1. Mancini, Edele, Christoph Beglinger, Jürgen Drewe, Davide Zanchi, Undine E. Lang, and Stefan Borgwardt. 2017. "Green Tea Effects On Cognition, Mood And Human Brain Function: A Systematic Review". Phytomedicine 34: 26-37. doi:10.1016/j.phymed.2017.07.008.
Green Tea Effects On Cognition, Mood And Human Brain Function: A Systematic Review
Abstract: Green tea (Camellia sinensis) is a beverage consumed for thousands of years. Numerous claims about the benefits of its consumption were stated and investigated. As green tea is experiencing a surge in popularity in Western culture and as millions of people all over the world drink it every day, it is relevant to understand its effects on the human brain.
Conclusions: The reviewed studies presented evidence that green tea influences psychopathological symptoms (e.g. reduction of anxiety), cognition (e.g. benefits in memory and attention) and brain function (e.g. activation of working memory seen in functional MRI). The effects of green tea cannot be attributed to a single constituent of the beverage. This is exemplified in the finding that beneficial green tea effects on cognition are observed under the combined influence of both caffeine and l-theanine, whereas separate administration of either substance was found to have a lesser impact. https://pubmed.ncbi.nlm.nih.gov/28899506/
2. Dietz, Christina, and Matthijs Dekker. 2017. "Effect Of Green Tea Phytochemicals On Mood And Cognition". Current Pharmaceutical Design 23 (19): 2876-2905. doi:10.2174/1381612823666170105151800.
Effect of Green Tea Phytochemicals on Mood and Cognition
Abstract: Green tea is traditionally known to induce mental clarity, cognitive function, physical activation and relaxation. Recently, a special green tea, matcha tea, is rapidly gaining popularity throughout the world and is frequently referred to as a mood- and brain food. Matcha tea consumption leads to much higher intake of green tea phytochemicals compared to regular green tea. Previous research on tea constituents caffeine, L-theanine, and epigallocatechin gallate (EGCG) repeatedly demonstrated benefits on mood and cognitive performance. These effects were observed when these phytochemicals were consumed separately and in combination.
Conclusion: Caffeine was found to mainly improve performance on demanding long-duration cognitive tasks and self-reported alertness, arousal, and vigor. Significant effects already occurred at low doses of 40 mg. L-theanine alone improved self-reported relaxation, tension, and calmness starting at 200 mg. L-theanine and caffeine combined were found to particularly improve performance in attention-switching tasks and alertness, but to a lesser extent than caffeine alone. No conclusive evidence relating to effects induced by EGCG could be given since the amount of intervention studies was limited. These studies provided reliable evidence showing that L-theanine and caffeine have clear beneficial effects on sustained attention, memory, and suppression of distraction. Moreover, L-theanine was found to lead to relaxation by reducing caffeine induced arousal. https://pubmed.ncbi.nlm.nih.gov/28056735/
3. Pervin, Monira, Keiko Unno, Tomokazu Ohishi, Hiroki Tanabe, Noriyuki Miyoshi, and Yoriyuki Nakamura. 2018. "Beneficial Effects Of Green Tea Catechins On Neurodegenerative Diseases". Molecules 23 (6): 1297. doi:10.3390/molecules23061297.
Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases
Abstract: Green tea contains a number of chemical compounds, including green tea catechins (GTCs), caffeine, and theanine, which may affect brain function. In a comprehensive review article, Chen et al. discussed the neuroprotective effects and mechanism of action of tea components, including tea catechins, theanine, caffeine, and theaflavins. They suggested that these bioactive tea components might be useful for neuronal degeneration treatment in the future.
Conclusion: Several epidemiological and human intervention studies have found beneficial effects of the consumption of tea and green tea on neurodegenerative impairment, such as cognitive dysfunction and memory loss. In more specific brain disorders, studies have supported the beneficial effects of tea on PD, but few studies have revealed such effects on AD. However, several human studies have failed to show tea’s favorable effects on neurodegenerative diseases. This discrepancy may be due to several confounding factors, including the method used to quantify consumption, beverage temperature, cigarette smoking, alcohol consumption, and differences in genetic and environmental factors such as race, sex, age, and lifestyle. Intestinal microbiota and genetic polymorphisms may also have influenced the results. Therefore, more rigorous human studies are required to understand teas’ neuroprotective effects. The results of a number of laboratory experiments have demonstrated the benefits of green tea and EGCG and proposed mechanisms of action. The targets of GTCs include the abnormal accumulation of fibrous proteins such as Aβ and α-synuclein, inflammation, elevated expression of pro-apoptotic proteins, and oxidative stress, which are associated with neuronal cell dysfunction and death in the cerebral cortex. CMDA revealed how EGCG can prevent the accumulation of fibrous proteins. These findings suggest that GTCs have the potential to be used in the prevention and treatment of neurodegenerative diseases and should be useful for the development of new drugs. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6099654/