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L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance
Open accessAbstract
Recent neuropharmacological research has suggested that certain constituents of tea may have modulatory effects on brain state. The bulk of this research has focused on either L-theanine or caffeine ingested alone (mostly the latter) and has been limited to behavioral testing, subjective rating, or neurophysiological assessments during resting. Here, we investigated the effects of both L-theanine and caffeine, ingested separately or together, on behavioral and electrophysiological indices of tonic (background) and phasic (event-related) visuospatial attentional deployment. Subjects underwent 4 d of testing, ingesting either placebo, 100 mg of L-theanine, 50 mg of caffeine, or these treatments combined. The task involved cued shifts of attention to the left or right visual hemifield in anticipation of an imperative stimulus requiring discrimination. In addition to behavioral measures, we examined overall, tonic attentional focus as well as phasic, cue-dependent anticipatory attentional biasing, as indexed by scalp-recorded alpha-band (8-14 Hz) activity. We found an increase in hit rate and target discriminability (d') for the combined treatment relative to placebo, and an increase in d' but not hit rate for caffeine alone, whereas no effects were detected for L-theanine alone. Electrophysiological results did not show increased differential biasing in phasic alpha across hemifields but showed lower overall tonic alpha power in the combined treatment, similar to previous findings at a larger dosage of L-theanine alone. This may signify a more generalized tonic deployment of attentional resources to the visual modality and may underlie the facilitated behavioral performance on the combined ingestion of these 2 major constituents of tea.
Overview
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Written from the paper’s full text.
TL;DR
In a four-day repeated-measures study, combined L-theanine (100 mg) and caffeine (50 mg) improved visuospatial attention performance and reduced tonic alpha-band EEG power relative to placebo. Caffeine alone improved discriminability but not hit rate, while L-theanine alone at this lower dose produced no significant behavioral or tonic-alpha effects.
Key findings
- The combined treatment increased hit rate and target discriminability relative to placebo; the hit-rate improvement was about 3%, and the discriminability effect size was larger for the combination (Cohen’s d = 0.55) than for caffeine alone (d = 0.42).
- Caffeine alone improved discriminability relative to placebo but did not improve hit rate; no treatment affected reaction time.
- L-theanine alone at 100 mg produced no significant behavioral effects and did not significantly lower tonic alpha, unlike prior findings at 250 mg.
- Tonic alpha power was significantly lower for the combined treatment than placebo; the alpha cueing effect was smaller for caffeine alone than placebo, but not for L-theanine alone or the combination.
Methods
- Sixteen neurologically normal paid volunteers (5 female; ages 21–40, mean 27.5 years) completed four counterbalanced testing days, receiving placebo, 100 mg L-theanine, 50 mg caffeine, or both combined, with task runs beginning 30 min after ingestion.
- Participants performed a cued visuospatial attention task requiring covert shifts to left or right locations and discrimination of target versus standard stimuli, while continuous EEG was recorded from 164 scalp electrodes plus EOG.
- Behavioral analyses used hit rate, false alarm rate, discriminability index, and reaction time; EEG analyses examined tonic alpha amplitude before cue onset and lateralized anticipatory alpha after cue onset using temporal spectral evolution.
Limitations
- The authors caution that synergy between L-theanine and caffeine cannot be strongly claimed because only single doses were tested and the combined condition did not differ significantly from caffeine alone on tonic alpha.
- The authors note that alpha effects of both compounds appear dose-dependent and call for future dose-response characterization; the caffeine-alone alpha reduction did not reach significance (P = 0.18).
- The unexpected reduction in the alpha cueing effect for caffeine alone is described as needing replication; more generally, the small sample and single-dose design limit generalization.
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Claims the paper makes
16 Own result · 9 No full text of the sources · 8 Own method · 8 Own interpretation · 1 Supported so far · 1 Partly supported · accuracy not yet measured
The sources with a verdict support this claim; the rest weren’t checked yet, have no full text we could read, or their verdicts aren’t rated yet.
In the paper
“Using electroencephalographic (EEG) recordings in humans, Kobayashi et al. (12) and Juneja et al. (13) reported that activity within the alpha frequency band (8-14 Hz) increased in reaction to L-theanine ingestion when measured during a state of rest.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Introduction
What the sources say
- Supportedcites [12] Kobayashi, 1998, Effects of L-theanine on the release of α-brain waves in human volunteers, Nihon Nogeikagaku Kaishi. source
The experimental results report increased alpha-wave activity after L-theanine ingestion in eight human volunteers. The methods describe EEG recordings while participants sat in a controlled room, consistent with measurement at rest (methods and results, indexed under Abstract, pp. 155–157). (LLM, conf=0.90)
- Not checked — no full text of the sourcecites [13] Juneja, 1999, L-Theanine—a unique amino acid of green tea and its relaxation effect in humans, Trends Food Sci Technol. source
plaindirect- Asserted: passes — The authors put it forward as true.
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- Supported
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Follow-up t-tests revealed that alpha was significantly lower for T1C than P (P , 0.02).”
- Also stated in: § Abstract · plain
“showed lower overall tonic alpha power in the combined treatment”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > ).
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
- Also stated in: § Abstract · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Behavioral performance was significantly improved on the combined treatment (T1C) in terms of hit rate (P , 0.016) and d# (P , 0.002).”
- Also stated in: § Abstract · plain
“We found an increase in hit rate and target discriminability (d#) for the combined treatment relative to placebo”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Results
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
- Also stated in: § Abstract · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“P did not differ from either T or C (see Fig. 2).”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > ).
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“There was also a significant improvement in d# on C compared with P (P , 0.016), but not in hit rate.”
- Also stated in: § Abstract · plain
“and an increase in d# but not hit rate for caffeine alone”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Results
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
- Also stated in: § Abstract · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“The typical alpha cueing effect was readily apparent in both the nonnormalized alpha amplitude waveforms and normalized pretarget measures (Fig. 3) for each treatment day.”
- Also stated in: § ). · boosted
“A strong attention 3 hemisphere interaction (P , 0.0005) was found on the pretarget anticipatory alpha measures as expected, reflecting the typically observed alpha-mediated cueing effect.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > ).
boostedcorrelational- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
- Also stated in: § ). · boosted
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“Behavioral performance was significantly improved on the combined treatment (T1C) in terms of hit rate (P , 0.016) and d# (P , 0.002).”
- Also stated in: § Abstract · plain
“We found an increase in hit rate and target discriminability (d#) for the combined treatment relative to placebo”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Results
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
- Also stated in: § Abstract · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“There was also a significant improvement in d# on C compared with P (P , 0.016), but not in hit rate.”
- Also stated in: § Abstract · plain
“and an increase in d# but not hit rate for caffeine alone”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Results
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
- Also stated in: § Abstract · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“In addition, there was a significant 3-way interaction among treatment, attention, and hemisphere (P , 0.05).”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > ).
plaincorrelational- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“When we reduced the alpha cueing effect to a single metric as described above, the effect was smaller on C than P (P , 0.02) but did not differ for the T or T1C conditions.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > ).
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
- Probably not a substantial claim. 12
- The quote only partly states this claim. 1
- It may state two separate claims as one. 9
The cited sources support only part of this claim — read each source’s verdict below.
In the paper
“Previous studies have reported a drop in absolute alpha power during resting with eyes open on ingestion of caffeine at higher dosages, e.g., 200 mg (30) and 400 mg (31).”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Discussion
What the sources say
- Supportedcites [30] Siepmann, 2002, Effects of caffeine on topographic quantitative EEG, Neuropsychobiology. source
The citation to this paper is attached to the 200 mg dose, not the separate 400 mg dose. The Abstract describes EEG recording during relaxation with eyes open, and the Results report significantly reduced absolute slow- and fast-alpha power after caffeine under that condition. (LLM, conf=0.94)
- Partly supportedcites [31] Deslandes, 2005, Effects of caffeine on the electrophysiological, cognitive and motor responses of the central nervous system, Braz J Med Biol Res. sourceExperimental — accuracy not yet measured
The Abstract reports that 400 mg of caffeine significantly reduced alpha absolute power, but specifies that the resting EEG was recorded with eyes closed. The Quantitative electroencephalographic analyses section distinguishes this study's eyes-closed condition from earlier studies with significant results in subjects tested with eyes open. This source therefore supports the 400 mg reduction, not the claimed eyes-open condition. (LLM, conf=0.90)
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it.
- Supported
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“There were no significant effects of L-theanine, and no effects of any of the 3 treatments on RT”
- Also stated in: § Abstract · plain
“whereas no effects were detected for L-theanine alone.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Results
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
The quote only partly states this claim.
- Rests on an assumption: A typical serving of tea contains roughly 100 mg L-theanine and 50 mg caffeine.
- Also stated in: § Abstract · plain
A result the paper reports from its own data — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“When we reduced the alpha cueing effect to a single metric as described above, the effect was smaller on C than P (P , 0.02) but did not differ for the T or T1C conditions.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > ).
plain- Asserted: passes — The authors put it forward as true.
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It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Thus, a normalization of these measures was necessary to remove the variance caused by practice, and this was carried out by transforming each data point to a z-score with respect to the mean and SD of all scores measured on that day (d 1, d 2, d 3, d 4).”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Methods
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
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Probably not a substantial claim.
A conclusion the paper draws from its own results — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“A tentative interpretation of the current pattern of results is that L-theanine works to enhance the tonic apportionment of attentional resources to the visual modality and does so to a significant degree when a large dosage is ingested by itself or in combination with caffeine when a smaller dosage is ingested.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Discussion
hedgeddirect- Asserted: passes — The authors put it forward as true.
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It may state two separate claims as one.
A claim is checked only against the cited paper’s full text, never its abstract, and none is available for its sources.
In the paper
“This was of interest to the attention community, as the alpha rhythm has long been known to be sensitive to overall attentional states (i.e., intensity aspects such as arousal) (14) and, further, is involved in the biasing of selective attention (15,16).”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Introduction
What the sources say
- Not checked — no full text of the sourcecites [14] Adrian, 1934, The Berger Rhythm: Potential changes in the occipital lobes in man, Brain. source
- Not checked — no full text of the sourcecites [15] Foxe, 1998, Parieto-occipital ∼10 Hz activity reflects anticipatory state of visual attention mechanisms, Neuroreport. source
- Not checked — no full text of the sourcecites [16] Kelly, 2006, Increases in alpha oscillatory power reflect an active retinotopic mechanism for distracter suppression during sustained visuospatial attention, J Neurophysiol. source
boostedcorrelational- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
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Probably not a substantial claim. It may state two separate claims as one.
In the paper
“Haskell et al. (33) administered a large battery of cognitive tests before and after consumption of a drink containing either placebo, 250 mg of L-theanine, 150 mg of caffeine, or their combination.These authors found improvements in simple and numeric working memory RT, sentence verification accuracy, and alertness ratings for the combined treatment but not for either treatment alone.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Discussion
What the sources say
- Not checked — no full text of the sourcecites [33] Haskell, 2008, The effects of L-theanine, caffeine and their combination on cognition and mood, Biol Psychol. source
plaindirect- Asserted: passes — The authors put it forward as true.
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- Load-bearing: passes — The paper’s conclusions depend on it.
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It may state two separate claims as one.
In the paper
“Parnell et al. (32) reported improved speed and accuracy on an attention-switching task at 60 min and reduced susceptibility to distracting information during a memory task at both 60 and 90 min following ingestion of a combination of L-theanine and caffeine in the same dosages as used here.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Discussion
What the sources say
- Not checked — no full text of the sourcecites [32] Parnell, 2006, Combined effects of L-theanine and caffeine on cognition and mood, Appetite. source
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
It may state two separate claims as one.
In the paper
“Using a similar crossover design but with a greater dosage of caffeine (250 mg) than L-theanine (200 mg), Rogers et al. (34) found that L-theanine tended to counteract the caffeine-induced rise in blood pressure but did not interact with caffeine-induced increases in either alertness or ''jitteriness'' on state anxiety scales.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Discussion
What the sources say
- Not checked — no full text of the sourcecites [34] Rogers, 2008, Time for tea: mood, blood pressure and cognitive performance effects of caffeine and L-theanine administered alone and together, Psychopharmacology (Berl). source
hedgeddirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“A 4-d balanced repeated-measures design was employed, with subjects receiving 1 of the 4 treatments (including placebo) on each day in counterbalanced order.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Statistical methods.
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Subjects were uninformed of the treatment, which was served in 100 mL of water, with the placebo treatment consisting only of water.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Methods
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
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Probably not a substantial claim.
- Rests on an assumption: L-theanine and caffeine are tasteless when dissolved in water.
In the paper
“In addition, tonic (background) alpha amplitude was relatively decreased for L-theanine, in apparent contradiction to the findings of Juneja et al. (13).”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Introduction
What the sources say
- Not checked — no full text of the sourcecites [13] Juneja, 1999, L-Theanine—a unique amino acid of green tea and its relaxation effect in humans, Trends Food Sci Technol. source
hedgeddirect- Asserted: fails — The authors may not put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: fails — The paper may give no reason why it holds.
Probably not a substantial claim. The authors may not put it forward as true. The paper’s conclusions may not depend on it. The paper may give no reason why it holds.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Because 3 t-tests were performed including the same placebo data, we applied a Bonferronicorrected a-level of 0.016 here.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Statistical methods.
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“EEG data were epoched from 2300 ms before to 1100 ms after cue onset and baseline-corrected relative to the interval 2100 to 0 ms, with an artifact rejection threshold of 6100 mV applied.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Methods
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it. It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Based on a calibrated mapping of EOG amplitude to visual angle, trials were rejected off-line if eye gaze deviated by .0.5° during the cue-target interval.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Methods
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: fails — The paper’s conclusions may not depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim. The paper’s conclusions may not depend on it.
A conclusion the paper draws from its own results — it cites no other source for it, so there is none to check. The quote shows it is in the paper.
In the paper
“This study marks the third finding of decreased alpha as a result of L-theanine ingestion (albeit a partial cause here) to date, demonstrating the reliability of the effect.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Discussion
boosteddirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
It may state two separate claims as one.
What the paper did — it cites no source for this, so there is none to check. The quote shows it is in the paper.
In the paper
“Subjects underwent 4 d of testing, ingesting either placebo, 100 mg of L-theanine, 50 mg of caffeine, or these treatments combined.”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Abstract
plain- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
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Probably not a substantial claim.
- Rests on an assumption: L-theanine and caffeine are tasteless when dissolved in water.
A claim is checked only against the cited paper’s full text, never its abstract, and none is available for its sources.
In the paper
“In intersensory attention tasks, where the relevant modality is cued ;1 s before a compound audiovisual target stimulus, parieto-occipital alpha power in the intervening period is increased for attend-visual trials relative to attend-auditory trials (15,17).”
§ L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance 1-3 > Introduction
What the sources say
- Not checked — no full text of the sourcecites [15] Foxe, 1998, Parieto-occipital ∼10 Hz activity reflects anticipatory state of visual attention mechanisms, Neuroreport. source
- Not checked — no full text of the sourcecites [17] Fu, 2001, Attention-dependent suppression of distracter visual input can be cross-modally cued as indexed by anticipatory parieto-occipital alpha-band oscillations, Brain Res Cogn Brain Res. source
plaindirect- Asserted: passes — The authors put it forward as true.
- Checkable: passes — It can be checked against evidence.
- Load-bearing: passes — The paper’s conclusions depend on it.
- Based: passes — The paper gives a reason why it holds.
Probably not a substantial claim.
The paper relies on this without support.
A typical serving of tea contains roughly 100 mg L-theanine and 50 mg caffeine.
“An immediate question, given this replication, is whether this tonic alpha reduction occurs at lower dosages of L-theanine, closer to the amount ingested through a typical serving of tea.In the present study, we administered a lower dosage of 100 mg to address this.”
The paper relies on this without support.
L-theanine and caffeine are tasteless when dissolved in water.
“Both theanine and caffeine are tasteless in water solution.”
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
The cited source doesn’t support the claim as written.
In the citing paper
“whereas in active and anticipatory conditions, studies have shown that theanine reduced alpha power at 100 mg,62”
From Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials (2025) · cites this paper as [62]
Checked by a reasoning model — may be wrong.
Experimental — accuracy not yet measuredThe source backs part of the claim, not all of it — or backs it for a different population, condition or comparison.
In the citing paper
“Caffeine has been known for decades to improve sustained attention in healthy adults (e.g. Refs.25–27, animal models with ADHD28 and even individuals with ADHD29,30.”
From Effects of l-theanine–caffeine combination on sustained attention and inhibitory control among children with ADHD: a proof-of-concept neuroimaging RCT (2020) · cites this paper as [25]
Experimental — accuracy not yet measuredThe cited source says what the claim attributes to it.
In the citing paper
“This is contrary to previous findings (Einother et al. 2010; Haskell et al. 2008; Kelly et al. 2008; Owen et al. 2008)”
From A Double-Blind, Placebo-Controlled Study Evaluating the Effects of Caffeine and L-Theanine Both Alone and in Combination on Cerebral Blood Flow, Cognition and Mood (2015) · cites this paper as Kelly et al. 2008
The cited source says what the claim attributes to it.
In the citing paper
“Individual studies have, however, suggested that co-ingestion of caffeine and L-theanine may have an additive effect, with additional benefits noted compared to when each is administered in isolation (20–27), although such findings have been somewhat inconsistent (28, 29) and would benefit from further behavioral and mechanistic evaluation.”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [24]
In the citing paper
“Likewise, improvements in cognitive performance, subject alertness and complex senses interactions have also been documented [62][63][64].”
From l-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion (2016) · cites this paper as [62]
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“Matching electroencephalographic recordings with cognitive task performance, it has been demonstrated that the unique tea amino acid theanine plays a role in attentional processing, in synergy with caffeine, enhancing cognition in humans (Kelly et al., 2008).”
Caffeine as an Attention Enhancer: Reviewing Existing Assumptions
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Green tea effects on cognition, mood and human brain function: A systematic review
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“L-Theanine Ten experimental studies (Einother et al., 2010; Giesbrecht et al., 2010; Haskell et al., 2008; Kelly et al., 2008; Kimura et al., 2007; Ota et al., 2014; Owen et al., 2008; Park et al., 2011; Ritsner et al., 2011; Yoto et al., 2012) focussed on the effects of L-theanine intake.”
BackgroundResultInfluentialL-Theanine, Unique Amino Acid of Tea, and Its Metabolism, Health Effects, and Safety
Türközü, D., & Şanlier, N. (2017) · Critical Reviews in Food Science and Nutrition · doi:10.1080/10408398.2015.1016141 · Cited by 207
“caffeine in increasing the attention process and cognitive performance in humans (Kelly et al., 2008).”
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“…Treatment on the broadband indices (all P > 0.1), there was a main effect of Treatment on alpha (F3,36 = 3.50, P 0.05), reflecting the reduction of tonic alpha, but not spatially-selective alpha biasing, on ingestion of both theanine and caffeine as described previously (Kelly et al., 2008).”
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“The regions of interest chosen for testing were based on scalp topographies in existing studies (Worden et al., 2000; Kelly et al., 2008) with electrode clusters over left and right parieto-occipital scalp.”
MethodSelf-citationPhytochemicals and cognitive health: Are flavonoids doing the trick?
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“…black tea consumption has shown that the amino acid theanine (c-N-ethylglutamine) alters brain activity associated with attentional functioning (Kelly et al., 2008) and increases feelings of calmness and relaxation (Nobre et al., 2008) similar to the current findings relating to acute EGCG…”
Targeting Multiple Neurodegenerative Diseases Etiologies with Multimodal-Acting Green Tea Catechins
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Bioavailability of Polyphenon E Flavan-3-ols in Humans with an Ileostomy4
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A Review of the Epidemiological Evidence on Tea, Flavonoids, and Lung Cancer2
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“In a series of studies from this laboratory, a clear link between theanine ingestion and alpha-band oscillatory brain activity during demanding selective attention tasks has been established (GomezRamirez et al., 2007, 2009; Kelly et al., 2008).”
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“the hit rate of attention tasks using a cathode ray tube monitor, which indicates an improvement in the subject’s attention.(37) However, there have been no interventional studies using a combination treatment of GTE and l-theanine and assessing cognitive performance.”
The combined effects of L-theanine and caffeine on cognitive performance and mood
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Tea Is the Major Source of Flavan-3-ol and Flavonol in the U.S. Diet
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Tea, Flavonoids, and Nitric Oxide-Mediated Vascular Reactivity
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Nongallated Compared with Gallated Flavan-3-ols in Green and Black Tea Are More Bioavailable
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“More recent research has shown that alpha activity is not simply associated with brain arousal states but indexes the operation of selective attention mechanisms (Vanni et al. 1997; Foxe et al. 1998; Worden et al. 2000; Fu et al. 2001; Bastiaansen and Brunia 2001; Bastiaansen et al. 2001; Kelly et al. 2005; Yamagishi…”
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Acute effects of tea consumption on attention and mood
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“This combination improved speed and accuracy on a range of tasks from the Cognitive Drug Research test battery (46), improved accuracy on an attention-switching test (47–49), improved accuracy on a cued attention test (50), and improved accuracy on a sustained attention test (51).”
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“Moreover, together with caffeine, L‐theanine has a synergistic positive effect on attention as demonstrated in human electroencephalography studies,[7] and in a behavioral study.”
BackgroundHuman disposition of L-theanine in tea or aqueous solution
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“…of distribution over the absolute bioavailability available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/jff EEG studies between 30 and 120 min (Kelly et al., 2008), and in a behavioural study after 60 min following L-theanine plus caffeine consumption (Owen et al., 2008).”
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“Previous studies which included L -theanine and/or caffeine in isolation (Haskell et al., 2008; Kelly et al., 2008; Owen et al., 2008) indicated that the L -theanine/caffeine combination had synergistic effects.”
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Black tea improves attention and self-reported alertness
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Diabetes and Alzheimer’s Disease: Can Tea Phytochemicals Play a Role in Prevention?
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BackgroundEffects of a single, oral 60 mg caffeine dose on attention in healthy adult subjects
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“When ingested alone, theanine has been found to induce calmness and synchronicity of brain activity [252], but when combined with caffeine it induces even greater synchronization [253], providing improvements in attention [254].”
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Stuck at the bench: Potential natural neuroprotective compounds for concussion
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Caffeine and theanine exert opposite effects on attention under emotional arousal
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“4 in that 35-50 mg caffeine and 90-100 mg theanine enhanced mental alertness, task switching attention, and recognition memory relative to placebo (Einother et al. 2010a; Giesbrecht et al. 2010; Kelly et al. 2008; Owen et al. 2008).”
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“…studied due to its beneficial properties for human health, since it interacts with diverse physiological and biochemical pathways, e.g. it elicits significant effects on the general state of mental alertness by increasing 𝛼 -wave brain activity and the reduction of anxiety ( Kelly et al., 2008 ).”
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“Extending this experimental work to human studies, Foxe and his colleagues (22) have matched electroencephalographic recordings with cognitive task performance to demonstrate that the unique tea amino acid L-theanine (g-glutamylethylamide) plays a role in attentional processing in synergy with caffeine.”
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“In terms of cognitive function, there are studies in the literature that suggest THE may cause performance decrements when administered single [62,68] or have no effect [69,70].”
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“…with mind wandering—also termed spontaneous thought 83 —and 1 study found positive effects of 100 mg theanine on behavioral cognition outcomes, 52 although 2 other studies found no effect, 55,62 and 1 study showed an effect in favor of placebo compared to theanine, 54 using doses ≥ 100 mg.”
Advantageous effect of theanine intake on cognition
Tamano, H., Fukura, K., Suzuki, M., Sakamoto, K., Yokogoshi, H., & Takeda, A. (2014) · Nutritional Neuroscience · doi:10.1179/1476830513y.0000000094 · Cited by 19
Behavioural effects of compounds co-consumed in dietary forms of caffeinated plants
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“A combination of 100 mg L-theanine and 50 mg caffeine was also capable of improving performance accuracy (as measured by increased hit rate and target discriminability) and reducing overall tonic (background) alpha power((143)), as well as simultaneously improving speed and accuracy on an attention-switching task at 6…”
Habitual tea drinking modulates brain efficiency: evidence from brain connectivity evaluation
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“Although individual constituents of tea have been related to the roles of maintaining cognitive abilities and preventing cognitive decline, a study with behavioural and neurophysiological measures showed that there was a degraded effect or no effect when a constituent was administered alone and a significant effect wa…”
Dassanayake, T. L., Kahathuduwa, C. N., & Weerasinghe, V. S. (2022) · Nutritional Neuroscience · doi:10.1080/1028415x.2020.1804098 · Cited by 16
“tion tasks employed by some previous researchers [25,26].”
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“Prior studies that have measured how stimulants affect hit rate versus false alarm rate suggest that different stimulants and dosages can have distinct effects on sensitivity versus criterion (43, 44).”
BackgroundDassanayake, T. L., Wijesundara, D., Kahathuduwa, C. N., & Weerasinghe, V. S. (2023) · Nutritional Neuroscience · doi:10.1080/1028415x.2022.2136884 · Cited by 14
“How L-theanine modi fi es perceptual processing in the cerebral neural circuits and enable attentional fi ltering is not well de fi ned, but few EEG [17, 21, 24] and fMRI [26, 27] studies point toward plausible mechanisms.”
BackgroundInfluentialIkar, M., & Sable, S. (2023) · Journal of Pharmacognosy and Phytochemistry · doi:10.22271/phyto.2023.v12.i2c.14660 · Cited by 14
“Potential cognitive benefits of combining L-theanine and caffeine ([108]).”
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“Previous studies have shown that supplementation with caffeine (38), the combination of caffeine and taurine (34), caffeine and L-theanine (39), tyrosine (40), and mango leaves extract (41) can improve the RT in different cognitive and computerized tests.”
BackgroundInfluentialThe effects of caffeine on option generation and subsequent choice
Häusser, J. A., Schlemmer, A., Kaiser, S., Kalis, A., & Mojzisch, A. (2014) · Psychopharmacology · doi:10.1007/s00213-014-3506-5 · Cited by 10
The effect of black tea on human cognitive performance in a cognitive test battery
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“We used a lower amount of BT since several studies suggeste BT does not influence certain cognitive functions [28], particularly at the dosage of less than 100 mg [22, 23].”
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“Although, it was also found in few studies that both theanine and caffeine exhibit synergistic effects at lower doses.([7,8]) There is no doubt that these major constituents of tea (catechins, caffeine, and theanine) are the main bioactive constituents responsible for numerous health beneficial properties of tea.”
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Caffeinated Beverages, Behavior, and Brain Structure
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Monitoring of cognitive processes in older persons
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“The method for calculating the TSE as described in [11] is uncomplicated: EEG data were epoched based on a trigger sent by the Sudoku interface indicating a correct solution had been arrived at.”
MethodDrinking tea improves the convergent creativity performance
Jiang, Y., Huang, Y., Wu, Y., & Wang, L. (2021) · Food Quality and Preference · doi:10.1016/j.foodqual.2021.104360 · Cited by 8
EFSA Panel on Dietetic Products, N. A. A. (., Turck, D., Bresson, J., Burlingame, B., Dean, T., Fairweather‐Tait, S., Heinonen, M., Hirsch‐Ernst, K. I., Mangelsdorf, I., McArdle, H. J., et al. (2018) · EFSA Journal · doi:10.2903/j.efsa.2018.5266 · Cited by 7
“, 2010) and two did not report on between-group statistical comparisons for the caffeine plus L-theanine vs the caffeine interventions (Haskell et al., 2008; Kelly et al., 2008).”
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“…have shown no significant improvement in choice reaction time with abstract visual stimuli [17] or in reaction time in visuospatial attention tasks [31], we found our findings to be more consistent with the series of placebo-controlled crossover trials that used visual recognition reaction tasks…”
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“It appears to increase alpha wave within 30-40 minutes [30], accordingly with relaxation and attention task performance [31].”
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“L-theanine, a typical amino-acid of green tea has been widely studied due to its beneficial properties for humans, as it interacts in diverse physiological and biochemical pathways: among others, L-theanine has been shown to elicit a significant effect on the general state of mental alertness by increasing α-wave brai…”
Background
Metadata
- Authors
- Kelly, S. P., Gomez-Ramirez, M., Montesi, J. L., & Foxe, J. J.
- Affiliations
- Nathan Kline Institute for Psychiatric Research (US)
- Corresponding author
- Foxe, John J.
- Venue
- The Journal of Nutrition
- Publisher
- Elsevier BV
- Published
- 2008-08
- Volume
- 138
- Issue
- 8
- Pages
- 1572S-1577S
- ISSN
- 0022-3166 (ISSN-L)
- OpenAlex
- W1955323883
- Semantic Scholar
- e5aa9a2bad9f3c3193ccf2cfe466cfbff42c9594
- Cited by
- 119
- References
- 44
- Citations by year
- 2026: 5 · 2025: 5 · 2024: 4 · 2023: 4 · 2022: 5 · 2021: 7 · 2020: 5 · 2019: 5 · 2018: 4 · 2017: 9 · 2016: 10 · 2015: 2 · 2014: 10 · 2013: 6 · 2012: 3
- FWCI
- 7.82
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- Journal of Nutrition (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Pharmacology (medical) › Coffee research and impacts
- Life Sciences › Neuroscience › Cognitive Neuroscience › Neural dynamics and brain function
- Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and Work-Related Fatigue
- Keywords
- theanine, caffeine, tea constituents, visuospatial attention, alpha activity, anticipatory attention, attentional deployment, combination supplementation, cognitive performance
- MeSH terms
- Adult, Central Nervous System Stimulants, Attention, Brain Mapping, Caffeine, Cognition, Cues, Drug Therapy, Combination, Electroencephalography, Female, Glutamates, Humans, Male, Task Performance and Analysis
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