Overnight caffeine abstinence and negative reinforcement of preference for caffeine-containing drinks

Valuing the Diversity of Research Methods to Advance Nutrition Science

The ASN Board of Directors appointed the Nutrition Research Task Force to develop a report on scientific methods used in nutrition science to advance discovery, interpretation, and application of knowledge in the field. The genesis of this report was growing concern about the tone of discourse among nutrition professionals and the implications of acrimony on the productive study and translation of nutrition science. Too often, honest differences of opinion are cast as conflicts instead of areas of needed collaboration. Recognition of the value (and limitations) of contributions from well-executed nutrition science derived from the various approaches used in the discipline, as well as appreciation of how their layering will yield the strongest evidence base, will provide a basis for greater productivity and impact. Greater collaborative efforts within the field of nutrition science will require an understanding that each method or approach has a place and function that should be valued and used together to create the nutrition evidence base. Precision nutrition was identified as an important emerging nutrition topic by the preponderance of task force members, and this theme was adopted for the report because it lent itself to integration of many approaches in nutrition science. Although the primary audience for this report is nutrition researchers and other nutrition professionals, a secondary aim is to develop a document useful for the various audiences that translate nutrition research, including journalists, clinicians, and policymakers. The intent is to promote accurate, transparent, verifiable evidence-based communication about nutrition science. This will facilitate reasoned interpretation and application of emerging findings and, thereby, improve understanding and trust in nutrition science and appropriate characterization, development, and adoption of recommendations.

Varied Effects of COVID-19 Chemosensory Loss and Distortion on Appetite: Implications for Understanding Motives for Eating and Drinking

A common symptom of COVID-19 is altered smell and taste. This qualitative study sought to further characterise this altered chemosensory perception and its effects on appetite for food and drink. Eighteen women and two men who had experienced chemosensory loss associated with COVID-19 participated in semi-structured interviews. Thematic analysis of the interview transcripts revealed five major themes. These confirmed that all participants had experienced an altered sense of smell (anosmia, and less frequently parosmia and phantosmia) of variable duration. Loss of taste (ability to detect sweetness, saltiness, etc.) was less common. Participants experienced decreased, no change or increased appetite, with six participants reporting weight loss. Consistent with evidence linking diminished appetite with inflammation, for two participants, decreased appetite preceded anosmia onset. Anosmia reduced enjoyment of food and drink. Compensatory strategies included choosing salty, sweet and ‘spicy’ foods, and increased attention to food texture, and there was evidence that the postingestive rewarding effects of food intake were also important for maintaining appetite. Some participants mentioned increased alcohol intake, in part facilitated by reduced intensity of disliked flavours of alcoholic drinks. The narratives also underlined the value placed on the sociability and structuring of time that daily meals provide. This research adds to the record and analysis of lived experiences of altered chemosensory perception resulting from SARS-CoV-2 infection, and it contributes insights concerning the role of smell and flavour in motivating and rewarding food ingestion.

Caffeine-Induced Severe Erosive Esophagitis

Caffeine is one of the most frequently used stimulants worldwide. It is, therefore, subject to frequent intentional and unintentional misuse. However, severe erosive esophagitis due to acute caffeine overdose is extremely rare. We report the case of a 43-year-old male with a past medical history of paranoid schizophrenia admitted to our hospital with esophageal symptoms (throat pain, retrosternal chest pain, dysphagia/odynophagia, nausea, and vomiting) two days after ingesting a bottle of caffeine pills containing about 30 g of caffeine in a suicide attempt. He was found to have rhabdomyolysis and acute renal failure warranting hemodialysis. Esophagogastroduodenoscopy done due to persistent retrosternal chest pain, dysphagia, odynophagia, and nausea despite being on oral famotidine 20 mg daily revealed severe erosive esophagitis. This case highlights the risk of concurrent renal and gastrointestinal injuries after acute ingestion of an excessive amount of caffeine tablets. Our experience suggests that in patients of caffeine overdose with persistent esophageal symptoms such as odynophagia, dysphagia, and retrosternal chest pain, endoscopic evaluation is advisable to rule out drug-induced esophagitis.

Caffeine Overdose Complicated by Acute Kidney Injury despite Mild Creatine Kinase Elevation

Caffeine is a commonly used stimulant in our society. Prior case reports have described acute caffeine overdose resulting in rhabdomyolysis and acute kidney injury (AKI). We present the case of a 29-year-old man who presented to the emergency department after ingesting 20.1 g of caffeine in a suicide attempt and experienced AKI with only mildly elevated creatine kinase (CK). This case highlights the possibility that AKI can result from a caffeine overdose, even if the patient’s CK is only slightly elevated.

Motivations Influencing Caffeine Consumption Behaviors among College Students in Korea: Associations with Sleep Quality

Caffeinated beverages are a part of daily life. Caffeinated beverages such as coffee, tea, energy drinks, and soft drinks are easy to purchase and are frequently consumed by young college students. Moreover, smoking influences the consumption of caffeinated beverages. The concentration of caffeine in these products is an attractive factor for individuals that desire the effects of caffeine; however, abusing such products may lead to poor sleep quality. The motivations that drive caffeinated beverage consumption were investigated in this study through a survey. Self-reported questionnaires were distributed on campus to students enrolled at a university in Korea. The motivations of the students for consuming each caffeinated beverage and their sleep quality were investigated. The results of exploratory factor analysis showed the motivations for caffeinated beverage consumption were alertness, taste, mood, socialization, health benefits, and habit. The motivations for consuming each caffeinated beverage product were different. For instance, coffee consumption was motivated by a desire for alertness (B = .107, SE = .049, t = 2.181, p < 0.05) and by habit (B = .345, SE = .046, t = 7.428, p < 0.001), whereas tea consumption was influenced by socialization (B = .142, SE = .060, t = 2.357, p < 0.05). Energy drink consumption was motivated by a desire for alertness (B = .100, SE = .034, t = 2.966, p < 0.01) and health benefits (B = .120, SE = .051, t = 2.345, p < 0.05), while the consumption of soft drinks was not motivated by any specific factors. Caffeinated beverage consumption did not show a significant relationship with sleep quality, although the general sleep quality of the respondents was poor. Smoking status showed significant differences in coffee and tea consumption as well as sleep quality. Smokers had a higher intake of coffee and a lower intake of tea than non-smokers. No interaction effect between smoking and coffee on sleep quality was found. Labeling detailing the amount of caffeine in products is necessary and a cautionary statement informing consumers that smoking cigarettes enhances the effects of caffeine should be included.

Urinary glucose and ketone bodies as indicators of acute caffeine poisoning

AIM

In various countries, many fatal health problems have been reported due to high intake of caffeine-rich energy drinks, tablets, and powders. In patients with acute caffeine poisoning, determination of blood caffeine concentration is an important yet difficult task. We aimed to assess whether the presence of glucose and ketone bodies in urine reflected the blood caffeine concentration in patients with acute caffeine poisoning.

METHODS

From April 2010 to March 2018, 25 patients with an overdose of only caffeine-rich tablets were admitted to our hospital. Their clinical features were investigated. In addition, we investigated whether the glucose and ketone bodies in the urine reflected blood caffeine concentration in 23 patients who underwent the urine qualitative test at admission.

RESULTS

The majority of the patients were young healthy women, whose average caffeine ingestion was 15.6 ± 8.1 g. Initial urine examinations showed glucose in 60% (14/23) of patients and ketone bodies in 57% (13/23) of patients. Ketone bodies or glucose were found in 78% (18/23) of the patients. The correlation between blood caffeine concentration and urinary glucose was R = 0.625, blood caffeine concentration and ketone bodies was R = 0.596, and blood caffeine and both was R = 0.76.

CONCLUSION

Urine qualitative test is effective for differential diagnosis and severity assessment of acute caffeine poisoning in patients.

Craving espresso: the dialetics in classifying caffeine as an abuse drug

Caffeine is the most consumed psychoactive substance in the world; in general, it is not associated to potentially harmful effects. Nevertheless, few studies were performed attempting to investigate the caffeine addiction. The present review was mainly aimed to answer the following question: is caffeine an abuse drug? To adress this point, the effects of caffeine in preclinical and clinical studies were summarized and critically analyzed taking account the abuse disorders described in the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). We concluded that the diagnostic criteria evidenced on DSM-V to intoxication-continued use and abstinence are not well supported by clinical studies. The fact that diagnostic criteria is not widely supported by preclinical or clinical studies may be due specially to a controversy in its exactly mechanism of action: recent literature point to an indirect, rather than direct modulation of dopamine receptors, and auto-limitant consumption due to adverse sensations in high doses. On the other hand, it reports clear withdrawal-related symptoms. Thus, based on a classical action on reward system, caffeine only partially fits its mechanism of action as an abuse drug, especially because previous research does not report a clear effect of dopaminergic activity enhance on nucleus accumbens; despite this, there are reports concerning dopaminergic modulation by caffeine on the striatum. However, based on human and animal research, caffeine withdrawal evokes signals and symptoms, which are relevant enough to include this substance among the drugs of abuse.

A Retrospective Study on the Epidemiological and Clinical Features of Emergency Patients with Large or Massive Consumption of Caffeinated Supplements or Energy Drinks in Japan

Objective We conducted a retrospective study on the epidemiological and clinical features of patients with acute caffeine poisoning in Japan. Methods Letters requesting participation were sent to 264 emergency departments of hospitals, and questionnaires were mailed to those that agreed to participate. Patients Participants were patients transported to emergency departments of hospitals between April 2011 and March 2016 after consuming large or massive amounts of caffeinated supplements and/or energy drinks (caffeine dose ≥1.0 g). Results We surveyed 101 patients from 38 emergency departments. Since April 2013, the number of patients has markedly increased. Of these young patients (median age, 25 years), 53 were men, and 97 had consumed caffeine in tablet form. Estimated caffeine doses (n=93) ranged from 1.2 to 82.6 g (median, 7.2 g). Serum caffeine levels on admission (n=17) ranged from 2.0 to 530.0 μg/mL (median level, 106.0 μg/mL). Common abnormal vital signs and laboratory data on admission included tachypnea, tachycardia, depressed consciousness, hypercreatinekinasemia, hyperglycemia, hypokalemia, hypophosphatemia, and hyperlactatemia. Common signs and symptoms in the clinical course included nausea, vomiting, excitement/agitation, and sinus tachycardia. Seven patients (6.9%) who had consumed ≥6.0 g of caffeine, or whose serum caffeine levels on admission were ≥200 μg/mL, developed cardiac arrest. Ninety-seven patients (96.0%) recovered completely, but 3 patients (3.0%) died. Conclusion The present analysis of data from more than 100 emergency patients revealed clinical features of moderate to fatal caffeine poisoning. We recommend highlighting the toxicity risks associated with ingesting highly caffeinated tablets.

Knowing too much: Knowledge of energy content prevents liking change through flavour-nutrient associations

Associations between flavours and the consequences of ingestion can lead to changes in flavour liking depending on nutrient content, an example of flavour-nutrient learning (FNL). Expectations about the consequences of ingestion can be modified by information at the point of ingestion, such as nutritional labelling. What is unknown is the extent to which these label-based expectations modify FNL. Since nutrient information can alter expectations about how filling a product would be, we hypothesised that labels predicting higher energy (HE) content would enhance satiety and so promote more rapid flavour learning. To test this, participants consumed either a lower energy (LE: 164 kcal) or HE (330 kcal) yoghurt breakfast on four separate days, either with no product label or with labels displaying either the actual energy content (Congruent label) or inaccurate energy (Incongruent label). Participants rated liking on all four days: on Days 1 and 4, they could also consume as much as they liked, but consumed a fixed amount (300 g) on Days 2 and 3. Both liking and intake increased with exposure in the HE, and decreased in the LE, condition when unlabelled in line with FNL. In contrast, no significant changes were seen in either the Congruent or Incongruent label conditions. Contrary to predictions, these data suggest that FNL occurs when there is an absence of explicit expectations of actual nutrient content, with both accurate and inaccurate information on nutrient content disrupting learning.

Flavour Liking and Preference Conditioned by Caffeine in Humans

When caffeine consumers repeatedly experience a novel flavoured drink containing caffeine, the rated pleasantness of the drink flavour increases progressively. These results could be interpreted in terms of the flavour acting as a Pavlovian conditioned stimulus (CS) predicting the consequences of caffeine ingestion. However, all studies of this phenomenon to date have used between-subjects designs, and one criticism of this is that changes in pleasantness might have arisen from nonspecific effects. A more rigorous test is to examine changes in pleasantness for two drinks, a CS+ flavour paired with caffeine and CS− paired with placebo. Accordingly, 20 moderate caffeine consumers consumed both CS+ and CS− drinks in counterbalanced order over eight conditioning trials at breakfast, with hedonic and sensory characteristics evaluated on each trial. As predicted, the rated pleasantness of the CS+ drink increased whereas pleasantness of the CS− drink did not change. Despite this, participants did not have an overall preference for the CS+ flavour posttraining. However, both those who chose the CS+ and those who chose the CS− at the end showed the same direction and rate of change in pleasantness for the two drinks during training, but spurious differences in baseline preference obscured this effect in terms of an overall change in preference. Overall these data suggest that changes in pleasantness of drinks paired with caffeine delivery are best explained in terms of Pavlovian associations between drink flavour and the postingestive effects of caffeine.

Caffeine Deprivation State Modulates Expression of Acquired Liking for Caffeine-Paired Flavours

Previous studies found that caffeine consumers acquired a liking for the flavour of novel caffeinated drinks when these drinks were consumed repeatedly in a caffeine-deprived, but not nondeprived, state. Expression of this acquired liking appeared acutely sensitive to current caffeine deprivation state, but the use of between-subjects designs confounded interpretation of those studies. The present study evaluated these findings further using a within-subject design, with one flavour paired with caffeine (CS +) and the second with the absence of caffeine (CS–). During four CS + and four CS– training days, 32 moderate caffeine consumers alternatively consumed a novel flavoured drink a CS + paired with caffeine and a CS– flavour paired with placebo. Participants evaluated both drinks before and after training in two motivational states: caffeine deprived and nondeprived. As predicted, pleasantness ratings for the caffeine-paired flavour increased overall. However, this acquired liking was only significant when tested in a caffeine-deprived state. These data are consistent with a conditioned-flavour preference model and imply that expression of acquired liking for a novel caffeinated flavour depends on the need for the effects of caffeine at the time when the drink is evaluated.

Why Do You Drink Caffeine? The Development of the Motives for Caffeine Consumption Questionnaire (MCCQ) and Its Relationship with Gender, Age and the Types of Caffeinated Beverages

Caffeine is the most popular psychoactive substance that is consumed worldwide. As motives influence behavior, investigation of the motivational background of caffeine consumption should help provide a better understanding of the popularity of caffeinated products. The present study aimed (i) to explore and operationalize the motives of caffeine consumption and (ii) to reveal possible differences in the motives regarding gender, age and the type of caffeinated products consumed. Motives for caffeine consumption were collected from regular caffeine consumers (N = 26) and were informed by a review of the relevant literature. Following this, a cross-sectional study was conducted on a convenience sample of Hungarian university students and working adults (N = 598). The participants completed the Motives for Caffeine Consumption Questionnaire and the Caffeine Consumption Questionnaire. Six motivational factors were identified: Alertness, Habit, Mood, Social, Taste and Symptom Management. Women had higher scores on Habit, Social, Taste and Symptom Management. Younger participants had higher scores on Alertness than the older group, and the older group had higher scores on Habit and Symptom Management. Five types of caffeine users were identified. Those who consumed (i) coffee, (ii) tea, (iii) energy drinks, (iv) coffee and tea and (v) mixed drinks. Several differences between the five groups were revealed across all motives except for Taste. The present study developed a robust psychometric instrument for assessing caffeine consumption motives. The factors varied in importance in relation to gender, age and caffeine consumption habits.

Caffeine increases sugar-sweetened beverage consumption in a free-living population: a randomised controlled trial

Excessive sugar-sweetened beverage (SSB) consumption has been associated with overweight and obesity. Caffeine is a common additive to SSB, and through dependence effects, it has the potential to promote the consumption of caffeine-containing foods. The objective of the present study was to assess the influence that caffeine has on the consumption of SSB. Participants (n 99) were blindly assigned to either a caffeinated SSB (C-SSB) or a non-caffeinated SSB (NC-SSB) group. Following randomisation, all participants completed a 9 d flavour-conditioning paradigm. They then completed a 28 d ad libitum intake intervention where they consumed as much or as little of C-SSB or NC-SSB as desired. The amount consumed (ml) was recorded daily, 4 d diet diaries were collected and liking of SSB was assessed at the start and end of the intervention. Participants (n 50) consuming the C-SSB had a daily SSB intake of 419 (sd 298) ml (785 (sd 559) kJ/d) over the 28 d intervention, significantly more than participants (n 49) consuming the NC-SSB (273 (sd 278) ml/d, 512 (sd 521) kJ/d) (P< 0·001). A trained flavour panel (n 30) found no difference in flavour between the C-SSB and NC-SSB (P>0·05). However, participants who consumed the C-SSB liked the SSB more than those who consumed the NC-SSB (6·3 v. 6·0 on a nine-point hedonic scale, P= 0·022). The addition of low concentrations of caffeine to the SSB significantly increases the consumption of the SSB. Regulating caffeine as a food additive may be an effective strategy to decrease the consumption of nutrient-poor high-energy foods and beverages.

Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis

A systematic review and meta-analysis was conducted on 11 randomized placebo-controlled human studies of acute effects of tea constituents L-theanine and epigallocatechin gallate, administered alone or in combination with caffeine, on cognitive function and mood. The outcome measures of mood were alertness, calmness, and contentedness, derived from the Bond-Lader scales, and state anxiety, from the State-Trait Anxiety Inventory. Cognitive measures assessed were attentional switch, intersensory attention, and rapid visual information processing. Standardized mean differences between placebo and treatment groups are presented for each study and outcome measure. Meta-analysis using a random-effects model was conducted when data were available for three or more studies. Evidence of moderate effect sizes in favor of combined caffeine and L-theanine in the first 2 hours postdose were found for outcome measures Bond-Lader alertness, attentional switching accuracy, and, to a lesser extent, some unisensory and multisensory attentional outcomes. Moderator analysis of caffeine and L-theanine doses revealed trends toward greater change in effect size for caffeine dose than for L-theanine dose, particularly during the first hour postdose.

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.

Factors that influence the reinforcing value of foods and beverages

Behavioral economic principles state that as the cost of a product increases, purchasing or consumption of that product will decrease. To understand the impact of behavioral economics on ingestive behavior, our laboratory utilizes an operant behavior paradigm to measure how much work an individual will engage in to get access to foods and beverages. This task provides an objective measure of the reinforcing value. We have shown that consumption of the same high fat snack food every day for two weeks reduces its reinforcing value in lean individuals, but increases its reinforcing value in a subset of obese individuals. This increase in the reinforcing value of food predicts future weight gain. Similarly, we have shown that repeated intake of caffeinated soda increases its reinforcing value in boys, but not in girls. This increase in reinforcing value is not related to usual caffeine consumption, but may be associated with positive, subjective effects of caffeine that are more likely to be reported by boys than by girls. Because food and beverage reinforcement relates to real-world consumption, it is important to determine factors that increase or decrease the reinforcing value and determine the consequences of these responses. We are especially interested in determining ways to shift the behavioral economic curve in order to develop novel strategies to decrease the reinforcing value of less healthy snack foods and beverages, such as soda, potato chips and candy and to increase the reinforcing value of healthier foods and beverages, such as water, fruits, and vegetables.

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 Use Disorder: A Comprehensive Review and Research Agenda

Caffeine is the most commonly used drug in the world. Although consumption of low to moderate doses of caffeine is generally safe, an increasing number of clinical studies are showing that some caffeine users become dependent on the drug and are unable to reduce consumption despite knowledge of recurrent health problems associated with continued use. Thus, the World Health Organization and some health care professionals recognize caffeine dependence as a clinical disorder. In this comprehensive literature review, we summarize published research on the biological evidence for caffeine dependence; we provide a systematic review of the prevalence of caffeine dependence and rates of endorsement of clinically meaningful indicators of distress and functional impairment among habitual caffeine users; we discuss the diagnostic criteria for Caffeine Use Disorder-a condition for further study included in the Diagnostic and Statistical Manual of Mental Disorders (5^th ed.); and we outline a research agenda to help guide future clinical, epidemiological, and genetic investigations of caffeine dependence. Numerous controlled laboratory investigations reviewed in this article show that caffeine produces behavioral and physiological effects similar to other drugs of dependence. Moreover, several recent clinical studies indicate that caffeine dependence is a clinically meaningful disorder that affects a nontrivial proportion of caffeine users. Nevertheless, more research is needed to determine the reliability, validity, and prevalence of this clinically important health problem.

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.

Breakfast consumption and exercise interact to affect cognitive performance and mood later in the day. A randomized controlled trial

The current study assessed the interactive effect of breakfast and exercise on cognition and mood. Twelve active males completed four trials; no breakfast-rest, breakfast-rest, no breakfast-exercise or breakfast-exercise in a randomized, cross-over design. The trials consisted of; breakfast or fast, a 2h rest, exercise (treadmill run) or equivalent rest, a chocolate milk drink, a 90 min rest and an ad libitum lunch. Cognitive performance and mood were recorded frequently throughout each trial. Data was analysed as pre-exercise/rest, during and immediately post exercise/rest and post-drink. No effects were found prior to consumption of the drink. Post-drink, fasting before exercise increased mental fatigue compared to consuming breakfast before exercise and fasting before rest. Tension increased when breakfast was consumed at rest and when exercise was undertaken fasted compared to omitting breakfast before rest. Breakfast before rest decreased rapid visual information processing task speed and impaired Stroop performance. Breakfast omission improved Four Choice Reaction Time performance. To conclude, breakfast before exercise appeared beneficial for post-exercise mood even when a post-exercise snack was consumed. Exercise reversed post-breakfast cognitive impairment in active males.

Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance

RATIONALE

Despite 100 years of psychopharmacological research, the extent to which caffeine consumption benefits human functioning remains unclear.

OBJECTIVES

To measure the effects of overnight caffeine abstinence and caffeine administration as a function of level of habitual caffeine consumption.

METHODS

Medium-high (n = 212) and non-low (n = 157) caffeine consumers completed self-report measures and computer-based tasks before (starting at 10:30 AM) and after double-blind treatment with either caffeine (100 mg, then 150 mg) or placebo. The first treatment was given at 11:15 AM and the second at 12:45 PM, with post-treatment measures repeated twice between 1:45 PM and 3:30 PM.

RESULTS

Caffeine withdrawal was associated with some detrimental effects at 10:30 AM, and more severe effects, including greater sleepiness, lower mental alertness, and poorer performance on simple reaction time, choice reaction time and recognition memory tasks, later in the afternoon. Caffeine improved these measures in medium-high consumers but, apart from decreasing sleepiness, had little effect on them in non-low consumers. The failure of caffeine to increase mental alertness and improve mental performance in non-low consumers was related to a substantial caffeine-induced increase in anxiety/jitteriness that offset the benefit of decreased sleepiness. Caffeine enhanced physical performance (faster tapping speed and faster simple and choice reaction times) in both medium-high and non-low consumers.

CONCLUSIONS

While caffeine benefits motor performance and tolerance develops to its tendency to increase anxiety/jitteriness, tolerance to its effects on sleepiness means that frequent consumption fails to enhance mental alertness and mental performance.

Glycaemic index and glycaemic load of breakfast predict cognitive function and mood in school children: a randomised controlled trial

The macronutrient composition of a breakfast that could facilitate performance after an overnight fast remains unclear. As glucose is the brain's major energy source, the interest is in investigating meals differing in their blood glucose-raising potential. Findings vary due to unaccounted differences in glucoregulation, arousal and cortisol secretion. We investigated the effects of meals differing in glycaemic index (GI) and glycaemic load (GL) on cognition and mood in school children. A total of seventy-four school children were matched and randomly allocated either to the high-GL or low-GL group. Within each GL group, children received high-GI and low-GI breakfasts. Cognitive function (CF) and mood were measured 95–140 min after breakfast. Blood glucose and salivary cortisol were measured at baseline, before and after the CF tests. Repeated-measures ANOVA was used to identify differences in CF, mood, glucose and cortisol levels between the breakfasts. Low-GI meals predicted feeling more alert and happy, and less nervous and thirsty (P < 0·05 for each); high-GL meals predicted feeling more confident, and less sluggish, hungry and thirsty (P < 0·05 for each). High-GL (P < 0·001) and high-GI (P = 0·05) meals increased glucose levels 90 min after breakfast, and high-GI meals increased cortisol levels (P < 0·01). When baseline mood, glucose and cortisol levels were considered, low-GI meals predicted better declarative-verbal memory (P = 0·03), and high-GI meals better vigilance (P < 0·03); observed GI effects were valid across GL groups. GI effects on cognition appear to be domain specific. On balance, it would appear that the low-GI high-GL breakfast may help to improve learning, and of potential value in informing government education policies relating to dietary recommendations and implementation concerning breakfast.

Theobromine and the pharmacology of cocoa

The effects of theobromine in man are underresearched, possibly owing to the assumption that it is behaviourally inert. Toxicology research in animals may appear to provide alarming results, but these cannot be extrapolated to humans for a number of reasons. Domestic animals and animals used for racing competitions need to be guarded from chocolate and cocoa-containing foods, including foods containing cocoa husks. Research ought to include caffeine as a comparative agent, and underlying mechanisms need to be further explored. Of all constituents proposed to play a role in our liking for chocolate, caffeine is the most convincing, though a role for theobromine cannot be ruled out. Most other substances are unlikely to exude a psychopharmacological effect owing to extremely low concentrations or the inability to reach the blood-brain barrier, whilst chocolate craving and addiction need to be explained by means of a culturally determined ambivalence towards chocolate.

A case of fatal caffeine poisoning

Caffeine is a natural alkaloid methylxanthine that is found in various plants such as coffee or tea. Symptoms of a severe overdose may present with hypokalemia, hyponatremia, ventricular arrhythmias, hypertension followed by hypotension, respiratory failure, seizures, rhabdomyolysis, ventricular fibrillation and finally circulatory collapse. A 21-year-old woman called for the ambulance herself soon after the ingestion of about 10,000 mg of caffeine. At the arrival of the ambulance, the patient went into cardiac arrest almost immediately. After a total resuscitation period of 34 min including seven counter-shocks and 2 mg epinephrine, the patient was stable enough to be transferred to the hospital. The patient soon went into VF again and received two more counter-shocks and 1 mg epinephrine and finally an intravenous bolus dose of 300 mg amiodarone. The initial arterial blood gas showed pH at 6.47, lactate at 33 mmol/l and potassium level at 2.3 mmol/l. Unfortunately, no blood samples for caffeine analysis were taken. Three days after hospital admission, the patient developed myoclonus, which did not respond to medical treatment. Excessive intake of caffeine may produce arrhythmias and pronounced hypokalemia and ensuing ventricular fibrillation. In case of counter-shock-resistant VF, it can be necessary to give an early loading dose of amiodarone. Furthermore, it may be beneficial to replace the potassium as early as possible. Epinephrine and buffer solutions used during resuscitation may further decrease blood potassium levels and should be administrated cautiously. Epinephrine can be replaced by other vasopressor drugs, such as vasopressin without effects on beta-receptors.

Comparing the benefits of caffeine, naps and placebo on verbal, motor and perceptual memory

Caffeine, the world's most common psychoactive substance, is used by approximately 90% of North Americans everyday. Little is known, however, about its benefits for memory. Napping has been shown to increase alertness and promote learning on some memory tasks. We directly compared caffeine (200mg) with napping (60-90min) and placebo on three distinct memory processes: declarative verbal memory, procedural motor skills, and perceptual learning. In the verbal task, recall and recognition for unassociated words were tested after a 7h retention period (with a between-session nap or drug intervention). A second, different, word list was administered post-intervention and memory was tested after a 20min retention period. The non-declarative tasks (finger tapping task (FTT) and texture discrimination task (TDT)) were trained before the intervention and then retested afterwards. Naps enhanced recall of words after a 7h and 20min retention interval relative to both caffeine and placebo. Caffeine significantly impaired motor learning compared to placebo and naps. Napping produced robust perceptual learning compared with placebo; however, naps and caffeine were not significantly different. These findings provide evidence of the limited benefits of caffeine for memory improvement compared with napping. We hypothesize that impairment from caffeine may be restricted to tasks that contain explicit information; whereas strictly implicit learning is less compromised.

Additive effects of flavour–caffeine and flavour–flavour pairings on liking for the smell and flavour of a novel drink

Previous research has established that caffeine consumption can reinforce changes in liking for caffeine-paired flavours, while pairing a novel flavour with a liked or dislike taste can also result in enduring changes in liking for the flavour. The present study examined how these two forms of flavour-learning interact. 72 habitual caffeine consumers who liked sweet tastes rated the odour and flavour of a novel tea drink before and after four training sessions where the flavour was paired with either 100 mg caffeine or placebo in one of three flavour contexts: added sweetness (aspartame), bitterness (quinine) or control. The liking for both the odour and flavour of the tea increased after pairing with caffeine regardless of flavour context, while pairing with bitterness reduced flavour liking regardless of the presence of caffeine. Pairing with quinine increased the rated bitterness of the tea odour, and reduced the rated sweetness of the tea flavour, post-training, independent of effects of caffeine. These data suggest that flavour-caffeine and flavour-flavour associations have additive effects on drink liking, while confirming that flavour-flavour associations can alter the immediate sensory experience of a flavour alone.

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.

Effects of hunger state on flavour pleasantness conditioning at home: Flavour–nutrient learning vs. flavour–flavour learning

This study examined acquired liking of flavour preferences through flavour-flavour and flavour-nutrient learning under hungry or sated conditions in a naturalistic setting. Each participant consumed one of three versions of a test drink at home either before lunch or after lunch: minimally sweetened (

CONTROL

3% sucrose, 40 kcal), artificially sweetened (3% sucrose 40 kcal plus artificial sweeteners ASPARTAME) and sucrose-sweetened (SUCROSE: 9.9% sugar, 132 kcal). The test drink was an uncarbonated peach-flavoured iced tea served in visually identical drink cans (330 ml). Participants preselected as "sweet likers" evaluated the minimally sweetened flavoured drink (conditioned stimulus, CS) in the same state (hungry or sated) in which they consumed the test drink at home. Overall, liking for the CS flavour increased in participants who consumed the SUCROSE drink, however, this increase in liking was significantly larger when tested and trained hungry than sated, consistent with a flavour-nutrient model. Overall increases in pleasantness for the CS flavour in participants who consumed the SUCROSE drink when sated or the ASPARTAME drink independent of hunger state, suggest that flavour-flavour learning also occurred. These results are discussed in light of current learning models of flavour preference.

Flavor-nutrient learning in restrained and unrestrained eaters

After we consume a novel food an association can form between its sensory characteristics (e.g., taste properties) and the effect it has on the body (rewarding). Associations of this kind underpin much of our everyday dietary behavior because they mediate both the affective quality of food (flavor-preference learning) and the amount that we choose to consume (learning satiation). Notwithstanding this fact, very few studies have successfully demonstrated the process of dietary learning in human adults. In addition, based on evidence from related research, we explored whether learning is less likely to occur in individuals who have high scores on a measure of dietary restraint. Female participants (N = 44) consumed two differently flavored desserts. Each was presented three times on separate days. One was formulated with a high-energy content (1882 kJ) and the other with a low-energy content (226 kJ). After training, we found little evidence for learned satiation. However, we did observe flavor-preference learning. Specifically, participants acquired a greater liking and desire-to-eat the dessert flavor that was paired with a higher energy density during training. Further analysis revealed that this effect on liking is qualified by dietary restraint. As predicted, unrestrained eaters demonstrated greater differential responding to the two desserts than did restrained eaters. These data provide further evidence for flavor-nutrient learning in adults and they highlight a hitherto unexplored and potentially important difference between restrained and unrestrained eaters.

Evidence of a role for conditioning in the development of liking for flavours in humans in everyday life

The development of liking for flavours through conditioning has so far been widely demonstrated in the laboratory. The impact of conditioning in the real world however is yet to be reported. This study investigated the development of liking for flavours through conditioning in the real world as part of everyday life. The study investigated the development of liking for four novel flavoured yoghurts paired with energy (high energy/low energy) and energy requirement (high energy requirement/low energy requirement). Liking was assessed before and after conditioning conducted in the laboratory using traditional laboratory procedures and in the real world using new interactive technology. Following conditioning, liking was found to develop for novel flavoured yoghurts when consumed in a state of high energy requirement. Furthermore, effects were comparable in the laboratory and in the real world. These findings suggest that likings for flavours can be conditioned in the real world as part of every day life as well as in the laboratory. This finding suggests that conditioning is a useful and valid explanation for the development of likings for flavours in everyday life.

Role of familiarity on effects of caffeine- and glucose-containing soft drinks

Familiarity, through conditioned responses and expectations, may play a significant role in the expression of liking for, and mood and performance effects of, food and drink constituents. The role of familiarity and the effects of caffeine and glucose in Lucozade Energy were investigated by testing this familiar soft drink, and its non-caffeine/non-CHO placebo match, against novel coloured/flavoured full and placebo drinks. Both the familiar drink and its placebo improved alertness, mental energy and mental performance compared to baseline and compared to the novel placebo drink. After repeated exposure, that is, after having gained familiarity with the novel drinks in addition to the already existing familiarity with Lucozade Energy, only the full (caffeine and CHO containing) drinks showed sustained beneficial effects compared to placebo drinks and baseline measures, as well as an increase in liking compared to placebo drinks. Therefore, participants appeared to have learned that beneficial effects were mainly linked to the full products. The results illustrate the restorative combination of caffeine and CHO in the drink, and emphasises the need to implement the appropriate placebo(s) in any study design employing familiar foods or drinks.

Relationships between the Food Expectancy Questionnaire (FEQ) and the Food Frequency Questionnaire (FFQ)

The outcome expectancies of 250 respondents were examined using the Food Expectancy Questionnaire (FEQ), comparing expectancies about four different foods: fruit, vegetables, chocolate and sweets and plain biscuits. These expectancies were related to diet as assessed by a Food Frequency Questionnaire. As with alcohol expectancies [Jones, B. T., Corbin, W. & Fromme, K. (2001). A review of expectancy theory and alcohol consumption. Addiction, 96, 57-72], on which this research was modelled, positive and negative outcomes were the main factors for all foods, accounting jointly for between 33 and 40% of expectancy variance in factor analysis and predicting as much as 16% of the variance in relevant food intake measures by linear regression. Expected positive and negative outcomes of eating were predominantly immediate psychological after-effects, rather than including orosensory experiences, or longer-term effects on health or well-being. Other expectancies varied from food to food. FEQ expectancies for different foods have similar factor structure and were related to self-reported diet, the FEQ therefore shows promise as a means of modelling cognitions about eating.

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.

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.

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.