L-Theanine: Understanding Its Benefits & Origin

Tea has been consumed since ancient times. Other than water, tea is the most widely consumed beverage in the world. One of the reasons why it has been so appreciated for so long is because of its perceived relaxing actions. These can be attributed to one of its main bioactive compounds: L-theanine. 

L-theanine is a psychoactive amino acid known for its ability to promote relaxation and a sense of calm alertness, attention, and mental energy [1–6]. This property has made L-theanine a popular nootropic. But L-theanine has other properties that can benefit not only brain function and cognitive performance, but human health in general. 

What Is L-Theanine?

L-theanine, also known as N-ethyl-L-glutamine or γ-glutamylethylamide, is a non-proteinaceous amino acid (i.e., it is an amino acid but it is not a building block for proteins) found predominantly in the leaves of Camellia sinensis, the plant used to make green and black tea. Along with caffeine and catechins, L-theanine is one of the major constituents of tea.

Figure 1. L-theanine structure

L-theanine comprises up to 50% of total amino acids in tea leaves and is responsible for the characteristic taste of tea, helping to balance the bitterness of caffeine and the astringency of tea polyphenols [7].

L-theanine was first isolated and identified in the leaves of C. sinensis in Japan in 1949 [8]. Since then, research has shown that L-theanine is responsible for many of the subjective benefits associated with tea consumption, particularly its relaxing effects. These, along with a support of neuroprotective functions, brain health, and cognitive function, have made L-theanine a popular nootropic compound.

How Does L-Theanine Work?

L-theanine is primarily recognized by its relaxing effects. These are the result of its actions in the brain, which L-theanine is able to reach by crossing the blood-brain barrier [9,10] 

One of the most noteworthy actions of L-theanine is its ability to support the production of alpha brain waves (α-waves), which has been demonstrated in several clinical studies [4–6,11–14]. Brain waves, or neural oscillations, are rhythmic patterns of neural activity generated by the synchronized firing of groups of neurons or the synchronized activity of specific brain regions. There are five basic types of brain waves (gamma, beta, alpha, theta, delta) that oscillate at specific frequencies and that are characteristic of specific brain states. One of them is alpha-waves, which are associated with a state of relaxed mental alertness and attention and are regarded as a measure of relaxation without drowsiness.

The influence of L-theanine on brain waves and the promotion of relaxed brain states may be a consequence of its capacity to influence several neurotransmitter systems in the brain, including serotonin, dopamine, and GABA, all of which are associated with mood regulation and psychological stress responses [9].

The influence of L-theanine on brain waves and the promotion of relaxed brain states may be a consequence of its capacity to influence several neurotransmitter systems in the brain, including serotonin, dopamine, and GABA, all of which are associated with mood regulation and psychological stress responses.

L-theanine is also structurally similar to glutamate, the main excitatory neurotransmitter in the central nervous system. Because of this structural similarity, L-theanine can bind to glutamate receptors, albeit with low affinity [15], and help to modulate their activation and glutamate signaling, resulting in an inhibitory action. 

L-theanine has also been shown to support neuroprotective functions. Some of L-theanine’s neuroprotective properties have been linked to binding to glutamate receptors [16]. Excessive glutamate receptor activation can have toxic effects on the brain, a process known as excitotoxicity, due to an excessive influx of calcium into neurons, which can cause neuronal death [17,18]. By modulating the activity of glutamate receptors, L-theanine may help to balance calcium influx into neurons. A way to think about this is that L-theanine may be supporting a more balanced mix of excitatory and inhibitory neurotransmission, which would explain some of its observed ability to promote attention and a sense of calm alertness.

L-theanine may also support neuroprotective functions by supporting the expression and activities of antioxidant enzymes [19–22]. Furthermore,L-theanine has also been shown to support immune signaling, metabolic regulation, and vascular function, all of which can contribute not only to healthy brain function but to the support of protective functions in several organs and systems, including the liver, kidney, gastrointestinal tract, and cardiovascular system [7,23]. These mechanisms of action underlie many of the benefits that have been reported for L-theanine.

What Are the Benefits of L-Theanine?

Mood and Stress Responses

By promoting relaxation, L-theanine may help to support healthy stress responses and mood. Accordingly, studies have shown that L-theanine promotes healthy affective and stress responses, a positive mental-emotional state, and a general calm and relaxed mood [3,6,24–29]. These effects have been observed in resting states as well as in contexts of stress. For example, L-theanine reduced psychological and physiological stress responses induced by a cognitive stress task, likely by attenuating sympathetic nervous system activation, responsible for our “fight-or-flight” responses [30]. In preclinical research, L-theanine also reduced cognitive impairments induced by stress [31,32].*

L-theanine reduced psychological and physiological stress responses induced by a cognitive stress task, likely by attenuating sympathetic nervous system activation, responsible for our “fight-or-flight” responses.

Cognitive Performance

L-theanine’s support of alpha-wave activity can manifest in different ways: it can promote relaxation in a state of rest or passive activity, but importantly, it can also promote relaxation while engaged in cognitively demanding tasks. For example, in a study with healthy adults, L-theanine promoted the generation of alpha waves while participants performed a demanding selective attention task [4]. 

L-theanine’s actions may help to promote cognitive performance in contexts of stress, as indicated in a study where L-theanine supported alpha-waves, attention performance, and reaction times, and lowered the heart rate in individuals with propensity to unbalanced stress responses [14].* 

Healthier Sleep

L-theanine’s relaxing effects may also contribute to healthier sleep [3,27,33,34]. In a study with healthy adults, L-theanine’s effects on sleep were evaluated using the Pittsburgh Sleep Quality Index (PSQI), a validated questionnaire that assesses sleep quality and disturbances. Results showed that four weeks of L-theanine administration reduced PSQI subscale scores for sleep latency, sleep disturbance, and use of pharmacological sleep aids [3].* 

Immune Function

Not all of L-theanine’s actions are a result of its relaxation-promoting effects. Another dimension of L-theanine’s biological activity is the support of healthy immune function. L-theanine is able to modulate immune signaling and immune cell function [35–44]. This property underlies the immune benefits observed in clinical trials, where L-theanine was linked to a support of general immune health, including in older individuals [43,45–47]. L-theanine was also associated with a support of immunity following intensive exercise [38,39,41,42], which is known to disrupt immune function. L-theanine is particularly helpful for immune support in combination with L-cysteine, another amino acid that supports immune cell function [38,40–43,45,48].*

Complementary Actions with Caffeine

Caffeine is one of the most popular nootropic compounds. Caffeine is a psychostimulant compound that promotes wakefulness, resistance to mental fatigue, capacity for mental work, and several other aspects of cognitive performance [49–56]. However, caffeine’s stimulatory actions can often cause jitteriness, which can curtail its benefits on cognitive performance. But through its relaxing effects, L-theanine can help to balance the stimulating action of caffeine, which is why they are often combined in nootropic stacks [57]. Caffeine and L-theanine work well together and can help to promote alertness, attention, mood, and mental performance [58–62].*

L-Theanine for Cognitive Support

L-theanine’s actions make it a great nootropic compound that can elevate any formula designed for cognitive support, particularly in combination with caffeine. L-theanine helps you to respond to cognitively demanding situations with a high level of cognitive performance while keeping a relaxed state of mind.* This is one of the reasons why we included it in Qualia Mind. You can learn more about it in our article on the science behind Qualia Mind. You may also learn more about nootropic complementarity and achieving a whole system upgrade in our article about The Science of Nootropic Stacks.

*These statements have not been evaluated by the Food and Drug Administration.  This product is not intended to diagnose, treat, cure, or prevent any disease.

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