Study Title and Description
Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance.
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||Faster but not smarter: effects of caffeine and caffeine withdrawal on alertness and performance.|
|Author||PJ Rogers,SV Heatherley,EL Mullings,JE Smith,|
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 measure the effects of overnight caffeine abstinence and caffeine administration as a function of level of habitual caffeine consumption.|
|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 The results reported here are from a total of 369 participants for whom there was evidence (salivary caffeine concentration) confirming their caffeine consumer status and compliance with the requirement to abstain from caffeine overnight before testing (see Rogers et al. (2010) for details) and complete data available for mental alertness, sleepiness, anxiety/jitteriness and task performance. These participants were aged between 18 and 62 years and were non- or light smokers (≤5 cigarettes or equivalent a day—smoking was not permitted during the test day until after the participants left the laboratory). Based on information recorded in a caffeine intake questionnaire (Rogers et al. 2010), the participants were divided into ‘non-low’ and ‘medium-high’ caffeine consumers (caffeine intake of <40 and ≥40 mg/day, respectively) and randomly assigned to receive caffeine (caffeine BP anhydrous powder) at 11:15 AM (100 mg) and 12:45 PM (150 mg) or placebo (cornflour) on both occasions. Each of these treatments was double-blindly administered in a single, white, size 1 cellulose capsule. They were identical in appearance and were swallowed with 50 ml of room temperature water. The two doses of caffeine ensured that systemic caffeine concentration during the afternoon modelled that expected for individuals consuming two to three cups of ground coffee previously that day. Measures The test battery, which included the mental performance and motor tasks and mental alertness, etc., rating scales, was programmed using E-Prime 1.0 (Psychology Software Tools, Science Plus Group bv, 9747 AA Groningen, The Netherlands) and run on networked PCs with 15-in. coloured monitors and standard QWERTY keyboards. Mental alertness, sleepiness and anxiety/jitteriness were measured using the following items from the Mood, Alertness and Physical Sensations Scales (Rogers et al. 2010): I feel mentally alert/attentive/able to concentrate/observant; I feel sleepy/drowsy/half awake; I feel anxious/tense/nervous/ on edge combined with I feel jittery/shaky. These are similar to three of 11 items (clusters) of Goldstein et al. (1969) (i.e. A 0 alert, attentive, observant, able to concentrate; E 0 sleepy, tired, drowsy, half-awake; C 0 jittery, nervous, shaky). Our participants indicated their current state using the horizontal number pad on the computer keyboard, where 1 represented ‘not at all’ and 9 represented ‘extremely’ (adjusted to a 0 to 8 scale for the presentation of the results here). Procedure Between two and six participants were tested on any single day. They arrived at the laboratory at 9:30 AM having been instructed to abstain from caffeine consumption from at least 7:00 PM of the previous evening, and they left at 4:15 PM. An initial briefing session was held in a communal room, and this same room was used for rest periods, lunch (a light lunch was served at 12:50 AM) and debriefing. The participants completed the mental performance and tapping tasks and the mental alertness, etc., ratings in a room close by, where each individual was accommodated in separate, private booths. They completed this battery of tasks a total of four times: before treatment (baseline, starting at 10:30 AM), starting at 45 min after the first dose of caffeine or placebo and starting at 60 and 135 min after the second dose of caffeine or placebo. This was part of a larger protocol described in fuller detail elsewhere (Rogers et al. 2010). Data analysis Post-treatment data were analysed for the effects of caffeine (caffeine versus placebo) and consumer status. In order to simplify the presentation, only the results from measures taken after the administration of the second dose of caffeine (means of the data from the third and fourth repeats of the task battery) are reported in detail here. For the post-treatment data, multiple paired comparisons were made using Tukey’s honestly significant difference test (Ferguson and Takane 1989). In further analyses of the effects of caffeine, pre-treatment baseline scores were included as a covariate. Because their scores for a majority of variables differed or tended to differ at baseline, these particular analyses were carried out separately for non-low and medium-high consumers (the purpose was to control for baseline differences within consumer status groups, not between these groups). Gender was included as a fixed factor, and age and smoking status (smoking tended to be associated with caffeine intake—see "Results") were included as covariates in all of the above analyses. We also examined the contributions of caffeine’s effects on sleepiness and anxiety/jitteriness to its effect on mental alertness. These analyses were done for only those participants who received caffeine and separately for non-low and medium-high caffeine consumers. Alpha was set at 0.05 (two-tail).|
|How many outcome-specific endpoints are evaluated?||2|
|What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately)||sleepiness|
|List additional health endpoints (separately).|
|List additional health endpoints (separately)|
|What is the study design?||Controlled Trial|
|Randomized or Non-Randomized?||RCT|
|What were the diagnostics or methods used to measure the outcome?||Subjective|
|Optional: Name of Method or short description||Mood, Alertness and Physical Sensations Scales|
|Caffeine (general)||Caffeine (general)|
|What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.)||placebo (0 mg caffeine) vs 250 mg caffeine (split dose, 100 mg + 150 mg)|
|What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods)|
|Provide a general description of results (as reported by the authors).||There was a significant main effect of caffeine for all measures except recognition memory (p00.065), a significant consumer status effect for all but anxiety/jitteriness, choice reaction time and tapping performance, and a significant or marginally insignificant caffeine by consumer status effect for all but sleepiness and tapping performance. Generally, the difference between caffeine and placebo treatments was larger for medium-high consumers, with the striking result being lower mental alertness, greater sleepiness and, with the exception of the tapping task, poorer performance on all tasks in medium-high consumers who received placebo than in the other three groups (Fig. 1). Except for anxiety/jitteriness, caffeine affected medium-high consumers’ responses on all measures: sleepiness, mental alertness, simple reaction time, choice reaction time, choice reaction time errors, recognition memory and tapping speed (dagger in Fig. 1). Caffeine did not affect mental alertness or the number of errors made on the recognition memory and choice reaction time tasks in non-low consumers, though it did reduce their sleepiness, increase their anxiety/jitteriness and speed up their tapping performance, and to a smaller extent it also speeded up their choice reaction time and simple reaction time performance (dagger in Fig. 1).|
|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?||although caffeine reduced sleepiness in non-low consumers, this appears to have been offset by an increase in anxiety/jitteriness, resulting in no net benefit for mental alertness. Mental alertness was lowest and sleepiness highest in medium-high consumers who received placebo, and the effect of caffeine was to normalise their mental alertness and sleepiness—medium-high consumers treated with caffeine displayed almost the same levels of mental alertness and sleepiness as non-low consumers treated with placebo. This is fully consistent with withdrawal reversal and indicates nearly complete tolerance to these effects of caffeine. Caffeine also reduced sleepiness in non-low consumers despite their placebo level of sleepiness being lower than that of the medium-high consumers.|
|What were the sources of funding?||This research was funded by a grant (BBS/B/01855) from the UK Biotechnology and Biological Sciences Research Council.|
|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.||sleepiness - NOAEL = 250 mg/day (in both non-low consumers and medium-high consumers) anxiety-jitteriness - LOAEL = 250 mg/day (non-low consumers); NOAEL = 250 (medium-high consumers)|
|Notes regarding selection/listing of endpoints and exposures/doses to be compared to Nawrot.||single (split) dose caffeine reduced sleepiness in both types of consumers effect on anxiety seen at levels below Nawrot in non-low consumers only|
|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.