The effects of black tea and other beverages on aspects of cognition and psychomotor performance

Nineteen healthy volunteers ingested 400 ml black tea, coffee, caffeinated water, decaffeinated tea or plain water on three occasions through the day (0900, 1400 and 1900 hours). A 2 × 2 factorial design with caffeine (0, 100 mg) and beverage type (water, tea) was employed, with coffee (100 mg caffeine) as a positive internal control, based on a five-way crossover. A psychometric test battery comprising critical flicker fusion (CFF), choice reaction time (CRT), short-term memory (STM) and subjective sedation (LARS) was performed at regular intervals throughout the day, and intensively so immediately following each beverage. Consumption of tea compared to water was associated with transient improvements in performance (CFF) within 10 min of ingestion and was not affected by the time of day. Caffeine ingestion was associated with a rapid (10 min) and persistent reduction in subjective sedation values (LARS), again independent of time of day, but did not acutely alter CFF threshold. Over the whole day, consumption of tea rather than water, and of caffeinated compared to decaffeinated beverages, largely prevented the steady decline in alertness (LARS) and cognitive capacity observed with water ingestion. The effects of tea and coffee were similar on all measures, except that tea consumption was associated with less variation in CFF over the whole day. No significant treatment effects were apparent in the data for the STM. Tea ingestion is associated with rapid increases in alertness and information processing capacity and tea drinking throughout the day largely prevents the diurnal pattern of performance decrements found with the placebo (no caffeine) condition. It appears that the effects of tea and coffee were not entirely due to caffeine per se; other factors either intrinsic to the beverage (e.g. sensory attributes or the presence of other biologically active substances) or of a psychological nature (e.g. expectancy) are likely to play a significant role in mediating the responses observed in this study. Received: 18 September 1997/Final version: 16 February 1998     

Effects of hot tea, coffee and water ingestion on physiological responses and mood: the role of caffeine, water and beverage type

Psychopharmacological studies using caffeinated beverages or caffeine have rarely considered temporal effects on psychological and physiological function or the specific contribution of caffeine, hot water, or beverage type to the observed effects. The effect of 400 ml hot tea, coffee, and water consumption on systolic and diastolic blood pressure (SBP and DBP), heart rate, skin conductance (a measure of sympathetic nervous system activation), skin temperature, salivary cortisol, and mood were monitored in 16 healthy caffeine-withdrawn (14 h) subjects in a complete crossover design. Beverages were ingested with/without 100 mg caffeine and milk (tea/coffee only). Hot beverage ingestion rapidly increased skin conductance and temperature (+1.7°C) with peak effects observed only 10–30 min post-consumption. Caffeine in the beverage rapidly augmented skin conductance responses but, in contrast to the effect of hot water, reduced the skin temperature response and increased SBP (+2.8 mmHg) and DBP (+2.1 mmHg) 30–60 min post-consumption. Both caffeine and milk addition to beverages independently improved mood and reduced anxiety 30 and 60 min post-consumption. Milk addition had no other effects apart from attenuating the transient increase in physiological responses associated with the drinking phase. There were no effects of beverage consumption on salivary cortisol or of beverage vehicle on salivary caffeine levels, the latter indicating that caffeine pharmacokinetics was similar in both tea and coffee, and not different from caffeinated water. In keeping with this, the responses to tea and coffee ingestion were similar and largely accounted for by the effects of hot water and caffeine. However, tea potentiated the increase in skin temperature compared to coffee and water indicative of a greater vasodilatory response plausibly related to the presence of flavonoids in tea. We conclude that ingestion of hot caffeinated beverages stimulates physiological processes faster than hitherto described, primarily via the effects of hot water and caffeine, but with beverage type and milk playing important modulatory roles. Received: 15 March 1997/Final version: 23 May 1997     

Beliefs,Behaviors, and Contexts of Adolescent Caffeine Use: A Focus Group Study

Background: Caffeinated products are widely available to adolescents, and consumption of caffeine products—energy drinks and coffee in particular—is on the rise in this age group (Branum, Rossen, & Schoendorf, 2014). Yet, little is known about the psychosocial context of caffeine use. Previous studies on adolescent caffeine use have focused on caffeine's acute physiological effects, rather than the psychosocial contexts and beliefs regarding different types of caffeinated beverages (e.g., coffee, energy drinks, soda). Objectives: The current research examines the contexts and beliefs associated with adolescents' use of caffeinated beverages (e.g., coffee, energy drinks, soda) using a focus group approach. Methods: Eleven focus group interviews (49 total participants) addressed adolescents' motivations for and patterns of caffeine use; they were transcribed and axial coding was used to identify common themes. Results: Coffee and energy drinks were perceived to be the most popular caffeinated beverages. Reasons for consuming caffeine included the effect of caffeine as a stimulant, the pleasant feelings experienced when drinking it, and the fact that caffeine was available. As for contexts, coffee was consumed in more diverse social contexts than other caffeinated beverages. Friends and sports were the most popular contexts for energy drink use. Conclusions: The present findings inform adolescent health promotion efforts and provide researchers and practitioners alike detailed information in adolescents' own words about how and why they use caffeine. Adolescents' beliefs about caffeinated products are not uniform; the reasons adolescents articulate regarding their use of coffee, soda, and energy drinks are different across contexts and beverage type.     

The acute physiological and mood effects of tea and coffee: the role of caffeine level

The objective of this study was to determine the effect of caffeine level in tea and coffee on acute physiological responses and mood. Randomised full crossover design in subjects after overnight caffeine abstention was studied. In study 1 (n = 17) the caffeine level was manipulated naturalistically by preparing tea and coffee at different strengths (1 or 2 cups equivalent). Caffeine levels were 37.5 and 75 mg in tea, 75 and 150 mg in coffee, with water and no-drink controls. In study 2 (n = 15) caffeine level alone was manipulated (water, decaffeinated tea, plus 0, 25, 50, 100, and 200 mg caffeine). Beverage volume and temperature (55 degrees C) were constant. SBP, DBP, heart rate, skin temperature, skin conductance, and mood were monitored over each 3-h study session. In study 1, tea and coffee produced mild autonomic stimulation and an elevation in mood. There were no effects of tea vs. coffee or caffeine dose, despite a fourfold variation in the latter. Increasing beverage strength was associated with greater increases in DBP and energetic arousal. In study 2, caffeinated beverages increased SBP, DBP, and skin conductance and lowered heart rate and skin temperature compared to water. Significant dose-response relationships to caffeine were seen only for SBP, heart rate, and skin temperature. There were significant effects of caffeine on energetic arousal but no consistent dose-response effects. Caffeinated beverages acutely stimulate the autonomic nervous system and increase alertness. Although caffeine can exert dose-dependent effects on a number of acute autonomic responses, caffeine level is not an important factor. Factors besides caffeine may contribute to these acute effects.     

A Preliminary Investigation of Caffeinated Alcohol Use During Spring Break

Background: Caffeinated alcoholic beverages (e.g., Red Bull and vodka) are popular but associated with negative consequences. CABs may be particularly popular during Spring Break, a potentially risky social event. Objectives: We aimed to identify the prevalence of Spring Break caffeinated alcohol use, determine how caffeinated alcohol use Spring Break drinking habits differ from usual, and examine the association between Spring Break caffeinated alcohol use and alcohol-related problems. Methods: Data were collected from 95 college students during March of 2013 and 2014. Students completed questionnaires of their alcohol and caffeinated alcohol use before and during Spring Break and Spring Break alcohol-related problems. Results: Approximately 54% of students used caffeinated alcohol during Spring Break. Spring Break caffeinated alcohol use was associated with more alcohol-related problems, even after controlling for other alcohol consumed and Spring Break vacation status. Conclusions/Importance: Caffeinated alcoholic beverages are commonly consumed during Spring Break and their use uniquely predicted harms. Prevention efforts placed on caffeinated alcoholic beverage users may be helpful in reducing Spring Break-related harms.     

Caffeine and caffeinated beverage consumption and fecundability in a preconception cohort

Caffeine is an adenosine receptor antagonist that may influence fertility by affecting ovulation, menstrual characteristics, or sperm quality. We studied the association between female and male preconception caffeine intake and fecundability in a North American prospective cohort study of 2135 pregnancy planners. Frequency of caffeinated beverage intake was self-reported at baseline. Outcome data were updated every 8 weeks until reported pregnancy; censoring occurred at 12 months. Adjusted fecundability ratios (FR) and 95% confidence intervals (CI) were estimated using proportional probabilities regression. Total caffeine intake among males, but not females, was associated with fecundability (FR for ≥300 vs. <100 mg/day caffeine among males = 0.72, 95% CI = 0.54–0.96), although the association was not monotonic. With respect to individual beverages, caffeinated tea intake was associated with slight reductions in fecundability among females, and caffeinated soda and energy drink intake were associated with reduced fecundability among males.     

Beverage caffeine intakes in the U.S.

Caffeine is one of the most researched food components, with the vast majority of dietary contributions coming from beverage consumption; however, there is little population-level data on caffeine intakes in the U.S. This study estimated the caffeine intakes of the U.S. population using a comprehensive beverage survey, the Kantar Worldpanel Beverage Consumption Panel. A nationally representative sample of 37,602 consumers (aged ⩾ 2 years) of caffeinated beverages completed 7-day diaries which facilitated the development of a detailed database of caffeine values to assess intakes. Results showed that 85% of the U.S. population consumes at least one caffeinated beverage per day. The mean (±SE) daily caffeine intake from all beverages was 165 ± 1 mg for all ages combined. Caffeine intake was highest in consumers aged 50–64 years (226 ± 2 mg/day). The 90th percentile intake was 380 mg/day for all ages combined. Coffee was the primary contributor to caffeine intakes in all age groups. Carbonated soft drinks and tea provided a greater percentage of caffeine in the younger (<18 years) age groups. The percentage of energy drink consumers across all age groups was low (⩽10%). These data provide a current perspective on caffeinated beverage consumption patterns and caffeine intakes in the U.S. population.     

Effect of decaffeination of coffee or tea on gastro-oesophageal reflux

Background: Coffee and tea are believed to cause gastrooesophageal reflux : however, the effects of these beverages and of their major component, caffeine, have not been quantified. The aim of this study was to evaluate gastro-oesophageal reflux induced by coffee and tea before and after a decaffeination process, and to compare it with water and water-containing caffeine. Methods: Three-hour ambulatory pH-metry was performed on 16 healthy volunteers, who received 300 ml of (i) regular coffee, decaffeinated coffee or tap water (n = 16), (ii) normal tea, decaffeinated tea, tap water, or coffee adapted to normal tea in caffeine concentration (n= 6), and (iii) caffeine-free and caffeine-containing water (n= 8) together with a standardized breakfast. Results: Regular coffee induced a significant (P < 0.05) gastro-oesophageal reflux compared with tap water and normal tea, which were not different from each other. Decaffeination of coffee significantly (P < 0.05) diminished gastro-oesophageal reflux, whereas decaffeination of tea or addition of caffeine to water had no effect. Coffee adapted to normal tea in caffeine concentration significantly (P < 0.05) increased gastro-oesophageal reflux. Conclusions: Coffee, in contrast to tea, increases gastrooesophageal reflux, an effect that is less pronounced after decaffeination. Caffeine does not seem to be responsible for gastro-oesophageal reflux which must be attributed to other components of coffee.     

Caffeine-induced sleep disruption: effects on waking the following day and its reversal with an hypnotic

The effects of 4 mg/kg and 8 mg/kg caffeine nocte as a model of insomnia, and its potential for reversal with an hypnotic (temazepam 20 mg) were investigated in two double-blind placebo controlled crossover studies, each with six healthy volunteers. Following an adaption night and day, two nights per treatment were assessed with multiple sleep latency tests (MSLTs), performance measures and subjective questionnaires undertaken the following day. In comparison to placebo significant (P < 0.05) increases in sleep onset latency of 30 and 40 min were seen for low and high doses respectively. Significant reductions in sleep duration were limited to the higher dose (total sleep time 80 min, sleep efficiency 17 per cent), as were reductions in slow wave sleep and non-REM sleep which contrasted with increased waking. However, contrast analysis revealed significant dose-related effects for these measures, whilst the lower dose produced more stable effects across nights, suggesting it as more suitable for a model of insomnia in healthy sleepers. Significant decrements in critical flicker fusion (CFF) performance and reduced MSLT latencies reflected increased daytime sleepiness following both doses; although significant subjective changes to sleep and sleep tendency next day were limited to the higher dose. Co-administration of temazepam elixir successfully reversed increased sleep latency seen with the lower caffeine dose and improved subjective sleep, but significant effects on other sleep measures were more limited despite improved mean trends. Similarly, improvements in CFF performance and MSLT latencies failed to achieve significance, suggesting a possible limitation of the hypnotic in overcoming the effects of sleep disturbance and consequences for waking function next day.     

Effect of caffeine-free beverages on elderly hospitalised patients

The objectives of the study were to determine whether, by providing caffeine-free tea and coffee, plasma caffeine concentrations would fall in elderly hospitalised patients, and whether, as a result, sleep profiles and urinary incontinence would be altered. Twenty-eight patients in two wards of an elderly care hospital received caffeine-containing or caffeine-free tea and coffee for consecutive three week periods in a study which was blinded to patients, nurses and investigator. Median caffeine concentration (μg/ml) was stable between the run in period at 2.3 (range 0–5.8) and the caffeine-containing period at 1.6 (range 0.4–6.0), but fell significantly to 0 (range 0–0.7), during the caffeine-free period (P<0.001). In spite of significantly lowered caffeine concentrations, no change in sleep patterns or urinary incontinence was noted. Of 12 patients with sleep problems a benefit to sleep quality was reported by two individuals, one of whom was prescribed hypnotics from which she subsequently successfully withdrew.     

Assessing dietary exposure to caffeine from beverages in the U.S. population using brand-specific versus category-specific caffeine values

Recent reports on caffeine intakes in the United States have highlighted the importance of obtaining accurate and valid measures of caffeine exposure. The objective of this study is to compare two methods of assigning caffeine values to beverages: brand-specific values versus an aggregate single value representing a broader range of products within a beverage category (i.e., category-specific). The two methods yielded some small, but statistically significant differences in the estimation of caffeine intake from coffee, tea, and carbonated soft drinks (CSDs) for all ages combined and within several of the adult age groups (i.e., 35–49, 50–64, and ≥65 years). These differences, while small, suggest that detailed brand-specific data, particularly for CSDs, commercially pre-packaged or bottled teas, coffee, and specialty coffee drinks, provide more accurate estimates of caffeine exposure for some age groups. Despite these differences, these data provide some assurance that studies using a single aggregate caffeine value provide reasonable measures of caffeine exposure, particularly for studies conducted over a decade ago when there were fewer caffeinated products and brand-specific data available. As the caffeinated beverage marketplace continues to evolve, the use of more detailed, brand-specific data will likely strengthen the assessment of caffeine exposure in the United States.     

Beverage caffeine intake in US consumers and subpopulations of interest: estimates from the Share of Intake Panel survey

Concerns exist about the potential adverse health effects of high consumption of dietary caffeine, especially in children and pregnant women. Recommended caffeine intakes corresponding to no adverse health effects have been suggested recently for healthy adults (400–450 mg/day), for women contemplating pregnancy (300 mg/day), and for young children age 4–6 years (45 mg/day). To determine whether current caffeine intake approaches these levels, intake from major dietary sources (coffee, tea and carbonated soft drinks) were measured in 10,712 caffeinated beverage consumers in the 1999 US Share of Intake Panel, a targeted beverage survey. Mean caffeine intakes in adult caffeinated beverage consumers ranged from 106 to 170 mg/day (90th percentile intake was 227–382 mg/day). In children 1–5 and 6–9 years, mean caffeine intakes were 14 and 22 mg/day, respectively; corresponding 90th percentile intakes were 37 and 45 mg/day. Pregnant women consumed an average of 58 mg/day (157 mg/day at the 90th percentile), and women of reproductive age ingested 91–109 mg/day (229–247 mg/day at the 90th percentile). These data show that while mean caffeine intakes are within recommended safe levels, heavy consumers of certain subpopulations, including young children and women contemplating pregnancy, might benefit from dietary advice.     

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.     

Influence of genetic polymorphisms and habitual caffeine intake on the changes in blood pressure,pulse rate,and calculation speed after caffeine intake: A prospective,double blind,randomized trial in healthy volunteers

The aim of this study was to investigate the contribution of gene polymorphisms, in combination with habitual caffeine consumption, to the effect of caffeine intake on hemodynamic and psychoactive parameters. A double-blind, prospective study was conducted with 201 healthy volunteers randomly allocated 2:1 to the caffeinated group (150 mL decaffeinated coffee with additional 200 mg caffeine) or decaffeinated group (150 mL decaffeinated coffee). We measured the changes in blood pressure (BP) and calculation speed upon coffee intake, stratifying with gene polymorphisms, e.g., those in adenosine A_2A receptor (ADORA2A) and cytochrome P450 (CYP) 1A2, and daily caffeine consumption (≤90 mg/day and >90 mg/day). Overall, caffeine intake independently increased BP and calculation speed (p-values < 0.05), irrespective of the polymorphisms. In stratified analysis, a statistical significance within the caffeinated group was observed for the change in systolic BP in the stratum of CYP1A2 polymorphism with daily caffeine consumption ≤90 mg/day: change in systolic BP in the CYP1A2 rs762551 CC group (mean ± SD = 11.8 ± 5.9) was higher than that in the AA/CA group (4.1 ± 5.5). Gene polymorphisms may limitedly modify the effect of caffeine intake on hemodynamic parameters in combination with habitual caffeine consumption.     

Effects of caffeinated vs. non-caffeinated alcoholic beverage on next-day hangover incidence and severity,perceived sleep quality,and alertness

Aims

Beliefs about the effects of mixing caffeine and alcohol on hangover or sleep may play a role in motivation to consume these mixtures; therefore, information is needed about actual effects. We investigated whether intoxication with caffeinated vs. non-caffeinated beer differentially affected perceived sleep quality, sleepiness, and hangover incidence and severity the next morning.

Methods

University students (89%) and recent graduate drinkers were randomized to receive: (1) beer with the equivalent of 69 mg caffeine/12 oz glass of regular beer (n = 28) or (2) beer without caffeine (n = 36), in sufficient quantity to attain a BrAC of 0.12 g%. After an 8-h supervised sleep period, participants completed measures of hangover, sleep quality, sleep latency and time asleep, and sleepiness.

Results

While caffeinated beer improved perceived sleep quality, effect sizes were greater for morning alertness than for quality while sleeping, with no effect on sleep latency or total sleep time. No effects were seen on hangover incidence or severity.

Conclusions

Mixing caffeine and alcohol does not significantly impair amount of sleep or sleep latency, hangover, or sleepiness the morning after drinking to intoxication in this population.     

The effects of tea on psychophysiological stress responsivity and post-stress recovery: a randomised double-blind trial

Rationale Tea has anecdotally been associated with stress relief, but this has seldom been tested scientifically.Objectives To investigate the effects of 6 weeks of black tea consumption, compared with matched placebo, on subjective, cardiovascular, cortisol and platelet responses to acute stress, in a parallel group double-blind randomised design.Materials and methods Seventy-five healthy nonsmoking men were withdrawn from tea, coffee and caffeinated beverages for a 4-week wash-out phase during which they drank four cups per day of a caffeinated placebo. A pretreatment laboratory test session was carried out, followed by either placebo (n = 38) or active tea treatment (n = 37) for 6 weeks, then, a final test session. Cardiovascular measures were obtained before, during and after two challenging behavioural tasks, while cortisol, platelet and subjective measures were assessed before and after tasks.Results The tasks induced substantial increases in blood pressure, heart rate and subjective stress ratings, but responses did not differ between tea and placebo treatments. Platelet activation (assessed using flow cytometry) was lower following tea than placebo treatment in both baseline and post-stress samples (P < 0.005). The active tea group also showed lower post-task cortisol levels compared with placebo (P = 0.032), and a relative increase in subjective relaxation during the post-task recovery period (P = 0.036).Conclusions Compared with placebo, 6 weeks of tea consumption leads to lower post-stress cortisol and greater subjective relaxation, together with reduced platelet activation. Black tea may have health benefits in part by aiding stress recovery.Funding: This research was supported by a Link award from the Biotechnology and Biological Sciences Research Council, UK, by Unilever Research Colworth, and by the British Heart Foundation.An erratum to this article can be found at     

Caffeine content of specialty coffees

Caffeine is the world's most widely consumed drug with its main source found in coffee. We evaluated the caffeine content of caffeinated and decaffeinated specialty coffee samples obtained from coffee shops. Caffeine was isolated from the coffee by liquid-liquid extraction and analyzed by gas chromatography with nitrogen-phosphorus detection. In this study, the coffees sold as decaffeinated were found to have caffeine concentrations less than 17.7 mg/dose. There was a wide range in caffeine content present in caffeinated coffees ranging from 58 to 259 mg/dose. The mean (SD) caffeine content of the brewed specialty coffees was 188 (36) mg for a 16-oz cup. Another notable find is the wide range of caffeine concentrations (259-564 mg/dose) in the same coffee beverage obtained from the same outlet on six consecutive days.     

Coffee and Caffeine Protect against Liver Injury Induced by Thioacetamide in Male Wistar Rats

Coffee intake has been inversely related to the incidence of liver diseases, although there are controversies on whether these beneficial effects on human health are because of caffeine or other specific components in this popular beverage. Thus, this study evaluated the protective effects of coffee or caffeine intake on liver injury induced by repeated thioacetamide (TAA) administration in male Wistar rats. Rats were randomized into five groups: one untreated group (G1) and four groups (G2–G5) treated with the hepatotoxicant TAA (200 mg/kg b.w., i.p.) twice a week for 8 weeks. Concomitantly, rats received tap water (G1 and G2), conventional coffee (G3), decaffeinated coffee (G4) or 0.1% caffeine (G5). After 8 weeks of treatment, rats were killed and blood and liver samples were collected. Conventional and decaffeinated coffee and caffeine intake significantly reduced serum levels of alanine aminotransferase (ALT) (p < 0.001) and oxidized glutathione (p < 0.05), fibrosis/inflammation scores (p < 0.001), collagen volume fraction (p < 0.01) and transforming growth factor β‐1 (TGF‐β1) protein expression (p ≤ 0.001) in the liver from TAA‐treated groups. In addition, conventional coffee and caffeine intake significantly reduced proliferating cellular nuclear antigen (PCNA) S‐phase indexes (p < 0.001), but only conventional coffee reduced cleaved caspase‐3 indexes (p < 0.001), active metalloproteinase 2 (p ≤ 0.004) and the number of glutathione S‐transferase placental form (GST‐P)‐positive preneoplastic lesions (p < 0.05) in the liver from TAA‐treated groups. In conclusion, conventional coffee and 0.1% caffeine intake presented better beneficial effects than decaffeinated coffee against liver injury induced by TAA in male Wistar rats.     

The use of caffeinated alcoholic beverages among underage drinkers: Results of a national survey

Objective

The mixing of alcoholic beverages with caffeine has been identified as a public health problem among college students; however, little is known about the consumption of such drinks among younger adolescents. We estimated the prevalence of caffeinated alcoholic beverage (CAB) use among a wide age range of underage drinkers, examined differences in traditional (i.e. self-mixed alcoholic beverages with soda, coffee and tea) and non-traditional CAB use (pre-mixed caffeinated alcoholic beverages or self-mixed alcoholic beverages with energy drinks or energy shots) among underage drinkers by age and other demographic characteristics, and examined differences in hazardous drinking behavior between CAB and non-CAB users.

Methods

We used an existing Internet panel maintained by Knowledge Networks, Inc. to assess the use of pre-mixed and self-mixed CABs in the past 30 days among a national sample of 1031 youth drinkers age 13–20. We conducted logistic regression analyses to estimate the relationship between traditional and non-traditional CAB use and risky drinking behavior as well as adverse outcomes of drinking, while controlling for age, gender, race/ethnicity, income, and general risk-taking (seat belt use).

Results

The overall prevalence of CAB use in the sample of underage drinkers was 52.4% (95% confidence interval [CI], 47.4%–57.4%). CAB prevalence was 48.4% among 13–15 year-old drinkers, 45.3% among 16–18 year-old drinkers, and 58.4% among 19–20 year-old drinkers. After controlling for other variables, we found a continuum of risk with non-traditional CAB use most significantly associated with binge drinking (odds ratio [OR] = 6.3), fighting (OR = 4.4), and alcohol-related injuries (OR = 5.6).

Conclusions

The problem of caffeinated alcoholic beverage use is not restricted to college-aged youth. The prevalence of CAB use among underage drinkers is higher than previously thought and begins in early adolescence. Adolescents who consume CABs, and particularly non-traditional CABs, are at increased risk of adverse outcomes.     

Caffeine-associated stimuli elicit conditioned responses: an experimental model of the placebo effect

Rationale: A neutral stimulus repeatedly paired with administration of a drug may elicit a conditioned response. This process, termed pharmacological classical conditioning, may be important in the understanding of placebo effects. Objective: The unconditioned response to caffeine is increased physiological and psychological arousal. The present study investigated whether stimuli associated with the use of caffeine, i.e. the smell and taste of coffee, elicited a conditioned increase in arousal. It was also investigated whether conditioned arousal modulated the unconditioned arousal induced by caffeine. Methods: Twenty subjects who drank at least two cups of coffee per day were exposed to four conditions in a within-subjects design, where the subjects received coffee or orange juice crossed with placebo or 2 mg/kg caffeine. Dependent variables were skin conductance responses and startle reflexes to 85 dB noise bursts, skin conductance levels, blood pressure, heart rate, and subjective measures of arousal. Results: Both caffeine (caffeinated juice) and caffeine-associated stimuli (decaffeinated coffee) increased subjective and physiological arousal. When caffeine and caffeine-associated stimuli were presented together (caffeinated coffee), a non-significant tendency towards an additive effect of the conditioned arousal on the unconditioned arousal to caffeine was seen in some dependent variables. Conclusions: Presentation of caffeine-associated stimuli to caffeine-users elicited conditioned responses similar to the unconditioned drug response. Thus, presentation of caffeine-associated stimuli could be used as an experimental model of placebo effects. Received: 23 November 1998/Final version: 16 February 1999