L-theanine is an amino acid found in the tea plant (Camellia sinensis). When tea is brewed, L-theanine passes from the tea leaves into the water. Consuming tea therefore provides a source of L-theanine, and studies show that the L-theanine from tea is bioavailable and absorbed to the blood, where it can pass into the brain. Within the brain, L-theanine has an effect within about 30 minutes of consumption, and this effect includes a calming effect due to an increase in the alpha wave state of the brain. Supplements of L-theanine are available, but it has been shown that the calming effects of L-theanine are available from consumption of realistic quantities of black and green tea. For example, in one study, researchers administered 20 mg L-theanine to healthy individuals, a dose that might be found in a typical cup of black or green tea. The results of the study showed that the L-theanine provided significant improvements in the arousal and attention of the subjects, suggesting that their alpha wave state had been enhanced.
The L-theanine in tea might be one of the reasons that tea is a calming drink. It may also explain some of the benefits tea drinkers obtain from regular consumption of tea.
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