Theanine /ˈθiːəniːn/, also known as L-γ-glutamylethylamide and N5-ethyl-L-glutamine, is an amino acid analogue of the proteinogenic amino acids L-glutamate and L-glutamine and is found primarily in particular plant and fungal species. It was discovered as a constituent of green tea in 1949 and in 1950 was isolated from gyokuro leaves, which have high theanine content.[3] Appearance of the name "theanine" without a prefix is understood to imply the L-enantiomer, which is the form found in fresh teas and in some, but not all dietary supplements. The opposite D-enantiomer has far less studied pharmacologic properties, but is present in racemic chemical
As an analogue of glutamate and glutamine, the theanine in common preparations (teas, enantiomer supplements, etc.) is absorbed in the small intestine after oral ingestion; its hydrolysis is to L-glutamate and ethylamine and occurs both in the intestine and liver. It can also cross the blood–brain barrier intact, and register pharmacological effects directly.
In Japan, L-Theanine has been approved for use in all foods, including herb teas, soft drinks, desserts, etc. with some restrictions applying to infant foods.[4][5] It provides a unique brothy or savory (umami) flavor to green tea infusions. It is generally recognized as safe (GRAS) as an ingredient by the Food and Drug Administration (FDA), and is sold as a dietary supplement in the US. However, the German Federal Institute for Risk Assessment, an agency of their Federal Ministry of Food and Agriculture, has objected to the addition of isolated theanine to beverages.
The European Food Safety Authority EFSA advised negatively on health claims related to L-theanine and cognitive function, alleviation of psychological stress, maintenance of normal sleep and reduction of menstrual discomfort.[6] Therefore, health claims for L-Theanine are prohibited in the European Union.
Pharmacodynamics
Theanine is structurally similar to the excitatory neurotransmitter glutamate, and in accordance, binds to glutamate receptors, though with much lower affinity in comparison. Specifically, it binds to ionotropic glutamate receptors in the micromolar range, including the AMPA and kainate receptors and, to a lesser extent, the NMDA receptor.[14][15][16][17] It acts as an antagonist of the former two sites[17] and as an agonist of the latter site.[18] Theanine also binds to group I mGluRs.[14][19] In addition, it inhibits glutamine transporters and glutamate transporters, and thus blocks the reuptake of glutamine and glutamate.[16][20][21] Lastly, theanine elicits umami taste, and this effect has been found to be a consequence of the fact that it directly binds to and activates the T1R1 + T1R3 heterodimer or umami (savory) taste receptor.[22]
Theanine increases serotonin, dopamine, GABA, and glycine levels in various areas of the brain, as well as BDNF and NGF levels in certain brain areas.[14][18][23][24] However, its effect on serotonin is still a matter of debate in the scientific community, with studies showing increases and decreases in brain serotonin levels using similar experimental protocols.[13][25] It has also been found that injecting spontaneously hypertensive mice with theanine significantly lowered levels of 5-hydroxyindoles in the brain.[26] Researchers also speculate that it may inhibit glutamate excitotoxicity.[14]
Effects
Able to cross the blood–brain barrier, theanine has reported psychoactive properties.[27] Theanine has been studied for its potential ability to reduce mental and physical stress,[28] improve cognition,[29] and boost mood and cognitive performance in a synergistic manner with caffeine.[30][31][32][33][34][35]
A Natural Standard monograph that reviews current research on theanine reports that it is likely safe in doses of 200–250 mg up to a maximum daily dose of 1,200 mg. Theanine is used to help with anxiety, blood pressure control, mood, and cognition. Natural Standard rates the evidence to support the usage for anxiety, blood pressure control, and mood as “unclear or conflicting scientific evidence” and the evidence for cognition as “fair negative scientific evidence.” Many of the studies of theanine were done in combination with caffeine as found in tea. While the studies found that the combination had some effect on mood, the studies found that theanine alone had little effect. More sufficiently designed studies in humans are warranted to further our understanding of the effects of theanine.[36]
Theanine is reported to promote alpha wave production in the brain.[27] Early studies of theanine involved much larger doses than those found in a typical cup of tea. Researchers wonder whether drinking tea might have the same effects found in those studies.[37] However, one recent study funded by Unilever found that smaller doses typical of those found in a cup of tea did induce changes in alpha waves as shown by EEG.[38]
Studies on test rats have shown even repeated, extremely high doses of theanine cause little to no harmful psychological or physical effects.[39] Theanine showed neuroprotective effects in one rat study.[40]
A placebo-controlled trial has shown adding theanine to ongoing antipsychotic medication is helpful in reducing some symptoms of schizophrenia.[41] [42]
Several beverage manufacturers are selling drinks containing theanine and are marketing them as drinks to help people focus and concentrate,[37] while other manufacturers claim relaxing and tranquillizing properties.[43]
The combination of theanine and caffeine has been shown to promote faster simple reaction time, faster numeric working memory reaction time and improved sentence verification accuracy