Tea is the most widely consumed beverage in the world after water. Tea is known to be a rich source of flavonoidantioxidants. However tea also contains a unique amino acid, L-theanine that may modulate aspects of brainfunction in humans. Evidence from human electroencephalograph (EEG) studies show that it has a direct effecton the brain (Juneja et al. Trends in Food Science & Tech 1999;10;199-204). L-theanine significantly increasesactivity in the alpha frequency band which indicates that it relaxes the mind without inducing drowsiness. However,this effect has only been established at higher doses than that typically found in a cup of black tea (~20mg).The aim of the current research was to establish this effect at more realistic dietary levels. EEG was measured inhealthy, young participants at baseline and 45, 60, 75, 90 and 105 minutes after ingestion of 50mg L-theanine(n=16) or placebo (n=19). Participants were resting with their eyes closed during EEG recording. There was agreater increase in alpha activity across time in the L-theanine condition (relative to placebo (p<0.05). A secondstudy replicated this effect in participants engaged in passive activity. These data indicate that L-theanine, at realisticdietary levels, has a significant effect on the general state of mental alertness or arousal. Furthermore, alphaactivity is known to play an important role in critical aspects of attention, and further research is thereforefocussed on understanding the effect of L-theanine on attentional processes.
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