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Abstract
L-Theanine is an amino acid contained in green tea leaves which is known to block
the binding of L-glutamic acid to glutamate receptors in the brain. Because the characteristics
of L-Theanine suggest that it may influence psychological and physiological states
under stress, the present study examined these possible effects in a laboratory setting
using a mental arithmetic task as an acute stressor. Twelve participants underwent
four separate trials: one in which they took L-Theanine at the start of an experimental
procedure, one in which they took L-Theanine midway, and two control trials in which
they either took a placebo or nothing. The experimental sessions were performed by
double-blind, and the order of them was counterbalanced. The results showed that L-Theanine
intake resulted in a reduction in the heart rate (HR) and salivary immunoglobulin
A (s-IgA) responses to an acute stress task relative to the placebo control condition.
Moreover, analyses of heart rate variability indicated that the reductions in HR and
s-IgA were likely attributable to an attenuation of sympathetic nervous activation.
Thus, it was suggested that the oral intake of L-Theanine could cause anti-stress
effects via the inhibition of cortical neuron excitation.