Kinetics of ʟ-Theanine Uptake and Metabolism in Healthy Participants Are Comparable after Ingestion of ʟ-Theanine via Capsules and Green Tea1–4

ʟ-Theanine, an amino acid in green tea, is suggested to improve cognition and mood. Therefore, ʟ-theanine is available as a supplement and is now used as an ingredient in functional drinks. Because data on the metabolic fate of ʟ-theanine from human studies are lacking, we investigated the kinetics of ʟ-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 ʟ-theanine via capsules or green tea. On further occasions, 3 participants received 50 and 200 mg ʟ-theanine via capsules. Blood and urine were collected before and up to 24 h postconsumption to determine the concentrations of ʟ-theanine, proteinogenic amino acids, and ethylamine in plasma, erythrocytes, and urine by HPLC. ʟ-Theanine increased in plasma, erythrocytes, and urine with comparable results after both treatments. The maximum plasma concentration of ʟ-theanine occurred 0.8 h after intake of 100 mg ʟ-theanine via capsules (24.3 ± 5.7 μmol/L) and tea (26.5 ± 5.2 μmol/L), respectively. The AUC of ʟ-theanine in plasma increased dose dependently after intake of 50, 100, and 200 mg ʟ-theanine via capsules. Moreover, ethylamine and glutamic acid increased in plasma and were excreted by urine after intake of capsules and tea. In conclusion, ʟ-theanine is rapidly absorbed and seems to be hydrolyzed to ethylamine and glutamic acid. A minor part of ʟ-theanine is retained in erythrocytes. Kinetics and urinary excretion of ʟ-theanine, ethylamine, and glutamic acid are comparable after both treatments. Thus, functional effects of ʟ-theanine intake may result from ʟ-theanine, ethylamine, or glutamic acid.