Green Tea and L-Theanine Effects on Cognition and Attention During Stress

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Green tea is made from the leaves of the plant Camellia sinensis and has been used as a medicinal herb for over 4000 years.^[1] Many health benefits are attributed to the catechin and caffeine content, as well as that of the compound l-theanine, accounting for about 50% of the total amino acids from these tea leaves.^[1] In addition to chemoprotective properties, green-tea consumption has been shown to enhance mental performance,^[2] decrease anxiety, promote relaxation,^[3] and protect liver tissue.^[1]

Chronic consumption may also help prevent cardiovascular disease, diabetes, depression, and dementia.^[2] Although l-theanine as a monotherapy agent can be extremely beneficial for acute stress, anxiety, and relaxation before sleep, the combination of compounds within green tea, specifically the combination of l-theanine and caffeine, may be more beneficial as a whole to support cognitive function and mental performance.

Benefits of l-Theanine During Acute Stress

l-Theanine is a naturally occurring amino acid found exclusively in tea leaves.^[1] Multiple studies have investigated the effects of l-theanine on the nervous system, especially as its chemical structure is similar to that of glutamate,^[4] and in that it can readily cross the blood-brain barrier.^[5] The calming and anxiolytic effect of l-theanine has been well-documented; meanwhile, other studies are investigating its effects on cognitive function, including learning and memory.^[5] The relaxing effect may be attributed to l-theanine’s modulation of the nervous system: By blocking the binding of l-glutamic acid to glutamate receptors in the brain, l-theanine may be able to attenuate activation of the central nervous system.^[6] This can lead to a mitigation of heart rate elevation after exposure to acute stress.^[6] This should not be taken to mean that l-theanine can be used to lower high blood pressure in general, but more so, after exposure to stressful stimuli, as the nervous and endocrine systems attempt to elicit stress responses, l-theanine may act as a modulator to reduce the startle reflex. Therefore, it can help reduce major elevations in blood pressure when caused by stress in an acute setting, and also preventively during mental stress.

In particular, researchers have shown that 200 mg can elicit significant changes (reductions) in both systolic and diastolic blood pressure after a stressful mental task.^[3] Additionally, subjects in this study reported decreased tension and anxiety with l-theanine supplementation.^[3] With exposure to stress chronically, blood pressure may tend to increase, leading to hypertension; however, l-theanine’s effect has only been shown to lower blood pressure elevations caused by the stress of mental tasks.^[3] Therefore, l-theanine may be more helpful in the prevention of hypertension from chronic stress, especially when due to mental tasks. Due to l-theanine’s involvement in glutaminergic neurotransmission, one study of patients with schizophrenia used doses of 200 mg and 400 mg of l-theanine and were able to decrease the startle reflex in response to stressful stimuli.^[4] Another study in patients with schizophrenia, by the same team of researchers, showed that supplementation with 250 mg of l-theanine for eight weeks led to improvements in sleep quality and on other measures on the positive syndrome scale.^[7] This allows for further exploration into using l-theanine therapeutically for other psychiatric disorders such as anxiety, panic disorder, and obsessive compulsive disorder. The anxiolytic effect of l-theanine has been attributed to the effect on dopamine and serotonin concentrations in the brain.^[3] It has also been noted that l-theanine can increase alpha brain wave activity in humans, eliciting a relaxed yet alert state.^[2][3] Many of these effects can be seen about 30–40 minutes after consumption, and peak plasma concentrations have been measured between 32 and 50 minutes after consumption.^[3]

l-Theanine’s Benefit on Cognition, Attention, and Memory

Current research has demonstrated that l-theanine exerts effects on the glutaminergic system and increases dopamine activity in animal models.^[8] These combined may be responsible for the cognitive enhancing effect in animal studies, with respect to learning and memory. Attention in general has been defined as the ability to effectively deal with a vast amount of sensory and cognitive input, which is constantly received by the nervous system, with the ability to focus only on relevant information.^[2] Objectively, this can be measured by the speed of a response, and the amount of correct and/ or accurate responses.^[2]

The combination of l-theanine and caffeine has been proposed as the key factor affecting attention, whereby one cup of tea contains approximately 35–60 mg of caffeine and 5–23 mg of theanine.^[2] Caffeine itself antagonizes adenosine receptors, leading to a potential increase in neurotransmission. Its effect on the dopaminergic system can also elicit arousal and promote higher-order attentional processes.^[2] One study compared the effect of 50 mg of caffeine with and without 100 mg of l-theanine on cognition, measuring rapid visual information processing, attention switching, and word recognition.^[9] Caffeine was shown to improve subject alertness at 60 minutes, and accuracy on attention-switching at 90 minutes; however, the combination of theanine and caffeine improved both speed and accuracy of mental performance during tasks, while decreasing susceptibility to distractions.^[9] Another study showed that 150 mg of caffeine led to faster digit vigilance reaction time, improved rapid visual information-processing accuracy, and improved self-reported “mental fatigue.”^[10] In combining that caffeine with 250 mg of l-theanine, researchers reported that subjects had faster reaction times, faster numeric working memory reaction times, and improved sentence verification accuracy.^[10] In part of its effects on neurotransmission, l-theanine has also been shown to have cerebroprotective benefits for the brain: Research has shown that l-theanine can prevent neuronal cell death after transient cerebral ischemia, which may be due to its ability to affect glutaminergic pathways.^[11] Specifically, l-theanine has been shown to act on glutamine transporters to inhibit the transport of extracellular glutamine into neurons.^[11] This would mitigate overexcitation responses when exposed to stressful stimuli. One study in elderly subjects with normal or slight cognitive dysfunction showed a slight improvement in cognitive parameters with the equivalent of 50 mg of theanine, delivered as green tea powder.^[11]

Conclusions

The effects of neuroprotection, improved reaction time, and processing of information all may lead to future studies in areas of reduced or problematic cognition. In particular, l-theanine, or the combination of l-theanine and caffeine found in green tea, may produce significant positive effects for the elderly, those with mild cognitive decline, students with the inability to perform on tests due to anxiety and issues with concentration, and those in stressful working conditions who have difficulties with multitasking, and concentrating on tasks in high-stress workplaces. Future research is needed, but the multiple pathways in which l-theanine is involved are promising for therapeutic effects related to anxiety and cognition. Also, l-theanine is measured in serum within an hour of consumption, eliciting its effect as quickly as 30 minutes postconsumption. This makes l-theanine, and green tea in general, a promising acute therapeutic agent, apart from the multitude of health benefits from chronic green tea consumption.