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A new study supports earlier evidence that tea can not only reduce blood pressure but also calm anxiety, despite its caffeine content.
Japanese researchers tested two compounds found in tea – L-theanine, the amino acid contained in tea leaves, and caffeine – and their effect in the body when under stress.
They enlisted 14 subjects who underwent three separate trials, in which they took L-theanine and a placebo, caffeine and a placebo, or a placebo only, the Journal of Physiological Anthropology reports.
The subjects were then asked to complete mental activities under varying degrees of stress, such as solving arithmetic questions with their non-dominant hand submerged in a bucket of ice water.
Ai Yoto and her team from the University of Shizuoka found that L-theanine significantly inhibited the blood pressure increases in a high-response group, which consisted of subjects whose blood pressure rose more than average while performing a mental task after taking a placebo.
Caffeine also had an effect on blood pressure but to a lesser degree than L-theanine.
In addition, the L-theanine was shown to reduce tension-anxiety scores on mood tests.