The polyphenols are a group of phytochemicals found in plants. Evidence suggests that humans who eat large amount of plant foods have significant intakes of polyphenols. Scientific studies have shown that polyphenols have a number of health effects, including anxiolytic properties in humans and animals. Green tea is rich in a group of polyphenols belonging to the flavonoid subgroup. In particular, green tea contains a number of flavonoids called flavan-3-ols that are often referred to as catechins. One of these catechins, epigallocatechin gallate (EGCG) has been investigated for it anti-anxiety effects in animals. For example, in one study, researchers administered EGCG to mice and then exposed them to a series of behavioural tests. One of these tests was designed to assess the levels of anxiety and learning in the mice. The results of the tests showed that EGCG conferred significant anxiolytic, amnesic and learning effects on the mice, and these effects were comparable to the benzodiazepine drug chlordiazepoxide.
Green tea may be an effective anxiolytic herb. The anxiolytic effects of green tea may be due to the presence of epigallocatechin gallate, a flavan-3-ol found in high concentrations in tea leaves. However, green tea also contains L-theanine, an amino acid that has been shown to decrease anxiety. Therefore both of these factors could contribute to the anti-anxiety effect of green tea.
In addition, the researchers also assessed the chemical changes caused by ECGC and chlordiazepoxide to the brain by assessing the electrophysiology of isolated mice neurones in culture. When they did this there was no discernable difference in the changes to the excitation of the neromnes between chlordiazepoxide and EGCG, indicating they caused similar physiological changes to the neurones. Further experimentation showed that these effects may have been mediated through modulation of GABA neurotransmitter channels in the neurones. In another study, researchers administered a green tea extract to rats for 5 weeks. The green tea extract caused a significant reduction in the anxiety experienced by the rats when they were exposed to experimental stress. This decrease in anxiety was accompanied by an increased turnover of dopamine and serotonin in the brains of the rats. The authors concluded that green tea extract may have anxiolytic effects because it is able to cause changes to neurochemistry.
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