two rounds of exercise did not differ between conditions (p > 0.05).

DISCUSSION

The present results indicate that a combination of a low-dose of caffeine with theanine and tyrosine may improve athletes' movement accuracy surrounding bouts of exhaustive exercise without altering subjective variables. Based on this finding, supplementation with caffeine, theanine and tyrosine could potentially hold ergogenic value for athletes in sports requiring rapid and accurate movements.

TRIAL REGISTRATION

NCT03019523. Registered 24 January 2017.

Relationships between use of dietary supplements, caffeine and sensation seeking among college students

Objective: Caffeine and dietary supplement (DS) use by college students is not well-documented. Given reported associations between energy drink consumption and sensation seeking, we used the Sensation Seeking Scale Form V (SSS-V) to assess relationships between sensation-seeking, caffeine, and DS use. Participants: Data from 1,248 college students from five US institutions were collected from 2009 to 2011. Methods: Linear regression was used to examine relationships between scores on the SSS-V and caffeine and DS use, demographic, and lifestyle characteristics. Results: Male sex, nonHispanic race-ethnicity, higher family income, tobacco use, consuming caffeinated beverages, more than 400 mg caffeine per day, and energy drinks with alcohol at least 50% of the time, were significantly associated with higher total SSS-V scores (P < 0.001). Those using protein DSs had higher total, disinhibition, and boredom susceptibility SSS-V scores (Ps < 0.001). Conclusions: Results demonstrate a positive correlation between sensation-seeking attitudes and habitual caffeine, energy drink, and DS consumption.

Dose-dependent effect of caffeine supplementation on judo-specific performance and training activity: a randomized placebo-controlled crossover trial

Background

Caffeine (CAF) supplementation could have a positive impact on physical performance and sport abilities. Nevertheless, the CAF-induced, dose-dependent influence on discipline-specific performance and combat activity in combat sports have not been sufficiently investigated. The aim of this study was to examine the effect of single ingestion of 3, 6, or 9 mg/kg body weight of CAF and placebo (PLA) on judo-specific performance and sparring combat activities.

Methods

In a randomised double-blind placebo-controlled cross-over design, acute pre-exercise supplementation with CAF (3, 6, or 9 mg/kg body weight) and placebo PLA in 22 male highly-trained judoists was examined. The study protocol involved five separate testing sessions using the Special Judo Fitness Test (SJFT) with heart rate monitoring, three judo sparring combats and evaluation of the rate of perceived exertion (RPE) using the Borg scale.

Results

Six and 9 mg/kg CAF improved SJFT performance, while 9 mg/kg increased combat activity. Three mg/kg CAF lacked any apparent positive ergogenic effect. Among athletes, who include CAF-containing products in their habitual diet (consumers), only 9 mg/kg CAF effectively enhanced SJFT performance, while in those who do not consume CAF-containing products at regular basis (non-consumers), the enhancing effect was achieved even at 6 mg/kg.

Conclusions

Regarding combat sports, higher (6–9 mg/kg) than currently recommended CAF dosages (3–6 mg/kg) are apparently more effective in terms of judo-specific performance. However, the ergogenic CAF effect is not only dose-dependent, but it is also related to customary CAF consumption.

Trial registration

Clinical Trials Gov, NCT03822663. Registered 28 January 2019 - Retrospectively registered

Electronic supplementary material

The online version of this article (10.1186/s12970-019-0305-8) contains supplementary material, which is available to authorized users.

Effects of strategic early-morning caffeine gum administration on association between salivary alpha-amylase and neurobehavioural performance during 50 h of sleep deprivation

Self-assessment is the most common method for monitoring performance and safety in the workplace. However, discrepancies between subjective and objective measures have increased interest in physiological assessment of performance. In a double-blind placebo-controlled study, 23 healthy adults were randomly assigned to either a placebo (n = 11; 5 F, 6 M) or caffeine condition (n = 12; 4 F, 8 M) while undergoing 50 h (i.e. two days) of total sleep deprivation. In previous work, higher salivary alpha-amylase (sAA) levels were associated with improved psychomotor vigilance and simulated driving performance in the placebo condition. In this follow-up article, the effects of strategic caffeine administration on the previously reported diurnal profiles of sAA and performance, and the association between sAA and neurobehavioural performance were investigated. Participants were given a 10 h baseline sleep opportunity (monitored via standard polysomnography techniques) prior to undergoing sleep deprivation (total sleep time: placebo = 8.83 ± 0.48 h; caffeine = 9.01 ± 0.48 h). During sleep deprivation, caffeine gum (200 mg) was administered at 01:00 h, 03:00 h, 05:00 h, and 07:00 h to participants in the caffeine condition (n = 12). This strategic administration of caffeine gum (200 mg) has been shown to be effective at maintaining cognitive performance during extended wakefulness. Saliva samples were collected, and psychomotor vigilance and simulated driving performance assessed at three-hour intervals throughout wakefulness. Caffeine effects on diurnal variability were compared with previously reported findings in the placebo condition (n = 11). The impact of caffeine on the circadian profile of sAA coincided with changes in neurobehavioural performance. Higher sAA levels were associated with improved performance on the psychomotor vigilance test during the first 24 h of wakefulness in the caffeine condition. However, only the association between sAA and response speed (i.e. reciprocal-transform of mean reaction time) was consistent across both days of sleep deprivation. The association between sAA and driving performance was not consistent across both days of sleep deprivation. Results show that the relationship between sAA and reciprocal-transform of mean reaction time on the psychomotor vigilance test persisted in the presence of caffeine, however the association was relatively weaker as compared with the placebo condition.

The Influence of Caffeine Expectancies on Sport, Exercise, and Cognitive Performance

Caffeine (CAF) is widely consumed across sport and exercise for its reputed ergogenic properties, including central nervous stimulation and enhanced muscular force development. However, expectancy and the related psychological permutations that are associated with oral CAF ingestion are generally not considered in most experimental designs and these could be important in understanding if/how CAF elicits an ergogenic effect. The present paper reviews 17 intervention studies across sport, exercise, and cognitive performance. All explore CAF expectancies, in conjunction with/without CAF pharmacology. Thirteen out of 17 studies indicated expectancy effects of varying magnitudes across a range of exercise tasks and cognitive skills inclusive off but not limited to; endurance capacity, weightlifting performance, simple reaction time and memory. Factors, such as motivation, belief, and habitual CAF consumption habits influenced the response. In many instances, these effects were comparable to CAF pharmacology. Given these findings and the lack of consistency in the experimental design, future research acknowledging factors, such as habitual CAF consumption habits, habituated expectations, and the importance of subjective post-hoc analysis will help to advance knowledge within this area.

Sucrose or sucrose and caffeine differentially impact memory and anxiety-like behaviours, and alter hippocampal parvalbumin and doublecortin

Caffeinated sugar-sweetened "energy" drinks are a subset of soft drinks that are popular among young people worldwide. High sucrose diets impair cognition and alter aspects of emotional behaviour in rats, however, little is known about sucrose combined with caffeine. Rats were allocated to 2 h/day 10% sucrose (Suc), 10% sucrose plus 0.04% caffeine (CafSuc) or control (water) conditions. The addition of caffeine to sucrose appeared to increase the rewarding aspect of sucrose, as the CafSuc group consumed more solution than the Suc group. After 14 days of intermittent Suc or CafSuc access, anxiety was assessed in the elevated plus maze (EPM) prior to their daily solution access, whereby CafSuc and Suc rats spent more time in the closed arms, indicative of increased anxiety. Following daily solution access, CafSuc, but not Suc, rats showed reduced anxiety-like behaviour in the open-field. Control and CafSuc rats displayed intact place and long-term object memory, while Suc showed impaired memory performance. Sucrose reduced parvalbumin immunoreactivity in the hippocampus, but no differences were observed between Control and CafSuc conditions. Parvalbumin reactivity in the basolateral amygdala did not differ between conditions. Reduced doublecortin immunoreactivity in the dentate gyrus relative to controls was seen in the CafSuc, but not Suc, treatment conditions. These findings indicate that the addition of caffeine to sucrose attenuated cognitive deficits. However, the addition of caffeine to sucrose evoked anxiety-like responses under certain testing conditions, suggesting that frequent consumption of caffeinated energy drinks may promote emotional alterations and brain changes compared to standard soft drinks.

Herbal medicine for sports: a review

The use of herbal medicinal products and supplements has increased during last decades. At present, some herbs are used to enhance muscle strength and body mass. Emergent evidence suggests that the health benefits from plants are attributed to their bioactive compounds such as Polyphenols, Terpenoids, and Alkaloids which have several physiological effects on the human body. At times, manufacturers launch numerous products with banned ingredient inside with inappropriate amounts or fake supplement inducing harmful side effect. Unfortunately up to date, there is no guarantee that herbal supplements are safe for anyone to use and it has not helped to clear the confusion surrounding the herbal use in sport field especially. Hence, the purpose of this review is to provide guidance on the efficacy and side effect of most used plants in sport. We have identified plants according to the following categories: Ginseng, alkaloids, and other purported herbal ergogenics such as Tribulus Terrestris, Cordyceps Sinensis. We found that most herbal supplement effects are likely due to activation of the central nervous system via stimulation of catecholamines. Ginseng was used as an endurance performance enhancer, while alkaloids supplementation resulted in improvements in sprint and cycling intense exercises. Despite it is prohibited, small amount of ephedrine was usually used in combination with caffeine to enhance muscle strength in trained individuals. Some other alkaloids such as green tea extracts have been used to improve body mass and composition in athletes. Other herb (i.e. Rhodiola, Astragalus) help relieve muscle and joint pain, but results about their effects on exercise performance are missing.

The Safety of Ingested Caffeine: A Comprehensive Review

Caffeine is the most widely consumed psychoactive drug in the world. Natural sources of caffeine include coffee, tea, and chocolate. Synthetic caffeine is also added to products to promote arousal, alertness, energy, and elevated mood. Over the past decade, the introduction of new caffeine-containing food products, as well as changes in consumption patterns of the more traditional sources of caffeine, has increased scrutiny by health authorities and regulatory bodies about the overall consumption of caffeine and its potential cumulative effects on behavior and physiology. Of particular concern is the rate of caffeine intake among populations potentially vulnerable to the negative effects of caffeine consumption: pregnant and lactating women, children and adolescents, young adults, and people with underlying heart or other health conditions, such as mental illness. Here, we review the research into the safety and safe doses of ingested caffeine in healthy and in vulnerable populations. We report that, for healthy adults, caffeine consumption is relatively safe, but that for some vulnerable populations, caffeine consumption could be harmful, including impairments in cardiovascular function, sleep, and substance use. We also identified several gaps in the literature on which we based recommendations for the future of caffeine research.

Effects of a single, oral 60 mg caffeine dose on attention in healthy adult subjects

Caffeine induces positive effects on sustained attention, although studies assessing the acute effects of low caffeine dose (<75 mg) on sustained attention are limited and use short-term tests. Therefore, we investigated the acute effects of a 60 mg dose of caffeine on sustained attention in tests lasting up to 45 minutes using 82 low or non-caffeine-consuming healthy male ( n=41) and female ( n=41) adults aged between 40 and 60 years. Vigilance was measured using Mackworth Clock test, Rapid Visual Information Processing Test, adaptive tracking test, saccadic eye movement and attention switch test. Effects on mood and fatigue were analysed using Bond and Lader and Caffeine Research visual analogue scales, and Samn-Perelli questionnaire. Saliva sampling was performed for both compliance and caffeine pharmacokinetic analysis. Administration of a 60 mg caffeine dose resulted in a significant improvement in sustained attention compared with the placebo. Also a significantly improved peak saccadic velocity and reaction time performance was found, and decreased error rate. Significantly increased feelings of alertness, contentment and overall mood after caffeine treatment compared with placebo were observed. This study demonstrated that in healthy adult subjects oral administration of a single 60 mg caffeine dose elicited a clear enhancement of sustained attention and alertness, measured both in multiple objective performances and in subjective scales.

Online Activity Levels Are Related to Caffeine Dependency

Online activity could serve in the future as behavioral markers of emotional states for computer systems (i.e., affective computing). Hence, this study considered relationships between self-reported stimulant use and online study patterns. Sixty-two undergraduate psychology students estimated their daily caffeine use, and this was related to study patterns as tracked by their use of a Learning Management System (Blackboard). Caffeine dependency was associated with less time spent online, lower rates of file access, and fewer online activities completed. Reduced breadth or depth of processing during work/study could be used as a behavioral marker of stimulant use.

Thought Speed, Mood, and the Experience of Mental Motion

This article presents a theoretical account relating thought speed to mood and psychological experience. Thought sequences that occur at a fast speed generally induce more positive affect than do those that occur slowly. Thought speed constitutes one aspect of mental motion. Another aspect involves thought variability, or the degree to which thoughts in a sequence either vary widely from or revolve closely around a theme. Thought sequences possessing more motion (occurring fast and varying widely) generally produce more positive affect than do sequences possessing little motion (occurring slowly and repetitively). When speed and variability oppose each other, such that one is low and the other is high, predictable psychological states also emerge. For example, whereas slow, repetitive thinking can prompt dejection, fast, repetitive thinking can prompt anxiety. This distinction is related to the fact that fast thinking involves greater actual and felt energy than slow thinking does. Effects of mental motion occur independent of the specific content of thought. Their consequences for mood and energy hold psychotherapeutic relevance.

No Enhancement of 24-Hour Visuomotor Skill Retention by Post-Practice Caffeine Administration

Caffeine is widely consumed throughout the world and appears to indirectly facilitate learning and memory through effects on attention and motivation. Animal work indicates that post-training caffeine administration augments inhibitory avoidance memory, spatial memory, and object memory. In humans, post-training caffeine administration enhances the ability to discern between familiar images and new, similar images. However, the effect of post-training caffeine administration on motor memory has not been examined. Therefore, we tested two groups of low caffeine consumers (average weekly consumption ≤500 mg) in a double-blind, placebo-controlled study involving acquisition of a continuous isometric visuomotor tracking skill. On Day 1, subjects completed 5 blocks (150 repetitions) of training on the continuous isometric visuomotor skill and subsequently ingested either 200 mg of caffeine or placebo. On day 2, subjects completed an additional 5 blocks of training. Day 1 mean performance and performance variability were both similar between groups, suggesting that both groups acquired the motor skill similarly. For mean performance on Day 2, patterns of re-learning, mean performance learning magnitudes, mean performance learning rates, and mean performance retention magnitudes were all similar between groups. For performance variability on Day 2, there was a small trend towards increased variability in the caffeine group during re-learning, but performance variability learning magnitudes and performance variability retention magnitudes did not differ between groups. Because motor skill acquisition can also be conceptualized as a reduction in performance variability, these results suggest that there may be a small negative effect of post-practice caffeine administration on memory of a newly-learned visuomotor skill. Overall, we found no evidence to suggest that post-training caffeine administration enhances 24-hour retention of a newly-learned continuous visuomotor skill, and these results support the notion that memory-enhancing effects of post-training caffeine ingestion may be task-specific.

Acute effects of dietary constituents on motor skill and cognitive performance in athletes

Performance in many sports is at least partially dependent on motor control, coordination, decision-making, and other cognitive tasks. This review summarizes available evidence about the ingestion of selected nutrients or isolated compounds (dietary constituents) and potential acute effects on motor skill and/or cognitive performance in athletes. Dietary constituents discussed include branched-chain amino acids, caffeine, carbohydrate, cocoa flavanols, Gingko biloba, ginseng, guarana, Rhodiola rosea, sage, L-theanine, theobromine, and tyrosine. Although this is not an exhaustive list, these are perhaps the most researched dietary constituents. Caffeine and carbohydrate have the greatest number of published reports supporting their ability to enhance acute motor skill and cognitive performance in athletes. At this time, there is insufficient published evidence to substantiate the use of any other dietary constituents to benefit sports-related motor skill or cognitive performance. The optimal dose and timing of caffeine and carbohydrate intake promoting enhanced motor skill and cognitive performance remain to be identified. Valid, reliable, and sensitive batteries of motor skills and cognitive tests should be developed for use in future efficacy studies.

The effect of caffeine on spontaneous pupillary oscillations

PURPOSE

Caffeine stimulates the central nervous system, but the duration and extent of its influence on the pupil are not known. The aim of this study was to determine whether caffeine could have an effect on pupillary sleepiness waves, measured with the Pupillographic Sleepiness Test (PST) during routine clinical PST testing, where the caffeine dose-response of a participant cannot be registered before recording.

METHODS

Twenty participants (aged between 22 and 51 years, (mean 30.9 years ± 8.9 SD, 11 women and nine men),.were tested at seven different time-points over 4.5 h. Each participant was tested under four conditions with coffee drunk or not between 1 and 2 h before the first measurement and/or 15 min afterwards.

RESULTS

Caffeine caused a reduction in the Pupillary Unrest Index (PUI) with a maximal effect 1.25 h after consumption. A prolonged effect is found if coffee was consumed between 1 and 2 h before the first measurement. More excessive coffee consumers show prolongation of the effect. Subjective scales of sleepiness, alertness and craving for caffeine were significantly correlated to linear logarithm of PUI (lnPUI).

CONCLUSIONS

We conclude that caffeine causes a dampening of the pupillary oscillations in well-rested participants. As caffeine consumption can affect the PST for up to 6.5 h after intake, it is recommended that if PST measurements are to be carried out in the morning, caffeine consumption should not be allowed after midnight.

Caffeine and cognitive performance: persistent methodological challenges in caffeine research

Human cognitive performance is widely perceived to be enhanced by caffeine at usual dietary doses. However, the evidence for and against this belief continues to be vigorously contested. Controversy has centred on caffeine withdrawal and withdrawal reversal as potential sources of experimental confounding. In response, some researchers have enlisted "caffeine-naïve" experimental participants (persons alleged to consume little or no caffeine) assuming that they are not subject to withdrawal. This mini-review examines relevant research to illustrate general methodological challenges that have been the cause of enduring confusion in caffeine research. At issue are the processes of caffeine withdrawal and withdrawal reversal, the definition of caffeine-naïve, the population representativeness of participants deemed to be caffeine-naïve, and confounding due to caffeine tolerance. Attention to these processes is necessary if premature conclusions are to be avoided, and if caffeine's complex effects and the mechanisms responsible for those effects are to be illuminated. Strategies are described for future caffeine research aimed at minimising confounding from withdrawal and withdrawal reversal.

Effects of caffeine in overnight-withdrawn consumers and non-consumers

RATIONALE

A number of recent studies have suggested that caffeine only improves mood and cognitive performance in regular caffeine consumers who are caffeine withdrawn at test (the "withdrawal hypothesis"). This can be tested by investigating the effects of caffeine in non-consumers of caffeine.

OBJECTIVES

To compare the effects of 2 mg/kg caffeine on mood and cognitive performance in overnight-withdrawn consumers and non-consumers of caffeine.

METHODS

Twenty-five overnight-withdrawn consumers and twenty-five non-consumers of caffeine were tested in a within-subjects design where they were given a drink containing 2 mg/kg caffeine on one test day and placebo on another test day. The order of conditions (caffeine/placebo) was counterbalanced. Mood and performance measures were taken before and after each drink, and pre-drink measures were used as covariates in the analysis of post-drink measures.

RESULTS

Analysis of baseline scores revealed no significant effects of caffeine withdrawal. Caffeine generally improved mood and cognitive performance, relative to placebo, in both subjects groups. These effects did not differ significantly between groups apart from three measures (fewer lapses of attention and ratings of alertness and anxiety) where the effects of caffeine were larger in the non-consumers.

CONCLUSIONS

The present study revealed no negative effects of caffeine withdrawal. Beneficial effects of caffeine were observed in both withdrawn consumers and in non-consumers. Therefore, the withdrawal hypothesis is not an adequate explanation for the effects of caffeine.

Caffeine increases liking and consumption of novel-flavored yogurt

RATIONALE

Caffeine has been shown to increase preference for beverages with which it is paired; however, it is not known if caffeine alters liking for foods with which it is paired indirectly.

OBJECTIVES

The purpose of the current experiment was to test the hypothesis that a caffeinated beverage paired with a novel-flavored yogurt will increase preference for that yogurt compared to one paired with placebo. We also tested the hypothesis that liking would increase more when caffeine was paired with high energy density yogurt.

METHODS

Men and women (n = 62) were randomized to receive a beverage containing placebo (PLA) or caffeine (CAF) and to consume a low (LED) or high energy density (HED), novel-flavored yogurt. Participants rated, ranked, and consumed seven novel-flavored yogurts and then had a target yogurt paired with either PLA or CAF over four consecutive days.

RESULTS

In general, yogurt liking increased over time, the HED yogurt was liked more than the LED yogurt, and yogurt paired with caffeine was liked more than yogurt paired with placebo. Participants showed a significant increase in liking of LED yogurt paired with caffeine compared to those with LED yogurt paired with placebo.

CONCLUSIONS

Caffeine administration may increase liking and consumption of novel-flavored foods, particularly if the food is not highly liked at baseline. This suggests that caffeine pairing may be a way to increase liking of LED foods, such as vegetables and fruit.

Acute and chronic caffeine administration increases physical activity in sedentary adults

Caffeine is a commonly used stimulant thought to have ergogenic properties. Most studies on the ergogenic effects of caffeine have been conducted in athletes. The purpose of this study was to test the hypothesis that caffeine reduces ratings of perceived exertion and increases liking of physical activity in sedentary adults. Participants completed treadmill walking at 60% to 70% of their maximal heart rate at baseline and for 6 subsequent visits, during which half of the participants were given caffeine (3 mg/kg) and half given placebo in a sports drink vehicle. To investigate the potential synergistic effects of acute and chronic caffeine on self-determined exercise duration, participants were rerandomized to either the same or different condition for the last visit, creating 4 chronic/acute treatment groups (placebo/placebo, placebo/caffeine, caffeine/placebo, caffeine/caffeine). Participants rated how much they liked the activity and perceived exertion at each visit. There was a main effect of time on liking of physical activity, with liking increasing over time and an interaction of sex and caffeine treatment on liking, with liking of activity increasing in female participants treated with caffeine, but not with placebo. There was no effect of caffeine on ratings of perceived exertion. Individuals who received caffeine on the final test day exercised for significantly longer than those who received placebo. These data suggest that repeated exposure to physical activity significantly increases liking of exercise and reduces ratings of perceived exertion and that caffeine does little to further modify these effects.

Caffeine as an attention enhancer: reviewing existing assumptions

RATIONALE

Despite the large number of studies on the behavioural effects of caffeine, an unequivocal conclusion had not been reached. In this review, we seek to disentangle a number of questions.

OBJECTIVE

Whereas there is a general consensus that caffeine can improve performance on simple tasks, it is not clear whether complex tasks are also affected, or if caffeine affects performance of the three attention networks (alerting, orienting and executive control). Other questions being raised in this review are whether effects are more pronounced for higher levels of caffeine, are influenced by habitual caffeine use and whether there effects are due to withdrawal reversal.

METHOD

Literature review of double-blind placebo controlled studies that assessed acute effects of caffeine on attention tasks in healthy adult volunteers.

RESULTS

Caffeine improves performance on simple and complex attention tasks, and affects the alerting, and executive control networks. Furthermore, there is inconclusive evidence on dose-related performance effects of caffeine, or the influence of habitual caffeine consumption on the performance effects of caffeine. Finally, caffeine's effects cannot be attributed to withdrawal reversal.

CONCLUSIONS

Evidence shows that caffeine has clear beneficial effects on attention, and that the effects are even more widespread than previously assumed.

Acute effects of caffeine on attention: a comparison of non-consumers and withdrawn consumers

Despite the large number of studies on caffeine and attention, interpretation is often difficult because of methodological weaknesses. In the present study, use of a small battery of tests with four key outcome measures, combined with an appropriate sample size, addresses many of these problems. This methodology was used to examine whether effects of caffeine (a dose of 2 mg/kg) could be explained in terms of reversal of the effects of caffeine withdrawal. This was achieved by examining effects in non-consumers (N = 35), who could not be withdrawn, and also in a group of consumers (N = 35) who had undergone withdrawal for a week and no longer reported symptoms of withdrawal. The results showed no effect of short-term withdrawal on the performance measures, even though subjective reports showed an increase in symptoms after withdrawal. In contrast, the caffeine challenge carried out on Day 8 showed that ingestion of caffeine was associated with faster simple reaction time, fewer long responses, greater detection of targets in the cognitive vigilance task, and faster encoding of new information. These results suggest that it is important to continue to investigate mechanisms underlying these effects of caffeine and to further evaluate the practical implications of such effects.

Caffeine improves left hemisphere processing of positive words

A positivity advantage is known in emotional word recognition in that positive words are consistently processed faster and with fewer errors compared to emotionally neutral words. A similar advantage is not evident for negative words. Results of divided visual field studies, where stimuli are presented in either the left or right visual field and are initially processed by the contra-lateral brain hemisphere, point to a specificity of the language-dominant left hemisphere. The present study examined this effect by showing that the intake of caffeine further enhanced the recognition performance of positive, but not negative or neutral stimuli compared to a placebo control group. Because this effect was only present in the right visual field/left hemisphere condition, and based on the close link between caffeine intake and dopaminergic transmission, this result points to a dopaminergic explanation of the positivity advantage in emotional word recognition.

Differential cognitive effects of energy drink ingredients: caffeine, taurine, and glucose

Energy drinks containing caffeine, taurine, and glucose may improve mood and cognitive performance. However, there are no studies assessing the individual and interactive effects of these ingredients. We evaluated the effects of caffeine, taurine, and glucose alone and in combination on cognitive performance and mood in 24-hour caffeine-abstained habitual caffeine consumers. Using a randomized, double-blind, mixed design, 48 habitual caffeine consumers (18 male, 30 female) who were 24-hour caffeine deprived received one of four treatments (200 mg caffeine/0 mg taurine, 0 mg caffeine/2000 mg taurine, 200 mg caffeine/2000 mg taurine, 0 mg caffeine/0 mg taurine), on each of four separate days, separated by a 3-day wash-out period. Between-participants treatment was a glucose drink (50 g glucose, placebo). Salivary cortisol, mood and heart rate were measured. An attention task was administered 30-minutes post-treatment, followed by a working memory and reaction time task 60-minutes post-treatment. Caffeine enhanced executive control and working memory, and reduced simple and choice reaction time. Taurine increased choice reaction time but reduced reaction time in the working memory tasks. Glucose alone slowed choice reaction time. Glucose in combination with caffeine, enhanced object working memory and in combination with taurine, enhanced orienting attention. Limited glucose effects may reflect low task difficulty relative to subjects' cognitive ability. Caffeine reduced feelings of fatigue and increased tension and vigor. Taurine reversed the effects of caffeine on vigor and caffeine-withdrawal symptoms. No effects were found for salivary cortisol or heart rate. Caffeine, not taurine or glucose, is likely responsible for reported changes in cognitive performance following consumption of energy drinks, especially in caffeine-withdrawn habitual caffeine consumers.

Herbs in exercise and sports

The use of herbs as ergogenic aids in exercise and sport is not novel. Ginseng, caffeine, ma huang (also called 'Chinese ephedra'), ephedrine and a combination of both caffeine and ephedrine are the most popular herbs used in exercise and sports. It is believed that these herbs have an ergogenic effect and thus help to improve physical performance. Numerous studies have been conducted to investigate the effects of these herbs on exercise performance. Recently, researchers have also investigated the effects of Eurycoma longifolia Jack on endurance cycling and running performance. These investigators have reported no significant improvement in either cycling or running endurance after supplementation with this herb. As the number of studies in this area is still small, more studies should be conducted to evaluate and substantiate the effects of this herb on sports and exercise performance. For instance, future research on any herbs should take the following factors into consideration: dosage, supplementation period and a larger sample size.

Does coffee enriched with chlorogenic acids improve mood and cognition after acute administration in healthy elderly? A pilot study

RATIONALE

Caffeine exerts positive effects on cognitive and behavioral processes, especially in sub-optimal conditions when arousal is low. Apart from caffeine, coffee contains other compounds including the phenolic compounds ferulic acid, caffeic acid, and the chlorogenic acids, which have purported antioxidant properties. The chlorogenic acids are the most abundant family of compounds found in coffee, yet their effects on cognition and mood have not been investigated.

OBJECTIVES

This study aims to ascertain whether a coffee rich in chlorogenic acid modulates brain function.

METHODS

The present pilot study examined the acute effects of decaffeinated coffee with regular chlorogenic acid content and decaffeinated coffee with high chlorogenic acid content on mood and cognitive processes, as measured by behavioral tasks and event-related potentials (ERPs). Performance and ERP responses to a battery of cognitive tasks were recorded at baseline and following the equivalent of three cups of coffee in a randomized, double-blind, crossover study of 39 healthy older participants.

RESULTS

Compared with the decaffeinated coffee with regular chlorogenic acid and placebo, caffeinated coffee showed a robust positive effect on higher-level mood and attention processes. To a lesser extent, the decaffeinated coffee high in chlorogenic acid also improved some mood and behavioral measures, relative to regular decaffeinated coffee.

CONCLUSIONS

Our pilot results suggest that non-caffeine compounds in coffee such as the chlorogenic acids may be capable of exerting some acute behavioral effects, thus warranting further investigation.

Adolescent substance use, sleep, and academic achievement: evidence of harm due to caffeine

Using academic achievement as the key outcome variable, 7377 Icelandic adolescents were surveyed for cigarette smoking, alcohol use, daytime sleepiness, caffeine use, and potential confounders. Structural equation modeling (SEM) was used to examine direct and indirect effects of measured and latent variables in two models: the first with caffeine excluded and the second with caffeine included. A substantial proportion of variance in academic achievement, which might otherwise have been attributed to the harmful effects of cigarette smoking and alcohol use, was found to be attributable to caffeine. Evidence was obtained that daytime sleepiness, which was found to be independently associated with usage of licit substances (nicotine and alcohol) and caffeine, may be an important mediator of the negative impact of those substances on academic achievement. Findings suggest the importance of including measurements of caffeine consumption in future studies of adolescent substance use.

Perceived treatment, feedback, and placebo effects in double-blind RCTs: an experimental analysis

INTRODUCTION

In double-blind randomized placebo-controlled trials (RCT) of therapeutic interventions, the effects of the treatment may provide feedback that undermines blinding and consequently distorts measures of the effectiveness of the intervention.

METHODS AND RESULTS

This possibility was confirmed in an experimental model using a dummy placebo procedure whereby participants were led to believe that they were taking part in testing a cognitive-enhancing drug. In two experiments, false feedback given about cognitive performance influenced participants' beliefs about whether they had been allocated to the active treatment or placebo. These beliefs also appeared to influence actual cognitive performance in that participants who believed they had taken the active treatment had higher accuracy in Experiment 1 and faster reaction times in Experiment 2 than those who believed they had been given a placebo. The addition of no treatment control groups in Experiment 2 showed that these effects could not be accounted for by the feedback manipulation itself, thereby supporting expectancy as a causal factor.

DISCUSSION

These results indicate the importance of assessing participants' beliefs about their treatment allocation in real double-blind RCTs and considering if and how these may have affected the trial's outcome.

Perceived treatment, feedback, and placebo effects in double-blind RCTs: an experimental analysis

INTRODUCTION

In double-blind randomized placebo-controlled trials (RCT) of therapeutic interventions, the effects of the treatment may provide feedback that undermines blinding and consequently distorts measures of the effectiveness of the intervention.

METHODS AND RESULTS

This possibility was confirmed in an experimental model using a dummy placebo procedure whereby participants were led to believe that they were taking part in testing a cognitive-enhancing drug. In two experiments, false feedback given about cognitive performance influenced participants' beliefs about whether they had been allocated to the active treatment or placebo. These beliefs also appeared to influence actual cognitive performance in that participants who believed they had taken the active treatment had higher accuracy in Experiment 1 and faster reaction times in Experiment 2 than those who believed they had been given a placebo. The addition of no treatment control groups in Experiment 2 showed that these effects could not be accounted for by the feedback manipulation itself, thereby supporting expectancy as a causal factor.

DISCUSSION

These results indicate the importance of assessing participants' beliefs about their treatment allocation in real double-blind RCTs and considering if and how these may have affected the trial's outcome.

A comparison of the effects of caffeine following abstinence and normal caffeine use

RATIONALE

Caffeine typically produces positive effects on mood and performance. However, tolerance may develop following habitual use, and abrupt cessation can result in withdrawal symptoms, such as fatigue. This study investigated whether caffeine has a greater stimulant effect in a withdrawn state compared to a normal caffeinated state, among moderate daily caffeine consumers.

MATERIALS AND METHODS

Using a within-subjects design, 17 caffeine consumers (mean +/- sd = 375 +/- 101 mg/day) ingested placebo or caffeine (250 mg) following 30-h of caffeine abstention or normal dietary caffeine use on four separate days. Self-reported mood and performance on choice reaction time, selective attention, and memory tasks were measured.

RESULTS

Caffeine had a greater effect on mood and choice reaction time in the abstained state than in the normal caffeinated state, but caffeine improved selective attention and memory in both states.

CONCLUSIONS

Although improvements in mood and reaction time may best explained as relief from withdrawal symptoms, other performance measures showed no evidence of withdrawal and were equally sensitive to an acute dose of caffeine in the normal caffeinated state.

Caffeine expectancies influence the subjective and behavioral effects of caffeine

OBJECTIVES

This study investigated the independent and interactive effects of caffeine pharmacology and expected effects of caffeine on performance and subjective outcomes.

METHODS

Abstinent coffee drinkers (n = 60) consumed decaffeinated coffee with either 280 mg or 0 mg added caffeine. Caffeine dose was crossed with varying instructions that the coffee would either enhance or impair performance in a 2 x 2 factorial design. Performance, mood, caffeine withdrawal, and negative somatic effects were assessed.

RESULTS

Relative to placebo, caffeine improved reaction time and accuracy on the rapid visual information processing task, a measure of vigilance. However, there was a significant dose by expectancy interaction that revealed that among participants given placebo coffee, "impair" instructions produced better performance than "enhance" instructions. Caffeine also improved psychomotor performance as indicated by a finger tapping task with no main effects of expectancy or interactions. Impair instructions produced greater reports of negative somatic effects than enhance instructions, but only when caffeine was administered.

CONCLUSIONS

Manipulating the expected effects of caffeine altered the behavioral and subjective effects of caffeine. A significant dose by expectancy interaction revealed a somewhat paradoxical outcome in the placebo conditions whereby those told "impair" performed better than those told "enhance." This may reflect compensatory responding as has been observed in similar studies using alcohol (Fillmore et al. Psychopharmacology 115:383-388, 1994). Impair instructions led to greater negative somatic effects only when caffeine was administered supporting the active placebo hypothesis.

Effects of caffeine in chewing gum on mood and attention

RATIONALE

Recent research has shown that even small doses (<40mg) of caffeine can improve alertness and increase performance efficiency on attention tasks. Previous studies have given the caffeine in a variety of beverages or in capsules and it was of interest to see whether similar effects could be observed when the caffeine was given in gum. In addition, chewing gum has been shown to have behavioural effects and the present study extended our knowledge of this topic.

OBJECTIVES

To compare the effects of caffeinated gum (40 mg), placebo gum and no gum conditions on mood and attention.

METHODS

A double blind placebo controlled study was conducted with volunteers being randomly assigned to one of the three conditions. Baseline measures of mood and attention were taken prior to chewing and a test session was then conducted. One hundred and eighteen young adults participated in the study.

RESULTS

Caffeinated gum was associated with a more positive mood and better performance on tasks requiring sustained attention. The caffeine improved the speed of encoding of new information which is consistent with previous findings. Chewing placebo gum was also found to be associated with more positive mood, both shortly after chewing and at the end of the study.

CONCLUSIONS

The implications of the present study are that chewing caffeinated gum has been shown to improve performance efficiency and mood by its alerting and energising effects. The profile of caffeine effects is what one would predict from the existing caffeine literature and such effects may be extremely beneficial in real-life situations. Prior chewing of placebo gum was associated with a more positive mood and this also confirms previous findings.

Genetics of coffee consumption and its stability

BACKGROUND

Coffee is a highly popular drink associated with the pathogenesis of several diseases and the use of tobacco and alcohol. Considering the worldwide consumption, coffee has a substantial effect on individual wellbeing and public health. The role of genetic factors contributing to interindividual differences and their stability in coffee use is not well known.

AIMS

We analysed the heritability of coffee consumption and its stability in a large population-based sample of Finnish twins.

DESIGN

In 1975 and 1981 a postal questionnaire on coffee consumption was sent to all Finnish same-sex twin pairs born before 1958. Responses were obtained from 10 716 complete twin pairs in 1975 (3409 monozygotic and 7307 dizygotic), of whom 8124 also responded in 1981. The data were analysed using classical twin modelling based on linear structural equations.

FINDINGS

Additive genetic and unique environmental factors affected coffee drinking, whereas shared environmental factors did not show any effect. Heritability of coffee consumption, adjusted for age and sex, was estimated as 0.56 in 1975 and 0.45 in 1981. Coffee consumption showed a moderate correlation between these two time-points (r = 0.58 in men and 0.55 in women). Genetic factors affecting coffee consumption were stable: additive genetic correlations were 0.84 in men and 0.83 in women, whereas unique environmental correlations were moderate (0.45 and 0.36). Additive genetic factors had the highest contribution in young adults.

CONCLUSIONS

Coffee consumption is affected by both additive genetic and unique environmental factors, each of which plays an almost equally important role. The long-term stability of coffee consumption is affected mainly by a stable set of additive genetic factors.