Kinetics of l-Theanine Uptake and Metabolism in Healthy Participants Are Comparable after Ingestion of l-Theanine via Capsules and Green Tea

摘要

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.