Tea is a unique source of an amino acid called L-theanine. L-theanine is of interest to nutritionists because evidence suggests that L-theanine can alter brain chemistry which result in changes to brain wave pattern. These changes cause the excitability of the brain to be diminished such that the overall effects of L-theanine are to cause a calming effect. Studies have investigated the L-theanine content of various teas, and the findings from these studies indicate that there is a large variation in the L-theanine content. One study investigated this variation by measuring the L-theanine content of two types of leaf, one of which was known to contain much higher concentrations of L-theanine. The observations of the researchers lead them to conclude that the reason that the high L-theanine leaf was able to accumulate more L-theanine was because the degradation of L-theanine to L-glutamate in the leaves was inhibited. Therefore certain tea varieties may accumulate more L-theanine due to reduced capacity to metabolise it.
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