L-theanine, a natural constituent in tea, and its effect on mental state by Nobre AC, Rao A, Owen GN.
Tea is the most widely consumed beverage in the world after
water. Tea is known to be a rich source of flavonoid antioxidants.
However tea also contains a unique amino acid, L-theanine that may
modulate aspects of brain function in humans. Evidence from human
electroencephalograph (EEG) studies show that it has a direct
effect on the brain (Juneja et al. Trends in Food Science &
Tech 1999;10;199-204). L-theanine significantly increases activity
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 (approximately 20mg). The aim of the current research
was to establish this effect at more realistic dietary levels. EEG
was measured in healthy, 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 a greater increase in alpha
activity across time in the L-theanine condition (relative to
placebo (p+0.05). A second study replicated this effect in
participants engaged in passive activity. These data indicate that
L-theanine, at realistic dietary levels, has a significant effect
on the general state of mental alertness or arousal. Furthermore,
alpha activity is known to play an important role in critical
aspects of attention, and further research is therefore focussed on
understanding the effect of L-theanine on attentional
processes.
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