Our randomized crossover trial shows that a bolus intake of
L-theanine via capsules or green tea increased the plasma
concentration of L-theanine (Fig. 1) with comparable kinetics
after both treatments (Table 2). This observation is in line with
data collected in parallel to our study by van der Pijl et al. (13)
after intake of L-theanine via an aqueous solution or black tea.
Thus, it is rather unlikely that additional ingredients in tea, e.g.,
specific proteinogenic amino acids (Table 1), compete with
L-theanine for intestinal absorption. For all participants,
L-theanine was predicted to be absorbed after a tlag of 10–24 min,
leading to a Cmax,70 of ;24–26 mmol/L. It can be assumed that
L-theanine is not only distributed in plasma but also in other
tissues with regard to the Vhyp of 16–17 L (Table 2). Our study
suggests that L-theanine is metabolized to ethylamine and
glutamic acid, because their concentrations in plasma increased
(Fig. 2) and both were excreted by urine (Table 3) after capsule
and tea intake. This is a new finding, because data on the
metabolic fate of L-theanine from human studies have not been
available yet. In rats, ethylamine and glutamic acids increased
dose dependently in plasma and urine after oral and i.g. intake of
L-theanine (8,15). In vitro, increasing amounts of ethylamine
and glutamic acid were observed after incubation of L-theanine