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Tea, Theanine & Polyphenols

Theanine and its effect on the body

Theanine is found primarily in plant and fungal species. It was discovered as a constituent of tea (Camellia sinensis). Theanine is substantially present in black, green, and white teas from Camellia sinensis in quantities of about 1% of the dry weight. Deliberately shading tea plants from direct sunlight, as is done for matcha and gyokuro green tea, increases L-theanine content. The L-enantiomer is the form found in freshly prepared teas and some, but not all, human dietary supplements.

 Green tea contained the highest content of theanine, followed by white, oolong and black teas.[1]

The way of processing has no determining effect on theanine content. Pu'er undergoes what is known as a solid-state fermentation where water activity is low to negligible. Both endo-oxidation (derived from the tea-leaves enzymes themselves) and microbial catalysed, exo-oxidation of tea polyphenols occurs. The microbes are also responsible for metabolizing the carbohydrates and amino acids present in the tea leaves.

Able to cross the blood–brain barrier, theanine has reported psychoactive properties. Theanine has been studied for its potential ability to reduce mental and physical stress, improve cognition, and boost mood and cognitive performance in a synergistic manner with caffeine.[2]

Theanine in the form of Supplements

There is some evidence of taking theanine supplements, which aids in alpha waves in the thalamic pacemaker in human cells. L-theanine significantly increases activity in the alpha frequency band which indicates that it relaxes the mind without inducing drowsiness. Tea is proven to relax the mind, and cause ease of sleep.

Glutamic acid is derived from theanine. Glutamic acid (glutamate) is an amino acid used by the body to build proteins. Glutamate is the most common excitatory (stimulating) neurotransmitter in the central nervous system.[3] 

Theanine and Cognitive Function

Because of its role in synaptic plasticity, glutamate is involved in cognitive functions such as learning and memory in the brain. The form of plasticity known as long-term potentiation takes place at glutamatergic synapses in the hippocampus, neocortex, and other parts of the brain.[4] Theanine does have beneficial effects on the brain.

 Able to cross the blood–brain barrier, theanine has reported psychoactive properties. Theanine has been studied for its potential ability to reduce mental and physical stress, improve cognition, and boost mood and cognitive performance in a synergistic manner with caffeine.[5]

 Catechins are powerful antioxidants. It has been suggested that green tea polyphenol may inhibit cell proliferation and observational studies have suggested that green tea may have cancer-preventative effects.[6]

 EGCG is a type of catechin. A 2016 review found that high daily doses of EGCG (107 to 856 mg/day) taken by human subjects over four to 14 weeks produced a small reduction of LDL cholesterol.

During black tea production, the catechins are mostly converted to theaflavins and thearubigins via polyphenol oxidases. [7] Theaflavins and thearubigins are polymeric polyphenols that are formed during enzymatic oxidation, with the participation of polyphenol oxidases during the fermentation reactions in black tea.

 A review conducted in 2016 showed that consumption of green tea EGCG resulted in a significant reduction of LDL-C (Low-density lipoprotein).[8]  EGCG is also known as epigallocatechin-3-gallate, and is a type of polyphenol.

LDL delivers fat molecules to the cells and can drive the progression of atherosclerosis if they become oxidized within the walls of arteries. Thus, EGCG will contribute to maintaining a healthy LDL level in the body.

 So, how much tea should you consume?

Drinking 2 cups of tea every day, per week would be considered a small amount of theanine to consume, however, over time, this can be healthy. As green tea contains the highest content of catechins, drinking green tea would be considered a healthier option than black, although it would also depend on your diet & overall supplements, in combination with the green tea consumed. Both green and black tea have health benefits that differ from one another.                                          

 Green Tea & its health benefits

The difference between green and black tea results from the manufacturing process. Black tea undergoes fermentation which transforms its color and flavor, whereas green tea remains unprocessed and retains its color. Green tea is grown in higher altitudes, more specifically the mountainous regions of East Asia. Some green tea is still picked by hand, and it is thought that handpicked teas are less bitter and yield a sweeter, more robust taste. Other factors such as the climate and soil can also affect the flavor.

Sencha is the most popular of Japan’s green teas. There are numerous grades which can affect the price and quality. Sencha leaves are first steamed and then shaped. Sencha tea produces a clear yellow/green tea with a sweet, grassy but slightly astringent flavor.

Matcha is made from green tea leaves grown in the shade. The leaves have a higher chlorophyll content which makes them a vibrant green colour. To make matcha, the entire leaf is ground down into a powder. The powder is mixed with boiling water and gently whisked before being served. [9]

In a study, matcha has shown to have much larger quantities of catechins, compared to normal green tea. Using a mg catechin/g of dry leaf comparison, results indicate that the concentration of epigallocatechin gallate (EGCG) available from drinking matcha is 137 times greater than the amount of EGCG available from China Green Tips green tea, and at least three times higher than the largest literature value for other green teas.

Black tea contains mainly thearubigins, theaflavins, flavonols and catechins. The total polyphenol content of green and black teas is similar, but with different types of flavonoids present due to the degree of oxidation during processing.[10] Both black and green tea are containing polyphenols and thearubigins and are healthy and should be consumed to maintain healthy hippuric acid excretion from the urine. Hippuric acid content may have antibacterial effects.[11]

They reported black tea consumption to be associated with a 3-fold increase in the urinary excretion of hippuric acid. Hippuric acid excretion after green tea consumption has not been studied, but hippuric acid may be a major metabolite produced from green tea catechins. In a study conducted in 2005, subjects shown consumption has shown an increase in urinary hippuric acid excretion, indicating that polyphenols from different dietary sources may have similar effects on the colonic flora. 

The study concluded that green tea consumption and black tea consumption result in similar amounts of microbial degradation products that are absorbed by the body. These microbial metabolites, and not the native tea flavonoids, may be responsible for at least some of the health effects attributed to tea consumption. Flavonoids from tea, wine, cider and coffee can aid the colonic flora. [12]

[1] Csupor, Dezső, et al. “Theanine and Caffeine Content of Infusions Prepared from Commercial Tea Samples.” Pharmacognosy Magazine, vol. 12, no. 45, Jan. 2016, pp. 75–79., doi:10.4103/0973-1296.176061.

[2] “Theanine”. Wikipedia. 11 July 2018. https://en.wikipedia.org/wiki/Theanine

[3] “Glutamite”. Wikiepdia. 11 July 2018. https://en.wikipedia.org/wiki/Glutamine

[4] “Glutamite”. Wikiepdia. 11 July 2018. https://en.wikipedia.org/wiki/Glutamine

[5] “Theanine”. Wikipedia. 11 July 2018. https://en.wikipedia.org/wiki/Theanine

[6] “Epigallocatechin”. July 13 2018. https://en.wikipedia.org/wiki/Epigallocatechin_gallate

[7] “Epigallocatechin”. July 13 2018. https://en.wikipedia.org/wiki/Epigallocatechin_gallate

[8] Momose, Yuko, et al. “Systematic Review of Green Tea Epigallocatechin Gallate in Reducing Low-Density Lipoprotein Cholesterol Levels of Humans.” International Journal of Food Sciences and Nutrition, vol. 67, no. 6, 20 Sept. 2016, pp. 606–613., doi:10.1080/09637486.2016.1196655.

[9] Lewin, Jo. “The health benefits of green tea.” BBCGoodFood.com. https://www.bbcgoodfood.com/howto/guide/health-benefits-green-tea (accessed July 15, 2018).

[10] Khan, Naghma, and Hasan Mukhtar. “Tea and Health: Studies in Humans.” Current Pharmaceutical Design, vol. 19, no. 34, 2013, pp. 6141–6147., doi:10.2174/1381612811319340008.

[11] "Hippuric Acid". https://pubchem.ncbi.nlm.nih.gov/compound/Hippuric-acid, pubchem CID 464 (Accessed 22 Jul 20190.

[12] Theo P Mulder, Anton G Rietveld & Johan M van Amelsvoort. "consumption of both black tea and green tea results in an increase in the excretion of hippuric acid into urine.' The american journal of clinical nutrition, vol. 81, no. 1, January 2005, Pages 256S–260S, https://doi.org/10.1093/ajcn/81.1.256S

This article was written by Dawn D, cofounder of Treebird Tea. She has a strong interest in tea and its influence on health and society. Dawn experiments with tea brewing methods and procures the best tasting teas from around the world.