Absence of reinforcing, mood and psychomotor performance effects of caffeine in habitual non-consumers of caffeine

"No thanks, it keeps me awake": the genetics of coffee-attributed sleep disturbance

STUDY OBJECTIVES

Previous genetic investigations of sleep disturbance have shown various measures of sleep quality and sleep pattern to be heritable. But none of these studies have investigated the genetic predisposition to sleep disturbance attributed to caffeine. In this study, the heritability of coffee-attributed sleep disturbance and its relationship with other sleep measures were estimated, and chromosomal regions influencing this trait were identified.

DESIGN

A classical twin design was used to estimate the heritability of coffee-attributed sleep disturbance and its genetic covariance with other measures of sleep disturbance (e.g., due to anxiety, depression) and sleep quality (e.g., variability in sleep quality). To locate quantitative trait loci influencing coffee-attributed sleep disturbance, a genome-wide linkage screen of 1395 microsatellite markers was performed.

PARTICIPANTS

The study included 3808 Australian adult twin pairs (n = 1799 monozygous pairs; n = 2009 dizygous pairs). A subsample of 1989 individuals from 1175 families was used for the linkage analysis.

MEASUREMENTS AND RESULTS

The heritability of coffee-attributed sleep disturbance (measured by self report) was approximately 0.40, with three fourths of this genetic variance explained by genes unrelated to the general sleep disturbance factor. One region of significant linkage to coffee-attributed sleep disturbance was identified on chromosome 2q (LOD score of 2.9).

CONCLUSIONS

Although no candidate genes known to be related to caffeine metabolism or sleep disorder were identified in the significant linkage region, 2 candidates were found under a smaller peak on chromosome 17q.

Differential responsiveness to caffeine and perceived effects of caffeine in moderate and high regular caffeine consumers

RATIONALE

Individual differences in responsiveness to caffeine occur even within a caffeine-consuming population, but the factors that mediate differential responsiveness remain unclear.

OBJECTIVES

To compare caffeine's effects on performance and mood in a group of high vs moderate consumers of caffeine and to examine the potential role of subjective awareness of the effects of caffeine in mediating any differential responsiveness.

MATERIALS AND METHODS

Two groups of regular caffeine consumers (<200 mg/day and >200 mg/day) attended two sessions at which mood and cognitive functions were measured before and 30 min after consumption of 400-mg caffeine or placebo in a capsule. Cognitive tests included visual information processing, match-to-sample visual search (MTS) and simple and choice reaction times. Post-session questionnaires asked participants to describe any perceived effect of capsule consumption.

RESULTS

High consumers, but not moderate consumers, demonstrated significantly faster simple and choice reaction times after caffeine relative to placebo. These effects were not attributable to obvious group differences in withdrawal or tolerance because there were no group differences in baseline mood or in reports of negative affect after caffeine. Instead, the high consumers were more likely to report experiencing positive effects of caffeine, whereas the moderate consumers were more likely to report no effect.

CONCLUSIONS

The sensitivity of caffeine consumers to the mood- and performance-enhancing effects of caffeine is related to their levels of habitual intake. High caffeine consumers are more likely than moderate consumers to perceive broadly positive effects of caffeine, and this may contribute to their levels of use.

A double-blind, placebo-controlled, multi-dose evaluation of the acute behavioural effects of guaraná in humans

The present study aimed to systematically assess acute, dose-related behavioural effects of an extract of guaraná plant for the first time in humans. This double-blind, counterbalanced, placebo-controlled study (n=26) assessed the acute mood and cognitive effects throughout the day of four different doses (37.5 mg, 75 mg, 150 mg and 300 mg) of a standardised guaraná extract (PC-102). Assessment included the Cognitive Drug Research computerized test battery and Bond-Lader mood scales. Guaraná improved secondary memory performance and increased alert and content mood ratings. The two lower doses produced more positive cognitive effects than the higher doses. This research supports previous findings of cognitive improvements following 75 mg guaraná and provides the first exploration of different dose effects of guaraná in humans. The findings suggest that the effects cannot be attributed to caffeine alone.

A combination of caffeine and taurine has no effect on short term memory but induces changes in heart rate and mean arterial blood pressure

Red Bull energy drink has become extraordinarily popular amongst college students for use as a study aid. We investigated the combined effects of Red Bull's two active ingredients, caffeine and taurine, on short term memory. Studies on the effects of these two neuromodulators on memory have yielded mixed results, and their combined actions have not yet been investigated. In this double-blind study, college student subjects consumed either caffeine and taurine pills or a placebo and then completed a memory assessment. Heart rate and blood pressure were monitored throughout the testing period. The combination of caffeine and taurine had no effect on short term memory, but did cause a significant decline in heart rate and an increase in mean arterial blood pressure. The heart rate decline may have been caused by pressure-induced bradycardia that was triggered by caffeine ingestion and perhaps enhanced by the actions of taurine.

Subjective, behavioral, and physiological effects of acute caffeine in light, nondependent caffeine users

RATIONALE

Caffeine produces mild psychostimulant effects that are thought to underlie its widespread use. However, the direct effects of caffeine are difficult to evaluate in regular users of caffeine because of tolerance and withdrawal. Indeed, some researchers hypothesize that the psychostimulant effects of caffeine are due largely to the reversal of withdrawal and question whether there are direct effects of caffeine consumption upon mood, alertness, or mental performance in nondependent individuals.

OBJECTIVE

This study investigated the physiological, subjective, and behavioral effects of 0, 50, 150, and 450 mg caffeine in 102 light, nondependent caffeine users.

METHODS

Using a within-subjects design, subjects participated in four experimental sessions, in which they received each of the four drug conditions in random order under double blind conditions. Participants completed subjective effects questionnaires and vital signs were measured before and at repeated time points after drug administration. Forty minutes after the capsules were ingested, subjects completed behavioral tasks that included tests of sustained attention, short-term memory, psychomotor performance, and behavioral inhibition.

RESULTS

Caffeine significantly increased blood pressure, and produced feelings of arousal, positive mood, and high. Caffeine increased the number of hits and decreased reaction times in a vigilance task, but impaired performance on a memory task.

CONCLUSION

We confirm that acute doses of caffeine, at levels typically found in a cup of coffee, produce stimulant-like subjective effects and enhance performance in light, nondependent caffeine users. These findings support the idea that the drug has psychoactive effects even in the absence of withdrawal.

Acute effects of caffeine in volunteers with different patterns of regular consumption

RATIONALE

The effects of caffeine on mood and performance are well established. One explanation of these effects is that caffeine removes negative effects induced by prior caffeine withdrawal. This was tested here by comparing effects of caffeine in withdrawn consumers and non-consumers (who by definition were not withdrawn).

OBJECTIVES

The present study aimed to determine whether caffeine withdrawal influenced mood and performance by comparing regular consumers who had been withdrawn from caffeine overnight with non-consumers. Following this the effects of acute caffeine challenges were compared in withdrawn consumers and non-consumers. In addition, comparisons were made between those with higher and lower caffeine consumption.

METHODS

One hundred seventy-six volunteers participated in the study. Regular caffeine consumption was assessed by questionnaire and this showed that 56 of the sample did not regularly consume caffeinated beverages. Volunteers were instructed to abstain from caffeine overnight and then completed a baseline session measuring mood and a range of cognitive functions at 08.00 the next day. Following this approximately half of the volunteers were given 1 mg/kg caffeine in a milkshake or water (in the 'no caffeine' condition they were given just the milkshake or water) and the test battery repeated one hour later. A second test battery was carried out at 12.00 and a second caffeine challenge at 13.00. A final test session was carried out at 15.00.

RESULTS

The baseline data revealed little evidence of effects of caffeine withdrawal on performance and mood. In contrast to this, caffeine produced a number of significant improvements in performance. There were some differences in the effects of caffeine on regular and non-consumers, with caffeine tending to reduce reaction time in regular consumers while the opposite was true for non-consumers.

CONCLUSIONS

The present results show little evidence of effects of caffeine withdrawal on performance. In contrast, caffeine challenge produced improvements in aspects of performance and these were often not modified by regular caffeine consumption patterns. The differences in effects of caffeine that were observed between non-consumers and regular consumers were in functions that were unaffected by caffeine withdrawal. These findings show that the observed beneficial effects of caffeine cannot be interpreted in terms of a reversal of caffeine withdrawal.

Psychostimulant and other effects of caffeine in 9- to 11-year-old children

BACKGROUND

Recent research on adults suggests that "beneficial" psychostimulant effects of caffeine are found only in the context of caffeine deprivation; that is, caffeine improves psychomotor and cognitive performance in habitual caffeine consumers following caffeine withdrawal. Furthermore, no net benefit is gained because performance is merely restored to "baseline" levels. The effects of caffeine in children is an under-researched area, with only a handful of studies being carried out in the US where children's consumption of caffeine appears to be lower on average than in the UK.

METHOD

Twenty-six children aged between 9 and 11 years completed a double-blind, placebo-controlled study. Habitual caffeine consumers (mean daily caffeine intake = 109 mg) and non/low-consumers (12 mg) were tested on two separate days following overnight caffeine abstinence. On each day measures of cognitive performance (a number search task), and self-rated mood and physical symptoms, including alertness and headache, were taken before and after administration of 50 mg of caffeine, or placebo.

RESULTS

At baseline (before treatment), the habitual consumers showed poorer performance on the cognitive test than did the non/low-consumers, although no significant differences in mood or physical symptoms were found between the two groups. There were significant habit by treatment (caffeine vs. placebo) interactions for accuracy of performance and headache, and a significant main effect of treatment for alertness. Post hoc comparisons showed that caffeine administration improved the consumers' accuracy on the cognitive test (to near the level displayed by the non/low-consumers at baseline), but that it had no significant effect on the non/low-consumers' performance. In the consumers, caffeine prevented an increase in headache that occurred after placebo, and it increased alertness relative to placebo. Again, however, caffeine did not significantly affect levels of headache or alertness in the non/low-consumers.

CONCLUSIONS

These results suggest that, like adults, children probably derive little or no benefit from habitual caffeine intake, although negative symptoms associated with overnight caffeine withdrawal are avoided or rapidly reversed by subsequent caffeine consumption.

Effects of caffeine on olfactory and visual learning in the honey bee (Apis mellifera)

Although caffeine is known to improve alertness and arousal in humans and other mammals, its impacts on specific behaviours, including complex cognitive processes, remain controversial. We reasoned that the availability of an easily manipulable, but behaviourally complex invertebrate organism with a simpler nervous system would be beneficial to this field of research. We used a popular behavioural model, the honeybee, to evaluate the effects of caffeine on (1) the development of olfactory learning and (2) the performance in complex learning paradigms, including a 'delayed-match-to-sample' task and visual associative learning. To evaluate the efficacy of caffeine treatment, a variety of doses (0.4-400 ng/1 mg of body mass) were applied topically to tethered individuals. Behavioural testing was performed with either tethered or free-flying adult honeybees. We show that caffeine has marked cognitive effects in this species. In young honeybees, it reduces the age at which restrained individuals are able to learn an olfactory associative task, whereas in older, free-flying bees, caffeine improves both motivation and cognitive performance in complex learning tasks. Our results suggest that the honeybee model may be useful in explaining caffeine-related behavioural changes not only in this species, but also in mammalian systems.

Effects of repeated doses of caffeine on mood and performance of alert and fatigued volunteers

Evidence for behavioural effects of caffeine is well documented in the literature. It is associated with increased subjective alertness, improved reaction time and enhanced encoding of new information. These effects are most prominent in low arousal situations. However, there is an ongoing debate as to whether such changes are in fact improvements or merely a reversal of the negative effects of a period of caffeine withdrawal (e.g. overnight abstinence). To avoid such a confound this study included multiple doses of caffeine which were administered under double-blind conditions to participants who had ingested their normal daily quota of caffeine. In the present study participants were fatigued by carrying out a prolonged testing schedule in the evening. Sixty volunteers, all regular caffeine consumers, took part in the study. They attended for three sessions on separate days. They were instructed to consume normal amounts of caffeinated beverages. Consumption was measured by a diary and saliva samples were taken and caffeine assays conducted. A baseline test session was carried out at 18.00h and following this a double blind placebo controlled caffeine challenge (1.5mg/kg) conducted. The test battery was repeated twice approximately 30 minutes after the caffeine challenge. Following this another drink was administered and the test battery repeated twice more. On one test session volunteers had placebo in both drinks, in another they had caffeine in both drinks and another caffeine in the first and placebo in the second. Order of conditions was balanced across subjects. The results showed that caffeine led to a more positive mood and improved performance on a number of tasks. Different effects of caffeine were seen depending on the person's level of arousal. Linear effects of caffeine dose were also observed. This is evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative effects of a long period of caffeine abstinence. The findings are discussed in relation to both noradrenergic and cholinergic neurotransmitter systems.

Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation

RATIONALE

Although it is widely believed that caffeine can enhance human performance and mood, the validity of this belief has been questioned, giving rise to debate. The central question is whether superior performance and mood after caffeine represent net benefits, or whether differences between caffeine and control conditions are due to reversal of adverse withdrawal effects.

OBJECTIVES

To provide a focussed review of relevant experimental studies with the aim of clarifying current understanding regarding the effects of caffeine on human performance and mood.

METHODS

To avoid the shortcomings of standard placebo-controlled studies, which are ambiguous due to failure to control for the confounding influence of withdrawal reversal, three main experimental approaches have been employed: studies that compare consumers and low/non-consumers, pre-treatment and ad lib consumption studies, and long-term withdrawal studies.

RESULTS

Of the three approaches, only long-term withdrawal studies are capable of unambiguously revealing the net effects of caffeine. Overall, there is little evidence of caffeine having beneficial effects on performance or mood under conditions of long-term caffeine use vs abstinence. Although modest acute effects may occur following initial use, tolerance to these effects appears to develop in the context of habitual use of the drug.

CONCLUSIONS

Appropriately controlled studies show that the effects of caffeine on performance and mood, widely perceived to be net beneficial psychostimulant effects, are almost wholly attributable to reversal of adverse withdrawal effects associated with short periods of abstinence from the drug.

The genetics of tea and coffee drinking and preference for source of caffeine in a large community sample of Australian twins

AIMS

To investigate the genetic and environmental influences on tea consumption and their commonalities with coffee consumption; and to further examine the genetic and environmental aetiology of preference for tea/coffee.

DESIGN

A classical twin design was used in which the similarity of identical and non-identical twins is compared, enabling estimates of genetic, common environmental and unique environmental influence on the trait.

SETTING AND PARTICIPANTS

An Australian population-based sample of 1796 identical (i.e. monozygotic) and 2013 non-identical (i.e. dizygotic) twin pairs aged 16-87 years was studied, roughly three-fifths of whom were female. The sample represented approximately 70% of those approached for study participation.

MEASUREMENTS

As part of a Health and Lifestyle Questionnaire, respondents were asked how many cups of each tea and coffee they consumed per day. Additional measures of 'total tea and coffee consumption' and 'preference for coffee' were calculated.

FINDINGS

Age was positively associated with tea consumption but negatively associated with coffee preference; women consumed more beverages than men, but showed a lower preference for coffee. An inverse relation between tea and coffee consumption--larger in females (-0.41) than males (-0.34)--was supported. This association was mediated entirely by the unique environment in males, and by both the unique environment (68.3%) and genes (31.7%) in females. Tea and coffee drinking were shown to have similar heritabilities (0.46) in males, but tea consumption was influenced by common environmental factors whereas coffee consumption was not. Coffee preference was shown to be influenced by genes (0.42) and the unique environment (0.58).

CONCLUSIONS

As the patterns of genetic and environmental variation were shown to differ for tea and coffee consumption it may be more informative to retain them as separate measures of caffeine intake in future studies of stimulant use and taste perception.

Attentional bias for caffeine-related stimuli in high but not moderate or non-caffeine consumers

RATIONALE

Attentional bias for drug-related cues has been reported with a wide range of drugs, but to date the extent to which caffeine consumers show similar biases for caffeine-related stimuli has not been tested. The present study therefore examined this issue in terms of differences in attentional bias for caffeine-related words in High, Moderate and Non-caffeine consumers using a dot-probe word task following overnight caffeine abstinence.

OBJECTIVES

This study was conducted to test whether caffeine consumers show an attentional bias for caffeine-related words, and whether such biases relate to habitual levels of caffeine use.

METHODS

Sixteen High, Moderate and Non-consumers of caffeine were asked to complete a modified dot-probe task in order to measure attentional bias for caffeine-related relative to neutral control word groups. The task was completed following overnight caffeine abstinence, and participants also completed mood and caffeine-craving measures.

RESULTS

The High consumer group showed a significant attentional bias for the caffeine-related words, but no such bias was seen in Moderate or Non-consumer groups. As expected, craving for caffeine was strongest in the High consumers and weakest in the Non-consumers. Attentional bias in the High group correlated with self-reported caffeine consumption and with craving for caffeine, but neither effect was significant in the Moderate group.

CONCLUSIONS

These data confirm that High caffeine consumers show attentional bias for caffeine-related stimuli, consistent with current theories of drug addiction.

Reinforcing effects of caffeine and theobromine as found in chocolate

RATIONALE

Although in a previous study we showed that caffeine and theobromine were the main psychopharmacologically active constituents in a 50-g bar of chocolate, mere activity does not guarantee a role in our liking for the food.

OBJECTIVES

Our aim was to see if liking for a drink repeatedly paired with these amounts of caffeine and theobromine would increase compared to a placebo-paired drink.

METHODS

Participants (n=64) consumed a 'novel' drink + treatment capsule on six non-consecutive mornings using a double-blind, placebo-controlled independent-sample design. Aspects of liking and intensity of various sensory descriptors for these drinks were measured at every drink collection. Treatment capsules contained either an ecologically relevant dose combination of 19-mg caffeine and 250-mg theobromine or a placebo.

RESULTS

Liking for the drink paired with the methylxanthine-containing capsules increased over time compared to the placebo-paired drink. This highly significant effect was confirmed by subjective, retrospective changes in liking for the drink.

CONCLUSIONS

Methylxanthines in amounts found in 50-g chocolate may well contribute to our liking for chocolate, especially to the more acquired taste for dark chocolate.

Dietary caffeine, performance and mood: enhancing and restorative effects after controlling for withdrawal reversal

This study aimed to determine whether sustained (i.e. dietary) use of caffeine has net effects on performance and mood compared with sustained abstinence, and whether dietary caffeine restores performance and mood adversely affected by sleep restriction. Participants (n = 96) alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for 4 consecutive weeks, while either rested or sleep restricted. Performance involved either a single task requiring sustained vigilance or a varied battery of brief psychomotor and cognitive tasks, and mood was assessed using the Profile of Mood States. Caffeine had no significant net enhancing effects for either performance or mood when participants were rested, and produced no net restorative effects when performance and mood were degraded by sleep restriction.

The effect of caffeine on cognitive task performance and motor fatigue

RATIONALE

In everyday life, people are usually capable of performing two tasks simultaneously. However, in a previous study we showed that during a fatiguing motor task, cognitive performance declined progressively. There is extensive literature on the (positive) effects of caffeine on cognitive and motor performance. These effects are most pronounced under suboptimal conditions, for example during fatigue. However, little is known about the effects of caffeine on cognitive performance during a fatiguing motor task.

OBJECTIVE

This study was aimed to investigate whether a moderate dose of caffeine could attenuate the decline in cognitive performance during a fatiguing motor task.

METHODS

The study consisted of a placebo and a caffeine (3 mg/kg) session. A total of 23 subjects completed these sessions in a semi-randomized and double-blind order. In each session, subjects performed maximal voluntary contractions of the index finger, a choice reaction time (CRT) task and a dual task consisting of a fatiguing motor task concomitantly with the same CRT task. After the fatiguing dual task, the CRT task was repeated.

RESULTS

Caffeine improved cognitive task performance, in both the single and dual task, as shown by decreased reaction times together with unchanged accuracy. Cognitive performance in the dual task deteriorated with increasing fatigue. However, the decrease in cognitive performance in the beginning of the dual task, as observed in the placebo condition, was partly prevented by caffeine administration (i.e., no increase in reaction times). We found no effects of caffeine on motor parameters (absolute force, endurance time or electromyographic amplitude).

CONCLUSIONS

Caffeine improved cognitive performance. This effect also extends under demanding situations, as was shown by the performance during the dual task, even during progressive motor fatigue.

Cognitive and mood improvements of caffeine in habitual consumers and habitual non-consumers of caffeine

RATIONALE

The cognitive and mood effects of caffeine are well documented. However, the majority of studies in this area involve caffeine-deprived, habitual caffeine users. It is therefore unclear whether any beneficial findings are due to the positive effects of caffeine or to the alleviation of caffeine withdrawal.

OBJECTIVES

The present placebo-controlled, double-blind, balanced crossover study investigated the acute cognitive and mood effects of caffeine in habitual users and habitual non-users of caffeine.

METHOD

Following overnight caffeine withdrawal, 24 habitual caffeine consumers (mean=217 mg/day) and 24 habitual non-consumers (20 mg/day) received a 150 ml drink containing either 75 or 150 mg of caffeine or a matching placebo, at intervals of > or =48 h. Cognitive and mood assessments were undertaken at baseline and 30 min post-drink. These included the Cognitive Drug Research computerised test battery, two serial subtraction tasks, a sentence verification task and subjective visual analogue mood scales.

RESULTS

There were no baseline differences between the groups' mood or performance. Following caffeine, there were significant improvements in simple reaction time, digit vigilance reaction time, numeric working memory reaction time and sentence verification accuracy, irrespective of group. Self-rated mental fatigue was reduced and ratings of alertness were significantly improved by caffeine independent of group. There were also group effects for rapid visual information processing false alarms and spatial memory accuracy with habitual consumers outperforming non-consumers. There was a single significant interaction of group and treatment effects on jittery ratings. Separate analyses of each groups' responses to caffeine revealed overlapping but differential responses to caffeine. Caffeine tended to benefit consumers' mood more while improving performance more in the non-consumers.

CONCLUSIONS

These results do not support a withdrawal alleviation model. Differences in the patterns of responses to caffeine by habitual consumers and habitual non-consumers may go some way to explaining why some individuals become caffeine consumers.

Effects of caffeine and caffeine withdrawal on mood and cognitive performance degraded by sleep restriction

RATIONALE

It has been suggested that caffeine is most likely to benefit mood and performance when alertness is low.

OBJECTIVES

To measure the effects of caffeine on psychomotor and cognitive performance, mood, blood pressure and heart rate in sleep-restricted participants. To do this in a group of participants who had also been previously deprived of caffeine for 3 weeks, thereby potentially removing the confounding effects of acute caffeine withdrawal.

METHODS

Participants were moderate to moderate-high caffeine consumers who were provided with either decaffeinated tea and/or coffee for 3 weeks (LTW) or regular tea and/or coffee for 3 weeks (overnight caffeine-withdrawn participants, ONW). Then, following overnight caffeine abstinence, they were tested on a battery of tasks assessing mood, cognitive performance, etc. before and after receiving caffeine (1.2 mg/kg) or on another day after receiving placebo.

RESULTS

Final analyses were based on 17 long-term caffeine-withdrawn participants (LTW) and 17 ONW participants whose salivary caffeine levels on each test day confirmed probable compliance with the instructions concerning restrictions on consumption of caffeine-containing drinks. Acute caffeine withdrawal (ONW) had a number of negative effects, including impairment of cognitive performance, increased headache, and reduced alertness and clear-headedness. Caffeine (versus placebo) did not significantly improve cognitive performance in LTW participants, although it prevented further deterioration of performance in ONW participants. Caffeine increased tapping speed (but tended to impair hand steadiness), increased blood pressure, and had some effects on mood in both groups.

CONCLUSIONS

The findings provide strong support for the withdrawal reversal hypothesis. In particular, cognitive performance was found to be affected adversely by acute caffeine withdrawal and, even in the context of alertness lowered by sleep restriction, cognitive performance was not improved by caffeine in the absence of these withdrawal effects. Different patterns of effects (or lack of effects) of caffeine and caffeine withdrawal were found for other variables, but overall these results also suggest that there is little benefit to be gained from caffeine consumption.

Cognitive and psychomotor performance, mood, and pressor effects of caffeine after 4, 6 and 8 h caffeine abstinence

RATIONALE

Many studies have found that caffeine consumed after overnight caffeine abstinence improves cognitive performance and mood. Much less is known, however, about the effects of caffeine after shorter periods of caffeine abstinence.

OBJECTIVES

The aim of this study was to measure the effects on psychomotor and cognitive performance, mood, hand steadiness, blood pressure and heart rate of caffeine administration after periods of 4, 6, and 8 h of caffeine abstinence.

METHODS

Participants (n = 49, 27 female) were moderate to moderate-high caffeine consumers (mean daily intake 370 mg/day). Following overnight caffeine abstinence, a 'pre-dose' of caffeine (1.2 mg/kg) was administered at 9 A.M, 11 A.M or 1 P.M. The participants started a baseline battery of measurements at 4 P.M.: before receiving caffeine (1.2 mg/kg) or placebo at 5 P.M.: They then performed the battery of tests again, starting at 5:30 P.M. This was a double-blind, placebo-controlled, randomised study.

RESULTS

Performance and mood measurements confirmed a psychostimulant action of caffeine (versus placebo), but only after 8 h of caffeine abstinence. Caffeine also increased blood pressure after 8-h abstinence, whereas hand steadiness was decreased and perception of task demand was increased by caffeine after 4 h, but not after 6- and 8-h abstinence.

CONCLUSIONS

A second cup-of-coffee equivalent dose of caffeine only reliably affected cognitive performance and mood after an 8-h interval between doses, but not after shorter intervals (when caffeine had some adverse effects). These results show that, apart from caffeine consumption soon after waking, the daily pattern of caffeine intake of many typical caffeine consumers is not well explained by the short-term psychostimulant effects of caffeine.

Effects of caffeine in non-withdrawn volunteers

RATIONALE

Evidence for the behavioural effects of caffeine is prevalent in the literature. It is associated with increased subjective alertness, improved reaction time and enhanced encoding of new information. However, there is an on-going debate as to whether such changes are in fact improvements or merely a reversal of the negative effects of caffeine withdrawal. Using participants who had consumed their normal daily quota of caffeine this study alleviated this potential confound as all participants were not withdrawn at the time of testing.

OBJECTIVES

To determine whether caffeine influenced the mood and performance of non-withdrawn volunteers.

METHODS

Sixty eight volunteers, all of whom were regular caffeine consumers, consumed their normal amount of caffeine over the course of the day. Baseline measures of mood and performance were then carried out followed by double-blind administration of caffeine (2 mg/kg) or placebo. The test battery was repeated again 30 min after ingestion of the drink.

RESULTS

Our findings showed improvements comparable to previous research. Mood was improved and performance on a number of cognitive measures was improved. The findings are discussed in relation to both noradrenergic and cholinergic neurotransmitter systems.

CONCLUSIONS

This study provided evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative withdrawal effects.

Methylxanthines are the psycho-pharmacologically active constituents of chocolate

RATIONALE

Liking, cravings and addiction for chocolate ("chocoholism") are often explained through the presence of pharmacologically active compounds. However, mere "presence" does not guarantee psycho-activity.

OBJECTIVES

Two double-blind, placebo-controlled studies measured the effects on cognitive performance and mood of the amounts of cocoa powder and methylxanthines found in a 50 g bar of dark chocolate.

METHODS

In study 1, participants ( n=20) completed a test battery once before and twice after treatment administration. Treatments included 11.6 g cocoa powder and a caffeine and theobromine combination (19 and 250 mg, respectively). Study 2 ( n=22) comprised three post-treatment test batteries and investigated the effects of "milk" and "dark" chocolate levels of these methylxanthines. The test battery consisted of a long duration simple reaction time task, a rapid visual information processing task, and a mood questionnaire.

RESULTS

Identical improvements on the mood construct "energetic arousal" and cognitive function were found for cocoa powder and the caffeine+theobromine combination versus placebo. In chocolate, both "milk chocolate" and "dark chocolate" methylxanthine doses improved cognitive function compared with "white chocolate". The effects of white chocolate did not differ significantly from those of water.

CONCLUSIONS

A normal portion of chocolate exhibits psychopharmacological activity. The identical profile of effects exerted by cocoa powder and its methylxanthine constituents shows this activity to be confined to the combination of caffeine and theobromine. Methylxanthines may contribute to the popularity of chocolate; however, other attributes are probably much more important in determining chocolate's special appeal and in explaining related self-reports of chocolate cravings and "chocoholism".

Cognitive and physiological effects of an "energy drink": an evaluation of the whole drink and of glucose, caffeine and herbal flavouring fractions

RATIONALE

Both glucose and caffeine can improve aspects of cognitive performance and, in the case of caffeine, mood. There are few studies investigating the effects of the two substances in combination.

OBJECTIVES

We assessed the mood, cognitive and physiological effects of a soft drink containing caffeine and glucose as well as flavouring levels of herbal extracts. The effects of different drink fractions were also evaluated.

METHODS

Using a randomised, double-blind, balanced, five-way crossover design, 20 participants who were overnight fasted and caffeine-deprived received 250 ml drinks containing 37.5 g glucose; 75 mg caffeine; ginseng and ginkgo biloba at flavouring levels; a whole drink (containing all these substances) or a placebo (vehicle). Participants were assessed in each drink condition, separated by a 7-day wash-out period. Cognitive, psychomotor and mood assessment took place immediately prior to the drink then 30 min thereafter. The primary outcome measures included five aspects of cognitive performance from the Cognitive Drug Research assessment battery. Mood, heart rate and blood glucose levels were also monitored.

RESULTS

Compared with placebo, the whole drink resulted in significantly improved performance on "secondary memory" and "speed of attention" factors. There were no other cognitive or mood effects.

CONCLUSIONS

This pattern of results would not be predicted from the effects of glucose and caffeine in isolation, either as seen here or from the literature addressing the effects of the substances in isolation. These data suggest that there is some degree of synergy between the cognition-modulating effects of glucose and caffeine which merits further investigation.

A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features

RATIONALE

Although reports of caffeine withdrawal in the medical literature date back more than 170 years, the most rigorous experimental investigations of the phenomenon have been conducted only recently.

OBJECTIVES

The purpose of this paper is to provide a comprehensive review and analysis of the literature regarding human caffeine withdrawal to empirically validate specific symptoms and signs, and to appraise important features of the syndrome.

METHODS

A literature search identified 57 experimental and 9 survey studies on caffeine withdrawal that met inclusion criteria. The methodological features of each study were examined to assess the validity of the effects.

RESULTS

Of 49 symptom categories identified, the following 10 fulfilled validity criteria: headache, fatigue, decreased energy/activeness, decreased alertness, drowsiness, decreased contentedness, depressed mood, difficulty concentrating, irritability, and foggy/not clearheaded. In addition, flu-like symptoms, nausea/vomiting, and muscle pain/stiffness were judged likely to represent valid symptom categories. In experimental studies, the incidence of headache was 50% and the incidence of clinically significant distress or functional impairment was 13%. Typically, onset of symptoms occurred 12-24 h after abstinence, with peak intensity at 20-51 h, and for a duration of 2-9 days. In general, the incidence or severity of symptoms increased with increases in daily dose; abstinence from doses as low as 100 mg/day produced symptoms. Research is reviewed indicating that expectancies are not a prime determinant of caffeine withdrawal and that avoidance of withdrawal symptoms plays a central role in habitual caffeine consumption.

CONCLUSIONS

The caffeine-withdrawal syndrome has been well characterized and there is sufficient empirical evidence to warrant inclusion of caffeine withdrawal as a disorder in the DSM and revision of diagnostic criteria in the ICD.