L-Theanine: How It Works Benefits, Dosage, and More
By Adin Smith, MS | Posted July 14, 2022
- Estimated reading time 10 minutes
L-theanine is a naturally occurring amino acid found in tea leaves that promotes sleep and supports a relaxed state of mind.[1]Wang, et al. How does tea L-theanine buffer stress and anxiety. Food Sci. Hum.Wellness. 2022. May;11(3):467-475.
Because tea is the world’s second most popular beverage, billions of people ingest L-theanine daily.
How much L-theanine is in a cup of tea?
Tea consumers can expect to ingest about 8-30 mg of L-theanine per cup.[2]de Mejia EG, et al. Bioactive components of tea: cancer, inflammation and behavior. Brain Behav Immun. 2009 Aug;23(6):721-31. Powdered or encapsulated forms offer higher concentrations ranging from 100 to 500 mg in a single dose.
How does L-theanine work?
Animal and cell culture models suggest that L-theanine inhibits glutamate, the major excitatory “fast” neurotransmitter released by nerve cells.[3]Kakuda T. Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction. Pharmacol Res. 2011 Aug;64(2):162-8. Glutamate activity in the brain and nervous system is tightly controlled but some people can have problems with its regulation.
Too much glutamate is associated with depression, anxiety, and neurological conditions such as Alzheimer’s, Huntington’s, and Parkinson’s disease.[4]Sanacora G, et al. Towards a glutamate hypothesis of depression: an emerging frontier of neuropsychopharmacology for mood disorders. Neuropharmacology. 2012;62(1):63-77. [5]Lewerenz J, et al. Chronic Glutamate Toxicity in Neurodegenerative Diseases-What is the Evidence? Front Neurosci. 2015 Dec 16;9:469.
Does L-theanine increase dopamine, serotonin, or GABA?
Compared to its potential glutamate inhibitory properties, the data is less clear on how L-theanine may affect other neurotransmitters such as serotonin, dopamine, and γ-aminobutyric acid (GABA).
For instance, researchers have found that feeding mice with a 4% L-theanine solution decreased GABA concentrations in the frontal cortex.[6]Schallier A, et al. L-Theanine intake increases threshold for limbic seizures but decreases threshold for generalized seizures. Nutr Neurosci. 2013 Mar;16(2):78-82. In contrast, mice receiving injections were shown to increase GABA, depending upon the dose.[7]Kimura R, et al. Influence of alkylamides of glutamic acid and related compounds on the central nervous system. Chem Pharm Bull (Tokyo). 1971 Jun;19(6):1257-61.
Whether these animal models are relevant to altering human neurotransmitter metabolism is unknown.
Promotes Alpha Brain Waves
Human studies show that L-theanine increases the electrical signals produced by neurons in the brain called alpha brain waves.[8]Nobre AC, et al. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-8. The range of the alpha frequency band occurs between 8-12 Hz, which indicates a state of wakeful relaxation without drowsiness.
Earlier studies observed L-theanines’ effects on alpha brain waves in participants during unstimulated or resting states. In contrast, its use in people challenged with specific tasks may increase or decrease alpha wave activity across different brain regions.[9]Gomez-Ramirez M, et al. The effects of L-theanine on alpha-band oscillatory brain activity during a visuo-spatial attention task. Brain Topogr. 2009 Jun;22(1):44-51. [10]Gomez-Ramirez M, et al. The deployment of intersensory selective attention: a high-density electrical mapping study of the effects of theanine. Clin Neuropharmacol. 2007 Jan-Feb;30(1):25-38.
This research implies that L-theanine may have a more nuanced way of altering alpha brain waves.
Benefits
Below is a summary of eight studies evaluating responses to L-theanine use among different populations.
1) May Lower cortisol
In a small 2021 study, healthy participants with moderate levels of self-reported stress were randomized to receive a single 200 mg dose of L-theanine or a placebo pill taken 45 minutes before a stressful task involving a ten-minute arithmetic test.[11]Evans M, et al. A Randomized, Triple-Blind, Placebo-Controlled, Crossover Study to Investigate the Efficacy of a Single Dose of AlphaWave® L-Theanine. Neurol Ther. 2021;10(2):1061-1078.
Researchers assessed participants’ salivary cortisol and brain waves before and after the math task. They also evaluated changes in blood pressure and heart rate during and after the arithmetic challenge.
At study completion, participants taking L-theanine experienced significant reductions in salivary cortisol compared to placebo treatment, one-hour post-dose.
No significant changes in heart rate, blood pressure, stress, anxiety, or alpha brain waves occurred between treatment or placebo groups after the stress task.
At three hours post-dose, however, the L-theanine group had more significant increases in alpha brain activity during the eyes open part of the brain wave test than the placebo group.
These results suggest that L-theanine may take up to three hours to promote increases in alpha brain waves, whereas its cortisol-reducing effects may respond within one hour or less.
2) Promotes sleep quality
In a double-blind, randomized placebo-controlled trial, researchers evaluated the effects of L-theanine on sleep quality, depression, anxiety, and cognitive function in a group of healthy middle-aged adults.[12]Hidese S, et al. Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults. Nutrients. 2019 Oct 3;11(10):2362. Participants received 200 mg per day of L-theanine or a matching placebo pill for four weeks.
At trial completion, results showed that, compared to the placebo, L-theanine treatment shortened the time it took to fall asleep, reduced sleep disturbance frequency, and lowered sleep medication use.
In contrast, there were no significant changes in anxiety, depression, and cognitive function scores between the placebo and treatment groups.
3) Supports sleep satisfaction in those with anxiety
In a double-blind, randomized, placebo-controlled trial, researchers investigated the effect of L-theanine treatment for two months on sleep quality, anxiousness, and cognition outcomes in people with Generalized Anxiety Disorder (GAD), followed by a two-week post-intervention period.[13]Sarris J, et al. L-theanine in the adjunctive treatment of generalized anxiety disorder: A double-blind, randomized, placebo-controlled trial. J Psychiatr Res. 2019 Mar;110:31-37.
Participants received 450 mg daily of L-theanine or a placebo pill for two months. Non-responders (the group of people not showing any benefits after the first month) were increased to 900 mg daily for the second month.
Participants completed a cognitive test and filled out questionnaires designed to measure anxiety, depression, and the insomnia severity index (ISI).
After eight weeks, those assigned to the L-theanine group reported better sleep satisfaction scores than the placebo group. However, insomnia severity, anxiety, mood, worry, or cognition scores did not show any improvement with L-theanine over the placebo treatment.
4) Healthier sleep quality changes in participants with ADHD
A randomized, double-blind study evaluated the effect of L-theanine on sleep quality among boys ages 8 to 12 with ADHD.[14]Lyon MR, et al. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD). Altern Med Rev. 2011 Dec;16(4):348-54. For six weeks, they received 200 mg of L-theanine in a chewable tablet form or a placebo equivalent in the morning and afternoon, totaling 400 mg daily.
At the end of the trial, boys treated with L-theanine experienced better sleep quality than the placebo group. More research is necessary to confirm these promising findings.
5) May reduce stress responses in anxiety-provoking situations
In a 17-day study, researchers assessed L-theanine’s effect on university students beginning a pharmacy placement practice (a highly stressful period).[15]Unno K, et al. Anti-stress effect of theanine on students during pharmacy practice. Pharmacol Biochem Behav. 2013 Oct;111:128-35.
Students were randomized to receive 200 mg of L-theanine twice daily or placebo equivalent, starting from 1 week before pharmacy practice through its 10-day duration.
Researchers obtained stress and anxiety-related questionnaires and a stress biomarker called salivary α-amylase.
Results showed that the treated group had lower pre-practice salivary α-amylase than the placebo group, indicating that L-theanine may suppress anticipatory stress. However, post-practice salivary α-amylase activity scores were not significant between groups.
The participants’ subjective stress scores were significantly lower in the L-theanine group compared to the placebo group. However, there were no differences in anxiety between groups.
Because this study was single-blinded, the results should be interpreted with caution.
6) Better anxiety and relaxation scores
In a randomized, double-blind, crossover study, researchers compared the effects of L-theanine (200 mg), 1 mg of alprazolam (a benzodiazepine medication and sedative), and a placebo pill on self-reported anxiety in healthy participants.[16]Lu K, et al. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol. 2004 Oct;19(7):457-65.
Subjects received one of the three treatments before exposure to an anticipatory anxiety condition involving an acute electric shock model.
At the end of the study, neither L-theanine nor alprazolam showed an ability to suppress anxiety in the acute stress model. However, during the relaxed condition of the study, participants assigned to L-theanine experienced significant improvements in anxiety and relaxation over those receiving alprazolam or placebo.
These results show that L-theanine was effective at inducing relaxation and subjective stress in a relaxed state but not in a stressed state.
Notably, the electric shock method used in this study may have been too intense for either treatment to work.
7) Favorable anxiety changes in people with schizophrenia
In a randomized, double-blind, placebo-controlled study involving people diagnosed with schizophrenia or schizoaffective disorder, participants were treated with either 400 mg of L-theanine or a placebo pill while maintaining their usual therapy for eight weeks.[17]Ritsner MS, et al. L-theanine relieves positive, activation, and anxiety symptoms in patients with schizophrenia and schizoaffective disorder. J Clin Psychiatry. 2011 Jan;72(1):34-42.
After study completion, individuals who took L-theanine capsules experienced more significant improvements in anxiety scores compared to the placebo group. Furthermore, they had better scores related to mood and tension, intellectual and muscular function, and fewer complaints related to the condition.
However, not all rating scales, such as general functioning and quality of life measures, were significantly affected.
In summary, these results show L-theanine may help reduce anxiety in those with schizophrenia, but further research is necessary.
8) Promotes attention performance in people prone to anxiety
In a randomized, double-blind trial, healthy university students with a high or low anxiety propensity received a 200 mg dose of L-theanine dissolved in water or a placebo equivalent, followed by visual and audio response tasks for measuring attention and reaction time.[18]Higashiyama, et al. Effects of l-theanine on attention and reaction time response. J. Funct. Foods. 2011;3(3):171-178.
After analysis, neither L-theanine nor the placebo treatment affected anxiety scores. On the other hand, the 200 mg dose of L-theanine lowered heart rate, improved reaction time, and increased attention performance in subjects prone to anxiety.
The participants with a minimal propensity for anxiety experienced no such benefits.
L-theanine’s potential effects on focus and attention
It’s important to note that overall, studies evaluating L-theanine’s effects on attention and focus are inconsistent.
Additionally, more research is needed to determine if gains in sleep quality from L-theanine use might be the reason for increased attention performance observed in some studies.
What are the typical doses of L-theanine?
Most clinical studies have used doses ranging from 200-400 mg per day, with one study using up to 900 mg per day.
How much L-theanine is absorbed?
L-theanine is absorbed in the small intestine by about 50% from capsules or tea.[19]Scheid L, et al. Kinetics of L-theanine uptake and metabolism in healthy participants. J Nutr. 2012 Dec;142(12):2091-6.
What is the half-life of L-theanine in the body?
L-theanine takes a little over an hour to be removed from the blood plasma by 50%, whereas complete elimination occurs after 24 hours.[20]Scheid L, et al. Kinetics of L-theanine uptake and metabolism in healthy participants. J Nutr. 2012 Dec;142(12):2091-6.
Safety
According to human research studies, L-theanine appears to be safe when taken short-term, even with doses of up to 900 mg/day. However, more research is necessary to determine its safety with chronic use when consumed in higher concentrations as a nutritional supplement.[21]Türközü D, et al. L-theanine, unique amino acid of tea, and its metabolism, health effects, and safety. Crit Rev Food Sci Nutr. 2017 May 24;57(8):1681-1687.
Conclusion
Excessive glutamate activity brought on by stress may negatively affect cognitive function and mood. Preliminary studies show that L-theanine may inhibit glutamate activity in the brain.
Human research consistently shows that L-theanine promotes sleep quality. Its use may also help lower cortisol and adrenaline triggered by the body’s fight-or-flight response.
L-theanine increases alpha brain waves while at rest but does not appear as effective in doing so during stressful states. Additionally, research on its ability to increase attention performance or induce relaxation during challenging tasks is inconsistent.
Supplementation with L-theanine has been shown to reduce feelings of stress and anxiety in some studies, but not all.
For those thinking of taking an l-theanine supplement, it is always best to consult with your doctor first.
References
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