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Study Title and Description

The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.



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 The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.
Author T Giesbrecht,JA Rycroft,MJ Rowson,EA De Bruin,
Country
Year 2010
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 non-proteinic amino acid L-theanine and caffeine, a methylxanthine derivative, are naturally occurring ingredients in tea. The present study investigated the effect of a combination of 97 mg L-theanine and 40 mg caffeine as compared to placebo treatment on cognitive performance, alertness, blood pressure, and heart rate in a sample of young adults (n = 44).
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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) Participants: Forty-four (28 female) young adults aged between 18–34 years (mean 21.2 years; SD, 3.2 years) took part in the study. Their mean habitual daily caffeine consumption was 173.0 mg (SD 86.8 mg). Nearly half this caffeine intake was from tea (mean, 79.4 mg/day; SD, 51.7 mg/day). Participants were all students at the University of Bristol, recruited through print and/or email advertisements. They were rewarded with course credit points, a combination of course credit points and money, or a monetary reward. The study was described as an investigation into the effects of a novel tea-based soft drink on attention and mood. Inclusion criteria were regular caffeinated tea/coffee consumption (i.e. at least five cups per week), nonsmoking, regular breakfast consumption, normal or corrected-to-normal vision, and a body mass index (BMI) between 20–30 kg/m2. Exclusion criteria were allergies to caffeine, artificial sweeteners or herbal supplements, colour blindness, dyslexia, pregnancy, breast-feeding, or medication use with the exception of the contraceptive pill. Participants reported that they were in good health and free from recreational drugs. Physiological measures: Systolic and diastolic blood pressure (BP) and heart rate (HR) were measured using the Omron 711 Intellisense Blood Pressure Monitor (Omron Healthcare, West Sussex, UK). BP and HR served as physiological measures of arousal. Participants had been seated for 5 min before the measurements were taken. As a minimum of two readings is required to obtain a reliable estimate of BP, three readings were taken at each time point. The average of these readings was used in the statistical analysis. Design: The study employed a randomized, placebo-controlled, double-blind, within-subjects design, in which participants received a drink with L-theanine and caffeine on one occasion and a matched placebo drink on the other occasion (treatment order was counterbalanced between participants). Treatment: The experimental treatment consisted of 40 mg of caffeine and 97 mg of L- theanine in a tea-based soft drink. This drink was made by dissolving powder containing tea, sweeteners, and lemon flavour into 500 ml mineral water (powders supplied by Lipton Institute of Tea, Unilever R&D, Colworth, UK). The iced tea powder contained colourings and tea flavourings, as well as sweeteners (sucralose) and lemon flavour to mask the taste of caffeine. The placebo drink matched the active drink except for the absence of L- theanine and caffeine. No interactions between the ingredients, which are present in the ice tea powder and L- theanine and/or caffeine, are expected. Participants consumed the drinks within 10 min. Procedure: On each test day, participants arrived at 9 am having abstained from caffeine, L- theanine and alcohol for a minimum of 12 h. Participants were tested in groups with the experimenter present and each participant being visually isolated from the others. Participants were not allowed to consume anything other than the test drinks until completion of the test day. First, BP and HR were measured and participants completed all cognitive tasks and questionnaires (i.e . baseline measurement; duration 30 min). Second, participants consumed the drink within 10 min, which was followed by a 10 min break. Third, participants completed all tasks and questionnaires again and HR and BP were measured starting at 20 min post-drink. After 20 min break, BP and HR were measured and all tasks and questionnaires were completed for a third time, followed by a BP and HR measurement (i.e . starting at 70 min post-drink). On completion of the study, participants were thanked for their participation and debriefed.
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How many outcome-specific endpoints are evaluated? 2
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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately) Blood pressure
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List additional health endpoints (separately). 2 Heart rate
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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? RCT
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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 Systolic and diastolic blood pressure (BP) and heart rate (HR) were measured using the Omron 711 Intellisense Blood Pressure Monitor (Omron Healthcare, West Sussex, UK).
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Caffeine (general)
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Coffee, Chocolate, energy drink, gum, medicine/supplement, soda, tea, other? Tea
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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 drink.
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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) Changes from pre-treatment baseline in blood pressure and heart rate, cognitive performance, and subjective measures were analyzed using an analysis of variance-based mixed model, with subjects modelled as a random effect and a repeated-measures covariance structure to accommodate likely correlation between subsequent assessments taken from the same individual with drink (experimental vs placebo) and time (20 min post-drink vs 70 min post-drink) as within-subjects factors. The proportion of correct responses on the attention switching task was analyzed with a logistic regression-based generalized linear mixed model, with aforementioned within subject factors. For the switch task, trial type (1st, 2nd, 3rd trial after a switch between task sets) and response type (correct hit, correct withhold) were used as additional within-subject factors. For all tasks, baseline scores were employed as co-variates and order of testing was entered as factor. Standard error and denominator degrees of freedom were estimated by the Kenward–Roger method. Inclusion criteria were regular caffeinated tea/coffee consumption (i.e. at least five cups per week), nonsmoking, regular breakfast consumption, normal or corrected-to-normal vision, and a body mass index (BMI) between 20–30 kg/m2. Exclusion criteria were allergies to caffeine, artificial sweeteners or herbal supplements, colour blindness, dyslexia, pregnancy, breast-feeding, or medication use with the exception of the contraceptive pill. Participants reported that they were in good health and free from recreational drugs.
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What conflicts of interest were reported? The authors are employees of Unilever, which markets food products some of which contain Ltheanine and caffeine.
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Refid 21040626
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What were the sources of funding? The study was sponsored by the Lipton Institute of Tea (<www.liptoninstituteoftea.org>), and was conducted at the Department of Experimental Psychology of the University of Bristol. Drinks were performance supplied by Lipton Institute of Tea, Unilever R&D Colworth, UK.
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