Summary
L-theanine, an amino acid found in Camellia sinensis tea leaves, is known for its calming effects by promoting relaxation without drowsiness by increasing alpha brain waves and enhancing the production of calming neurotransmitters like GABA.* This natural compound is often used to support occasional anxiety and brain function,* making it a useful supplement for those seeking mental clarity and improved quality of life.*
Each year the American Psychological Association conducts a survey of stress among Americans. According to their report, “The number of people who say they’re significantly stressed… is stunning relative to what we’ve seen since we began the survey in 2007.”[1] Stress and occasional anxiety are inter-related, and they have substantial impacts on human health. Persistent stress contributes to changes to blood pressure, vascular vitality, gastrointestinal health, mental well-being.[2],[3] It’s no surprise that people are seeking ways to improve the stress response and improve their quality of life. Thankfully, L-theanine – an amino acid derived from the tea plant (Camellia sinensis) – is a compound that may help.*[4]
The health benefits of tea have been celebrated as far back as 2737 BCE.[5]According to Chinese scholars, “Drinking tea can allow people to acquire a peaceful, relaxed, refreshed and cheerful enjoyment, and even longevity.”[6]
Modern science confirms the value of tea
Tea consumption helped people to recover more quickly from a stressful task, leading to lower post-stress cortisol levels and greater relaxation. Conducted over six weeks, the trial involved 75 healthy, non-smoking men aged between 18 and 55 years who were randomly assigned to consume either black tea or a placebo drink that looked and tasted like tea but did not contain its active ingredients. The stressor used was a combination of tasks designed to induce stress, including a public speaking task and a mental arithmetic task performed in front of an audience known as the Trier Social Stress Test (TSST). This combination is a well-established method for inducing acute stress in a laboratory setting. Salivary cortisol was used to assess their stress.*[7]
Of course, the rituals that surround tea drinking contribute to a sense of calm – but so do the bioactive ingredients found within the tea leaves themselves. The relaxing effect is mainly due to L-theanine (γ-glutamylethylamide or N-ethyl-L-glutamine).* This non-protein amino acid and phytonutrient derived from Camellia sinensis, the evergreen shrub that is used to produce black, green, and oolong teas.[8]
L-theanine’s chemical structure is similar to glutamate, the primary excitatory neurotransmitter in the central nervous system.[9] This structural similarity allows L-theanine to interact with glutamatergic receptors, leading to reduced cortical neuron excitation and decreased sympathetic nervous system activation.*
L-theanine appears to exert its effects on the hypothalamic-pituitary-adrenal (HPA) axis by affecting corticosterone and cortisol levels and normalizing HPA axis hyperactivity, potentially mitigating the physiological and psychological stress responses as seen in mechanistic studies.*[1] It also modulate GABAergic activity by increasing gamma aminobutyric acid (GABA)-A, the principal inhibitory neurotransmitter in the human brain.*[10] The combination of these effects underlies some of the relaxing properties of L-theanine.*[11],[12]
L-Theanine and the Stress Response
The stress response is a complex physiological and psychological reaction to perceived threats or challenges, involving the HPA axis and the sympathetic nervous system. This response results in the release of stress hormones such as cortisol and catecholamines, where prepare the body for a “fight or flight” reaction. Persistent activation of the stress response stimulates the nervous system to produce large amounts of vasoconstricting hormones that lead to changes in blood pressure. Fortunately, L-theanine may have a modest ability to modulate heart rate and blood pressure during stressful events and mentally challenging tasks.*[13],[14]
A singular dose of 200 mg of L-theanine helped normalize blood pressure and reduce perceived tension-anxiety scores amongst 18 healthy 18–20-year-old male university students while they were asked to perform a challenging mental task involving an experimentally induced visual attentional task along with audio response tests.* L-theanine did not cause drowsiness or impair concentration in this trial.*[15]
In another study in which 12 male undergraduate student volunteers were asked to complete a challenging mental test, a single dose of 200 mg L-theanine reduced heart rate, subjective stress scores, and salivary immunoglobulin A (IgA) levels, which may be used as an objective marker of stress response.* L-theanine increased alpha brain wave activity, which is associated with a state of relaxed alertness.* [16]
Students training for pharmacy practice, supplemental L-theanine reduced subjective stress levels. Theanine also lowered salivary α-amylase activity, a marker of sympathetic nervous system activity and the “fight or flight” response. The study was conducted on 20 students who were randomly assigned to receive either L-theanine or a placebo. The L-theanine group took 200 mg of theanine twice daily for one week prior to and ten days into the pharmacy practice period. To measure subjective stress levels, a validated questionnaire was utilized.[17]
Human electroencephalograph (EEG) studies have shown that alpha brain waves are generated within 40 minutes after the oral administration of L-theanine (50-200 mg).*[18] Alpha brain-wave activity is indicative of relaxation, as well as increased creativity, better performance under stress, and improved learning and concentration.*[19] For comparison, 200 mg of theanine is equivalent to about eight cups of black tea, so it takes a lot of tea to equal the effects of supplemental L-theanine.[20]
L-Theanine and Cognitive Performance
Tea from Camellia sinensis contains caffeine and L-theanine, in a ratio of 2:1 to 4:1, depending on the type of tea and its method of preparation.[21] Caffeine, a well-known stimulant, enhances alertness and cognitive performance. L-theanine, on the other hand, can promote relaxation without sedation and may counteract the negative effects often associated with caffeine consumption.*[22]
When comparing the effects of caffeine, L-theanine, or combination of caffeine and L-theanine, several studies demonstrate that the combination of caffeine and L-theanine can enhance selective attention and cognitive performance by exuding synergistic effects.* However, L-theanine is unique in that a single 200 mg dose was found to reduce susceptibility to distraction and improve selective attention amongst healthy male subjects while also exhibiting a calming effect.*[23] Clinical trials have confirmed that L-theanine sharpens human attention.*[24],[25],[26] Attention is defined as the concentration of awareness on certain phenomena to the exclusion of other stimuli. Electrophysiological recordings in humans confirm that theanine has a specific effect on the brain’s attention circuitry, enabling the brain to sustain attention throughout difficult or tedious tasks.*[27],[28],[29] The net result is that L-theanine allows individuals to focus their attention more efficiently on their goals, without getting distracted.*[30]
In a double-blind, placebo-controlled study involving 24 sleep-deprived young adults, a 200 mg dose of L-theanine was found to enhance performance on a visual recognition reaction task.*[31] Specifically, L-theanine significantly reduced false alarms and improved target-distractor discriminability without notable differences in reaction time compared to placebo.* These findings suggest that high doses of L-theanine enhance selective visual attention by improving information processing speed and accuracy in sleep-deprived individuals.*
In a study of generally healthy adults, consistent L-theanine administration increased verbal fluency and decision-making functions, while improving overall mood.*[32] Thirty (30) healthy adults (9 men and 21 women) with an average age of 48.3 years were given 200 mg of L-theanine daily or a placebo for four weeks, with a crossover after a washout period. Three different validated questionnaires were used to measure stress response. L-theanine’s ability to boost mood may be due to its ability to increase the neurotransmitters dopamine, serotonin, and GABA as seen in mechanistic studies.*[33]
L-Theanine Supports and Protects Brain Health
Drinking tea (and/or L-theanine supplementation) may protect the brain.*[34] Among other effects, L-theanine affects genes that promote the regeneration of brain neurons.*[35] L-theanine also boosts the expression of brain-derived neurotrophic factor (BDNF), a protein that enhances learning and memory.*[36] Therefore, L-theanine has the potential to protect neurocognitive health through multiple stages of life.*[37] Consistent with these findings, a combination of 360 mg of green tea extract (GTE) and 60 mg of L-theanine supplements twice daily for 16 weeks significantly improved memory and attention in 48-67 year old adults.*[38]
L-theanine, an amino acid found in tea leaves, promotes relaxation without drowsiness by increasing alpha brain waves and enhancing calming neurotransmitters like GABA.* Studies show that L-theanine can reduce stress, improve cognitive performance, and protect brain health by modulating stress responses, improving attention, and supporting neurocognitive functions.* Its calming effects, coupled with enhanced focus, make it a beneficial option for stress management and mental clarity.*
The information provided is for educational purposes only. Consult your physician or healthcare practitioner if you have specific questions before instituting any changes in your daily lifestyle including changes in diet, exercise, and supplement use.