Effects of dietary caffeine on mood when rested and sleep restricted

Influence of Food Type on Human Psychological-Behavioral Responses and Crime Reduction

The purpose of this narrative review is to emphasize the importance of food consumption and meal selection on mental health and brain function, including psychological and behavioral reactions such as mood, loving relationships, violence, and criminal activity. Additionally, by being aware of the link between food and mental health, the community can be encouraged to make informed food choices in order to avoid unfavorable outcomes like criminality. Food behaviors are shifting significantly over the world. There are also significant changes in mood, sadness, happiness, and violence, as well as the spread of the variety and severity of mental diseases that lead to violent acts. Food intake and meal selection have evolved over the last ten years as the variety and accessibility of food options have become easier and more diverse. These modifications might have both beneficial and bad consequences. This article examines the relationship between food intake and its impact on marital satisfaction. The goal of this review is to support or refute the claim that food influences mood, love, or criminal behavior, or vice versa. Various diets can have an impact on one's mental health and brain, influencing psychological reactions and behavioral responses such as mood, loving relationships, violence, and even criminal activity. Food insecurity has been demonstrated in various studies to have a negative impact on health and psychological well-being, leading to despair, loss of happiness, marital conflict, and violence. For example, herbal extracts and flavonoids have the potential to improve gut microbiota and treat mood disorders. Understanding how the gut-brain axis communicates might help guide interventions for mood and cognitive function. Since the root of most diseases and behaviors is significantly related to the type of food consumed, this research addresses this issue in order to reduce the cost of treatment and prevention of crime and delinquency at the community level by consciously choosing the food consumed by the society. In other words, prevention is always better than cure.

Adenosine, caffeine, and sleep-wake regulation: state of the science and perspectives

For hundreds of years, mankind has been influencing its sleep and waking state through the adenosinergic system. For ~100 years now, systematic research has been performed, first started by testing the effects of different dosages of caffeine on sleep and waking behaviour. About 70 years ago, adenosine itself entered the picture as a possible ligand of the receptors where caffeine hooks on as an antagonist to reduce sleepiness. Since the scientific demonstration that this is indeed the case, progress has been fast. Today, adenosine is widely accepted as an endogenous sleep‐regulatory substance. In this review, we discuss the current state of the science in model organisms and humans on the working mechanisms of adenosine and caffeine on sleep. We critically investigate the evidence for a direct involvement in sleep homeostatic mechanisms and whether the effects of caffeine on sleep differ between acute intake and chronic consumption. In addition, we review the more recent evidence that adenosine levels may also influence the functioning of the circadian clock and address the question of whether sleep homeostasis and the circadian clock may interact through adenosinergic signalling. In the final section, we discuss the perspectives of possible clinical applications of the accumulated knowledge over the last century that may improve sleep‐related disorders. We conclude our review by highlighting some open questions that need to be answered, to better understand how adenosine and caffeine exactly regulate and influence sleep.

The effect of caffeine on tinnitus: Randomized triple-blind placebo-controlled clinical trial

Objective

To test the hypothesis that caffeine can influence tinnitus, we recruited 80 patients with chronic tinnitus and randomly allocated them into two groups (caffeine and placebo) to analyze the self-perception of tinnitus symptoms after caffeine consumption, assuming that this is an adequate sample for generalization.

Methods

The participants were randomized into two groups: one group was administered a 300-mg capsule of caffeine, and the other group was given a placebo capsule (cornstarch). A diet that restricted caffeine consumption for 24 hours was implemented. The participants answered questionnaires (the Tinnitus Handicap Inventory—THI, the Visual Analog Scale—VAS, the profile of mood state—POMS) and underwent examinations (tonal and high frequency audiometry, acufenometry (frequency measure; intensity measure and the minimum level of tinnitus masking), transient otoacoustic emissions—TEOAE and distortion product otoacoustic emissions—DPOAE assessments) at two timepoints: at baseline and after capsule ingestion.

Results

There was a significant change in mood (measured by the POMS) after caffeine consumption. The THI and VAS scores were improved at the second timepoint in both groups. The audiometry assessment showed a significant difference in some frequencies between baseline and follow-up measurements in both groups, but these differences were not clinically relevant. Similar findings were observed for the amplitude and signal-to-noise ratio in the TEOAE and DPOAE measurements.

Conclusions

Caffeine (300 mg) did not significantly alter the psychoacoustic measures, electroacoustic measures or the tinnitus-related degree of discomfort.

Total sleep deprivation reduces top-down regulation of emotion without altering bottom-up affective processing

Sleep loss is reported to influence affective processing, causing changes in overall mood and altering emotion regulation. These aspects of affective processing are seldom investigated together, making it difficult to determine whether total sleep deprivation has a global effect on how affective stimuli and emotions are processed, or whether specific components of affective processing are affected selectively. Sixty healthy adults were recruited for an in-laboratory study and, after a monitored night of sleep and laboratory acclimation, randomly assigned to either a total sleep deprivation condition (n = 40) or a rested control condition (n = 20). Measurements of mood, vigilant attention to affective stimuli, affective working memory, affective categorization, and emotion regulation were taken for both groups. With one exception, measures of interest were administered twice: once at baseline and again 24 hours later, after the sleep deprived group had spent a night awake (working memory was assessed only after total sleep deprivation). Sleep deprived individuals experienced an overall reduction in positive affect with no significant change in negative affect. Despite the substantial decline in positive affect, there was no evidence that processing affectively valenced information was biased under total sleep deprivation. Sleep deprived subjects did not rate affective stimuli differently from rested subjects, nor did they show sleep deprivation-specific effects of affect type on vigilant attention, working memory, and categorization tasks. However, sleep deprived subjects showed less effective regulation of negative emotion. Overall, we found no evidence that total sleep deprivation biased the processing of affective stimuli in general. By contrast, total sleep deprivation appeared to reduce controlled processing required for emotion regulation.

Food and Mood: the Corresponsive Effect

PURPOSE OF REVIEW

The question whether food choice and eating behavior influence the mood or are influenced by the mood has been inquisitive to scientists and researchers. The purpose of this review is to support or refuse the argument that mood is affected by food or vice versa.

RECENT FINDINGS

The association between food and mood has been comprehensively elucidated in this review based on several studies that include participants from different ages, cultural backgrounds, and health status. The correlation among food, mood, and diseases such as diabetes mellitus, obesity, and depression was thoroughly investigated. The effect of different foods and nutrients on the mood was further explained. It is concluded that the mood significantly affects food intake and food choices. On the other hand, food also influences the mood, which affects the diseases either positively or negatively. Appropriate food choices play a significant role in mood enhancement. Advertisement is another crucial factor that negatively affects food choices and mood and contributes to many diseases. Understanding the interaction between food and mood can help to prevent or alleviate undesired health issues.

The acute effects of decaffeinated versus caffeinated coffee on reaction time, mood and skeletal muscle strength

Background Caffeinated coffee, a psycho-stimulant, is widely consumed throughout the globe. However, its chronic consumption has deleterious effects on human health. Meanwhile, decaffeinated coffee has low content of caffeine and thus can be an alternative to caffeinated coffee. Therefore, the study was undertaken to explore and compare the acute effects of decaffeinated and caffeinated coffee on reaction time, mood and skeletal muscle strength in healthy volunteers. Methods This was a prospective, interventional, comparative type of study. The study included 70 healthy adults divided into two groups (Caffeinated coffee group and Decaffeinated coffee group). The following parameters were assessed: reaction time was assessed by digital display multiple-choice apparatus, mood by Visual Analogue Scale (VAS) and Profile of Mood States revised version (POMS) and skeletal muscle strength by hand dynamometer. All parameters in both groups were assessed pre-intervention (baseline) and 30 min post-intervention. Results In both groups (decaffeinated and caffeinated coffee) post-intervention, there was a statistically significant (p < 0.05) improvement in the reaction time (VRT) and mood (VAS, POMS) from the baseline. However, both groups did not show any significant effects on the skeletal muscle strength. Upon comparing the two groups, we found that caffeinated coffee showed higher and significant improvement of mood than decaffeinated coffee. Conclusions Decaffeinated coffee exerts an acute significant stimulatory effect on the reaction time and mood. However, these effects in comparison to caffeinated coffee are low. Further randomized control clinical trials are thus needed to validate these interesting findings.

Potentially addictive properties of sugar-sweetened beverages among adolescents

Sugar-sweetened beverages (SSBs) increase risk of cardiometabolic disease. Young people consume the largest amounts of SSBs and have experienced the greatest relative gains in obesity in the past several decades. There is evidence of addictive properties of both caffeine and sugar, the primary ingredients in SSBs, but little research into such properties of SSBs in naturally occurring consumption patterns. Thus, in this exploratory study, we sought to examine potentially addictive properties of SSBs during a 3-day SSB cessation intervention in overweight and obese adolescents who typically consume ≥3 SSBs daily. Participants (n = 25) were aged 13-18 years, mostly female (72%), and African American (56%) or Hispanic (16%) with a BMI≥95th percenttile (76%). Withdrawal symptoms and SSB craving were assessed approximately 1-week apart, during both regular SSB consumption and a 3-day period of SSB cessation in which participants were instructed to drink only plain milk and water. During SSB cessation, adolescents reported increased SSB cravings and headache and decreased motivation, contentment, ability to concentrate, and overall well-being (uncorrected Ps < 0.05). After controlling the false discovery rate, changes in motivation, craving, and well-being remained significant (corrected Ps < 0.05). Using 24-hr recalls and drink journals, participants reported lower total daily consumption of sugar (-80 g) and added sugar (-16 g) (Ps < 0.001) during cessation. This study provides preliminary evidence of withdrawal symptoms and increased SSB cravings during cessation in a diverse population of overweight or obese adolescents.

Caffeine alters emotion and emotional responses in low habitual caffeine consumers

Caffeine reliably increases emotional arousal, but it is unclear whether and how it influences other dimensions of emotion such as emotional valence. These experiments documented whether caffeine influences emotion and emotion regulation choice and success. Low to abstinent caffeine consumers (maximum 100 mg/day) completed measures of state anxiety, positive and negative emotion, and salivary cortisol before, 45 min after, and 75 min after consuming 400 mg caffeine or placebo. Participants also completed an emotion regulation choice task, in which they chose to employ cognitive reappraisal or distraction in response to high and low intensity negative pictures (Experiment 1), or a cognitive reappraisal task, in which they employed cognitive reappraisal or no emotion regulation strategy in response to negative and neutral pictures (Experiment 2). State anxiety, negative emotion, and salivary cortisol were heightened both 45 and 75 min after caffeine intake relative to placebo. In Experiment 1, caffeine did not influence the frequency with which participants chose reappraisal or distraction, but reduced negativity of the picture ratings. In Experiment 2, caffeine did not influence cognitive reappraisal success. Thus, caffeine mitigated emotional responses to negative situations, but not how participants chose to regulate such responses or the success with which they did so.

Emotion, emotion regulation and sleep: An intimate relationship

In recent years, research has witnessed an increasing interest in the bidirectional relationship between emotion and sleep. Sleep seems important for restoring daily functioning, whereas deprivation of sleep makes us more emotionally aroused and sensitive to stressful stimuli and events. Sleep appears to be essential to our ability to cope with emotional stress in everyday life. However, when daily stress is insufficiently regulated, it may result in mental health problems and sleep disturbances too. Not only does emotion impact sleep, but there is also evidence that sleep plays a key role in regulating emotion. Emotional events during waking hours affect sleep, and the quality and amount of sleep influences the way we react to these events impacting our general well-being. Although we know that daytime emotional stress affects sleep by influencing sleep physiology, dream patterns, dream content and the emotion within a dream, its exact role is still unclear. Other effects that have been found are the exaggeration of the startle response, decrease in dream recall and elevation of awakening thresholds from rapid eye movement (REM), REM-sleep, increased or decreased latency to REM-sleep, increase in percentage of REM-density, REM-sleep duration, as well as the occurrence of arousals in sleep as a marker of sleep disruption. Equally, the way an individual copes with emotional stress, or the way in which an individual regulates emotion may modulate the effects of emotional stress on sleep. The research presented here supports the idea that adaptive emotion regulation benefits our follow-up sleep. We thus conclude the current review with a call for future research in order to clarify further the precise relationship between sleep, emotion and emotion regulation, as well as to explain further how sleep dissolves our emotional stress.

Caffeine and theanine exert opposite effects on attention under emotional arousal

Tea is perceived as more relaxing than coffee, even though both contain caffeine. L-theanine in tea may account for the difference. Consumed together, caffeine and theanine exert similar cognitive effects to that of caffeine alone, but exert opposite effects on arousal, in that caffeine accentuates and theanine mitigates physiological and felt stress responses. We evaluated whether caffeine and theanine influenced cognition under emotional arousal. Using a double-blind, repeated-measures design, 36 participants received 4 treatments (200 mg caffeine + 0 mg theanine, 0 mg caffeine + 200 mg theanine, 200 mg caffeine + 200 mg theanine, 0 mg caffeine + 0 mg theanine) on separate days. Emotional arousal was induced by highly arousing negative film clips and pictures. Mood, salivary cortisol, and visual attention were evaluated. Caffeine accentuated global processing of visual attention on the hierarchical shape task (p < 0.05), theanine accentuated local processing (p < 0.05), and the combination did not differ from placebo. Caffeine reduced flanker conflict difference scores on the Attention Network Test (p < 0.05), theanine increased difference scores (p < 0.05), and the combination did not differ from placebo. Thus, under emotional arousal, caffeine and theanine exert opposite effects on certain attentional processes, but when consumed together, they counteract the effects of each other.

Salivary α-Amylase Reactivity to Laboratory Social Stress With and Without Acute Sleep Restriction

A growing literature suggests that salivary α-amylase (sAA) may serve as a minimally invasive marker of psychophysiological stress-induced activity of the sympathetic-adrenal-medullary system (SAM). Previous inconsistencies in the experimental literature relating sAA response to short sleep duration may be as a result of poor reliability of self-reported sleep time, suggesting that further examination of sAA response following verified sleep loss is required. With regard to the potential usefulness of sAA as a biomarker of psychosocial stress in the laboratory, previous research has also relied primarily on traditional psychosocial stress protocols, including physically present evaluative observers. The present study aimed to examine sAA response following a period of verified acute sleep restriction compared to a rested condition, in addition to examining the sensitivity of sAA response to a laboratory stress protocol that exposed participants to negative social evaluation presented by video relay. One hundred and eight healthy young adults (age 17–22 years; M = 18.39 years, SD = 0.87) completed a laboratory social stress task and provided saliva samples pre- and post-stressor presentation, after a night of partial sleep restriction or a full night’s rest. Marked increases in sAA activity to the video-relayed stressor were observed in both rested and sleep restricted groups. Further, sleep restricted participants exhibited significantly increased basal levels of sAA activity. The data corroborate previous limited data indicating a general upregulation of sAA activity following poor sleep and support previous findings concerning the efficacy of an experimental paradigm that presents laboratory social stress by means of video recording.

How to measure mood in nutrition research

Mood is widely assessed in nutrition research, usually with rating scales. A core assumption is that positive mood reinforces ingestion, so it is important to measure mood well. Four relevant theoretical issues are reviewed: (i) the distinction between protracted and transient mood; (ii) the distinction between mood and emotion; (iii) the phenomenology of mood as an unstable tint to consciousness rather than a distinct state of consciousness; (iv) moods can be caused by social and cognitive processes as well as physiological ones. Consequently, mood is difficult to measure and mood rating is easily influenced by non-nutritive aspects of feeding, the psychological, social and physical environment where feeding occurs, and the nature of the rating system employed. Some of the difficulties are illustrated by reviewing experiments looking at the impact of food on mood. The mood-rating systems in common use in nutrition research are then reviewed, the requirements of a better mood-rating system are described, and guidelines are provided for a considered choice of mood-rating system including that assessment should: have two main dimensions; be brief; balance simplicity and comprehensiveness; be easy to use repeatedly. Also mood should be assessed only under conditions where cognitive biases have been considered and controlled.

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.

Subjective State, Blood Pressure, and Behavioral Control Changes Produced by an "Energy Shot"

Background: Energy drinks and energy shots are popular consumer beverages that are advertised to increase feelings of alertness. Typically, these products include high levels of caffeine, a mild psychostimulant drug. The scientific evidence demonstrating the specific benefits of energy products to users in terms of subjective state and objective performance is surprisingly lacking. Moreover, there are rising health concerns associated with the use of these products. Therefore, the purpose of this study was to investigate the acute effects of a popular energy shot (5-Hour Energy^®) on subjective and objective measures that were assessed hourly for 6 hours following consumption. Methods: Participants (n=14) completed a three-session study where they received the energy shot, a placebo control, and no drink. Following dose administration, participants completed subjective Profile of Mood States ratings hourly for 6 hours. Participants also repeatedly completed a behavioral control task (the cued go/no-go task) and provided blood pressure and pulse rate readings at each hour. Results: Consumption of the energy shot did improve subjective state, as measured by increased ratings of vigor and decreased ratings of fatigue. However, the energy shot did not alter objective performance, which worsened over time. Importantly, the energy shot elevated both systolic and diastolic blood pressure. Conclusions: Consumption of one energy shot may only result in modest benefits to subjective state. Individuals with preexisting hypertension or other medical conditions should be cautious about using these new consumer products.

The effects of energy drink in combination with alcohol on performance and subjective awareness

RATIONALE

This study investigated the coadministration of an energy drink with alcohol to study the effects on subjective intoxication and objective performance.

OBJECTIVES

This study aims to evaluate the objective and subjective effects of alcohol versus placebo at two alcohol doses, alone and in combination with an energy drink, in a balanced order, placebo-controlled, double-blind design.

METHODS

Two groups of ten healthy volunteers, mean (SD) age of 24 (6.5), participated in the study. One group consumed energy drink containing 80 mg of caffeine and the other consumed a placebo drink, with both receiving two alcohol doses (0.046 and 0.087% breathalyser alcohol concentration). Tests included breath alcohol assessment, objective measures of performance (reaction time, word memory and Stroop task) and subjective visual analogue mood scales.

RESULTS

Participants showed significantly impaired reaction time and memory after alcohol compared to the no alcohol condition and had poorer memory after the higher alcohol dose. Stroop performance was improved with the energy drink plus alcohol combination compared to the placebo drink plus alcohol combination. Participants felt significant subjective dose-related impairment after alcohol compared to no alcohol. Neither breath alcohol concentration nor the subjective measures showed a significant difference between the energy drink and the placebo energy drink when combined with alcohol.

CONCLUSIONS

Subjective effects reflected awareness of alcohol intoxication and sensitivity to increasing alcohol dose. There were no overall significant group differences for subjective measures between energy drink and placebo groups in the presence of alcohol and no evidence that the energy drink masked the subjective effects of alcohol at either dose.

Effects of Alcohol, Coffee, and Tobacco, Alone or in Combination, on Physiological Parameters and Anxiety in a Young Population

OBJECTIVE

The objective was to evaluate the effects of a single dose of alcohol, caffeine, and nicotine, alone or in combination, on physiological parameters (systolic and diastolic blood pressure [SBP and DBP] and heart rate [HR]) and state-trait anxiety in healthy young volunteers.

METHOD

The procedure reproduces the conditions under which the subjects (n=76) usually ingest alcohol (through an alcoholic beverage), caffeine (through a cup of coffee), and nicotine (by smoking a cigarette), separately or in combination, according to their consumption habits of each individual. SBP and DBP, HR, and state anxiety (SA) were registered before (phase 1) and after (phase 2) treatment.

RESULTS

Intake of alcohol or alcohol-nicotine reduced DBP. Comparisons between control and combined treatment (coffee-alcohol-nicotine) groups revealed a decrease in HR in the former group but not in the latter. The coffee consumers alone exhibited a tendency toward an increase in SA, while the control group showed a tendency toward a decrease in this measure. When Phase 1 and Phase 2 were compared, a decrease was observed in SBP (alcohol and coffee-alcohol groups), DBP (alcohol and alcohol-nicotine groups), HR (all groups, except coffee-alcohol and coffee-alcohol-nicotine groups), and SA (coffee-alcohol-nicotine group).

CONCLUSIONS

(i) A low dose of alcohol, either alone or in combination with a cigarette, decreases DBP but not SBP; (ii) the polyconsumption of coffee, alcohol, and nicotine blocks the adaptation response (the reduction in HR in control subjects in the second phase); (iii) an increase of SA is observed after consuming coffee, while the opposite occurs in control subjects (a decrease of SA).

Effects of dietary caffeine on EEG, performance and mood when rested and sleep restricted

RATIONALE

Until recently, little account had been taken of the confounding effects of caffeine withdrawal and withdrawal reversal when examining the net effects of dietary caffeine.

OBJECTIVES

By including a manipulation involving sleep restriction, the present study aimed to extend recent findings from research in which caffeine withdrawal and withdrawal reversal were controlled. The main aims of the study were to examine the net effects of caffeine, as well as its potential restorative effects following sleep restriction, on EEG, performance and mood.

METHOD

A randomised cross-over design was used in which 15 participants alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) three times daily for four consecutive weeks following either usual sleep or sleep restriction. EEG activity was measured at 32 sites during eyes closed, eyes open and performance of a vigilance task.

RESULTS

Modest effects of caffeine were found in the delta and beta bandwidths, but no main effects of caffeine were observed in the theta or alpha bandwidths. Overall, the effects of caffeine on EEG activity were relatively few, weak and inconsistent, and no evidence was found of net restorative effects of caffeine for any outcome variables.

CONCLUSIONS

The findings do not support the use of caffeine as a means for enhancing human function or as an antidote to the negative effects of sleep loss.

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.

Effects of dietary caffeine on topographic EEG after controlling for withdrawal and withdrawal reversal

BACKGROUND/AIMS

Despite several decades of research into the effects of caffeine on EEG, few consistent findings have emerged. Notwithstanding the likelihood that differences in methodology may explain some of the inconsistency, confidence in the published findings is undermined by the failure in previous studies to control for the effects of caffeine withdrawal and withdrawal reversal.

METHODS

Participants (n = 22) alternated weekly between ingesting placebo and caffeine (1.75 mg/kg) 3 times daily for 4 consecutive weeks. EEG activity was measured at 32 sites during eyes closed, eyes open, and performance of a vigilance task.

RESULTS

Caffeine was found to have few and modest effects on EEG in the theta and alpha bandwidths, and no effects in the delta and beta bandwidths. Evidence was found of withdrawal, withdrawal reversal, and tolerance in relation to observed increases in theta power during task performance; withdrawal and withdrawal reversal in relation to increases in alpha power during all three behavioural conditions (eyes closed, eyes open, and task performance), and withdrawal-induced adverse effects in relation to aspects of subjective mood.

CONCLUSION

The finding of similar increases in theta power following caffeine challenge and acute caffeine withdrawal casts doubt on whether caffeine may be viewed as having direct stimulant effects. Results could suggest that change in drug state, whether in the form of acute caffeine withdrawal or challenge, may be disruptive to electrophysiological activity in the brain.

"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.

Caffeine, sleep and wakefulness: implications of new understanding about withdrawal reversal

The broad aim of this review is to critically examine the implications of new understanding concerning caffeine withdrawal and withdrawal reversal in the context of research concerned with the effects of caffeine on sleep and wakefulness. A comprehensive search was conducted for relevant experimental studies in the PubMED and PsycINFO databases. Studies were assessed with particular reference to methodological adequacy for controlling against confounding due to caffeine withdrawal and withdrawal reversal. This assessment was used to clarify evidence of effects, highlight areas of ambiguity and derive recommendations for future research. It was found that researchers have generally failed to take account of the fact that habitual use of caffeine, even at moderate levels, leads to physical dependence evidenced by physiological, behavioural and subjective withdrawal effects during periods of abstinence. Consequently, there has been near-complete absence of adequate methodological controls against confounding due to reversal of withdrawal effects when caffeine is experimentally administered. The findings of what has been a substantial research effort to elucidate the effects of caffeine on sleep and wakefulness, undertaken over a period spanning decades, are ambiguous. Current shortcomings can be redressed by incorporating suitable controls in new experimental designs.

The effects of sleep deprivation on symptoms of psychopathology in healthy adults

BACKGROUND

Sleep loss leads to temporary changes in mood and cognition, and is associated with reduced cerebral metabolism within the prefrontal cortex, similar to findings observed in some psychiatric disorders. However, the extent to which sleep deprivation may be associated with the emergence of clinical symptoms of psychopathology in healthy normal individuals is not clear.

METHODS

The Personality Assessment Inventory (PAI) was administered to 25 healthy adults at rested baseline and again after 56h of continuous wakefulness.

RESULTS

Comparisons showed a significant global increase in PAI psychopathology scores from baseline to sleep-deprived sessions, particularly for somatic complaints, anxiety, depression, and paranoia. Mean elevations for the clinical scales remained within normal limits, however. In contrast, sleep loss was not associated with significant changes in anxiety-related disorders, manic symptoms, borderline, schizophrenic, or antisocial features.

CONCLUSIONS

Two nights without sleep may lead to a sub-clinical increase in self-reported affective symptoms of psychopathology while having little effect on symptoms of thought disorder, psychotic processes, or behavioral dysregulation. These data suggest that sleep loss may be differentially disruptive to regions of the brain involved in affective regulation and may, therefore, serve as a model for understanding the brain dysfunction associated with affective psychopathology.

Impaired decision making following 49 h of sleep deprivation

Sleep deprivation reduces regional cerebral metabolism within the prefrontal cortex, the brain region most responsible for higher-order cognitive processes, including judgment and decision making. Accordingly, we hypothesized that two nights of sleep loss would impair decision making quality and lead to increased risk-taking behavior on the Iowa Gambling Task (IGT), which mimics real-world decision making under conditions of uncertainty. Thirty-four healthy participants completed the IGT at rested baseline and again following 49.5 h of sleep deprivation. At baseline, volunteers performed in a manner similar to that seen in most samples of healthy normal individuals, rapidly learning to avoid high-risk decks and selecting more frequently from advantageous low-risk decks as the game progressed. After sleep loss, however, volunteers showed a strikingly different pattern of performance. Relative to rested baseline, sleep-deprived individuals tended to choose more frequently from risky decks as the game progressed, a pattern similar to, though less severe than, previously published reports of patients with lesions to the ventromedial prefrontal cortex. Although risky decision making was not related to participant age when tested at rested baseline, age was negatively correlated with advantageous decision making on the IGT, when tested following sleep deprivation (i.e. older subjects made more risky choices). These findings suggest that cognitive functions known to be mediated by the ventromedial prefrontal cortex, including decision making under conditions of uncertainty, may be particularly vulnerable to sleep loss and that this vulnerability may become more pronounced with increased age.

Random number generation during sleep deprivation: effects of caffeine on response maintenance and stereotypy

Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. Previous neuropsychological studies indicate that sleep deprivation causes impairments in prefrontal cortical function. Random number generation (RNG) is thought to provide a sensitive index of executive functions that rely on the prefrontal cortex. The present study tested the hypothesis that sleep deprivation would impair RNG and that caffeine would mitigate this impairment. Healthy young men (n = 21) participated in two 40-h sleep deprivations 1 week apart. During each sleep deprivation period subjects received either caffeine or placebo according to a randomized, double-blind cross-over design, and they completed an oral RNG task at 3-h intervals. Comparison of test sessions at analogous times of day revealed that sleep deprivation was associated with significant drops in the number of responses, a threefold increase in the percentage of rule violations, 59% greater response redundancy and a 20% increase in stereotypy of adjacent response pairs. Sleep deprivation did not consistently alter counting tendency. Caffeine ameliorated the decrease in the number of responses but did not mitigate other deficits in RNG that arose during sleep deprivation. These findings are consistent with prior reports of diminished vigilance and increased perseveration during extended wakefulness. They support the conclusion that caffeine preserves simple aspects of cognitive performance during sleep deprivation, whereas caffeine may not prevent detrimental effects of sleep deprivation on some complex cognitive functions.

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.

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.