Psychotropic effects of caffeine in man. 3. A questionnaire survey of coffee drinking and its effects in a group of housewives

Caffeine supplementation in the hospital: Potential role for the treatment of caffeine withdrawal

Caffeine use in the population is widespread. Caffeine withdrawal in the hospital setting is an underappreciated syndrome with symptoms including drowsiness, difficulty concentrating, mood disturbances, low motivation, flu-like symptoms, and headache. Withdrawal may occur upon abstinence from chronic daily exposure at doses as low as 100 mg/day and following only 3-7 days of consumption at higher doses. There are limited data investigating how caffeine withdrawal contributes to hospital morbidity. Some studies suggest caffeine withdrawal may contribute to intensive care delirium and that caffeine may promote wakefulness post-anesthesia. Caffeine supplementation has also shown promise in patients at risk of caffeine withdrawal, such as those placed on nil per os (NPO) status, in preventing caffeine withdrawal headache. These data on caffeine supplementation are not entirely consistent, and routine caffeine administration has not been implemented into clinical practice for patients at risk of withdrawal. Notably, caffeine serves a therapeutic role in the hospital for other conditions. Our review demonstrates that caffeine is largely safe in the general population and may be an appropriate therapeutic option for future studies, if administered properly. There is a need for a randomized controlled trial investigating in-hospital caffeine supplementation and the population that this would best serve.

Daily Patterns of Caffeine Intake and the Association of Intake with Multiple Sociodemographic and Lifestyle Factors in US Adults Based on the NHANES 2007-2012 Surveys

BACKGROUND

Caffeine increases alertness when consumed in single servings of various products including coffee, tea, soft drinks, and energy drinks. Although not a nutrient, caffeine is consumed by 90% of the adult population in the United States.

OBJECTIVE

This study examined the daily pattern of caffeine intake and its relationship to multiple demographic variables.

METHODS

Data from the National Health and Nutrition Examination Survey (NHANES) 2007-2012 (adults aged 19+ years; n=16,173) were used to determine the time of day at which caffeine is consumed and demographic factors associated with intake. Regression analyses characterized factors associated with caffeine intake including sex, age, ethnicity, education, smoking status, physical activity, employment status, total work hours, alcohol, and energy intake.

RESULTS

Mean adult per capita caffeine intake was 169±4 mg/d (mean±standard error). Most caffeine (70%) was consumed before noon, often at breakfast, and intake decreased progressively over the day, with little consumed after 9:00 pm. Intake was associated with age, ethnicity, smoking status, total calorie intake, and work hours (P<0.01) but not physical activity, economic status, education level, or employment status. Variables with the largest associations with intake were, respectively, ethnicity and age. Non-Hispanic black individuals consumed the smallest amounts (80±2 mg/d), non-Hispanic white individuals consumed the greatest amounts (194±3 mg/d), and Asian individuals (126±7 mg/d) and Hispanic individuals consumed intermediate amounts (127±3 mg/d). Middle-aged individuals (aged 50 to 54 years) consumed more caffeine (211±6 mg/d) than younger (107±4 mg/d, aged 20 to 24 years) and older individuals (153±4 mg/d, aged 75 to 79 years).

CONCLUSION

Most caffeine is consumed in the morning, when alertness is lowest, and very little in the evening before sleep. Ethnicity and age were the variables most strongly associated with intake; work hours, occupation, energy and alcohol intake, and smoking were also associated with intake. Because caffeine increases alertness, it is not surprising that its pattern of consumption and factors associated with its intake vary from those of most other food constituents.

Distinct sensitivity to caffeine-induced insomnia related to age

Caffeine acts by antagonizing the effect of the endogenous homeostatic sleep factor adenosine. In the current study we aimed to evaluate the pattern of caffeine-induced insomnia and its relation to age and sex in a general population sample derived from a web survey. The sample included 75,534 participants (28.1% men) from 18 to 75 years who answered self-report questionnaires by accessing a website in Brazilian Portuguese (BRAINSTEP project). In our sample, 3620 (17.0%) men and 9920 (18.3%) women reported insomnia due to caffeine intake. Caffeine-induced insomnia increased with aging in both men and women. This difference remained after adjusting for sociodemographic, psychiatric and sleep related variables as well as caffeine intake. Women showed higher proportion of caffeine-induced insomnia than men, but this difference did not remain after controlling for covariates. Also, individuals with caffeine-induced insomnia reported poorer sleep quality, higher latency to fall asleep and a higher proportion of psychiatric diagnoses and daily use of hypnotic drugs. In conclusion, our results show an age-associated increase in caffeine-induced insomnia and poorer mental health indicators among people with caffeine-induced insomnia complaints.

Caffeine-Withdrawal Headache. The Vågå Study of Headache Epidemiology

In connection with the Vågå study of headache epidemiology, a search was made for caffeine-withdrawal headache in 1741 parishioners. Female to male ratio 1.05; mean age 44.2 years (range 18-65 years). A face-to-face interview technique was used. The mean consumption of coffee was 4.7 cups a day. Males on an average consumed more coffee (5.1 ± 3.3 cups/day) than females (4.4 ± 3.1 cups/day). Neither in those with a high consumption of coffee: ≥10 cups a day ( n = 134), nor in those with a considerable variation in consumption: ≥10 cups/day ( n = 31) did there seem to be a definite increase in headache resembling caffeine-withdrawal headache, for instance during weekends. In seven parishioners, however, there did seem to be such a headache, and in two of them, the evidence was rather convincing. This headache generally seemed to be mild and global and occurred mainly in the morning hours on weekends. There was no nausea, no throbbing quality of the pain, and no reported use of analgesics. Coffee seemed to abate the headache. This frequency (0.4%) should, clearly, be regarded as a minimum figure. Caffeine-withdrawal headache at the grassroots level may be a rather rare, generally vague, symptom-poor headache.

Organic and Hyperventilatory Causes of Anxiety-type Symptoms

In treating anxiety and phobic disorders it is helpful to be aware of physical illnesses that can present with anxiety-type features. This paper discusses a number of organic conditions whose presenting features could be mistaken for an anxiety state, viz. hyperthyroidism, Cushing's syndrome, hypoparathyroidism, phaeochromocytoma, hypoglycaemia, mitral valve prolapse, paroxysmal tachycardia, temporal lobe epilepsy, caffeinism, and food and chemical allergy. Hyperventilation is also discussed since it is an important but frequently neglected mechanism in many cases of anxiety and phobia.

Fourteen well-described caffeine withdrawal symptoms factor into three clusters

RATIONALE

Abrupt cessation of caffeine often results in several withdrawal symptoms among habitual caffeine consumers.

OBJECTIVE

The objective of the study was to determine whether caffeine withdrawal symptoms co-exist as clusters in some individuals.

MATERIALS AND METHODS

Withdrawal symptoms and caffeine intake were assessed for men (n=126) and women (n=369), aged 20-29, using a caffeine habits questionnaire and a semi-quantitative food frequency questionnaire, respectively. Principal components factor analysis was used to identify common underlying factors among 14 well-described caffeine withdrawal symptoms. Odds ratios (OR) and 95% confidence intervals (CI) were calculated to determine if the likelihood of reporting a withdrawal factor was associated with habitual caffeine consumption.

RESULTS

The 14 withdrawal symptoms were grouped into three factors termed "fatigue and headache", "dysphoric mood", and "flu-like somatic". The likelihood of reporting the fatigue and headache and dysphoric mood factors increased with higher levels of habitual caffeine consumption. Compared to <100 mg/day of caffeine, the ORs (95% CI) of reporting the fatigue and headache factor with a habitual intake of 100-200 mg/day and >200 mg/day were 1.97 (1.21, 3.21) and 4.44 (2.50, 7.86), respectively. The corresponding ORs (95% CI) for the dysphoric mood factor were 1.55 (0.96, 2.52) and 3.34 (1.99, 5.60).

CONCLUSIONS

The 14 well-described caffeine withdrawal symptoms factor into three clusters, suggesting the existence of three distinct underlying mechanisms of caffeine withdrawal. Increasing habitual caffeine consumption is associated with an increased likelihood of reporting the fatigue and headache and dysphoric mood symptoms, but not the flu-like somatic symptoms.

Coffee and cigarette consumption and perceived effects in recovering alcoholics participating in Alcoholics Anonymous in Nashville, Tennessee, USA

BACKGROUND

Alcoholics Anonymous (AA) members represent an important and relatively understudied population for improving our understanding of alcohol dependence recovery as over 1 million Americans participate in the program. Further insight into coffee and cigarette use by these individuals is necessary given AA members' apparent widespread consumption and the recognized health consequences and psychopharmacological actions of these substances.

METHODS

Volunteers were sought from all open-AA meetings in Nashville, TN during the summer of 2007 to complete a questionnaire (n = 289, completion rate = 94.1%) including timeline followback for coffee, cigarette, and alcohol consumption; the Alcoholics Anonymous Affiliation Scale; coffee consumption and effects questions; the Fagerstrom Test for Nicotine Dependence (FTND); and the Smoking Effects Questionnaire.

RESULTS

Mean (+/-SD) age of onset of alcohol consumption was 15.4 +/- 4.2 years and mean lifetime alcohol consumption was 1026.0 +/- 772.8 kg ethanol. Median declared alcohol abstinence was 2.1 years (range: 0 days to 41.1 years) and median lifetime AA attendance was 1000.0 meetings (range: 4 to 44,209 meetings); average AA affiliation score was 7.6 +/- 1.5. Most (88.5%) individuals consumed coffee and approximately 33% of coffee consumers drank more than 4 cups per day (M = 3.9 +/- 3.9). The most common self-reported reasons for coffee consumption and coffee-associated behavioral changes were related to stimulatory effects. More than half (56.9%) of individuals in AA smoked cigarettes. Of those who smoked, 78.7% consumed at least half a pack of cigarettes per day (M = 21.8 +/- 12.3). Smokers' FTND scores were 5.8 +/- 2.4; over 60% of smokers were highly or very highly dependent. Reduced negative affect was the most important subjective effect of smoking.

CONCLUSIONS

A greater proportion of AA participants drink coffee and smoke cigarettes in larger per capita amounts than observed in general U.S. populations. The effects of these products as described by AA participants suggest significant stimulation and negative affect reduction. Fundamental knowledge of the quantitative and qualitative aspects of coffee and cigarette consumption among AA members will enable future research to discern their impact on alcohol abstinence and recovery.

Is caffeine addictive?--a review of the literature

The common-sense use of the term addiction is that regular consumption is irresistible and that it creates problems. Caffeine use does not fit this profile. Its intake does no harm to the individual or to society and its users are not compelled to consume it. Though cessation of regular use may result in symptoms such as headache and lethargy, these are easily and reliably reversed by ingestion of caffeine. Some have argued that continued caffeine use is an attempt to suppress low grade withdrawal symptoms such as sleepiness and lethargy. In some moderate users, this is possible; however, in experimental contexts, the phenomenon is too inconsistent to constitute a reliably valid syndrome.

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

RATIONALE

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Caffeine: behavioral effects of withdrawal and related issues

Acquired tolerance to some behavioral effects of caffeine in humans is widely assumed to occur but is poorly documented and appears, at most, to be of low magnitude. Withdrawal from regular consumption of caffeine has been reported to result in a variety of symptoms, including: irritability, sleepiness, dysphoria, delerium, nausea, vomiting, rhinorrhea, nervousness, restlessness, anxiety, muscle tension, muscle pains and flushed face. Some of these same symptoms have been reported following excess intake of caffeine. The prevalence of symptoms reported on withdrawal in different studies also covers a wide range from 11% or less to 100%. It is suggested that the evidence leads to the conclusion that non pharmacological factors related to knowledge and expectation are the prime determinants of symptoms and their reported prevalence on withdrawal of caffeine after regular consumption.

Are we dependent upon coffee and caffeine? A review on human and animal data

Caffeine is the most widely used psychoactive substance and has been considered occasionally as a drug of abuse. The present paper reviews available data on caffeine dependence, tolerance, reinforcement and withdrawal. After sudden caffeine cessation, withdrawal symptoms develop in a small portion of the population but are moderate and transient. Tolerance to caffeine-induced stimulation of locomotor activity has been shown in animals. In humans, tolerance to some subjective effects of caffeine seems to occur, but most of the time complete tolerance to many effects of caffeine on the central nervous system does not occur. In animals, caffeine can act as a reinforcer, but only in a more limited range of conditions than with classical drugs of dependence. In humans, the reinforcing stimuli functions of caffeine are limited to low or rather moderate doses while high doses are usually avoided. The classical drugs of abuse lead to quite specific increases in cerebral functional activity and dopamine release in the shell of the nucleus accumbens, the key structure for reward, motivation and addiction. However, caffeine doses that reflect the daily human consumption, do not induce a release of dopamine in the shell of the nucleus accumbens but lead to a release of dopamine in the prefrontal cortex, which is consistent with caffeine reinforcing properties. Moreover, caffeine increases glucose utilization in the shell of the nucleus accumbens only at rather high doses that stimulate most brain structures, non-specifically, and likely reflect the side effects linked to high caffeine ingestion. That dose is also 5-10-fold higher than the one necessary to stimulate the caudate nucleus, which mediates motor activity and the structures regulating the sleep-wake cycle, the two functions the most sensitive to caffeine. In conclusion, it appears that although caffeine fulfils some of the criteria for drug dependence and shares with amphetamines and cocaine a certain specificity of action on the cerebral dopaminergic system, the methylxanthine does not act on the dopaminergic structures related to reward, motivation and addiction.

Caffeine consumption in hospitalized psychiatric patients

A total of 98 consecutively admitted psychiatric inpatients were asked for their daily consumption of coffee, tea and other products containing caffeine. Calculation of the corresponding daily caffeine intake was performed using data from the literature and from caffeine measurements carried out in different coffee and tea preparations in the hospital. Of the patients 13% presented a high (> or = 750 mg daily) caffeine consumption before hospitalization. The average caffeine consumption per day decreased from 405 mg before to 332 mg during hospitalization (P < 0.04), but the before and during hospitalization caffeine consumptions were highly correlated (rho = 0.651; P < 0.00001). The decrease in caffeine consumption seems to be influenced by a lower availability of caffeine at hospital. Among the diagnostic groups (DSM-III-R criteria), the caffeine intake was highest in schizophrenia and lowest in anxiety and major depression patients. Patients under a neuroleptic treatment before admission presented a higher caffeine intake. At hospital the high caffeine users showed the highest score on the factor depression (Hopkins Symptom Checklist; HSCL-58). However, the influence of other factors, such as weight and cigarette consumption, which correlated also with the caffeine intake (rho = 0.359; P < 0.001; and rho = 0.83; P < 0.00001, respectively), have also to be considered. Our data suggest that inquiry into caffeine consumption should be included routinely for psychiatric patients, e.g. at admission, because patients with a psychotic disorder undergo a higher risk for an excessive caffeine consumption.

Caffeine withdrawal symptoms and rate of metabolism

Forty normal subjects (mean age 36) had their caffeine intake estimated by keeping a diary (n=40) and also by analysing provided samples of tea and coffee (n=28). A test dose of caffeine (500 mg) was given and a series of salivary samples analysed to estimate pharmacokinetic measures of the rate of caffeine metabolism. They then underwent 48 h of placebo substitution using double-blind procedures. A wide range of physiological, psychological and subjective measures were taken on successive days during withdrawal and resumption of caffeine. On withdrawal, 27 subjects reported tiredness and 18 developed headache. Electroencephalograph, skin conductance and blood pressure changes were apparent. Sleep improved on withdrawal but subjects reported feeling less alert and more tired. The higher the usual caffeine intake, the greater the unpleasant feelings on withdrawal and the more marked the reversal of feelings on resumption. The faster the metabolism of caffeine, the less the drop in anxiety during withdrawal and the less its return on resumption. These correlations were, however, rather weak and sporadic.

Mood and performance effects of caffeine in relation to acute and chronic caffeine deprivation

The mood and performance effects of caffeine deprivation (either 90 min, overnight, or at least 7 days) and ingestion (70 and 250 mg) were compared in young adults who were normally either moderate consumers (n = 49) or nonconsumers of caffeine (n = 18). Overnight caffeine deprivation produced dysphoric symptoms characteristic of caffeine withdrawal that were reduced, but still present, after longer-term abstinence. Acute caffeine intake affected the withdrawn consumers, nonwithdrawn consumers, and nonconsumers similarly. It increased jitteriness and decrease tiredness and headache. Furthermore, hand steadiness decreased as caffeine dose increased, whereas 70 mg, but not 250 mg, of caffeine was found to enhance performance on a simple reaction time task. These findings support the view that the negative effects experienced after overnight and longer-term caffeine deprivation play a significant role in influencing consumption of caffeine-containing drinks. Therefore, it would appear that to avoid the dysphoric symptoms resulting from both under- and overconsumption, regular caffeine consumers would have to regulate their caffeine intake fairly precisely.

Pharmacokinetic and pharmacodynamic responses to caffeine in poor and normal sleepers

Pharmacokinetic and pharmacodynamic responses to caffeine (2.5 mg/kg) were compared between ten healthy self-rated poor sleepers and ten normal sleepers. Sleep pattern assessed by the Pittsburgh Sleep Quality Index (PSQI). There was no significant difference in mean estimated daily caffeine consumption between the groups. The poor sleepers had significantly higher scores for neuroticism on the Eysenck Personality Questionnaire (EPQ) and anxiety on the Hospital Anxiety Depression (HAD) scale, compared with normal sleepers. Caffeine pharmacokinetics were assessed by measurement of saliva caffeine concentrations. Poor sleepers showed significantly greater variability in caffeine Cmax, clearance had half-life, compared to normal sleepers. Pharmacodynamic measures included heart rate, blood pressure, visual analogue scales for concentration, vigilance and relaxation, psychomotor performance [Digit Symbol Substitution Test (DSST) and tapping rate (TR)] and EEG activity [Contingent negative variation (CNV), auditory evoked potential and power spectral analysis]. Prior to caffeine administration, poor sleepers compared to normal sleepers had faster heart rates, lower ratings for concentration and relaxation, poorer performance on the DSST, greater CNV magnitude, faster peak alpha frequency and lower delta, theta and beta power. These differences persisted after caffeine ingestion and overall differences between the groups on these measures were significant (P < 0.01-.001). Post-dose, but not pre-dose, scores for vigilance and TR were significantly lower overall in poor compared with normal sleepers. Despite the baseline differences between poor and normal sleepers, the changes following caffeine administration were similar in direction and magnitude in both groups.

[Experimental and clinical pharmacology of psychostimulants]

OBJECTIVE

To examine the fact that, after 50 years, the introduction of amphetamines for therapeutic purposes, psychostimulants such as methylphenidate have proved to be effective medications used in the treatment of childhood hyperactivity, yet misunderstood.

METHOD

A review of the literature is undertaken on the use of psychostimulants in children and adults.

RESULTS

Studies evaluating their helpfulness in adults are for the most part outdated and nonexploratory.

CONCLUSION

their rehabilitation could prove to be useful for young and older adults, on condition that their target syndromes are studied more thoroughly.

Effects of caffeine on cognition and mood without caffeine abstinence

The objective of this study was to evaluate the effects of low doses (75 mg and 150 mg) of caffeine on mood and cognition in healthy people, with minimal abstinence of 1 h from caffeine. Improvements were obtained in cognition for attention, problem solving and delayed recall, but not immediate recall or working memory, but performance in the placebo condition was close to the maximum, giving little margin for improvement. For mood, there were statistically significant increase in clearheadedness, happiness and calmness and decreases in tenseness. These mood and performance-enhancing effects of caffeine cannot be seen as representing an alleviation of deficits induced by caffeine abstinence, because there was only minimal deprivation from caffeine.

Caffeine and smoking: subjective, performance, and psychophysiological effects

The effects of caffeine and smoking on cognitive performance, subjective variables, heart rate, and EEG were assessed in two sessions. In one session, subjects received caffeine (2.5 mg/kg bodyweight), while in the other they received placebo. In both sessions they smoked a cigarette (8 cued puffs) having a nicotine yield of 1.2 mg. Caffeine produced an increase in self-reported muscular tension and tended to increase anxiety and delta magnitude. Smoking facilitated performance of a paper-and-pencil math task and increased heart rate. Smoking also appeared to produce cortical activation as indexed by decreased right frontal delta, decreased right centro-parietal theta, globally increased alpha, and increased centro-occipital/decreased posterior-temporal beta 1. Smoking also increased central/decreased posterior-temporal beta 2. Smoking and caffeine did not interact for any measure, suggesting that the epidemiological link between smoking and coffee drinking may have a non-pharmacological basis.

Selected health and behavioral effects related to the use of caffeine

This paper reviews the research literature concerning health and selected behavioral effects of caffeine. Epidemiological and laboratory findings are reviewed to determine the health risks associated with both acute and chronic caffeine exposure. Common sources of caffeine, its properties, and physiological effects are considered. The relationships between caffeine and various health conditions are examined including caffeine's association with heart disease, cancer, and benign breast disease. Caffeine's possible contribution to enhanced exercise performance is discussed along with a brief overview of caffeine's effects on mental and emotional health. Over 100 references cited in this review were part of a more extensive literature base obtained from several on-line services including MEDLINE and LEXIS/NEXIS medical data bases. Other sources of relevant literature included manual searches of research journals and the use of selected references from appropriate articles. The relationship between caffeine consumption and various illnesses such as cardiovascular disease and cancer remains equivocal. Prudence might dictate that pregnant women and chronically ill individuals exercise restraint in their use of caffeine, although research suggests relatively low or nonexistent levels of risk associated with moderate caffeine consumption.

Caffeine and nicotine: a review of their joint use and possible interactive effects in tobacco withdrawal

There is a strong, significant relationship between coffee consumption and smoking. In six epidemiological studies reviewed and analyzed here, 86.4% of smokers consumed coffee versus 77.2% of nonsmokers. Exsmokers use more coffee than nonsmokers but somewhat less than smokers. Seventeen experimental studies suggest that the pharmacologic effect of caffeine in coffee may be partially but not totally responsible for the relationship. Conditioning, a reciprocal interaction (caffeine intake increases anxiety/arousal--nicotine decreases it), or joint effect of a third variable (e.g., stress, alcohol) may account for the relationship. In abstinent smokers, blood caffeine levels increase and remain elevated for as long as 6 months. These higher caffeine plasma levels may be sufficient to produce caffeine toxicity syndrome. A review of 86 studies of nicotine withdrawal, caffeine withdrawal, and caffeine toxicity suggests that the symptoms are similar enough to be confused, and that reported nicotine withdrawal symptoms may be a mixture of nicotine withdrawal and caffeine toxicity.

Does caffeine intake enhance absolute levels of cognitive performance?

The relationship between habitual coffee and tea consumption and cognitive performance was examined using data from a cross-sectional survey of a representative sample of 9003 British adults (the Health and Lifestyle Survey). Subjects completed tests of simple reaction time, choice reaction time, incidental verbal memory, and visuo-spatial reasoning, in addition to providing self-reports of usual coffee and tea intake. After controlling extensively for potential confounding variables, a dose-response trend to improved performance with higher levels of coffee consumption was observed for all four tests (P < 0.001 in each case). Similar but weaker associations were found for tea consumption, which were significant for simple reaction time (P = 0.02) and visuo-spatial reasoning (P = 0.013). Estimated overall caffeine consumption showed a dose-response relationship to improved cognitive performance (P < 0.001 for each cognitive test, after controlling for confounders). Older people appeared to be more susceptible to the performance-improving effects of caffeine than were younger. The results suggest that tolerance to the performance-enhancing effects of caffeine, if it occurs at all, is incomplete.

An update on research with coffee/caffeine (1989-1990)

The interest in research with coffee has been increasing in recent years, and this has resulted in a surge of publications dealing with a variety of pharmaco-physiological effects of coffee/caffeine. This review attempts to update the information on the research with coffee/caffeine, including epidemiological studies, laboratory investigations and tests with volunteers, published in 1989 and 1990. It groups published articles according to observed or investigated biological effects. The most significant findings and differences between studies are pointed out with brief commentaries on the results. The overall assessment for the safety of drinking coffee and the effect of coffee on human health, based on the literature published in 1989 and 1990, indicates that certain controversial issues are still unresolved.

Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects

Caffeine is the most widely consumed central-nervous-system stimulant. Three main mechanisms of action of caffeine on the central nervous system have been described. Mobilization of intracellular calcium and inhibition of specific phosphodiesterases only occur at high non-physiological concentrations of caffeine. The only likely mechanism of action of the methylxanthine is the antagonism at the level of adenosine receptors. Caffeine increases energy metabolism throughout the brain but decreases at the same time cerebral blood flow, inducing a relative brain hypoperfusion. Caffeine activates noradrenaline neurons and seems to affect the local release of dopamine. Many of the alerting effects of caffeine may be related to the action of the methylxanthine on serotonin neurons. The methylxanthine induces dose-response increases in locomotor activity in animals. Its psychostimulant action on man is, however, often subtle and not very easy to detect. The effects of caffeine on learning, memory, performance and coordination are rather related to the methylxanthine action on arousal, vigilance and fatigue. Caffeine exerts obvious effects on anxiety and sleep which vary according to individual sensitivity to the methylxanthine. However, children in general do not appear more sensitive to methylxanthine effects than adults. The central nervous system does not seem to develop a great tolerance to the effects of caffeine although dependence and withdrawal symptoms are reported.

Stimulus functions of caffeine in humans: relation to dependence potential

The interoceptive stimulus functions common to drugs of dependence include positive subjective effects, discriminative functions, and reinforcing functions. Data from studies measuring these stimulus functions constitute the objective assessment of a drug's dependence potential. This paper reviews the subjective effects, discriminative stimulus, and reinforcing stimulus functions of caffeine in humans to assess the dependence potential of caffeine. The stimulus effects of caffeine are compared with those of d-amphetamine, a prototypic CNS stimulant that has been studied under similar conditions, to evaluate the relative dependence potential of caffeine. Finally, caffeine's effects are evaluated in terms of generally accepted criteria for defining drug dependence. It is concluded that caffeine partially meets the primary criteria of drug dependence: 1) the majority of caffeine use is highly controlled, but not compulsive; 2) caffeine is psychoactive; and 3) caffeine functions as a reinforcer under certain conditions in humans, but not in animals. Caffeine thus has limited dependence potential. Additionally, although caffeine shares stimulus functions with d-amphetamine, it does so under limited conditions and should be considered to have a relatively lower dependence potential.

Behavioral effects of exposure to caffeine during gestation, lactation or both

Open-field behavior and latencies of emergence from a darkened chamber to a brightly lit arena were recorded at 1, 2, 4 and 6 months after birth in male and female rats that had been exposed to 26 or 45 mg/kg/day caffeine ingested by dams in their drinking water during gestation, 25 or 35 mg/kg/day during lactation or to the two low or high doses ingested during both gestation and lactation. One or both of the gestational or lactational doses reduced locomotor activity and increased defecation in the open field at all ages for males only. Rearing was decreased for both sexes by 25 mg/kg/day lactational caffeine. Numbers of rats that failed to or took longer than 1 min to emerge into the brightly lit arena were increased by 26 mg/kg/day gestational caffeine. All rats that had been exposed to either dose combination of caffeine during both gestation and lactation showed less locomotor and rearing activity, reduced tendencies to emerge within 1 min and, at 6 months of age only, more defecation in the open field. It was concluded that the effects of gestational and lactational exposure to caffeine were additive in their modification of the developing brain as reflected in decreased motor activity possibly arising from heightened emotional reactivity to the testing situation. Hypersensitivity of males to caffeine exposure during either gestation or lactation separately seemed to diminish when exposure was increased for all rats through experience of the drug during both gestation and lactation. Possible involvement of caffeine-induced increases in adenosine receptors in the type of results obtained was discussed.

Caffeine withdrawal: a contrast of withdrawal symptoms in normal subjects who have abstained from caffeine for 24 hours and for 7 days

Two groups of normal subjects were withdrawn from caffeine for either 24 h (n = 9) or 7 days (n = 12). Following a pre-drug test sequence, subjects were given either 250 mg or 500 mg of anhydrous caffeine or a placebo. Tests were repeated 1, 3 and 5 h later. Tiredness, as measured by a visual analogue scale, was the most sensitive indicator of caffeine withdrawal. Headache was only apparent for subjects off caffeine for 24 h and given placebo, confirming this as a specific withdrawal effect, coming on 24-30 h after stopping caffeine. Alertness was increased by caffeine only in the group abstinent for 24 h. After longer term abstention, caffeine had no effects, confirming that drowsiness and lethargy are transient caffeine withdrawal symptoms.

A review of the relationship between coffee consumption and coronary heart disease

A review of the literature dealing with the relationship between coffee consumption and coronary heart disease revealed that most of the studies did not find coffee consumption to be a risk factor. However, many studies are plagued with methodological difficulties which operate to minimize the probability of identifying coffee consumption as a risk factor. A significant percentage of the studies do not rule out coffee consumption as a significant risk factor in coronary heart disease.

Reinforcing effects of caffeine in coffee and capsules

In a residential research ward the reinforcing and subjective effects of caffeine were studied under double-blind conditions in volunteer subjects with histories of heavy coffee drinking. In Experiment 1, 6 subjects had 13 opportunities each day to self-administer either a caffeine (100 mg) or a placebo capsule for periods of 14 to 61 days. All subjects developed a clear preference for caffeine, with intake of caffeine becoming relatively stable after preference had been attained. Preference for caffeine was demonstrated whether or not preference testing was preceded by a period of 10 to 37 days of caffeine abstinence, suggesting that a recent history of heavy caffeine intake (tolerance/dependence) was not a necessary condition for caffeine to function as a reinforcer. In Experiment 2, 6 subjects had 10 opportunities each day to self-administer a cup of coffee or (on different days) a capsule, dependent upon completing a work requirement that progressively increased and then decreased over days. Each day, one of four conditions was studied: caffeinated coffee (100 mg/cup), decaffeinated coffee, caffeine capsules (100 mg/capsule), or placebo capsules. Caffeinated coffee maintained the most self-administration, significantly higher than decaffeinated coffee and placebo capsules but not different from caffeine capsules. Both decaffeinated coffee and caffeine capsules were significantly higher than placebo capsules but not different from each other. In both experiments, subject ratings of "linking" of coffee or capsules covaried with the self-administration measures. These experiments provide the clearest demonstrations to date of the reinforcing effects of caffeine in capsules and in coffee.

Psychophysiological aspects of caffeine consumption

Caffeine may be the psychoactive compound most widely used in the United States. Caffeine appears in coffee, tea, cola drinks, chocolate bars and cocoa, cold and diet medications, and sleep-prevention compounds; the amount of caffeine varies in different substances and according to preparations. Research on caffeine's effects on alcoholic drinks, alertness, anxiety, heart rate, performance, and sleep is reviewed. Caffeine is usually not harmful, although long-range effects of caffeine have not been thoroughly investigated. Caffeine's effects often have been studied by means of ingestion of coffee but substances other than caffeine may be active in coffee and tea. The placebo effect contributes to some of the effects experienced by coffee-caffeine users.

Reinforcing properties of caffeine: studies in humans and laboratory animals

Three types of experimental studies are reviewed: (1) intravenous and oral caffeine self-administration by laboratory animals, (2) oral caffeine self-administration by humans, and (3) human subjective effects of caffeine relevant to reinforcing effects. These studies show that, under appropriate conditions, caffeine can serve as a reinforcer and can produce elevations in subjective drug liking and/or euphoria. In this regard, caffeine can be distinguished from a wide range of behaviorally active compounds, such as the amphetamine analog fenfluramine and the major tranquilizer chlorpromazine, which do not produce such effects. Caffeine can also be distinguished from classic drugs of abuse such as cocaine, d-amphetamine or pentobarbital which generally maintain high levels of self-administration (or liking) in contrast to caffeine which tends to maintain lower levels of self-administration (or liking) or maintain self-administration under a more narrow range of parametric conditions. Several human studies and one animal experiment suggest that physical dependence substantially potentiates the reinforcing effects of caffeine. Other human and animal studies indicate that there may be substantial differences between individual subjects in the reinforcing effects of caffeine. An important challenge for future human and animal drug self-administration research will be to delineate more precisely the conditions under which caffeine does and does not serve reliably as a reinforcer.

Caffeine physical dependence: a review of human and laboratory animal studies

Although caffeine is the most widely used behaviorally active drug in the world, caffeine physical dependence has been poorly characterized in laboratory animals and only moderately well characterized in humans. In humans, a review of 37 clinical reports and experimental studies dating back to 1833 shows that headache and fatigue are the most frequent withdrawal symptoms, with a wide variety of other signs and symptoms occurring at lower frequency (e.g. anxiety, impaired psychomotor performance, nausea/vomiting and craving). When caffeine withdrawal occurs, severity can vary from mild to extreme (i.e. incapacitating). The withdrawal syndrome has an onset at 12-24 h, peak at 20-48 h, and duration of about 1 week. The pharmacological specificity of caffeine withdrawal has been established. The proportion of heavy caffeine users who will experience withdrawal symptoms has been estimated from experimental studies to range from 25% to 100%. Withdrawal symptoms have been documented after relatively short-term exposure to high doses of caffeine (i.e. 6-15 days of greater than or equal to 600 mg/day). Although animal and human studies suggest that physical dependence may potentiate the reinforcing effects of caffeine, human studies also demonstrate that a history of substantial caffeine intake is not a necessary condition for caffeine to function as a reinforcer. The similarities and differences between caffeine and classic drugs of abuse are discussed.

Reasons for consumption and heavy caffeine use: generalization of a model based on alcohol research

The extent of alcohol consumption and problems has been found to be related to the types of reasons for consuming. At least two types of motives have been identified ("personal effects" and "social") with "personal effects" motives related to higher consumption and more alcohol problems. The present study tested the applicability of this model to caffeine consumption, in particular, coffee and tea. Eighteen motives for consuming coffee and tea were used to predict coffee/tea consumption, dependence, and problems. Principal component analyses identified four types of motives: two social ("sociability" and "beverage") and two personal effects ("stimulant" and "relief"). Overall, the "relief" and "stimulant" types of motives were the best predictors for all criterion measures (consumption, dependence and problems); "beverage" motives strongly predicted consumption and dependence; and "sociability" motives were least useful in predicting all criterion measures. These results are consistent with research on the relationship between extent of alcohol consumption/problems and reasons for consuming.

Inherent hyporesponsiveness to methylxanthine-induced behavioral changes associated with supersensitivity to 5'-N-ethylcarboxamidoadenosine (NECA)

Two inbred mouse strains, SWR and CBA, differed significantly in their susceptibility to acute dose dependent theophylline- and caffeine-induced stimulation of locomotor activity. The efficacy of both methylxanthines was reduced in the SWR strain compared to the CBA strain. When brain levels of theophylline were determined at a dose (32 mg/kg IP) which gave maximal behavioral separation of the two strains, no significant differences were found between them (SWR levels 12.5 +/- 1.9, CBA levels 14.3 +/- 1.7 micrograms/g wet weight brain). The dose dependent ability of several adenosine agonists (N6-cyclohexyladenosine, (-)-N6-phenylisopropyladenosine, 5'-N-ethylcarboxamidoadenosine) to depress locomotor activity was investigated. SWR mice were found to be significantly more sensitive to NECA-induced depression of locomotor activity and the NECA-induced hypothermia than were CBA mice (respective ED50 values for inhibition of activity, 11.6 and 30.5 nmoles/kg IP). No differences were found in brain [3H]-NECA levels at doses which produced marked differences in behavioral effects between the two strains. The differences in adenosine agonist sensitivity between the strains were both agonist- and behavior-specific. These data indicate that an inherited alteration in behavioral responsiveness to methylxanthine administration can be inversely associated with inherent alterations in susceptibility to the action of specific adenosine analogs. An adenosine A-2 receptor sub-class may be involved in these changes in in vivo pharmacological susceptibility to the action of both methylxanthines and adenosine agonists on locomotor activity.

Complex genetic determinants of susceptibility to methylxanthine-induced locomotor activity changes

The intent of this study was to investigate the role of inheritance in the determination of susceptibility to methylxanthine-induced behavioral changes. Two strains of inbred mice, SWR and CBA, which differ significantly in their response to caffeine- and theophylline-induced stimulation of locomotor activity, were used in classical genetic crosses to produce reciprocal F1 hybrids, reciprocal backcross progeny F2 progeny. Theophylline dose response curves in the reciprocal F1 hybrid strains were identical to each other and to their methylxanthine-responsive (CBA) parent. These results indicated that theophylline responsiveness behaved as a simple autosomal dominant trait. Behavioral responses of these F1 hybrid strains to caffeine showed the same maximal enhancement of locomotor activity as their CBA progenitor at a dose 10 mg/kg IP, but locomotor activity stimulation also occurred at 32 mg/kg IP, a dose which inhibited their CBA parent. These data suggest that the genes specifying caffeine responsiveness differ from those encoding theophylline responsiveness. For both caffeine and theophylline, behavioral phenotypes and their expected frequencies of occurrence among backcross and F2 progeny differed significantly from the segregation ratios expected for a trait determined by a single gene. These non-Mendelian segregation ratios suggest that locomotor activity stimulation by both of these methylxanthines is polygenically determined. It was anticipated that the same genetically encoded neurochemical mechanism would underlie the difference in behavioral response to the two methylxanthines. However, no significant correlation between caffeine-induced and theophylline-induced stimulation of locomotor activity was observed among progeny derived from backcrosses of F1 self-crosses.(ABSTRACT TRUNCATED AT 250 WORDS)

Caffeine-induced taste aversion and mimetic responses

Novel tastes preceded a range of caffeine doses (10-80 mg/kg) in a taste aversion training trial. One week later rats which had doses of 30 mg or higher showed strong aversions as measured by a single bottle consumption test. The 10 and 20 mg dose produced the most hyperactivity and apparently enhanced intake of the taste paired with caffeine. During the training trial, rats receiving the 80 mg dose exhibited copious gapes and chin-rubs, mimetic responses to noxious tastes. Gapes also occurred in these subjects during the aversion test. Consumption was more sensitive than mimetic responding as a measure of the aversive effects of caffeine. Only the 80 mg dose produced neophobia. Tests with isotonic injections indicated that tonicity was not the source of the aversions.