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Nutritional Neuroscience 2010 Vol 13 No 6 283
The combination of L-theanine and caffeine
improves cognitive performance and increases
subjective alertness
T. Giesbrecht1, J.A. Rycroft2, M.J. Rowson3, E.A. De Bruin1
1Sensation, Perception, and Behaviour, Unilever R&D, Vlaardingen, The Netherlands
2Lipton Institute of Tea and 3Data Sciences Group, Unilever R&D Colworth House, Sharnbrook, Bedford, UK
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). Cognitive
performance, self-reported mood, blood pressure, and heart rate were measured before L-theanine
and caffeine administration (i.e. at baseline) and 20 min and 70 min thereafter. The combination of
moderate levels of L-theanine and caffeine significantly improved accuracy during task switching
and self-reported alertness (both P< 0.01) and reduced self-reported tiredness (P< 0.05). There
were no significant effects on other cognitive tasks, such as visual search, choice reaction times, or
mental rotation. The present results suggest that 97 mg of L-theanine in combination with 40 mg of
caffeine helps to focus attention during a demanding cognitive task.
Keywords: caffeine, theanine, attention, alertness
Introduction
Traditionally, tea consumption has been associated
with mental clarity.1This effect has been attributed to
the non-proteinic amino acid L-theanine and caffeine,
a methylxanthine derivative, which are naturally
occurring ingredients in tea. Both have been associated
with behavioural and physiological effects (for a
review, see Bryan2). The psychostimulant effects of
caffeine have been frequently demonstrated (for a
review, see Ruxton3). Specifically, caffeine has been
shown to increase self-reported alertness, improve
mood, and enhance psychomotor and cognitive
performance.4,5 Furthermore, studies investigating the
effects of caffeine on different aspects of attention
have provided support for enhanced vigilance,6faster
reaction times,7and narrowing of the focus of
attention.8
L-Theanine has been demonstrated to influence
resting-state cortical activity as measured by the
electroencephalogram (EEG). For example, Ito et al.9
showed that 200 mg of L-theanine increased power in
the alpha frequency in higher anxiety individuals (see
also Song et al.10). This finding has recently been
replicated and extended by Nobre et al.11 who showed
that the normal increase of alpha power during
prolonged rest is facilitated by intake of 50 mg of L-
theanine irrespective of anxiety status.
Interestingly, higher levels of resting state alpha
power are thought to be associated with superior
attentional capacities.12 That is why the aforementioned
resting state EEG findings have inspired two EEG
studies directed at the specific effect of L-theanine on
Research article
Correspondence to: Timo Giesbrecht, Unilever Food and Health
Research Institute, PO Box 114, 3130 AC Vlaardingen, The Netherlands
Tel: +31 10 460 6166; Fax: +31 10 460 5794;
E-mail: Timo.Giesbrecht@unilever.com
Received 4 November 2009, manuscript accepted 29 September 2010
© W. S. Maney & Son Ltd 2010
DOI 10.1179/147683010X12611460764840
Published by Maney Publishing (c) W.S Maney & Son Limited
the brain’s attentional circuitry during the execution of
demanding cognitive tasks.13,14
Specifically, Gomez-Ramirez et al.13 used an
intersensory attention cueing task and found that
250 mg of L-theanine increased the difference in
phasic (task-induced) alpha band activity between
attending to auditory or visual stimuli whilst
suppressing information from the other modality, and
at the same time synchronised tonic (background)
alpha activity.15 Both increased task-induced alpha
and increased background alpha synchronisation
during the task indicate more efficient attentional
processing. The latter finding seemingly contradicts
prior studies. However, it is important to keep in mind
that tonic activity was measured while participants
were engaged in a highly demanding task in this study,
rather than in a passive resting state. In a follow-up
study, Gomez-Ramirez et al.14 replicated the latter
effect in a visuospatial task.
In contrast to the robust relationship between L-
theanine and power in the alpha band of the EEG,
relatively few beneficial effects of L-theanine in
isolation have been found in studies using behavioural
measures of alertness and cognitive performance.16,17
However, L-theanine is virtually only found in tea.
Therefore, theanine is commonly consumed in
combination with caffeine rather than in isolation.
Nevertheless, only few studies have focused on the
interactive effects of L-theanine and caffeine on mood
and cognitive performance, comparing their effects
alone and in combination. Owen et al.18 used
moderate doses of 100 mg of L-theanine and 50 mg of
caffeine and found that both caffeine alone and the
combination of L-theanine and caffeine improved
accuracy on an attention-switching task and reduced
distractibility in a memory task compared to placebo.
Likewise, Haskell et al.16 examined the effects of
250 mg of L-theanine and 150 mg of caffeine and
found a significant positive L-theanine by caffeine
interaction on delayed word recognition reaction time.
L-Theanine consumed in isolation was associated with
reduced performance on the serial sevens task and
increased headache ratings. Further investigation of
the main effects showed that both caffeine alone and
the combination of L-theanine and caffeine improved
accuracy on a rapid information processing task and
decreased self-reported mental fatigue. The
combination of L-theanine and caffeine also led to
faster simple reaction times and numeric working
memory reaction time, improved sentence verification
accuracy, increased alertness and decreased tired
ratings compared to placebo while caffeine alone did
not.16
A recent study by Kelly et al.19 extended the findings
of both Owen et al.18 and Gomez-Ramirez et al.13 by
exploring whether the beneficial effects of L-theanine
and caffeine on attention could also be found at lower
doses (i.e. 100 mg L-theanine and 50 mg caffeine) using
both behavioural measures and EEG. No behavioural
or electrophysiological effects were observed for caffeine
or L-theanine alone, but the combination of L-theanine
and caffeine was shown to improve performance on a
visuospatial cueing task and to modulate alpha brain
activity. Both findings suggest enhanced preparatory
attentional deployment as compared to the placebo
condition.20 Thus, both behavioural and neuro-imaging
studies seem to indicate that L-theanine and caffeine
together may have greater positive effects on cognitive
performance and attention in particular than either
ingredient alone. Likewise, a recent fMRI study
compared a tea base with L-theanine (135 mg) in
combination with caffeine (350 mg) or without the latter
two (L-theanine, 6 mg; caffeine, 21 mg). The active
treatment modulated activation in the executive control
network,21 including increased activation of the
ventrolateral prefrontal cortex, which is involved in
inhibition. Activity in the alerting/orienting network
was also influenced including increased activity at the
border of the dACC and supplementary motor area,
precentral gyrus, the left lateral occipital cortex, superior
portions of the middle frontal gyrus bilaterally, and the
inferior frontal gyrus bilaterally.22
The aim of the present study was to investigate
further the cognitive and subjective effects of L-theanine
in combination with caffeine. In line with previous
research, it was hypothesized that the combination of L-
theanine and caffeine would improve attention
especially on demanding cognitive tasks13 such as the
attention switching task. To investigate the specificity of
possible findings, a choice-reaction-time, an egocentric
mental-rotation task, and a visual-search task were
added to the design. These tasks have been shown to be
sensitive to the cognitive effects of caffeine;8,23,24 however,
most studies used higher levels than the ones found in
the present study or found in regular tea for that matter.
Moreover, it was hypothesized that the combination of
L-theanine and caffeine would improve self-reported
alertness and would reduce experienced task demands.
Subjects and 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
284 Nutritional Neuroscience 2010 Vol 13 No 6
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Published by Maney Publishing (c) W.S Maney & Son Limited
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). Estimated mean daily L-theanine
intake for this sample was 39.7 mg (SD, 25.9 mg).
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. The protocol for this
study was approved by the University of Bristol,
Faculty of Science Human Research Ethics Committee,
and all participants provided informed consent.
Inclusion criteria were regular caffeinated tea/coffee
consumption (i.e. at least five cups per week), non-
smoking, 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.
Cognitive tasks
Choice-reaction-time task
This task was based on the two-choice reaction time
task developed by Eriksen and Eriksen25 (see also
Broadbent et al.26). On each trial, three warning
crosses were presented on the monitor for 500 ms and
then replaced by a target letter (A or B). This target
was either presented alone or accompanied by
distracter stimuli on both sides. The distracters were
stars, letters the same as the target or letters different
to the target letter that were positioned either near or
far from the target. Participants were required to
indicate as quickly and accurately as possible whether
the target was an A or B by means of a key press. Ten
continuous blocks of 16 trials were completed. Trials
were self-paced. The order of these trials was
randomized. The dependent variables were mean
reaction time and accuracy. A practice block of 32
trials was completed during the training session.
Visual-search task
This task was based on the feature search task
developed by Treisman and Gelade.27 On each trial,
participants were required to detect the presence or
absence of a target arrow (upward facing arrow)
amongst a visual display of 16 arrows. The distracter
arrows either all faced the same direction or different
directions. An upward arrow was present on some
trials and absent on others. Participants were required
to indicate the presence or absence of the target
stimulus as quickly and accurately as possible by key
press. Stimuli were presented for 1200 ms and trials
were terminated on response. Trials were spaced 300
ms from each other. 320 trials were completed.
Reaction times and correct responses were measured.
A practice block of 40 trials was completed during the
training session.
Egocentric mental-rotation task
This task was based on the mental own-body
transformation task developed by Parsons28 and Zacks
et al.29 Left–right judgments about the position of a
target shape (black square) located on the hand or foot
of a schematic human figure were required after
having imagined being in the body position of the
figure. A number of possible shapes were located on
the body, including a black square (BS), black circle
(BC), white circle (WC) and/or white square (WS).
There were 5 different shape combinations, three of
which required a left/right response (i.e. BS–WS,
BS–WC, BS–WS) and two that required no response
(i.e. BC–WC, BC–WS). The schematic figure could be
facing to the front or backwards, the right way up or
upside down. On each trial, a fixation cross was
presented for 300 ms followed by the stimulus, which
was presented for 2000 ms being terminated on
response. Next, they were presented with a blank
screen for 1000 ms during which participants could
still respond. Two continuous blocks of 96 trials
presented in randomized order were completed.
Reaction times and correct responses were quantified.
A practice block of 42 trials was completed during the
training session.
Attention-switching task
This task was based on the methods described by
Rogers and Monsell.30 On each trial, a pair of
characters consisting of a letter and a number was
presented on the screen simultaneously. The letters
used were drawn from a set of letters containing four
vowels (A, E, I, U) and four consonants (G, K, M, R)
and the numbers were drawn from a set containing
four even numbers (2, 4, 6, 8) and four odd numbers
(3, 5, 7, 9). The letter and number were drawn at
random with the only constraint being that neither the
letter nor the number was repeated with respect to the
previous trial. Numbers and letters were presented 1º
to the left or right of the central fixation point. Each
set of character pairs was displayed on the screen for
1000 ms. Stimuli were coloured and alternated
Nutritional Neuroscience 2010 Vol 13 No 6 285
Giesbrecht et al. L-theanine, caffeine and cognitive performance
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between three red and three purple sets. Participants
were instructed to respond by pressing the space bar
on the keyboard as quickly as possible to even
numbers only if the stimulus colour was purple and
respond to vowels only if stimuli were red.
Participants completed four blocks of 144 trials per
session. Performance was evaluated in terms of
reaction times and hits. Four practice blocks of 42
trials were completed during the training session.
Self-report measure
Task demand rating scale
This scale was used in previous research on caffeine.8
On completing the test battery, participants rated how
difficult, effortful, and tiring they experienced the
tasks on 9-point scales (anchors: 1, not at all and 9,
extremely).
Bond–Lader visual analogue mood scale31
This mood scale comprises 16 bipolar items. Each
item consisted of an adjective pair (e.g. tense/relaxed)
which serve as anchors for a 100 mm visual-analogue
(VAS) scale on which participants are required to
indicted how they feel. Three factors can be derived
from the individual scores: alertness, calmness and
contentedness.
Cognitive tasks and self-report measures were
completed in the order in which they are presented
and took about 30 min to complete.
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,32 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). Participants
attend a practice session to familiarize themselves with
the test battery and to limit the influence of trainings
effects. Experimental sessions were conducted at least
6 days but no more than 14 days apart. The order of
conditions was balanced.
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.
L-Theanine is nearly universally consumed in
combination with caffeine with a regular cup of tea
containing 35–61 mg of caffeine and 4.5–22.5 mg of
L-theanine. As we were specifically interested in the
role L-theanine and in line with prior studies,18,33 we
increased the amount of theanine relative to caffeine
to amplify possible effects of L-theanine.
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.
Statistical analysis
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
286 Nutritional Neuroscience 2010 Vol 13 No 6
Giesbrecht et al. L-theanine, caffeine and cognitive performance
Published by Maney Publishing (c) W.S Maney & Son Limited
as a random effect and a repeated-measures co-
variance 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. Statistical tests were all
two-sided with alpha = 0.05. All analyses were
conducted using the SAS statistical package.
Results
Cognitive performance
Attention-switching task
A main effect was found for L-theanine in
combination with caffeine significantly improving
accuracy as compared to placebo (see Fig. 1; F(1,44.73) =
13.55; P< 0.01). Interactions of treatment with switch
type and response type were not statistically
significant (all F<1,allP> 0.1). Importantly,
improved accuracy was not the result of a trade-off
between speed and accuracy, as there was no evidence
for a main or interaction effect of treatment on
reaction time (main effect – F(1,469) = 0.54, P> 0.05;
interaction – F(2,469) = 2.63, P> 0.05). To investigate
whether our findings are likely to be fuelled by the
relief of caffeine withdrawal, we re-ran the statistical
analysis, while including either habitual caffeine or tea
consumption in the model. The critical interactions
between treatment and habitual caffeine or habitual
tea consumption or any higher order interactions
including both terms were non-significant (all F<1,
all P> 0.1).
Choice-reaction-time task
There was no evidence of a main or interaction effect of
treatment on reaction time (all F< 2.4, all P> 0.12).
However, there was a significant drink by time
interaction for accuracy (F(1,86.18) = 4.94; P< 0.04)
indicating a switch in relative accuracy in the two
conditions between sessions. This interaction is,
however, qualified by the fact that post-hoc tests did not
reveal any differences between conditions (P> 0.05).
Visual-search task and egocentric mental-rotation task
For the visual-search task and the egocentric mental-
rotation task, reaction times and accuracy were not
affected by treatment (all F< 1.59, all P> 0.21).
Self-report measures
Task demand
No main or interactive treatment effects emerged for the
effort and difficult subscales of self-reported task
demand (all F< 1.98, all P> 0.16). However, self-
reported tiredness increased during the course of the test
day as evidenced by a main effect of time (F(1,86) = 13.27;
P< 0.01). Moreover, the experimental manipulation
significantly reduced self-reported tiredness as
compared to placebo as demonstrated by a main effect
of treatment (F(1,38.8) = 5.13; P< 0.05; see Fig. 2).
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Giesbrecht et al. L-theanine, caffeine and cognitive performance
Figure 1 Accuracy on the attention switching task (mean ±
SE). Main effect of drink (P< 0.01)
Figure 2 Change in self-reported tiredness on the task demand
scale (mean ± SE). Main effect of drink (P< 0.05)
Published by Maney Publishing (c) W.S Maney & Son Limited
Bond–Lader visual analogue mood scales
A main effect emerged for experimental treatment
significantly increasing self-reported alertness as
compared to placebo (F(1,36.5) = 10.3; P< 0.01; see
Fig. 3). There was no evidence for a treatment-related
main or interaction effect self-reported calmness or
contentedness (all F<1,allP> 0.39).
Physiological measures
Table 1 presents mean changes in blood pressure and
heart rate for both treatments and time point
separately. A main effect of treatment on systolic
blood pressure (SBP) was found with SBP being raised
by the treatment as compared to placebo treatment
(F(1,41.4) = 8.08; P< 0.01). A similar trend into the same
direction toward a main effect of treatment on
diastolic blood pressure (DBP) was also found (F(1,36.7)
= 2.93; P= 0.096). Moreover, significant drink by time
interaction was found for HR (F(1,86) = 4.10; P< 0.05).
This interaction is due to a reversal in HR change
between the two conditions between time points. This
interaction is, however, qualified by the fact that post-
hoc tests did not reveal any differences between
conditions (P> 0.05).
Discussion
The main findings of the present study can be
summarized as follows. First, the combination of
moderate levels of L-theanine and caffeine improved
task switching accuracy as compared to placebo
treatment in the context of comparable response
speed. This effect was specific in that other cognitive
tasks, such as visual search, choice reaction times, and
mental rotation were not affected. Second, the
combination of L-theanine and caffeine also increased
self-reported alertness and reduced task-induced
fatigue. Third, this increase in alertness was
accompanied by a slight increase in systolic blood
pressure, but not, to a demonstrable extent, in
diastolic blood pressure or heart rate.
Task switching performance accuracy was
specifically improved by our treatment. Importantly,
response speed was not negatively affected by our
treatment demonstrating that our findings cannot be
accounted for by a speed–accuracy trade-off. Other
cognitive tests, such as choice reaction times, remained
unaffected. This specificity agrees with the findings of
Owen et al.,18 who showed a specific beneficial effect
of the combination of L-theanine and caffeine on task
switching and critical flicker fusion threshold, but not
on rapid visual information processing or word
recognition. It also corresponds with those of Kelly et
al.,19 who demonstrated positive effects of a
combination of 100 mg L-theanine and 50 mg caffeine
on performance on a visuospatial cueing task. On the
other hand, the lack of improvements in response
speed is in contrast with findings of Haskell et al.16
Together, this suggests that the effects of the L-
theanine and caffeine combination are most
prominent in the attention domain, and that L-
theanine and caffeine combined effects are best
demonstrated with relatively challenging tests of
attention. We would like to note that this is in sharp
contrast to findings on the cognitive effects of caffeine
only, where one consistently finds increased
288 Nutritional Neuroscience 2010 Vol 13 No 6
Giesbrecht et al. L-theanine, caffeine and cognitive performance
Figure 3 Change in self-reported alertness on the
Bond–Lader visual analogue mood scales (mean ±
SE). Main effect of drink (P< 0.01)
Table 1 Changes in systolic and diastolic blood pressure and heart rate
Treatment Time after Systolic blood pressure Diastolic blood pressure Heart rate
treatment (min) Mean SE Mean SE Mean SE
L-Theanine-caffeine
20 1.78 0.83 2.42 0.62 –14.11 0.90
70 1.31 0.83 2.32 0.62 –12.63 0.90
Placebo
20 –1.16 0.83 1.33 0.62 –13.17 0.90
70 –0.90 0.83 1.20 0.62 –13.30 0.90
Common variance across treatment groups, resulting in identical standard errors, is assumed by the model fitted.
Published by Maney Publishing (c) W.S Maney & Son Limited
performance after caffeine on simple,34 but not
complex tasks.4,35 Nevertheless, the current study did
not include a treatment condition with caffeine only.
Therefore, we cannot completely rule out the
possibility that our pattern of findings could also be
obtained from caffeine administered in isolation.
In line with findings of improved cognitive
performance in terms of task switching performance,
self-reported alertness was also increased and
perceived fatigue was reduced by the combination of
L-theanine and caffeine. This finding is in line with
Haskell et al.,16 who found increased alertness and
decreased tiredness following a combination of
250 mg L-theanine and 150 mg caffeine. A similar
effect was also evident in a study by Owen et al.,18 who
used more moderate doses of 100 mg of L-theanine
and 50 mg of caffeine.
Nevertheless, some authors argue that the
psychostimulant effects of caffeine actually represent
reversal of withdrawal effects.36,37 This interpretation
of caffeine effects stems from the fact that most
studies investigate habitual consumers who are asked
to abstain from caffeine for a given time. To test the
merits of this assumption regarding the effects of
caffeine, Haskell et al.7compared habitual caffeine
consumers to non-consumers after overnight caffeine
withdrawal. The idea is that, if alleviation of
withdrawal symptoms underlies the psychostimulant
effects of caffeine, habitual consumers would be most
likely to show beneficial effects on cognitive tasks.
However, in contrast to this prediction, performance
in terms of faster reaction times was increased to the
same extent in both habitual consumers and non-
consumers. Thus, in general, it seems that psycho-
stimulant effects of caffeine cannot be attributed
solely to the reversal of withdrawal effects (see also
Christopher et al.38). More specifically, in the context
of the present study, no benefit was apparent for
cognitive tasks other than the switch task. If effects
were fuelled by withdrawal, one would be expected
positive findings on other tasks, too. Moreover,
participants with higher habitual levels of caffeine
consumption did not appear to be specifically affected
by withdrawal symptoms, as evidenced by the absence
of a moderating effect of caffeine consumption on
task performance. Taken together, the specific pattern
of findings is difficult to explain as the result of
caffeine withdrawal.
The drink with theanine and caffeine also slightly
increased systolic blood pressure as compared to the
control drink. The present blood pressure findings (i.e.
increase of 2.94 mmHg and 2.20 mmHg as compared
to placebo at 20–50 min and 70–100 min, respectively)
are of slightly smaller magnitude than the ones reported
by Quinlan et al.,39 who found that both one cup of tea
or coffee significantly increased systolic blood pressure
by 4.1–4.5 mmHg as compared to hot water 10–60 min
after ingestion. Of course, caffeine is a stimulant and
well-known to lead to an acute increase in blood
pressure even at dietary levels.40 In contrast, L-theanine
has been demonstrated to lower blood pressure in
rats41,42 and to counteract the blood-pressure-increasing
effects of caffeine at high doses in humans (200 mg L-
theanine and 250 mg caffeine).17 However, due to the
fact that the present study did not include a caffeine-
only condition, it is impossible to discern whether the
seemingly smaller blood pressure effects in the present
study are due to the addition of theanine. Moreover,
despite the acute effect of tea on blood pressure, meta-
analyses suggest that long-term intake of black or green
tea does not increase blood pressure chronically,43 and
may even reduce stroke incidence.44
Two limitations of the present study deserve
discussion. First, in the context of the present study,
we assumed an interaction between L-theanine and
caffeine based on previous studies16–19 and chose not to
include a L-theanine- and caffeine-only condition.
Therefore, the design of the current study precludes
attribution of the effects to L-theanine or caffeine and
conclusions about the interaction between the two
ingredients per se. Moreover, the treatment contained
higher levels of L-theanine, in combination with the
same amount caffeine which is naturally present in tea
to amplify possible effects of L-theanine. In order to
extend the current conclusions to tea, future studies
should employ a full dose-range effect of L-theanine
and caffeine.
Conclusions
The present study clearly demonstrates attentional
benefits after consumption of 97 mg L-theanine
together with 40 mg caffeine Moreover, L-theanine
and caffeine increased self-reported alertness and
decreased feelings of tiredness. Taken together with
previous studies, these findings indicate that L-
theanine in combination with caffeine may help to
focus attention during cognitively demanding tasks.
Acknowledgements
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
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Giesbrecht et al. L-theanine, caffeine and cognitive performance
Published by Maney Publishing (c) W.S Maney & Son Limited
supplied by Lipton Institute of Tea, Unilever R&D
Colworth, UK. We would like to thank Jessica E.
Smith for her help in collecting the data and Peter J.
Rogers, Jessica E. Smith, and Gail Owen for their
input during the design stage of the study.
The authors are employees of Unilever, which
markets food products some of which contain L-
theanine and caffeine.
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