This nutrient does not make you jittery or wired like caffeine nor does it induce drowsiness.1 It promotes a deep state of relaxation and mental focus, similar to what is achieved with meditation. Its effects on the brain begin to happen within 30 to 40 minutes after ingestion. It is L-theanine, an amino acid found almost exclusively in tea.2 It crosses the blood brain barrier where it exerts its effects on alpha brain wave activity and gamma-aminobutyric acid (GABA) A receptors. Since L-theanine is similar in structure to glutamic acid, it functions as a glutamate reuptake inhibitor as well as a glutamate receptor antagonist. Subsequently, L-theanine supplementation can acutely reduce stress and anxiety, improve sleep quality and enhance cognitive function.3,4
More than a few trials illustrate L-theanine’s ability to enhance attention and concentration. At 100 or 200 mg, L-theanine can improve visuomotor speed (reaction time),5 working memory task performance (in older adults),6 and help to maintain vigilance, which is the ability to maintain focus on repetitive tasks over extended time periods.7 At 400 mg, L-theanine can improve selective auditory attention.8 Combined with caffeine, 200 mg of L-theanine can increase selective attention9,10 and decrease mind wandering.11 L-theanine and caffeine taken together have even been shown to enhance reaction time and accuracy in elite curling athletes, which was reflected in their shooting performance.12 Overall this indicates that L-theanine helps to sustain attention, keep the brain focussed on the task at hand and process information more efficiently.
While L-theanine may act synergistically with caffeine, enhancing its nootropic effects while reducing its excessive stimulatory effects,3,4 there is also clinical evidence to show that theanine and caffeine exert opposite, negating effects on certain attentional processes during emotional stress. One double-blind trial found that caffeine consumption worsened emotional stress but improved executive function, which is reflective of acute stress enhancing performance. Conversely, theanine reduced emotional stress and executive function, indicative of its anxiolytic properties. Caffeine increased global visual attention (big picture thinking), whereas theanine increased local visual attention (attention to detail). This suggests that ingesting either of these cognition-enhancing substances can not only change how attentive we are to the world around us but reframe the way in which we perceive it.13
It can be assumed that L-theanine is at least partly responsible for the inverse relationship between drinking tea and risk of depression reported in the literature.14,15 Two trials provide evidence supporting the use of L-theanine as an adjuvant to antidepressant medications for the management of major depressive disorder (MDD). Sixty patients with MDD were assigned to receive sertraline with either 200 mg of L-theanine or placebo in a six-week, double-blind, randomised, controlled study. Twenty-five participants in each group completed the study. Significant reductions in Hamilton depression rating scale (HAM-D) scores were observed in the L-theanine group from baseline to weeks two, four and six. L-theanine was superior to placebo regarding response to treatment (100% versus 84%; p=0.05) and remission rates at week six (68% versus 32%; p=0.02).16 These findings consolidated those of an earlier, open-label clinical trial, wherein 250 mg of L-theanine was added to current medication in 20 patients with MDD. L-theanine improved depressive symptoms, anxiety and sleep disturbance; and enhanced cognitive function in patients with relatively mild MDD.17
A systematic review of nine randomised, controlled trials found evidence to suggests that 200 to 400 mg of L-theanine can help to reduce stress and anxiety in acutely stressful conditions. However, there was insufficient evidence to determine an effect in generalised anxiety disorder (GAD).18 A double-blind, randomised, placebo-controlled, crossover trial did find that four weeks of L-theanine (200 mg/day) administration significantly reduced stress-related symptoms (i.e. self-rated depression, state-trait anxiety inventory-trait and sleep) while improving cognitive function (i.e. verbal fluency and executive function) in 30 healthy adults.19 Its effects on acute stress have also been studied in a triple-blind, randomised, placebo-controlled, crossover study that administered 200 mg of AlphaWave® L-theanine to moderately stressed but otherwise healthy adults. This trial reported changes in alpha power within the brain that reflected relaxation and demonstrated a calming response, supported by lower salivary cortisol levels, decreased values for anxiety/tension and reduced heart rate.20 This shows that L-theanine can be taken acutely, as needed, to manage stress and anxiety; for example, to calm your mind and collect your thoughts before a job interview, presentation, exam, etc.
Other trials show benefit from L-theanine in schizophrenic patients. At a dose of 400 mg/day for eight weeks, taken alongside risperidone, L-theanine could significantly improve negative, general psychopathology and total scores of positive and negative syndrome scale (PANSS) better than placebo co-treatment.21 A lower dose of L-theanine (250 mg/day), added to patients' ongoing antipsychotic treatment for eight weeks, similarly showed significant differences in PANSS and Pittsburgh sleep quality index (PSQI) total scores before and after the trial. Levels of glutamate plus glutamine in the brain were also examined in this open-label study with findings drawing attention to L-theanine’s ability to stabilise excitatory glutamatergic neurotransmission in the brain.22
By blocking some of glutamate’s effects, L-theanine may be neuroprotective for the ageing brain.6 A 16-week, double-blind, randomised, placebo-controlled study investigated the effect of a combination of green tea extract (1440 mg/day) and L-theanine (240 mg/day) on memory and attention in 91 individuals with mild cognitive impairment (MCI) [age 40 to 75 years]. A marginal improvement in delayed recognition in the Rey-Kim memory test (p=0.0572) was reported in those assigned to the treatment group. Stratified analyses also showed improved memory and selective attention by significantly increasing the Rey-Kim memory quotient (p=0.0478 at 16 weeks) and word reading (p=0.0306 at eight weeks) in those with mini mental state examination-Korean (MMSE-K) scores of 21 to 23, which indicates relatively severe cognitive impairment according to this scale. Electroencephalograms (EEGs) in 24 randomly selected subjects showed that brain theta waves,23 an indicator of working memory, associative learning24 and relaxed concentration,25 were increased significantly in the brain in the eyes-open state and reading state after a single dose. Together, this evidence suggests that this combination has the potential to enhance cognition.23
In addition, animal studies indicate that L-theanine may prove to be a useful intervention for the treatment of tobacco addiction26 and opioid abuse,27 Alzheimer’s disease,28 Parkinson’s disease,29 and multiple sclerosis (MS),30 among other applications.
These studies demonstrate that the novel nutrient L-theanine can be used acutely to improve focus and attention. L-theanine and caffeine can be taken together with opposite but seemingly complementary effects on cognition and mood. Research supports the use of add-on L-theanine in the treatment of MDD and schizophrenia, and to relieve anxiety in acutely stressful situations (e.g. sitting exams or public speaking). Those with MCI can expect some acute benefits in working memory when taking L-theanine. Reap the cognition-enhancing and calming benefits of tea in a capsule with L-theanine!
References
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