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Study Title and Description

Caffeine increases psychomotor performance on the effort expenditure for rewards task.



Key Questions Addressed
1 For [population], is caffeine intake above [exposure dose], compared to intakes [exposure dose] or less, associated with adverse effects on cardiovascular outcomes?
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Primary Publication Information
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TitleData
Title Caffeine increases psychomotor performance on the effort expenditure for rewards task.
Author MC Wardle,MT Treadway,H de Wit,
Country
Year 2012
Numbers

Secondary Publication Information
There are currently no secondary publications defined for this study.


Extraction Form: Cardiovascular Design
Design Details
Question... Follow Up Answer Follow-up Answer
What outcome is being evaluated in this paper? Cardiovascular
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What is the objective of the study (as reported by the authors)? The current study examined acute effects of 200 mg of caffeine on willingness to exert effort for monetary rewards at varying levels of reward value and reward probability, in young adult light caffeine users.
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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) The subjects arrived at the lab at 9:00 am, completed breath and urine tests and completed subjective and cardiovascular measures of drug effects every 30 min until noon. At 9:30 they ingested placebo capsules (part of the large study protocol not further described here), and at noon they ingested four opaque size 00 gelatin capsules containing either 200 mg caffeine or placebo. At 12:30 pm participants completed subjective and cardiovascular measures of drug effects, as well as cognitive tests not reported here. At 1:30 participants completed the EEfRT. At 1:50 pm they completed final measures of subjective and cardiovascular drug effects, and left the laboratory. We also measured blood pressure using portable monitors (Life Source, A&D Company, Tokyo, Japan), with mean arterial pressure (MAP; [Systolic BP + 2* Diastolic BP] /3) as our measure of cardiovascular effects. They arrived at the lab at 9:00 am, completed breath and urine tests and completed subjective and cardiovascular measures of drug effects every 30 min until noon.
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How many outcome-specific endpoints are evaluated? 1
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Mean arterial pressure
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List additional health endpoints (separately). 2
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List additional health endpoints (separately).3
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List additional health endpoints (separately).4
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List additional health endpoints (separately).5
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List additional health endpoints (separately).6
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Clinical, physiological, other Physiological
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What is the study design? Controlled Trial
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Randomized or Non-Randomized? NCT
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What were the diagnostics or methods used to measure the outcome? Objective
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Optional: Name of Method or short description We also measured blood pressure using portable monitors (Life Source, A&D Company, Tokyo, Japan), with mean arterial pressure (MAP; [Systolic BP + 2* Diastolic BP] /3) as our measure of cardiovascular effects.
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Caffeine (general) Caffeine (general)
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Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other?
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Measured or self reported? Measured
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Children, adolescents, adults, or pregnant included? Adults
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What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.) Placebo vs. caffeine treatment
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What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models.  Copy from methods) Inclusion criteria were: Body Mass Index between 19 and 26, no medical or psychiatric contraindications, no prescription medication or herbal supplement use, not pregnant, nursing, or trying to become pregnant, not smoking in the last 6 months, alcohol consumption below 21 units/week for females or 28 units/week for males, no history of adverse reactions to caffeine, fluency in English and reported caffeine consumption of <500 mg/week, including all dietary sources. Estimated average caffeine consumption (based on self-report of types/quantities of caffeinated beverages) was 227 mg/week (SD = 139, range = 25 mg–500 mg), or around two cups of drip coffee per week. Effects of caffeine on EEfRT choices were analyzed using generalized linear mixed effect (GLME) models. Button press rates on the EEfRT indexed general psychomotor speeding, and were analyzed using linear mixed effect (LME) models. Repeated measures of "feel drug" and MAP indexed typical caffeine effects and were also analyzed using LME models. All analyses were completed in the lme4 package (v 0.999375-42; Bates et al., 2011) of the R statistical computing environment (v. 2.14.0; R Development Core Team, 2011). (G)LME models offer significant advantages relative to traditional repeated-measures ANOVA in handling of missing data, relaxation of assumptions of normality and homogeneity of variance, and increased statistical power for smaller sample sizes (as they focus on the pertrial level rather than the per-subject level; Raudenbush and Bryk, 2002). EEfRT models (choice and press rate) included reward magnitude of the HC/HR option (RM), probability (P) and Expected value (EV; or the RMÅ~P interaction) as independent (fixed) variables, and also included trial number and effect of session as covariates to control for possible fatigue over the task or over sessions. Subjective and cardiovascular drug effect models included the effect of time as an independent variable and effect of session as a covariate. The effect of drug in all models was a linear contrast between caffeine and placebo (all models included data from the other drug sessions to allow better estimation of order and session effects, but did not estimate effects of the other test substance on the DVs). All models also included a random effect for participant to account for non-independence of trials within participants. Effect sizes are reported as unstandardized coefficients (B ) with standard errors (SE ).
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What conflicts of interest were reported? Not mentioned.
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Refid 22750066
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What were the sources of funding? The research was supported by grants from the National Institute on Drug Abuse (R01 DA002812) to HdW. MCW is supported by a National Institute on Drug Abuse Training grant, T32 DA007255. The contribution of MTT to this work was supported by F31 MH1087015-02 from the National Institute of Mental Health.
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Results & Comparisons

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