Effects of L-theanine on the Release of alpha-Brain Waves in Human Volunteers

L-Theanine is an amino acid found in the leaf of green tea and its infusion, and is known to control excitement caused by caffeine. It is also known that the oral administration of L-theanine to rats results in a decrease of serotonin and an increase of catecholamine in the brain. L-Theanine had been confirmed to be safe in animal experiments. We found that the oral intake of L-theanine caused a feeling of relaxation among the human volunteers examined. These observations led us to conduct experiments on the effects of the administration of L-theanine on brain waves. Eight female university students were selected as volunteers. Four of them were ranked as Grade I (the highest anxiety) and the remaning four as Grade V (lowest anxiety) in an investigation done by the manifest anxiety scale method. An oral administration of 200 mg of L-theanine dissolved in 100 mL of water resulted in the generation of alpha-electric waves in the occipital and parietal regions of the subjects brains. The emission intensity of alpha-brain waves (integrated as a function of investigation times and area) was significantly greater in the Grade I than that of Grade V. These results indicate the possibility for L-theanine to be applied to foods and beverages as a new functional food ingredient for its relaxation effect. Kobayashi K, Nagato Y, Aoi N, Juneja LR, Kim M, Yamamoto T, Sugimoto S. Nippon Noegikagaku Kaishi 1998;72(2):153-7.