L-Theanine (γ-glutamylethylamide), is an amino acid predominantly found in green tea. It has been shown to affect brain functions by relieving stress disorders, improving mood, and maintaining normal sleep. Many products enriched in L-theanine are available in the market today. However, the question remains whether L-Theanine really has any beneficial effect on the human body.
A double-blind, randomized, placebo-controlled study aimed to clarify which cognitive functions are positively affected by intake of L-theanine was conducted in 2018. The subjects were Japanese men and women aged 50–69 years. A test named Mini Mental State Examination-Japanese version was conducted among these individuals before and after the administration of L-Theanine.
The Mini‐Mental State Examination (Folstein 1975), or MMSE, is a simple pen‐and‐paper test of cognitive function based on a total possible score of 30 points. It includes tests of orientation, concentration, attention, verbal memory, naming and visuo-spatial skills.
The study found that the participants performed exceptionally well after they were administered L-Theanine. Cognitrax, a computerized testing system designed to measure and monitor brain performance was used to measure cognitive function. Evaluations were performed before the intervention, after a single dose of L-theanine, and after 12 weeks of regular intake. The single dose of L-theanine significantly reduced the reaction time of attention tasks (Stroop test, Part 1), and it increased the number of correct answers and decreased the number of omission errors in working memory related tasks (4-Part continuous performance test, Part 4). The study concluded that, L-Theanine may contribute to improving attention, thus enhancing working memory and executive functions. Many related studies similarly report that L-Theanine enhances brain function.
Another study was designed to evaluate the effect of L-Theanine on attention and reaction time response in 18 normal healthy University student volunteers. In accordance with preliminary analysis of the manifest anxiety scale (MAS), the subjects were divided into two groups referred to as high anxiety propensity group and the minimal anxiety propensity group. Both groups received L-Theanine (200 mg/100 ml water) and placebo (100 ml water) in a double blind repeated measurement design protocol.
Assessments were performed for 15–60 min after consumption under a relaxed condition upon exerting an experimentally induced visual attentional task as well as audio response tests. Additional, self-reports of anxiety as State-Trait Anxiety Inventory (STAI) were characterized after the experiments. However, Alpha bands electroencephalographic activity and heart rate were recorded throughout the trial.
The results clearly demonstrated the significant enhanced activity of alpha bands, descending heart rate, elevated visual attentional performance, and improved reaction time response among high anxiety propensity subjects compared to a placebo. This clearly indicates that L-Theanine not only reduces anxiety and heart rate but also enhances cognitive abilities. The results evidently demonstrated that L- Theanine clearly has a definitive effect on attention performance and reaction time response in normal healthy subjects, that are prone to have high anxiety.
Given that L-Theanine is a relaxant, it is directly or indirectly involved at the neurochemical level and thus it is impacted by a number of neurotransmitter systems, wherein the major target may include glutamate, gamma-aminobutyric acid (GABA), dopamine, and serotonin.
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Baba Y, Inagaki S, Nakagawa S, Kaneko T, Kobayashi M, Takihara T. Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study. J Med Food. 2021 Apr;24(4):333-341. doi: 10.1089/jmf.2020.4803. Epub 2021 Mar 22. PMID: 33751906; PMCID: PMC8080935.
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