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L-Theanine is an amino acid found in green tea leaf and in 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 increase of catecholamines in their brain. L-Theanine has been confirmed to be safe in animal experiments. We found recently that oral intake of L-theanine caused a feeling of relaxation among the human volunteers examined. These observations led us to do experiments on the effects of administration of L-theanine on the brain electric waves. Eight female university students were selected as volunteers. Four of them were ranked to be Grade I (the highest anxiety) and the remaining four, Grade V (the lowest anxiety) in an investigation done by the manifest anxiety scale method. A dose of oral administration of 200mg of L-theanine dissolved in 100 ml of water resulted in the generation of a-electric waves in the occipital and parietal regions of the brains of the subjects. The emission intensity of a-brain waves (integrated as a function of investigation times and area) was significantly greater in the group of 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 type of functional food ingredient for its relaxation effect.

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