A new study supports prior evidence that tea can not only reduce blood pressure but 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 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.

The study was published this week in the Journal of Physiological Anthropology.

In a separate study published this January in the Archives of Internal Medicine, Australian researchers found that people who drank three cups of tea a day lowered their blood pressure levels by an average of two to three points.

Meanwhile, flavonoids in tea are thought to improve the blood vessels' tone and reduce body weight and abdominal fat. A Dutch population study also found that high tea consumption is associated with a reduced risk of death from heart disease.