L-Theanine reduces psychological and physiological stress responses by Kimura K, Ozeki M, Juneja LR, Ohira H.
The amino acid L-Theanine exhibited significant anti-stress
activity in human subjects, researchers in Japan reported.
L-Theanine, which is found in green tea leaves and can be
consumed in supplement form, is known to block the binding of
L-glutamic acid to glutamate receptors in the brain,
characteristics that suggest L-Theanine may influence psychological
and physiological states under stress. To test this hypothesis,
researchers conducted a clinical trial to determine how subjects
consuming L-Theanine reacted to an acute stress task.
In the study, twelve subjects participated in four separate
trials. In one trial they consumed L-theanine at the start of being
exposed to the stressful experience, in another trial they consumed
L-theanine midway through the stressful experience, a third trial
where they consumed a placebo and a fourth trial where they
The results showed that L-theanine intake resulted in a
reduction in the heart rate and salivary immunoglobulin A (s-IgA)
responses to an acute stress task compared to when the subjects
were in the control groups. Furthermore, the analyses of heart rate
variability indicated that the reductions in heart rate and s-IgA
responses were likely attributable to a lessening of sympathetic
The researchers concluded, "the oral intake of L-Theanine could
cause anti-stress effects via the inhibition of cortical neuron
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