Theanine
Theanine (
/ˈθiːəniːn/), also gamma-glutamylethylamide or 5-N-ethyl-glutamine, is an amino acid and a glutamic acid analog commonly found in tea (infusions of Camellia sinensis), primarily in green tea,[1] and also in the basidiomycete mushroom Boletus badius and in guayusa.[2]
More specifically, this compound is called L-theanine, being the L- amino acid (note: this is different than being the levorotatory enantiomer). In 1950, the tea laboratory of Kyoto successfully separated theanine from gyokuro leaf, which has high theanine content.
Theanine is an analog to glutamine and glutamate, and can cross the blood–brain barrier.[3] It is sold in the US as a dietary supplement, and is FDA confirmed as generally recognized as safe (GRAS).[4] The Japanese Ministry of Health and Welfare approved the use of theanine for universal consumption in 1964.[5]
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Effects on the brain
Able to cross the blood–brain barrier, theanine has psychoactive properties.[6]
Theanine has been shown to reduce mental and physicalstress,[7] and improves cognition[8] and mood in a synergistic manner with caffeine.[9][10]
While structurally related to the excitatory neurotransmitter glutamate, theanine only has weak affinity for the glutamate receptor on postsynaptic cells.[11] Rather, its primary effect seems to increase the overall level of the brain inhibitory transmitter GABA. Theanine also increases brain dopamine levels and has a low affinity for AMPA, kainate and NMDA receptors.[12] 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][14] It has also been found that injecting spontaneously hypertensive mice with theanine significantly lowered levels of 5-hydroxyindoles in the brain.[15] Researchers also speculate it may inhibit glutamic acid excitotoxicity.[12] Theanine also promotes alpha wave production in the brain.[6]
Studies on test rats have shown even repeated, extremely high doses of theanine cause little to no harmful psychological or physical effects.[16] Theanine showed neuroprotective effects in one rat study.[17]
A placebo-controlled trial has shown adding theanine to ongoing antipsychotic medication is helpful in reducing some symptoms ofschizophrenia.[18]
Several beverage manufacturers are selling drinks containing theanine and are marketing them as drinks to help people focus and concentrate,[19] while other manufacturers claim relaxing and tranquillizing properties.[18]
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Immune system benefits
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 by the Brigham and Women's Hospital, 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.[20]
[edit]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.[18]
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.[16] Large studies in humans have not been undertaken.
Theanine has also been found to be potentially useful for treating allergies and asthma in an animal model.[21]