L-Theanine was discovered as a constituent of green tea in 1949 and was approved in Japan in 1964 for unlimited use in all foods, including chocolates, soft drinks, and herb teas, except infant foods. It also provides a unique umami (brothy or savory) taste and flavor to green tea infusion.
Early studies of theanine involved much larger doses than are found in an everyday cup of tea. Researchers wonder whether drinking tea might have the same effects found in those studies. 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.
Theanine promotes alpha wave production in the brain. While structurally similar to the excitatory neurotransmitter glutamate, theanine has only weak affinity for the glutamate receptor on postsynaptic cells. It also has low affinity for AMPA, kainate, and NMDA receptors but does however increase brain dopamine levels. 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. It has also been found that injecting spontaneously hypertensive mice with theanine significantly lowered levels of 5-hydroxyindoles in the brain. Researchers also speculate it may inhibit glutamateexcitotoxicity thereby increasing glutamate.
Studies on test rats have shown even repeated, extremely high doses of theanine cause little to no harmful psychological or physical effects. Theanine showed neuroprotective effects in one rat study.
Several beverage manufacturers are selling drinks containing theanine and are marketing them as drinks to help people focus and concentrate, while other manufacturers claim relaxing and tranquillizing properties.
As a supplement
In 2003, the German Federal Institute for Risk Assessment (Bundesinstitut für Risikobewertung, BfR) objected to the addition of isolated theanine to beverages. The institute stated the amount of theanine consumed by regular drinkers of tea or coffee is virtually impossible to determine. While it was estimated the quantity of green tea consumed by the average Japanese tea drinker per day contains about 20 mg of the substance, there are no studies measuring the amount of theanine being extracted by typical preparation methods, or the percentage lost by discarding the first infusion. Therefore, with the Japanese being exposed to possibly much less than 20 mg per day, and Europeans presumably even less, pharmacological reactions to drinks typically containing 50 mg of theanine per 500 millilitres cannot be excluded, in the opinion of the BfR. Such reactions could include impairment of psychomotor skills and amplification of the sedating effects of alcohol and hypnotics.
In 2006, a study found no consistent, statistically significant treatment-related adverse effects on behavior, morbidity, mortality, body weight, food consumption and efficiency, clinical chemistry, hematology, or urinalysis in rats fed high doses of theanine for 13 weeks. Large studies in humans have not been undertaken, however several smaller-scale studies (less than 100 participants) have shown increased alpha wave generation and lowered anxiety, along with benefits to sleep quality in patients with ADHD.
The combination of L-theanine and caffeine has been shown to promote faster simple reaction time, faster numeric working memory reaction time and improved sentence verification accuracy.
L-Theanine may help the body's immune response to infection by boosting the disease-fighting capacity of gamma delta T cells. The study, published in 2003, included a four-week trial with 11 coffee drinkers and 10 tea drinkers, who consumed 600 milliliters of coffee or black tea daily. Blood sample analysis found the production of antibacterial proteins was up to five times higher in the tea drinkers, an indicator of a stronger immune response. L-Theanine may contain mast cell-stabilizing properties in an animal model.
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^Keenan, Emma K.; Finnie, Mike D.A.; Jones, Paul S.; Rogers, Peter J.; Priestley, Caroline M. (2011). "How much theanine in a cup of tea? Effects of tea type and method of preparation". Food Chemistry125 (2): 588–94. doi:10.1016/j.foodchem.2010.08.071.
^Casimir, J.; Jadot, J.; Renard, M. (1960). "Séparation et caractérisation de la N-éthyl-γ-glutamine à partir de Xerocomus badius" [Separation and characterization of N-ethyl-gamma-glutamine from Xerocomus badius]. Biochimica et Biophysica Acta (in French) 39 (3): 462–8. doi:10.1016/0006-3002(60)90199-2. PMID13808157.
^ abcdRitsner, Michael S.; Miodownik, Chanoch; Ratner, Yael; Shleifer, Tatyana; Mar, Maria; Pintov, Leonid; Lerner, Vladimir (2011). "L-Theanine Relieves Positive, Activation, and Anxiety Symptoms in Patients with Schizophrenia and Schizoaffective Disorder". The Journal of Clinical Psychiatry72 (1): 34–42. doi:10.4088/JCP.09m05324gre. PMID21208586.
^Park, Sang-Ki; Jung, In-Chul; Lee, Won Kyung; Lee, Young Sun; Park, Hyoung Kook; Go, Hyo Jin; Kim, Kiseong; Lim, Nam Kyoo et al. (2011). "A Combination of Green Tea Extract andl-Theanine Improves Memory and Attention in Subjects with Mild Cognitive Impairment: A Double-Blind Placebo-Controlled Study". Journal of Medicinal Food14 (4): 334–43. doi:10.1089/jmf.2009.1374. PMID21303262.|displayauthors= suggested (help)
^ abHaskell, Crystal F.; Kennedy, David O.; Milne, Anthea L.; Wesnes, Keith A.; Scholey, Andrew B. (2008). "The effects of l-theanine, caffeine and their combination on cognition and mood". Biological Psychology77 (2): 113–22. doi:10.1016/j.biopsycho.2007.09.008. PMID18006208.
^Raloff, Janet (September 29, 2007). "Distracted? Tea might help your focus". Science News172 (13): 206. doi:10.1002/scin.2007.5591721319. "John J. Foxe of the Nathan S. Kline Institute for Psychiatric Research in Orangeburg, N.Y., and his colleagues recruited 16 people for tests of attentiveness on four days. Before testing, each individual drank a glass of water. On 3 days, the drink was spiked with 100 milligrams of theanine, 60 mg of caffeine, or both. The theanine dose was equivalent to that in 4 to 5 cups of tea, and the caffeine translated to about 2.5 cups of tea. In the difficult tests, participants watched a computer screen and pressed a button when a designated shape appeared on the side of a busy visual field to which an arrow had previously pointed. Participants' accuracy differed little between days when they got water alone or with only one additive. Accuracy improved dramatically, however, on the day that they got the theanine-caffeine combination. The attention benefit lasted throughout the 3 hours of testing."
^ abOwen, Gail N.; Parnell, Holly; De Bruin, Eveline A.; Rycroft, Jane A. (2008). "The combined effects of L-theanine and caffeine on cognitive performance and mood". Nutritional Neuroscience11 (4): 193–8. doi:10.1179/147683008X301513. PMID18681988.
^Einöther, Suzanne J.L.; Martens, Vanessa E.G.; Rycroft, Jane A.; De Bruin, Eveline A. (2010). "L-Theanine and caffeine improve task switching but not intersensory attention or subjective alertness". Appetite54 (2): 406–9. doi:10.1016/j.appet.2010.01.003. PMID20079786.
^Giesbrecht, T.; Rycroft, J.A.; Rowson, M.J.; De Bruin, E.A. (2010). "The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness". Nutritional Neuroscience13 (6): 283–90. doi:10.1179/147683010X12611460764840. PMID21040626.
^Kakuda, Takami; Nozawa, Ayumu; Sugimoto, Akio; Niino, Hitoshi (2002). "Inhibition by Theanine of Binding of [3H]AMPA, [3H]Kainate, and [3H]MDL 105,519 to Glutamate Receptors". Bioscience, Biotechnology, and Biochemistry66 (12): 2683–6. doi:10.1271/bbb.66.2683. PMID12596867.
^ abNathan, Pradeep; Lu, Kristy; Gray, M.; Oliver, C. (2006). "The Neuropharmacology of L-Theanine(N-Ethyl-L-Glutamine)". Journal of Herbal Pharmacotherapy6 (2): 21–30. doi:10.1300/J157v06n02_02. PMID17182482.
^Yokogoshi, Hidehiko; Mochizuki, Mikiko; Saitoh, Kotomi (1998). "Theanine-induced Reduction of Brain Serotonin Concentration in Rats". Bioscience, Biotechnology, and Biochemistry62 (4): 816–7. doi:10.1271/bbb.62.816. PMID9614715.
^Yokogoshi, Hidehiko; Kato, Yukiko; Sagesaka, Yuko M.; Takihara-Matsuura, Takanobu; Kakuda, Takami; Takeuchi, Naokazu (1995). "Reduction Effect of Theanine on Blood Pressure and Brain 5-Hydroxyindoles in Spontaneously Hypertensive Rats". Bioscience, Biotechnology, and Biochemistry59 (4): 615–8. doi:10.1271/bbb.59.615. PMID7539642.
^Kobayashi, Kanari; Nagato, Yukiko; Aoi, Nobuyuki; Juneja, Lekh Raj; Kim, Mujo; Yamamoto, Takehiko; Sugimoto, Sukeo (1998). "L-テアニンのヒトの脳波に及ぼす影響" [Effects of L-Theanine on the Release of α-Brain Waves in Human Volunteers]. Journal of the Agricultural Chemical Society of Japan (in Japanese) 72 (2): 153–7. doi:10.1271/nogeikagaku1924.72.153.