Kinetics of ʟ-Theanine Uptake and Metabolism in Healthy Participants Are Comparable after Ingestion of ʟ-Theanine via Capsules and Green Tea4
Open accessAbstract
L-Theanine, an amino acid in green tea, is suggested to improve cognition and mood. Therefore, L-theanine is available as a supplement and is now used as an ingredient in functional drinks. Because data on the metabolic fate of L-theanine from human studies are lacking, we investigated the kinetics of L-theanine uptake and its metabolites, ethylamine and glutamic acid, in healthy participants. Within a randomized crossover study, 12 participants ingested a bolus of 100 mg L-theanine via capsules or green tea. On further occasions, 3 participants received 50 and 200 mg L-theanine via capsules. Blood and urine were collected before and up to 24 h postconsumption to determine the concentrations of L-theanine, proteinogenic amino acids, and ethylamine in plasma, erythrocytes, and urine by HPLC. L-Theanine increased in plasma, erythrocytes, and urine with comparable results after both treatments. The maximum plasma concentration of L-theanine occurred 0.8 h after intake of 100 mg L-theanine via capsules (24.3 ± 5.7 μmol/L) and tea (26.5 ± 5.2 μmol/L), respectively. The AUC of L-theanine in plasma increased dose dependently after intake of 50, 100, and 200 mg L-theanine via capsules. Moreover, ethylamine and glutamic acid increased in plasma and were excreted by urine after intake of capsules and tea. In conclusion, L-theanine is rapidly absorbed and seems to be hydrolyzed to ethylamine and glutamic acid. A minor part of L-theanine is retained in erythrocytes. Kinetics and urinary excretion of L-theanine, ethylamine, and glutamic acid are comparable after both treatments. Thus, functional effects of L-theanine intake may result from L-theanine, ethylamine, or glutamic acid.
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- Findingown data
Plasma ethylamine and glutamic acid concentrations increased after 100 mg L-theanine via capsules or tea.
“Moreover, ethylamine and glutamic acid increased in plasma and were excreted by urine after intake of capsules and tea.”
- Also stated in: § Results · plain
“After intake of 100 mg L-theanine, the ethylamine and glutamic acid concentrations in plasma increased (Fig. 2).”
Quote in the paperSubstantial claim - Also stated in: § Results · plain
- Findingown data
Plasma kinetics of L-theanine, ethylamine, and glutamic acid were comparable between capsule and tea treatments.
“The plasma kinetics of L-theanine, ethylamine, and glutamic acid were comparable after both treatments (Table 2).”
Quote in the paperSubstantial claim - Findingown data
L-Theanine, ethylamine, and glutamic acid were excreted in urine from 0-3 h and up to 24 h after intake.
“After intake, L-theanine, ethylamine, and glutamic acid were excreted within 3 h and up to 24 h postconsumption.”
Quote in the paperNot a substantial claim - Findingown data
Urinary L-theanine excretion over 24 h corresponded to 3.1% of ingested dose for capsules and 2.4% for tea.
“The total amount of L-theanine excreted within 24 h after intake of both capsules (17.3 mmol) and tea (14.2 mmol) corresponded to 3.1 and 2.4% of ingested L-theanine (100 mg 575 mmol), respectively.”
Quote in the paperNot a substantial claim - Findingown data
Plasma L-theanine AUC increased dose-dependently across 50, 100, and 200 mg capsule doses.
“The AUC of L-theanine in plasma increased dose dependently after intake of 50, 100, and 200 mg L-theanine via capsules.”
- Also stated in: § Results · plain
“The AUC 70 of L-theanine in plasma increased dose dependently from 50 mg [35.5 6 10.7 mmol/L 3 h; n = 3] to 100 mg [65.4 6 17.6 mmol/L 3 h; n = 3] and to 200 mg L-theanine [173 6 23.0 mmol/L 3 h; n = 3]”
Quote in the paperNot a substantial claim - Also stated in: § Results · plain
- Findingown data
Urinary excretion of L-theanine, ethylamine, and glutamic acid was comparable between capsule and tea treatments.
“The excretions of L-theanine, ethylamine, and glutamic acid were comparable after both treatments (Table 3).”
Quote in the paperSubstantial claim - Findingown data
L-Theanine concentration in erythrocytes increased after 100 mg intake compared with baseline.
“In erythrocytes, the L-theanine concentration increased after intake of 100 mg L-theanine compared with baseline (Supplemental Fig. 2)”
Quote in the paperNot a substantial claim - Findingown data
There was relatively high inter-individual variability in plasma concentration-time curves for L-theanine and especially for ethylamine and glutamic acid, despite correction to 70 kg body weight.
“We observed a relatively high inter-individual variability in the plasma concentration-time curves of L-theanine and, in particular, of ethylamine and glutamic acid, despite data correction to a body weight of 70 kg.”
Quote in the paperNot a substantial claim - Study design and conductown data
Plasma L-theanine concentration-time curves were modeled for each participant with good predictions for kinetic parameters.
“Plasma concentration-time curves of L-theanine were modeled for each participant (Fig. 1 is a representative one) with good predictions for kinetic parameters (Table 2).”
Quote in the paperNot a substantial claim- The authors state this as an assumption: The one-compartment model with first-order absorption and elimination and a lag time is appropriate for L-theanine plasma concentration-time data.
- Interpretationown data
L-Theanine is rapidly absorbed in healthy participants after intake via capsules or green tea.
“In conclusion, L-theanine is rapidly absorbed in healthy participants after intake of capsules and green tea.”
Quote in the paperSubstantial claim - Interpretationown data
Overall kinetics and urinary excretion of L-theanine, ethylamine, and glutamic acid are comparable between capsule and green tea intake.
“Kinetics and urinary excretion of L-theanine, ethylamine, and glutamic acid are comparable after both treatments.”
- Also stated in: § Discussion · plain
“The kinetics and urinary excretion of L-theanine, ethylamine, and glutamic acid are comparable after intake of capsules and green tea.”
Quote in the paperSubstantial claim - Also stated in: § Discussion · plain
- Premisenone given
This is the first study to investigate both L-theanine uptake kinetics and its metabolites ethylamine and glutamic acid in healthy participants.
“To the best of our knowledge, this is the first study to investigate both the kinetics of L-theanine uptake and its metabolites, ethylamine and glutamic acid, in healthy participants.”
Quote in the paperNot a substantial claim- Rests on an assumption: Human studies lack data on L-theanine's metabolic fate.
- Interpretationcitation
The comparable kinetics after capsules and tea agree with van der Pijl et al.'s data after aqueous solution or black tea.
“This observation is in line with data collected in parallel to our study by van der Pijl et al. (13) after intake of L-theanine via an aqueous solution or black tea.”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [13] van der Pijl, 2010, Human disposition of L-theanine in tea or aqueous solution., J Funct Food. source
- Interpretationown data
A minor portion of L-theanine is retained in erythrocytes.
“A minor part of L-theanine is retained in erythrocytes.”
- Also stated in: § Discussion · hedged
“Because L-theanine in erythrocytes was still detectable 24 h after treatments, a part of L-theanine may be retained in cells.”
Quote in the paperNot a substantial claim - Also stated in: § Discussion · hedged
- Interpretationreasoning
Additional tea ingredients, such as proteinogenic amino acids, are unlikely to compete with L-theanine for intestinal absorption.
“Thus, it is rather unlikely that additional ingredients in tea, e.g., specific proteinogenic amino acids (Table 1), compete with L-theanine for intestinal absorption.”
Quote in the paperSubstantial claim - Interpretationreasoning
Functional effects of L-theanine intake may be mediated by L-theanine, ethylamine, or glutamic acid.
“Thus, functional effects of L-theanine intake may result from L-theanine, ethylamine, or glutamic acid.”
Quote in the paperSubstantial claim- The authors state this as an assumption: L-Theanine is hydrolyzed to ethylamine and glutamic acid in vivo.
- Interpretationreasoning
The results, together with rat data, provide valuable hints about L-theanine's metabolic fate.
“Nevertheless, our results in addition to those obtained in rats provide valuable hints about the metabolic fate of L-theanine.”
Quote in the paperSubstantial claim - Interpretationcitation
The glutamic acid amounts observed in vivo cannot be fully attributed to ingested L-theanine because glutamic acid is continuously formed in amino acid metabolism.
“However, in contrast to ethylamine, the amounts of glutamic acid observed in vivo cannot be completely ascribed to orally ingested L-theanine, because glutamic acid is continuously formed in amino acid metabolism by glutaminase, glutamate dehydrogenase, and the transamination of 2-oxoglutarate (21).”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [21] Nedergaard, 2002, Beyond the role of glutamate as a neurotransmitter., Nat Rev Neurosci. source
- Interpretationown data
The results permit good prediction of L-theanine uptake kinetics in healthy participants.
“Our results allow a good prediction of the kinetics of L-theanine uptake in healthy participants.”
Quote in the paperSubstantial claim- The authors state this as an assumption: The one-compartment model with first-order absorption and elimination and a lag time is appropriate for L-theanine plasma concentration-time data.
- Premisecitation
In rats, only 2.1% of orally ingested L-theanine (100 mg) was excreted.
“This corresponds to the observation in rats, where only 2.1% of the orally ingested L-theanine (100 mg) was excreted (8).”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [8] Unno, 1999, Metabolism of theanine, gamma-glutamylethylamide, in rats., J Agric Food Chem. source
- Premisecitation
Incubating L-theanine with rat kidney homogenate, but not small intestine, liver, or brain homogenate, increased ethylamine and glutamic acid.
“Moreover, incubation of L-theanine with homogenate from ratsÕ kidney, but not from ratsÕ small intestine, liver, and brain, increased the concentration of ethylamine and glutamic acid (8,20).”
Quote in the paperNot a substantial claim0 of 2 sources checked - Premisecitation
In vitro, ethylamine and glutamic acid increased after incubating L-theanine with glutaminase or γ-glutamyltranspeptidase.
“In vitro, increasing amounts of ethylamine and glutamic acid were observed after incubation of L-theanine with either glutaminase or g-glutamyltranspeptidase (19).”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [19] Sadzuka, 2006, Efficacy of theanine is connected with theanine metabolism by any enzyme, not only drug metabolizing enzymes., Food Chem Toxicol. source
- Classified as probably not a substantial claim. 13
- May combine two claims. 21
- The quote only partly states this claim. 1
Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.
PremisecitationIn rats, oral or i.g. isolated L-theanine caused temporary increases in plasma, liver, brain, and urine, followed by higher plasma and urine ethylamine and glutamic acid, likely via hydrolysis.
“In rats, oral as well as i.g.administration of isolated L-theanine led to its temporary increase in plasma, liver, brain, and urine.This was followed by raised concentrations of ethylamine and glutamic acid in plasma and urine, probably due to hydrolysis of L-theanine (8,9).”
Quote in the paperNot a substantial claim1 of 2 sources checked- cites [8] Unno, 1999, Metabolism of theanine, gamma-glutamylethylamide, in rats., J Agric Food Chem. source
- cites [9] Terashima, 1999, Time-dependent changes of amino acids in the serum, liver, brain and urine of rats administered with theanine., Biosci Biotechnol Biochem. source
Materials and Methods (p. 1) describes intragastric administration, but not a separate oral-administration group. Results and Discussion (pp. 1–2) reports transient theanine increases in serum, liver and brain; urinary theanine instead continued to increase through 24 hours. The paper reports increased ethylamine and glutamic acid in urine and a tendency toward higher serum levels, and suggests degradation of theanine, but does not establish hydrolysis as the mechanism. (LLM, conf=0.88)
Experimental — accuracy not yet measured
Classified as probably not a substantial claim. May combine two claims.
PremisecitationBlood sampling times were selected because rat maximum plasma L-theanine occurred 0.5-1.0 h after administration and L-theanine remained detectable after 16 h.
“These intervals were chosen, because the maximum plasma concentration of L-theanine in rats occurred 0.5-1.0h after L-theanine administration (8,15) and L-theanine was still detectable after 16 h (8,9,15).”
Quote in the paperSubstantial claim1 of 3 sources checked- cites [8] Unno, 1999, Metabolism of theanine, gamma-glutamylethylamide, in rats., J Agric Food Chem. source
- cites [15] Desai, 2005, Pharmacokinetics of theanine enantiomers in rats., Chirality. source
- cites [9] Terashima, 1999, Time-dependent changes of amino acids in the serum, liver, brain and urine of rats administered with theanine., Biosci Biotechnol Biochem. source
The Results and Discussion (p. 1) report that rat serum theanine rose at 1 hour and then sharply decreased, supporting a peak around the measured 1-hour time point. The Methods (p. 1) show that 0.5 hours was not sampled, and the text does not explicitly establish that theanine remained detectable in serum at 16 hours; the reported detection through 24 hours concerns urine (Results and Discussion, p. 2). (LLM, conf=0.82)
Experimental — accuracy not yet measured
May combine two claims.
Findingown dataErythrocyte AUC70, Cmax70, and tmax for L-theanine were comparable between capsule and tea treatments.
“and the AUC 70 , C max,70 , and t max were comparable after intake of capsules and tea (Table 2).”
Quote in the paperSubstantial claimMay combine two claims.
Findingown dataErythrocyte proteinogenic amino acids did not change, and ethylamine was not detectable in erythrocytes.
“Proteinogenic amino acids did not change and ethylamine could not be detected in erythrocytes.”
Quote in the paperNot a substantial claimMay combine two claims.
Findingown dataPlasma L-theanine concentration rose over time up to 3.0 h after intake and returned to baseline by 24 h.
“In plasma, the L-theanine concentration increased time dependently up to 3.0 h postconsumption (for each comparison, P < 0.001) and returned to baseline 24 h after intake.”
Quote in the paperNot a substantial claimMay combine two claims.
Findingown dataPlasma proteinogenic amino acids other than L-theanine were unaffected by time, and no treatment or time×treatment effects were found for any amino acid including L-theanine.
“Other proteinogenic amino acids in plasma were not affected by time.For all amino acids, including L-theanine, effects by the kind of treatment and time 3 treatment were not observed.”
Quote in the paperNot a substantial claimMay combine two claims.
Findingown dataAfter 100 mg L-theanine, maximum plasma L-theanine concentration occurred at 0.8 h, with values 24.3 ± 5.7 μmol/L for capsules and 26.5 ± 5.2 μmol/L for tea.
“The maximum plasma concentration of L-theanine occurred 0.8 h after intake of 100 mg L-theanine via capsules (24.3 6 5.7 mmol/L) and tea (26.5 6 5.2 mmol/L), respectively.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing). May combine two claims. The quote only partly states this claim.
Findingown dataUrinary glutamic acid was detectable at baseline (1.2 ± 0.7 μmol/L), while L-theanine and ethylamine were not.
“As expected, glutamic acid was already detectable at baseline (1.2 6 0.7 mmol/L) in contrast to L-theanine and ethylamine.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
Findingown dataFasting plasma glutamic acid concentration was 20.7 ± 6.2 μmol/L.
“The glutamic acid concentration in the plasma of fasting participants was 20.7 6 6.2 mmol/L.”
Quote in the paperNot a substantial claimMay combine two claims.
Findingown dataL-Theanine was predicted to be absorbed after a lag time of 10-24 min, yielding Cmax70 of about 24-26 μmol/L.
“For all participants, L-theanine was predicted to be absorbed after a t lag of 10-24 min, leading to a C max,70 of ;24-26 mmol/L.”
Quote in the paperNot a substantial claim- The authors state this as an assumption: The one-compartment model with first-order absorption and elimination and a lag time is appropriate for L-theanine plasma concentration-time data.
May combine two claims.
Findingown dataOnly 2.4-3.1% of ingested L-theanine was excreted in urine, while urinary ethylamine and glutamic acid excretion was relatively high.
“This assumption is supported by our observation that only 2.4-3.1% of ingested L-theanine was excreted by urine in contrast to the relatively high excretion of ethylamine and glutamic acid (Table 3).”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
Premisecitationvan der Pijl et al. found increased plasma L-theanine in healthy men after 25, 50, and 200 mg via aqueous solution or black tea.
“In a recent trial, van der Pijl et al. (13) observed an increase of L-theanine in the plasma of healthy men after an intake of 25, 50, and 200 mg L-theanine provided via an aqueous solution or black tea.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [13] van der Pijl, 2010, Human disposition of L-theanine in tea or aqueous solution., J Funct Food. source
Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing), S4 (based). May combine two claims.
Study design and conductown dataThe HPLC assay had LOD 0.01 μmol/L for L-theanine and 0.08 μmol/L for ethylamine, linear standard curves 0.005-50 μmol/L, and inter- and intra-assay variances below 5%.
“The LOD was 0.01 mmol/L for L-theanine and 0.08 mmol/L for ethylamine (signal to noise ratio = 2.5:1).The corresponding limit of quantifications were 0.02 and 0.12 mmol/L, respectively.The standard curve of L-theanine and ethylamine was linear between 0.005 and 50 mmol/L (r > 0.95).Inter-and intra-assay variances were <5%.”
Quote in the paperNot a substantial claimMay combine two claims.
PremisecitationThe 100 mg L-theanine dose is physiological because it can be obtained from about 4 cups of green tea or a single functional drink.
“The given dose of 100 mg L-theanine is physiological, because it can be ingested by 4 cups (;500 mL) of green tea (4) or by a single portion of functional drinks.”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [4] Hänsel, 1992
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
Classified as probably not a substantial claim. May combine two claims.
Study design and conductown dataThe study used a randomized crossover design with at least 2-week washout, randomization by lot, and blinded sample evaluation.
“Within a randomized crossover trial, participants ingested a bolus of 100 mg L-theanine, either in isolated form via capsules or via 250 mL green tea, after a 12-h overnight fast.”
- Also stated in: § Participants. · plain
“Randomization was done by lot and all samples were coded to allow test evaluation on blinded samples.”
Quote in the paperSubstantial claim- Also stated in: § Participants. · plain
Probably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationA 250 mL serving of green tea prepared under recommended conditions provides about 40 mg L-theanine.
“A serving size of 250 mL green tea prepared under the recommended brewing conditions provides ;40 mg L-theanine (4).”
Quote in the paperNot a substantial claim0 of 1 sources checked- cites [4] Hänsel, 1992
Couldn’t be matched to a paper in Crossref, so it can’t be checked.
Probably not a substantial claim: may not pass S3 (load-bearing).
Study design and conductnone givenAll participants completed the study.
“All participants completed the study.”
Quote in the paperNot a substantial claimMay combine two claims.
Study design and conductreasoningDietary restriction compliance was excellent, and L-theanine and ethylamine were undetectable in fasting plasma, erythrocytes, and urine.
“According to the food records, compliance with dietary restrictions was excellent (data not shown).Consequently, L-theanine and ethylamine were not detectable in the plasma, erythrocytes, and urine of fasting participants.”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.
Study design and conductown dataThe protocol was approved by the University of Bonn Ethics Committee and all participants gave written informed consent.
“The study protocol was approved by the Ethics Committee of the University of Bonn (no.185/10).Written informed consent was obtained from all participants prior to enrolment.”
Quote in the paperNot a substantial claimProbably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.
Study design and conductown dataTwo participants did not collect urine, so urinary analyses used 10 participants.
“Because 2 participants did not collect their urine, data on urinary variables were based on the samples obtained from 10 participants.”
Quote in the paperNot a substantial claimClassified as probably not a substantial claim.
Study design and conductnone givenThe analytical method does not distinguish L- from D-theanine.
“It should be mentioned that our analytical method does not distinguish between L-and D-theanine.”
Quote in the paperSubstantial claimMay combine two claims.
InterpretationcitationAssuming equimolar conversion of L-theanine to ethylamine in vitro, the mean 24-h urinary ethylamine excretion of 272 and 308 μmol after capsules and tea corresponds to 47% and 54% of ingested L-theanine.
“Considering that L-theanine is metabolized to equimolar amounts of ethylamine in vitro (19), the mean excretion of 272 and 308 mmol ethylamine within 24 h after intake of capsules and tea, respectively (Table 3), corresponds to 47 and 54% of ingested L-theanine (575 mmol).”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [19] Sadzuka, 2006, Efficacy of theanine is connected with theanine metabolism by any enzyme, not only drug metabolizing enzymes., Food Chem Toxicol. source
May combine two claims.
InterpretationreasoningBecause participants were comparable in age, BMI, and health status, the variability may reflect inter-individual differences in absorption, metabolism, and excretion.
“Because our participants were comparable in age, BMI, and health status, this variability may be attributed to inter-individual differences in absorption, metabolism, and excretion.”
Quote in the paperNot a substantial claimMay combine two claims.
InterpretationcitationBecause green tea contains 98.2% L-theanine and Suntheanine capsules are pure L-theanine, the enantiomer limitation is not relevant to the results.
“However, because green tea delivers 98.2% L-theanine (22) and Suntheanine capsules contain even pure L-theanine, the lack of differentiation between enantiomers is not relevant for our results.”
Quote in the paperSubstantial claim0 of 1 sources checked- cites [22] Desai, 2004, Analysis of derivatized and underivatized theanine enantiomers by high-performance liquid chromatography/atmospheric pressure ionization-mass spectrometry., Rapid Commun Mass Spectrom. source
May combine two claims.
Interpretationown dataL-Theanine bioavailability is probably greater than 47-54% because L-theanine also increased in erythrocytes.
“However, bioavailability of L-theanine is probably higher than 47-54%, because L-theanine also increased in erythrocytes (Supplemental Fig. 2).”
Quote in the paperSubstantial claimProbably not a substantial claim: may not pass S3 (load-bearing).
PremisecitationIn rats, plasma and urine ethylamine and glutamic acid increased dose-dependently after oral and i.g. L-theanine.
“In rats, ethylamine and glutamic acids increased dose dependently in plasma and urine after oral and i.g.intake of L-theanine (8,15).”
Quote in the paperNot a substantial claim0 of 2 sources checkedMay combine two claims.
Interpretationown dataUsing Cmax70 and Vhyp from the one-compartment model, 72% and 74% of ingested L-theanine should reach the organism after capsules and green tea, respectively.
“If we consider the C max,70 and V hyp of L-theanine in plasma, calculated by the use of the 1-compartment model (Table 2), 72 and 74% of ingested L-theanine should reach the organism after intake of capsules and green tea, respectively.”
Quote in the paperSubstantial claim- The authors state this as an assumption: The one-compartment model with first-order absorption and elimination and a lag time is appropriate for L-theanine plasma concentration-time data.
The paper relies on this without support.
Human studies lack data on L-theanine's metabolic fate.
“However, data on the metabolic fate of L-theanine from human studies are lacking.”
“Because data on the metabolic fate of L-theanine from human studies are lacking”
The authors state this as an assumption.
L-Theanine is hydrolyzed to ethylamine and glutamic acid in vivo.
“Thus, L-theanine may be hydrolyzed to ethylamine and glutamic acid in vivo.This assumption is supported by our observation that only 2.4-3.1% of ingested L-theanine was excreted by urine in contrast to the relatively high excretion of ethylamine and glutamic acid (Table 3).”
The authors state this as an assumption.
L-Theanine distributes into tissues beyond plasma.
“It can be assumed that L-theanine is not only distributed in plasma but also in other tissues with regard to the V hyp of 16-17 L (Table 2).”
The authors state this as an assumption.
The one-compartment model with first-order absorption and elimination and a lag time is appropriate for L-theanine plasma concentration-time data.
“Each plasma concentration time curve of L-theanine was fitted using a 1-compartment model with first-order absorption and elimination.A lag time (t lag ) was included in this model to account for the delay between L-theanine intake and its appearance in blood (13,18).”
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?
Following oral ingestion, L-theanine is rapidly absorbed with plasma concentrations increasing in a linear dose-dependent manner in humans, peaking approximately 45-50 min post-consumption.
“Following oral ingestion, L-theanine is rapidly absorbed with plasma concentrations increasing in a linear dose-dependent manner in humans, peaking approximately 45–50 min post-consumption (6, 7).”
From Effects of L-theanine on cognition, mood and sleep: evidence from human trials (2026) · cites this paper as [6]
The Discussion concludes that L-theanine is rapidly absorbed in healthy participants, and Table 2 reports a plasma peak at 0.8 hours (about 48 minutes). The Results report a dose-dependent increase in plasma exposure (AUC) at 50, 100, and 200 mg, but do not establish that plasma concentrations increase linearly with dose. Page numbers were not available in our copy. (LLM, conf=0.88)
Experimental — accuracy not yet measuredThe effect of l-theanine might only last a few hours after consumption and does not stay or accumulate in the body for a longer period of time, as it might have efficiently been metabolized by the body.
“The current study suggests the effect of l-theanine might only last a few hours after consumption and does not stay or accumulate in the body for a longer period of time, as it might have efficiently been metabolized by the body [28].”
If the remaining L-theanine in erythrocytes is considered and a one-compartment model is used, L-theanine bioavailability might be higher, reaching 72% to 74%.
“Scheid et al. [7] further proposed that if the remaining part of L-theanine in erythrocytes was considered, and using the one-compartment model, the bioavailability might be higher and reaching 72% 74%.”
From How does the tea L-theanine buffer stress and anxiety (2022) · cites this paper as [7]
In healthy participants, 100 mg of L-theanine is predicted to be absorbed after a tlag of 10-24 min, leading to a Cmax of 24-26 mol/L.
“In the study of healthy participants, 100 mg of L-theanine was predicted to be absorbed after a t lag of 10-24 min, leading to a C max,70 of 24-26 mol/L.”
From How does the tea L-theanine buffer stress and anxiety (2022) · cites this paper as [7]
The bioavailability of L-theanine is between 47% and 54% via intake of capsules and tea, respectively, calculated from equimolar amounts of ethylamine.
“The bioavailability of L-theanine remains between 47% and 54% via intake of capsules and tea, respectively, by calculating the equimolar amounts of ethylamine [7].”
From How does the tea L-theanine buffer stress and anxiety (2022) · cites this paper as [7]
Because the blood concentration peak of theanine occurs later than that of caffeine, after ingesting the test food caffeine's central nervous system stimulative effect would be temporarily greater than that of theanine.
“The blood concentration peak of theanine occurs later than that of caffeine; therefore, after ingesting the test food, caffeine's central nervous system stimulative effect would be temporarily greater than that of theanine.”
From Theanine maintains sleep quality in healthy young women by suppressing the increase in caffeine-induced wakefulness after sleep onset (2023) · cites this paper as [37]
Caffeine blood concentration peaks at 30-120 min, and theanine blood concentration peaks at 60 min.
“The concentration of caffeine peaks in the blood at 30-120 min; 36 it peaks at 60 min for theanine.37”
From Theanine maintains sleep quality in healthy young women by suppressing the increase in caffeine-induced wakefulness after sleep onset (2023) · cites this paper as [37]
Pharmacokinetic clinical data involving ingestion of pure L-THE (25-200 mg) suggest peaks in physiological and blood plasma effects occur between 32 and 50 min post oral ingestion in a fasted state.
“Pharmacokinetic clinical data [35] that involved the ingestion of pure L-THE (25−200 mg) suggest peaks in physiological and blood plasma effects occur between 32 and 50 min post oral ingestion (in a fasted state) [29].”
A 48 h washout period was used between clinics 3 and 4 to ensure adequate time for L-THE clearance from the body.
“A 48 h washout period was used between clinics 3 and 4 ensuring the adequate time for the L-THE clearance from the body [29].”
The 200 mg L-THE dose was selected based on findings of previous studies.
“The dosage of L-THE (200 mg) was selected based on the findings of previous studies [29].”
The most physiologically relevant doses of L-THE in humans range from 0.05-0.4 g, equivalent to consumption of 2-15 cups of green tea.
“Human studies in which consumption of pure L-THE was provided in capsule form, indicate the most physiologically relevant doses of L-THE range from 0.05−0.4 g, equivalent to a consumption of 2−15 cups of green tea [6,29,30].”
L-THE is metabolised to ethylamine and glutamic acid, with increased concentrations in blood plasma, and excreted in urine with some retention in erythrocytes.
“It was also suggested that L-THE is metabolised to ethylamine and glutamic acid, as their respective concentrations in blood plasma increased in the subjects, and that it was excreted in the urine with some retention in erythrocytes [47].”
From l-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion (2016) · cites this paper as [47]
Human kinetic data from Scheid et al. showed L-THE is absorbed from the intestinal tract into systemic circulation within 10-24 min and transported into tissues including the brain.
“Human kinetic data from a study by Scheid et al. [47] showed that L-THE is absorbed from the intestinal tract into the systemic circulation within 10-24 min followed by its transportation into a range of tissues, including the brain.”
From l-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion (2016) · cites this paper as [47]
Maximal plasma concentrations of L-THE occurred 0.8 h after capsule (100 mg) and tea administration containing the same amount of L-THE.
“In the same study, it was reported that the maximal plasma concentrations of L-THE occurred 0.8 h after capsule (100 mg) and tea administration, which contained the same amount of L-THE [47].”
From l-Theanine as a Functional Food Additive: Its Role in Disease Prevention and Health Promotion (2016) · cites this paper as [47]
Self-check
Percentages, sums and reported differences re-computed from the paper’s own numbers.
Capsule urinary-excretion percentage does not match the stated dose
MinorDividing the reported 17.3 mmol excreted by the stated 575 mmol ingested gives 3.0% to one decimal place, not 3.1%.
Reported 3.1 · recomputed 3.008696
“The total amount of L-theanine excreted within 24 h after intake of both capsules (17.3 mmol) and tea (14.2 mmol) corresponded to 3.1 and 2.4% of ingested L-theanine (100 mg 575 mmol), respectively.”
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Nonsedating neurotransmitter-modulating supplement for nonvasomotor sleep disturbance in menopause
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“Following oral ingestion, L-theanine is rapidly absorbed with plasma concentrations increasing in a linear dose-dependent manner in humans, peaking approximately 45– 50 min post-consumption (6, 7).”
InfluentialL-THEANINE’S EFFECTS ON LEARNING AND MEMORY IN COLLEGE STUDENTS
Nickel, M. M. (2017)
- Authors
- Scheid, L., Ellinger, S., Alteheld, B., Herholz, H., Ellinger, J., Henn, T., Helfrich, H.-P., & Stehle, P.
- Affiliations
- University of Bonn (DE)
- University Hospital Bonn (DE)
- Corresponding author
- Ellinger, Sabine
- Venue
- The Journal of Nutrition
- Publisher
- Elsevier BV
- Published
- 2012-12
- Volume
- 142
- Issue
- 12
- Pages
- 2091-2096
- ISSN
- 0022-3166 (ISSN-L)
- OpenAlex
- W2109714479
- Cited by
- 70
- References
- 21
- Citations by year
- 2026: 8 · 2025: 7 · 2024: 5 · 2023: 3 · 2022: 8 · 2021: 4 · 2020: 5 · 2019: 8 · 2018: 4 · 2017: 6 · 2016: 3 · 2015: 3 · 2014: 3 · 2013: 2
- FWCI
- 1.52
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- Journal of Nutrition (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Pathology and Forensic Medicine › Tea Polyphenols and Effects
- Life Sciences › Neuroscience › Biological Psychiatry › Tryptophan and brain disorders
- Health Sciences › Medicine › Complementary and alternative medicine › Ginkgo biloba and Cashew Applications
- Keywords
- theanine, ethylamine, glutamate, absorption kinetics, dose dependence, urinary excretion, green tea, functional beverages
- MeSH terms
- Adult, Capsules, Female, Glutamates, Health, Humans, Kinetics, Male
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