Often referred to as the calming amino acid, L-theanine is a neurologically active compound which has repeatedly demonstrated its utility as a relaxing agent1,2 . Along with catechins and caffeine, L-theanine is a key ingredient in tea leaves – which may be why tea is so often associated with a sense of calm and relaxation.
L-theanine can be found in white, green and black varieties harvested from the Camellia sinensis plant3,4. Its presence was first discovered by Japanese researchers between 1949 and 19505 when it was isolated from the gyokuro leaf; a type of green tea leaf with a high theanine content. In order to increase the overall theanine content in tea, the leaves are often shaded from direct sunlight when preparing concentrated varieties such as matcha or gyokuro green tea3.
Many consider L-theanine as an anxiolytic compound due to its calming effect on the mind and body; it may support those who experience anxiety, hyperactivity and sleep disturbances1,6,7. This is likely due to its influence on nerve impulses and neurotransmitters such as gamma-aminobutyric acid or GABA which stimulate calming and relaxation. For these reasons, L-theanine has fast become a popular supplement for those turning to nutraceuticals in support of stress and mental wellbeing.
Unlike other amino acids, L-theanine is not required to build proteins or create enzymes in the body. In fact, it is a non-dietary compound. As such, tea consumption and supplementation are the primary sources of L-theanine.
In this article, we will be taking a closer look into the research on L-theanine while discussing exactly how this unique amino acid functions in the body.
How does L-theanine function in the body?
L-theanine, also known as 5-N-ethyl-glutamine, is structurally similar to glutamine; the precursor to glutamate and GABA. L-theanine is absorbed in the small intestine and hydrolysed to L-glutamate and ethylamine in the liver and intestine8. Researchers believe that this structural similarity may be responsible for the rapid effects elicited on the brain following ingestion. L-theanine easily crosses the blood brain barrier where it may support the development of the hippocampus – the area in the brain responsible for memory storage; while also protecting neurons from cell death and injury9.
While the exact mechanism is still unknown, L-theanine also appears to regulate the hypothalamic pituitary adrenal (HPA) axis thus influencing levels of catecholamines in the system10, 11. Researchers speculate that this may be related to L-theanine’s antioxidant activity.
Is there a difference between theanine and L-theanine?
L-theanine is an enantiomer or molecular form of the theanine compound most readily available in green tea. D-theanine is another form of the amino compound also present in tea, however it is only L-theanine which has been linked to the benefits discussed here. It should be noted that these terms can be used interchangeably, so it is important to read the label before supplementing if you decide to do so.
The benefits of L-theanine – what the research has to say.
Sleep, stress and relaxation
The therapeutic application of L-theanine for stimulating feelings of calm and relaxation is perhaps one of the most widely evidenced properties of this amino acid. In particular, L-theanine is quite unique in its ability to elicit these feelings without the sedative effect associated with similar compounds16. This is due to its ability to increase alpha brain waves and the brain neurotransmitter GABA.
Alpha brain waves
A central mechanism of relaxation is the stimulation of alpha brain waves as can be observed during periods of meditation17 and rapid eye movement (REM) sleep18. Results from a recent trial showed increases in alpha wave function just 30 minutes post ingestion of 200mg L-theanine. These alterations were predominantly present in the occipital and frontal lobes of the brain; areas responsible for memory and information processing2. These results were confirmed by a further study which also observed improvements in alpha band activity, as well as heart rate, visual attentional performance and reaction time response19.
GABA is the primary inhibitory neurochemical in the brain; responsible for creating a state of relaxation through mediation of brain activity. L-theanine dampens sensations of restlessness, anxiety and rumination in the brain through GABA activation20; supporting feelings of relaxation and contentment. Following supplementation, researchers observed significant increases in alpha-wave patterns, while beta waves were reduced20,21. In fact, GABA influences the entire neuroendocrine response22. L-theanine elevates levels of GABA in the brain23 and can be taken during the day due to its lack of sedation. When compared to the commonly prescribed anxiolytic drug alprazolam or Xanax, L-theanine appeared to elicit an even greater calming effect on participants at a 200mg dose1.
While L-theanine’s influence on GABA and alpha brain wave stimulation naturally supports improved sleep quality, this amino acid also acts as a precursor to serotonin – which is required for melatonin production; the sleep hormone and is central to controlling sleep and wake cycles24. Further studies have identified the utility of L-theanine supplementation for the improvement of sleep efficiency in boys with ADHD25, while preliminary studies have demonstrated that L-theanine can reverse caffeine induced decreases in non-REM sleep7.
The stimulation of GABA in the brain as evidenced above naturally aids stress reduction and a sense of calm, however L-theanine goes further in its ability to elicit changes to the stress response. Reductions in heart rate, salivary immunoglobulin A (sIgA) and activation of the sympathetic nervous system during tasks which provoke an acute stress response were all recorded following L-theanine supplementation1,26. A study published in Nutrients investigated the effect of a 200mg L-theanine drink on patients’ stress response. Within just one hour, participants observed reductions in feelings of stress; within three hours, salivary cortisol levels were significantly reduced and an increase in alpha wave brain activity was observed27. As alterations in cortisol, the body’s key stress hormone can impair memory retrieval as well as trigger hippocampal dysfunction, L-theanine may also have a therapeutic application in memory preservation and cognitive functioning.
Due to L-theanine’s structural similarities to glutamate, it has been primarily investigated for its neuroprotective effects on the body. While memory preservation and improvement have largely been linked to L-theanine in the research, this is not the only neuroprotective mechanism associated with the amino acid:
- Neurotransmitters serotonin and dopamine are increased following ingestion of L-theanine; enhancing cognition and general brain functioning12.
- L-theanine boosts glutathione levels, a major antioxidant known to minimise the effects of oxidative damage13.
- It elevates brain derived neurotrophic factor (BDNF) which supports neuron maintenance and survival14.
- L-theanine may protect the brain from heavy metals such as cadmium which have been implicated in the development of neurodegenerative diseases15.
Mood, memory and cognitive decline
L-theanine increases the expression of BDNF in the brain28, which not only boosts neural plasticity, but also promotes the neurogenesis of both serotonergic and dopaminergic neurons29. L-theanine’s ability to promote neural development may aid in memory preservation14, while also supporting an improved ability to recognise objects, people or events which have been previously encountered30. This may be particularly beneficial in elderly subjects where 4g daily of L-theanine rich matcha tea resulted in marked improvements in attention and reaction time35,36.
With BDNF activation believed to be central to the action of many anti-depressant SSRIs32-34, researchers have also investigated the possible benefits of L-theanine as an aid in anxiety and depression. Daily administration of 250mg L-theanine over an 8-week period showed a reduction in symptoms of depression, anxiety, sleep disturbances and cognitive impairment in patients with clinically diagnosed major depressive behaviour35.
Inflammation and antioxidant protection
Pre-clinical trials have shown that L-theanine can reduce amyloid beta plague levels which is often over-expressed in the brains of Alzheimer patients36. Researchers believe that this is at least in part supported by L-theanine’s ability to boost levels of the antioxidant glutathione in brain tissue36. This antioxidant ability may further provide protection against damage from oxidative stress37; a common factor in Alzheimer’s progression. L-theanine also appears to reduce oxidative damage in the brain by regulating Nuclear Factor kappa B (NF-kB), a key inflammatory gene signal36.
Mild cognitive impairment is often observed in early stage Alzheimer’s or dementia. In a group of 91 Alzheimer’s patients, improvements in cognitive impairment and brain theta activity which is associated with increased alertness, was observed in those taking 1680mg of combined L-theanine and green tea38.
It has been speculated that L-theanine’s ability to stimulate the neurogenesis of dopaminergic neurons may make it a useful tool in the treatment of Parkinson’s disease, however further research is still required to confirm this theory39,40.
L-theanine and caffeine
Several studies have found that L-theanine and caffeine work synergistically in the body as a nootropic. Increases in memory and attention as recorded via changes in alpha brain pattern were observed following the combined administration of 100mg L-theanine and 50mg caffeine41. Improvements in accuracy, attention and memory skills, as well as altertness were all recorded; minus the reduced blood flow to the brain observed when caffeine was administered alone42.
Where to find L-theanine
Green tea is by far the most concentrated dietary source of this amino acid, however theanine may have a reduced bioavailability when consumed through tea alone43. Researchers observed a hindered rate of intestinal absorption in concentrations below 4mM43; a phenomenon which is believed to be due to the presence of D-theanine in tea competing for absorption with L-theanine43,44.
A study which tested the L-theanine content in various teas45, found that:
- White tea = 6.26mg/cup
- Green tea =6.56mg/cup
- Oolong = 6.09mg/cup
- Black tea =5.13mg/cup
- L-theanine is a non-dietary amino acid found in tea leaves; it is not easily found in the diet. Green tea is the most concentrated dietary source.
- Research has shown it helps to regulate neurotransmitter levels, exerts neuroprotective effects and boosts antioxidant levels in the body.
- L-theanine supports relaxation by increasing alpha brain waves; which are also associated with mediation and REM sleep. It also increases the calming brain neurotransmitter GABA.
- L-theanine supports relaxation without the sedative effect associated with other similar compounds such as valerian. For this reason, it can be taken during the daytime.
- L-theanine diminishes the stress response, reduces heart rate and salivary cortisol; as well as perceived anxiety and stress. Its effects on lowering stress hormones may have a positive knock-on effect on memory and learning.
- This amino acid is low risk, with few side-effects being reported following use.
If you have any questions regarding the topics that have been raised, or any other health matters please do contact me (Tracey) by phone or email at any time.
email@example.com, 01684 310099
Tracey Hanley and the Cytoplan Editorial Team
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L-Theanine – An amino acid, found in tea leaves, that is used to support the relaxation response, sleep quality and memory.
- Lu K, Gray MA, Oliver C, Liley DT, Harrison BJ, Bartholomeusz CF, et al. The acute effects ofL-theanine in comparison with alprazolam on anticipatory anxiety in humans. Hum Psychopharmacol Clin Exp [Internet]. John Wiley & Sons; 2004 Oct 1 [cited 2018 Jul 30];19(7):457–65. Available from: http://doi.wiley.com/10.1002/hup.611
- Song CH, Jung JH, Oh JS, Kim KS. Effects of Theanine on the Release of Brain Alpha Waves. Korean J Nutr [Internet]. Tong Hakhoe; 1968 Nov 1 [cited 2018 Aug 3];36(9):918–23. Available from: https://koreamed.org/SearchBasic.php?RID=0124KJN/2003.36.9.918&DT=1
- Finger A, Kuhr S, Engelhardt UH. Chromatography of tea constituents. J Chromatogr A [Internet]. Elsevier; 1992 Oct 30 [cited 2018 Aug 10];624(1–2):293–315. Available from: https://www.sciencedirect.com/science/article/pii/002196739285685M?via%3Dihub
- Casimir J, Jadot J, Renard M. Séparation et caractérisation de la N-éthyl-γ-glutamine à partir de Xerocomus badius. Biochim Biophys Acta [Internet]. Elsevier; 1960 Apr 22 [cited 2018 Aug 10];39(3):462–8. Available from: https://www.sciencedirect.com/science/article/pii/0006300260901992?via%3Dihub
- Sakato Y. The chemical constituents of tea: III. A new amide theanine. Nippon Nogeikagaku Kaishi [Internet]. 1949 [cited 2018 Aug 10];23:262–7. Available from: http://www.suntheanine.com/wp-content/uploads/2013/06/2007.01.rao_.suntheanine.nutracos.pdf
- Lyon MR, Kapoor MP, Juneja LR. The effects of L-theanine (Suntheanine®) on objective sleep quality in boys with attention deficit hyperactivity disorder (ADHD): a randomized, double-blind, placebo-controlled clinical trial. Altern Med Rev [Internet]. 2011 Dec [cited 2018 Aug 1];16(4):348–54. Available from: http://www.ncbi.nlm.nih.gov/pubmed/22214254
- Jang H-S, Jung JY, Jang I-S, Jang K-H, Kim S-H, Ha J-H, et al. L-theanine partially counteracts caffeine-induced sleep disturbances in rats. Pharmacol Biochem Behav [Internet]. 2012 Apr [cited 2018 Aug 1];101(2):217–21. Available from: http://www.ncbi.nlm.nih.gov/pubmed/22285321
- Kurihara S, Shibakusa T, Tanaka KA. Cystine and theanine: amino acids as oral immunomodulative nutrients. Springerplus [Internet]. Nature Publishing Group; 2013 Nov 26 [cited 2018 Aug 10];2(1):635. Available from: http://springerplus.springeropen.com/articles/10.1186/2193-1801-2-635
- Cho H-S, Kim S, Lee S-Y, Park JA, Kim S-J, Chun HS. Protective effect of the green tea component, l-theanine on environmental toxins-induced neuronal cell death. Neurotoxicology [Internet]. 2008 Jul [cited 2018 Aug 3];29(4):656–62. Available from: http://www.ncbi.nlm.nih.gov/pubmed/18452993
- Tian X, Sun L, Gou L, Ling X, Feng Y, Wang L, et al. Protective effect of l-theanine on chronic restraint stress-induced cognitive impairments in mice. Brain Res [Internet]. Elsevier; 2013 Mar 29 [cited 2018 Aug 3];1503:24–32. Available from: https://www.sciencedirect.com/science/article/pii/S0006899313001856
Further references available upon request.