Caffeine & L-theanine
Caffeine and L-theanine can act synergistically to improve alertness and attention. L-theanine can also potentially reverse some of the less favorable physiological effects of caffeine - including increased blood pressure, and reduced flow of oxygenated blood to the head.
Caffeine is the most widely used psychoactive susbstance in the world. Tea, coffee, mate, soft drinks, cocoa products and candies all contain significant amount of caffeine, and are widely consumed. Caffeine has been shown to have powerful effects on attention and vigilance, memory, and mood. (Learn more)
L-Theanine is an amino acid analog of the proteinogenic amino acids L-glutamic acid and L-glutamine and is found primarily in black, green, and white teas. L-theanine has been shown to have effects on glutamate receptor signaling, and nitric oxide production. L-theanine used in combination with caffeine can have significant effects on attention and working memory, and blood pressure.(Learn more)
Combined Effects on Attention
Multiple studies have shown that caffeine and L-theanine have synergistic effects on cognition.
In a 2008 study, caffeine and L-theanine acted synergistically to increase the speed and the accuracy of performance of the attention-switching task. Susceptibility to distracting information in the memory task was also reduced.1
In another 2008 study, L-theanine by itself increased 'headache' ratings and decreased correct serial seven subtractions. Caffeine alone led to faster digit vigilance reaction time, improved Rapid Visual Information Processing (RVIP) accuracy and attenuated increases in self-reported 'mental fatigue'. In addition to improving RVIP accuracy and 'mental fatigue' ratings, the combination also led to faster simple reaction time, faster numeric working memory reaction time and improved sentence verification accuracy. 'Headache' and 'tired' ratings were reduced and 'alert' ratings increased. There was also a significant positive caffeine x L-theanine interaction on delayed word recognition reaction time. These results suggest that beverages containing L-theanine and caffeine may have a different pharmacological profile to those containing caffeine alone.2
Figure 1. Psychological Effects of placebo, caffeine, L-theanine, and caffeine + L-theanine. For caffeine and theanine, statistically significant improvements in simple reaction time, rapid visual information processing (RVIP), numeric memory reaction time, sentence verification accuracy, and word recognition reaction time were observed.
Figure 2. In addition to objective improvements in cognitive function, caffeine and L-theanine also result in self reported improvements in alertness as measured by the Bond-Lader scale, reduced tiredness and mental fatigue ratings, and reduced headache ratings at 90 minutes post administration (as opposed to caffeine alone, which increased headache ratings at the same time point).
In a series of follow up studies, combination of L-theanine and caffeine significantly improved attention on a switch task as compared to the placebo, while subjective alertness and intersensory attention were not improved significantly. The results support previous evidence that L-theanine and caffeine in combination can improve attention.3The combination of moderate levels of L-theanine (97 mg) and caffeine (40 mg) also increased accuracy during task switching and self-reported alertness and decreased self-reported tiredness.4
Combined Effects on Physiology
L-theanine is known to attenuate some of the negative effects observed with caffeine. In particular, caffeine use has been shown to increase blood pressure, and reduce the flow of oxygenated blood to the cerebrum. L-theanine has been shown to reverse these effects.5,6
Owen, G. N., Parnell, H., De Bruin, E. A., & Rycroft, J. A. (2008). The combined effects of L-theanine and caffeine on cognitive performance and mood. Nutr Neurosci, 11(4), 193-198. doi:10.1179/147683008x301513
Haskell, C. F., Kennedy, D. O., Milne, A. L., Wesnes, K. A., & Scholey, A. B. (2008). The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol, 77(2), 113-122. doi:10.1016/j.biopsycho.2007.09.008
Giesbrecht, T., Rycroft, J. A., Rowson, M. J., & De Bruin, E. A. (2010). The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. Nutr Neurosci, 13(6), 283-290. doi:10.1179/147683010x12611460764840
Dodd, F. L., Kennedy, D. O., Riby, L. M., & Haskell-Ramsay, C. F. (2015). A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. Psychopharmacology (Berl), 232(14), 2563-2576. doi:10.1007/s00213-015-3895-0
Rogers, P. J., Smith, J. E., Heatherley, S. V., & Pleydell-Pearce, C. W. (2008). Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. Psychopharmacology (Berl), 195(4), 569-577. doi:10.1007/s00213-007-0938-1
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