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Open Access Highly Accessed Original article

Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses

Ai Yoto*, Mao Motoki, Sato Murao and Hidehiko Yokogoshi

Author Affiliations

Laboratory of Nutritional Biochemistry, School of Food and Nutritional Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan

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Journal of Physiological Anthropology 2012, 31:28  doi:10.1186/1880-6805-31-28

Published: 29 October 2012

Abstract

Background

L-theanine, an amino acid contained in green tea leaves, is known to block the binding of L-glutamic acid to glutamate receptors in the brain, and has been considered to cause anti-stress effects by inhibiting cortical neuron excitation. Both L-theanine and caffeine, which green tea contains, have been highlighted for their beneficial effects on cognition and mood.

Methods

In this study, we investigated the effects of orally administered L-theanine or caffeine on mental task performance and physiological activities under conditions of physical or psychological stress in humans. Fourteen participants each underwent three separate trials, in which they orally took either L-theanine + placebo, caffeine + placebo, or placebo only.

Results

The results after the mental tasks showed that L-theanine significantly inhibited the blood-pressure increases in a high-response group, which consisted of participants whose blood pressure increased more than average by a performance of a mental task after placebo intake. Caffeine tended to have a similar but smaller inhibition of the blood-pressure increases caused by the mental tasks. The result of the Profile of Mood States after the mental tasks also showed that L-theanine reduced the Tension-Anxiety scores as compared with placebo intake.

Conclusions

The findings above denote that L-theanine not only reduces anxiety but also attenuates the blood-pressure increase in high-stress-response adults.

Keywords:
L-theanine; Caffeine; Blood pressure; Acute stress; Profile of mood states