Study Title and Description
Differential responsiveness to caffeine and perceived effects of caffeine in moderate and high regular caffeine consumers.
Key Questions Addressed
|1||For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on behavior*?|
Primary Publication Information
|Title||Differential responsiveness to caffeine and perceived effects of caffeine in moderate and high regular caffeine consumers.|
|Author||AS Attwood,S Higgs,P Terry,|
Secondary Publication Information
There are currently no secondary publications defined for this study.
Extraction Form: Behavior - Design Details - INCLUDED Studies
No arms have been defined in this extraction form.
|Question... Follow Up||Answer||Follow-up Answer|
|What outcome is being evaluated in this paper?||Behavior|
|What is the objective of the study (as reported by the authors)?||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.|
|Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods)||Participants Forty-nine students and staff from the University of Birmingham, UK (18 male; mean age 23.2 years, range 18–41 years) responded to poster advertisements to take part in a study examining the cognitive effects of over-the counter drugs in return for cash or course credits. Participants were screened by means of an e-mailed intake questionnaire to ensure that all were non-smoking, habitual caffeine consumers. Three participants were excluded due to not turning up for a scheduled session, and one participant was excluded due to being unable to swallow the capsule; thus, 45 participants were included in the analyses. The participants were separated into two groups (moderate vs high consumers) whose daily caffeine intake was less than or greater than 200 mg/day, respectively (see Table 1). To minimize expectancy effects, participants were informed that they could receive one of several possible substances (paracetamol, caffeine, ibuprofen or aspirin). Experimental design Each participant attended two sessions (caffeine and placebo). Inter-session intervals did not fall below 24 h or exceed 14 days. All testing took place between 1200 and 1800 h, and participants attended their sessions at approximately the same time of day. Test times were balanced between consumer groups. Capsule administration was double blind, and approximately equal groups received placebo first vs caffeine first (14 moderate and 9 high consumers had placebo first, and 10 moderate and 12 high consumers had caffeine first). Before each session, participants were asked to abstain from all psychoactive substances from 2300 h the previous night. To promote compliance, a reminder e-mail was sent the day before each session, a saliva assay (which was not analysed) was taken on arrival, and a form confirming abstinence was signed. Capsule administration Caffeine (400 mg; Sigma-Aldrich, Poole, UK) was administered in a gelatin capsule (Shionogi Qualicaps, size-00, Madrid, Spain) with water. The placebo capsule contained arrowroot (Supercook, Leeds, UK). Mood measures Participants completed a pen-and-paper mood questionnaire on arrival and also immediately before and after completion of the computer test battery (approximately 30 and 55 min post-capsule ingestion). Seventeen adjectives were rated on 100-mm VAS (adapted from Rogers et al. 1995) from 0 (not at all) to 100 mm (extremely): "Friendly", "Headache", "Alert", "Cheerful", "Drowsy", "Anxious", "Energetic", "Angry", "Muddled", "Calm", "Tired", "Dejected", "Tense", "Clear-headed", "Relaxed", "Thirsty" and "Jittery". Participants were told to consider each line as the extreme spectrum of that emotion and to transect the line appropriately to show how they were feeling at that specific moment. Post-session questionnaires The post-session questionnaire asked participants to report any perceived effects of the capsule. First, they were asked to tick "yes" or "no" to the question "Did you feel any effect of the capsule?" If they ticked "yes", space was provided for participants to describe these effects. For analysis, these responses were classified as either positive, negative or no effect. The positive responses mentioned were alertness, cheerfulness, increased well-being, decreased drowsiness/tiredness and decreased headache. The negative responses mentioned were anxiety, tension, jitteriness, deflated mood, headache and nausea. "No effect" was recorded when participants ticked "no" to the first part of the question. Procedure On arrival, participants confirmed overnight abstinence from any psychoactive substances and provided a saliva sample. A baseline mood questionnaire and practice on the SRT and CRT (two blocks each) were completed immediately before capsule ingestion. An interval of 30 min then elapsed to allow for drug absorption, during which time the participants were asked to sit quietly (reading material, e.g. current periodicals, was provided). After this interval, the experimenter returned to administer the tests in the following order: second mood questionnaire, RVIP, MTS, SRT, CRT, third mood questionnaire. Finally, participants completed the post-session questionnaire. Statistical analyses Statistical analyses were conducted using Statistical Package for the Social Sciences (SPSS; version 11.5) for Windows. For SRT and CRT movement duration data, reaction times below 100 ms or more than three standard deviations above an individual’s mean score were deemed outliers and removed. There were no differences in the mood changes observed over 30–50 min vs the changes over 0–50 min, so only the changes from baseline to 50 min (i.e. the whole test session) are presented. Independent t-tests examined between-group differences at baseline for reaction time performance and mood. Gender and order of treatment (capsule to be consumed) were included as blocking factors in these analyses but did not influence the outcome. Two-way analyses of variance (ANOVAs) with group (high consumer, moderate consumer) and drug (caffeine, placebo) as between- and within-subject factors, respectively, were conducted on data from the cognitive tasks. A priori planned comparisons were conducted to analyse the effect of capsule on mood and performance scores in the high and moderate consumer groups. Because baseline scores were found to correlate with the test measures, baseline score was included as a covariate where possible. Two participants were omitted from the analyses of the SRT and CRT experimental trials due to corrupt data. For the mood ratings, a principle components analysis was performed using varimax rotation. Analysis of the 17 mood items revealed five factors with eigenvalues greater than 1 that accounted for 69% of the variance. Items with loadings greater than 0.5 were retained on each factor unless the same items had a loading greater than 0.4 on another factor. The five factors were: "Tense negative mood" (items loaded onto this factor were: Tense, Jittery, Angry, Dejected), "Sleepiness/hydration" (items loaded onto this factor were: Drowsy, Tired, Thirsty), "Generalpositive mood" (items loaded onto this factor were: Energetic, Cheerful, Friendly) "Mental clarity" (items loaded onto this factor were: Alert, Clear-headed, Muddled) and "Mental repose" (items loaded onto this factor were: Calm, Relaxed). Participant’s scores for each factor were calculated by adding the scores of all the items loading onto the factor. Two ratings did not load clearly onto any factor (anxiety and headache) and were analysed separately. A two-way ANOVA was conducted on each mood factor with consumer group as a betweensubjects factor. This analysis reduced the number comparisons, thus reducing the likelihood of a Type II error due to conservative corrections for multiple comparisons (Bonferroni correction). Gender and order of capsule administration were included as blocking factors in the analyses of performance and mood; however, their inclusion did not change an outcome, so these results are not reported. Correlation analyses also showed that time since having eaten and time of day of testing did not correlate with the test measures. All post-hoc multiple comparisons employed the Bonferonni correction.|
|How many outcome-specific endpoints are evaluated?||4|
|What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately)||Tense|
|List additional health endpoints (separately).|
|List additional health endpoints (separately)|
|Notes||mood factors for tense and sleepy were based on condensed visual analogue scale results with more information|
|What is the study design?||Controlled Trial|
|Randomized or Non-Randomized?||NCT|
|What were the diagnostics or methods used to measure the outcome?||Subjective|
|Optional: Name of Method or short description||visual analogue scale|
|Caffeine (general)||Caffeine (general)|
|What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.)||placebo (no caffeine) vs 400 mg caffeine|
|What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods)||N/A|
|Provide a general description of results (as reported by the authors).||Caffeine, relative to placebo, significantly increased ratings of "tense negative mood" [F(1, 43)=9.30; p<0.005] and "anxious" [F(1, 43)=4.68; p<0.05] and decreased ratings of "mental repose" [F(1, 43)=9.31; p<0.005] and "sleepiness" [F(1, 43)=6.88; p<0.02]. There were no other significant main effects of caffeine. There were no differences between groups in terms of the number of participants reporting negative effects of caffeine. In contrast, the high consumers were significantly more likely to report positive consequences of caffeine, and the moderate consumers were more likely to report "no effect" [χ2(2, N=45)=7.92; p<0.05; see Table 4].|
|Did the authors perform a dose-response analysis (or trend/related analysis)?||No|
|What were the authors's observations re: trend analysis?|
|What were the author's conclusions?||However, the post-consumption mood measures demonstrated that all participants showed evidence of increases in tense negative mood and anxiety after caffeine and a reduction in mental repose, and analysis of the postsession questionnaire (which examined participants’ perceptions of the effects of capsule ingestion) showed that the two groups did not differ in their reports of negative effects. This suggests that the group differences were not due to stronger experiences of aversive effects among the moderate consumers.|
|What were the sources of funding?||None listed|
|What conflicts of interest were reported?||N/A|
|Does the exposure (dose) need to be standardized to the SR?||No|
|Provide calculations/conversions for the exposure based on the decision tree in the guide (for all endpoints/exposure levels of interest).|
|List all the endpoint(s) followed by the dose (mg) which will be used in comparison to Nawrot. Characterize value as LOAEL/NOAEL, etc. if possible.||Tense - LOAEL = 400 mg/day Anxious - LOAEL = 400 mg/day Sleepy - NOAEL = 400 mg/day Headache - NOAEL = 400 mg/day|
|Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot.||single dose Effects at the level comparable to Nawrot.|
|What is the importance of the study with respect to the adverseness of the outcome?||Important|
No baseline characteristics have been defined for this extraction form.
Results & Comparisons
No Results found.
|Arm or Total||Title||Description||Comments|
No quality dimensions were specified.
No quality rating data was found.