In particular, theanine, a major amino acid found in green tea, was the element that exhibited a stress-reducing effect in both mice and humans.
Matcha, a theanine-rich powdered green tea, is therefore said to have stress-reducing properties. However, it also has a high caffeine content, which has a strong antagonistic effect against theanine.
Researchers at Japan’s University of Shizuoka and National Agriculture and Food Research Organisation sought to examine matcha’s stress-reducing effect using an animal experiment and a clinical trial, assessing this effect in matcha marketed in Japan and abroad, based on its composition.
Mice on matcha
In the animal experiment, the anti-stress effect of matcha was evaluated as suppressed adrenal hypertrophy using territorially-based loaded stress in mice.
The researchers reported that high theanine and arginine content in matcha exhibited a strong anti-stress effect, but added that this was only possible when the molar ratio of caffeine and epigallocatechin gallate (EGCG) to theanine and arginine was the lesser of the two.
They had used one of the experiment’s seven matcha samples — whose theanine content represented the median of all seven samples — to examine the link between the amount of matcha intake and suppression of adrenal hypertrophy.
The researchers wrote that a minimum of 0.32mg/kg of theanine, along with arginine (the most and second-most abundant amino acids in Japanese matcha respectively), had a significant stress-reducing effect, while glutamate and glutamine (the third- and fourth-most abundant amino acids) had no such effect.
There was no direct relationship between caffeine intake and adrenal hypertrophy, but the co-existence of caffeine and EGCG may have somewhat inhibited the anti-stress effect of theanine.
Trial on tea
In the clinical trial, 39 participants consumed test matcha that was expected to exhibit a stress-reducing effect, or placebo matcha that was expected to have no effect; both samples were taken from those used in the mouse study.
Subsequently, the researchers reported that anxiety — a reaction to stress — was “significantly lower in the test matcha group than in the placebo group”.
They added that to predict the mental function of each type of matcha, the quantity of theanine and the ratios of caffeine, EGCG, and arginine against theanine needed to be verified.
Subjective stress was also lower in the test group than in the placebo group, though this was not a statistically significant difference, as nerve excitation would normally be down-regulated by the morning after consuming the placebo.
Furthermore, they noted that the test matcha may have regulated recovery rather than suppress excitation.
Composition and conclusion
The researchers also measured the components of 76 samples of matcha marketed in Japan and 67 samples of matcha marketed overseas.
They observed that 3g of daily matcha intake in a human could have a stress-reducing effect if the sample taken contains more than 17mg/g of theanine
Therefore, 50 out of 76 Japanese samples fulfilled this criteria. In stark contrast were the samples sold overseas, of which only six fulfilled the critera.
In addition, the molar ratio of caffeine and EGCG to theanine and arginine would probably need to be the lower of the two, which suggested that 32 out of the 76 Japanese samples fulfilled the aforementioned criteria, while only one overseas sample did so.
In conclusion, they wrote: “We evaluated the effects of quantity and ratio of matcha components on its stress-reducing properties using an animal model of psychosocial stress. The stress-reducing effect in humans was confirmed using two kinds of matcha selected based on the animal study.
“In addition, we assessed the stress-reducing effect of matcha marketed in Japan and overseas. As a result, 42% of matcha samples marketed in Japan, and only one sample marketed abroad, were expected to have a stress-reducing effect. When using matcha samples to study mental function, a quality check is critical.”
“Stress-Reducing Function of Matcha Green Tea in Animal Experiments and Clinical Trials”
Authors: Keiko Unno, et al.