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Theanine is an amino acid found in Tea (Camellia sinensis), and in particularly high amounts in green tea. It has been used effectively to help prevent some of the adverse effects of Caffeine, and has been shown to help promote relaxation. It has also been implicated in improving immune function.
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The Human Effect Matrix looks at human studies (excluding animal/petri-dish studies) to tell you what effect Theanine has in your body, and how strong these effects are.
|Grade||Level of Evidence|
|A||Robust research conducted with repeated double blind clinical trials|
|B||Multiple studies where at least two are double-blind and placebo controlled|
|C||Single double blind study or multiple cohort studies|
|D||Uncontrolled or observational studies only|
|Level of Evidence ||Effect||Change||Magnitude of Effect Size ||Scientific Consensus||Comments|
|C||Symptoms of Schizophrenia|
Activation and anxiety symptoms of schizophrenia appear to be reduced with high dose (400mg) Theanine
Possible anxiety reducing effects
No significant influence on subjective well being and mood state per se
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Oral consumption of 2-4mg/kg L-Theanine daily to mice for 5 weeks via the drinking water was able to attenuate the toxic effects on memory of Abeta(1-42) injection, and appeared to work via suppressing proinflammatory responses via ERK/p38 and nF-kB.
In comparison to 50mg caffeine in isolation, the addition of 100mg of L-Theanine to the caffeine was able to beneficially influence parameters of accuracy and attention when it came to cognitive testing in otherwise healthy adults which has been replicated elsewhere with similar doses in improving sustained attention and ratings of fatigue. A study using these two doses (in isolation or in combination) did not note any differences in reducing the number of errors in a sustained attention task when comparing combination therapy against either in isolation.
The usage of caffeine in isolation (150mg) is able to improve perceptions of fatigue, rapid visual information processing (RVIP), and reaction time while adding 250mg L-Theanine to this preserved those benefits while improving alertness and improving reaction time further and reducing ratings of headache (which increased in caffeine control). Reaction time (as well as the ability to switch between tasks) has been improved with combination therapy at lower doses (50mg caffeine and 100mg L-Theanine) with this study also noting an improvement in attention via less interference with distracting stimuli.
At least one study noted that the increase in attention (assessed via tasks requiring switching of attention with some distracting stimuli) occurred independently of the subject's perception of alertness.
At least one study has noted that Theanine may have reduced bioavailability when consumed vicariously through Green Tea, as assessed by Caco-2 cell studies. Theanine is absorbed via passive diffusion and is generally well absorbed with concentrations above 4mM being effluxed back out of intestinal cells, but under this dose had two-fold absorption into intestinal cells (apical to basolateral) relative to secretion and incubation with green tea noted that while absorption rate was only hindered 35% the efflux rate was increased dramatically. Although no causation was shown, it was thought that small mounts of D-Theanine in green tea (2.2-4.7% of total content) may have competed with absorption due to their lower absorption rates; the authors cast doubt on this possibility though.
Glutamine appears to share the same intestinal transporter as L-Theanine (a sodium-coupled brush border transporter) except with much higher affinity. The kinetics of both glutamine and L-Theanine across the intestinal membrane is via passive diffusion, suggesting similar absorption kinetics. A study noting less absorption of L-Theanine in the form of green tea relative to Theanine suggested that Glutamine in green tea could be responsible for this effect, but did not demonstrate this beyond the hypothesis.
Tannic acid (a major constituent of green tea) may inhibit the mitochondrial glutamate transporter, Tannic acid has not been investigated on the intestinal glutamine transporter (different than mitochondrial glutamate).
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