Theanine Enhances Immunity
and Bolsters Memory

New possibilities for Alzheimer’s, enhanced word recognition,
mood improvement, reduced sensitivity to overstimulation, and more
By Will Block


s we have previously reported, L-theanine enhances immune function. A distinctive amino acid that is found in minute amounts in tea (Camellia sinensis), theanine exerts a significant effect on the immune system, by activating—in the event of bacterial infection—gammadelta T cells to a state of readiness.1 These cells, comprising a line of defense among total peripheral blood T cells, are mobilized (expanding by up to 50-fold) in response to bacteria, and theanine acts as the precursor to an antigen that primes gammadelta T cells in a manner that is like cocking a gun, pulling its trigger back.

This doesn’t directly result in firing, but it prepares the immune system to invoke gammadelta T killer activity against bacteria, while increasing the speed of action.

How important is theanine? Well, the researchers have found that primed gammadelta T cells protected immune-deficient mice against bacteria that normally would kill them.1 And, the adoptive transfer of gammadelta T enhanced survival against a variety of cancers including myelomas, carcinomas, and lymphomas.

Important in this year of the swine flu (see article on page 15), a recently published double-blind, placebo-controlled trial using theanine along with the catechin EGCG found that healthy human subjects (aged 18–70 years) taking a proprietary formulation for three months had a 32 per cent reduction in the incidence of cold and flu symptoms.2 They also had 23% fewer overall illnesses of at least 2 days duration, and nearly 36% fewer symptom days, compared to subjects taking placebo. These results were attributed to enhancement of the activity of gammadelta T cells.

Memory Protection and Enhancement

A quintet of new and recent studies demonstrate that theanine can:

  1. Be useful for treating Alzheimer’s disease. In the formidable Free Radical Biology and Medicine, researchers found that theanine can reduce amyloid beta levels and amyloid-induced neuronal cell death in the cortex and hippocampus of the brain.3 Additionally, theanine reduces oxidative damage and the activation of pathways that can result in cognitive dysfunction and neurotoxicity. Theanine may thus be helpful for both the prevention and treatment of Alzheimer’s disease.

  2. Improve word recognition, rapid visual information processing, critical flicker fusion threshold, attention switching and mood. Combined with 50 mg of caffeine, 100 mg of theanine improved cognition and frame of mind in 27 healthy volunteers.4 The theanine and caffeine combination improved both speed and accuracy of performance of the attention-switching task at 60 min, and reduced susceptibility to distracting information in the memory task at both 60 min and 90 min. Wrote the authors, “These results replicate previous evidence which suggests that L-theanine and caffeine in combination are beneficial for improving performance on cognitively demanding tasks.”

  3. Enhance alpha brain wave activity, and consequently mood, relaxation and alertness. Using 100 mg of L-theanine and 50 mg of caffeine (as in the above study), researchers measured not only cognitive behavior but brain waves as well in 16 healthy subjects.5 Subjects were tested each of 4 successive days after ingesting either placebo, 100 mg of L-theanine, 50 mg of caffeine, or the last two combined. While neither theanine nor caffeine alone had any discernable effects, together they improved the subjects’ performance on cognitive tests. Furthermore, alpha brain wave activity increased in those taking theanine with caffeine, with results that were similar to prior studies using larger dosage of L-theanine alone. During wakefulness and relaxation, alpha brain waves are present. Alpha waves are associated with effortless alertness and believed to be the mechanism underlying the cognitive benefits.

  4. Enhance higher-level cognitive activity and reduce sensitivity to the detrimental effects of overstimulation. In a review of the literature, performance enhancement, in terms of attention switching and the ability to ignore distraction, was found similar to the prior study.6 While theanine alone increased choice reaction time, it resulted in slower memory and delayed word recall. Therefore, there were almost no cognitive benefits from it alone. However, when taken with caffeine, cognitive benefits were increased with regards to simple reaction time and accuracy of rapid information processing, along with a reduction of mental fatigue and tiredness. Unfortunately, theanine reduced the positive effects of caffeine on spatial memory and choice reaction time. The review also reported that caffeine and theanine together in low doses interact to enhance focus attention along with speed and accuracy improvement.

  5. Reduce blood pressure increases associated with taking caffeine alone. In a double-blind, placebo-controlled study, 48 healthy adult participants were randomized to receive either 250-mg caffeine or 200-mg theanine, or both or neither.7 All subjects were rated for mood, including anxiety, and alertness. Also, blood pressure was taken at the start of the test. While caffeine increased alertness, it also increased jitteriness and blood pressure. Theanine helped prevent the effect of caffeine on blood pressure, yet it did not significantly affect jitteriness, alertness or other aspects of mood. However, 250 mg of caffeine is a lot, and based on other studies reviewed, it is probable that theanine could have a positive effect on blood pressure caused by lower doses of caffeine, doses low enough to avoid the negative consequences of caffeine while preserving the positive effects.


  1. Bukowski JF, Percival SS. L-theanine intervention enhances human gammadeltaT lymphocyte function. Nutr Rev 2008 Feb;66(2):96-102.
  2. Rowe CA, Nantz MP, Bukowski JF, Percival SS. Specific formulation of Camellia sinensis prevents cold and flu symptoms and enhances gamma delta T cell function: a randomized, double-blind, placebo-controlled study. J Am Coll Nutr 2007 Oct;26(5):445-52.
  3. Kim TI, Lee YK, Park SG, Choi IS, Ban JO, Park HK, Nam SY, Yun YW, Han SB, Oh KW, Hong JT. L-Theanine, an amino acid in green tea, attenuates beta-amyloid-induced cognitive dysfunction and neurotoxicity: Reduction in oxidative damage and inactivation of ERK/p38 kinase and NF-kappaB pathways. Free Radic Biol Med 2009 Sep 16. [Epub ahead of print]
  4. Owen GN, Parnell H, De Bruin EA, Rycroft JA. The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci 2008 Aug;11(4):193-8.
  5. Kelly SP, Gomez-Ramirez M, Montesi JL, Foxe JJ. L-theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance. J Nutr 2008 Aug;138(8):1572S-7S.
  6. Bryan J. Psychological effects of dietary components of tea: caffeine and L-theanine. Nutr Rev 2008 Feb;66(2):82-90.
  7. Rogers PJ, Smith JE, Heatherley SV, Pleydell-Pearce CW. Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology (Berl) 2008 Jan;195(4):569-77.

Will Block is the publisher and editorial director of Life Enhancement magazine.

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