Nos actifs 17/04/2022
Spotlight on a magical elixir: Green Tea
Before being the second most consumed beverage in the world after water, green tea is first and foremost a medicinal plant favored by traditional Asian medicine. Crowned with numerous virtues, green tea is renowned for its benefits on the body and mind. Its leaf contains over 400 constituents with tonic, diuretic, digestive, purifying, cardioprotective, and anti-inflammatory powers. But what makes green tea unique are its catechins, polyphenols that give it the highest antioxidant capacity among all foods. Focus on an elixir that is both stimulating, invigorating, and soothing.
Properties and benefits of green tea
Of all teas (black, white, red, smoked…), green tea is the most renowned for its health benefits. It is indeed the variety that has undergone the least processing: it is not fermented, its leaves are simply dried and not oxidized, unlike black tea leaves. Its antioxidant powers are therefore superior to other teas.
The virtues of green tea are mainly concentrated in its polyphenols, and more specifically in its catechins. Present in large quantities, these powerful antioxidants have the ability to counteract free radicals, thus preserving immune defenses. Rich in tannins, flavonoids, theanine, caffeine, and gallic acid, green tea also contains vitamins, amino acids, minerals, trace elements, and essential oils.
Catechins
Most studies on the benefits of green tea focus on catechins, particularly epigallocatechin-3-gallate (EGCG). Green tea indeed contains 4 catechins: epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG). In the spotlight since the 1980s, EGCG is described as the "miracle molecule" of green tea. This polyphenol, which makes up 50-75% of green tea catechins, is a powerful antioxidant. Clinical tests have shown that EGCG prevents the formation of free radicals and helps regulate oxidative stress induced by external aggressions (UV rays, tobacco, etc.) and internal ones (degenerative diseases, diabetes, tumors, etc.).
Scientists have also shown that EGCG inhibits the synthesis of an enzyme involved in the production of a hormone called cortisol. Cortisol plays a key role in regulating many physiological processes such as blood pressure, cardiovascular function, carbohydrate metabolism, and immunity. Prolonged cortisol secretion can therefore lead to various disorders such as type 2 diabetes, hypertension, obesity, and decreased immune defenses.
Theanine or L-theanine
Found only in tea, theanine is an amino acid that acts on the brain. It induces a reduction in mental and physical stress and produces a relaxing effect. Theanine is believed to increase the concentration of serotonin and dopamine, the famous "happiness hormones."
Caffeine
The caffeine in tea, also called theine, produces an effect on physical and mental energy. Unlike the caffeine in coffee, that in green tea is bound to its tannins, making it more tolerable. The process of caffeine absorption from green tea into the bloodstream is indeed gentler and more gradual, and its benefits last longer. Thus, it gently tones the nervous system, in a prolonged and more relevant way.
Green tea under the scientists' microscope
The richness of green tea components has fascinated researchers for decades. It was in the 1970s in Japan that the first clinical studies began. Since then, thousands of studies from the United States, China, and Europe have highlighted the many benefits of green tea on the body.
Antioxidant properties
The powerful antioxidant effect of green tea mainly comes from its high concentration of polyphenols and catechins. These capture and help eliminate harmful free radicals in the body and support proper metabolic function.
Anti-inflammatory virtues
Green tea owes its anti-inflammatory properties to its richness in polyphenols, notably EGCG. This catechin has an antioxidant power about 200 times greater than that of vitamin E. Studies have shown that this molecule could have strong potential to treat rheumatoid arthritis thanks to its ability to block the TAK1 protein, which plays a key role in inflammation.
Cardiovascular protection
The cardioprotective effect of green tea would be linked to its high concentration of EGCG. This catechin would stimulate cardiac activity, soften the walls of blood vessels, and limit the formation of fatty plaques that can lead to artery blockage. Green tea would therefore have positive effects on arteriosclerosis, strokes, myocardial infarctions, as well as other cardiovascular diseases.
Glycemic balance
A meta-analysis published in 2013 shows that green tea EGCG would reduce the risk of insulin resistance, thus helping people with type 2 diabetes. The effects of polyphenols on glucose metabolism would be explained by a decrease in intestinal glucose absorption, better sensitivity of pancreatic receptors to glucose, and better glucose absorption by peripheral tissues.
Cholesterol
The flavonoids contained in green tea would prevent the intestine from absorbing bad cholesterol. Studies show that regular consumption of green tea would lower bad cholesterol levels and increase good cholesterol.
Brain, memory, concentration
Several scientific studies have shown the protective role of green tea catechins in the onset of dementias and neurodegenerative diseases, such as Alzheimer's and Parkinson's. Its high concentration of polyphenols, particularly EGCG, would help stop the formation of certain proteins responsible for cognitive decline.
In addition to its neuroprotective effects, researchers have highlighted two compounds in green tea that would help reduce mental fatigue and increase attention. Caffeine – a powerful brain stimulant – and L-theanine. The combination of these two molecules would improve brain function.
Weight management
Highly appreciated when trying to control weight, green tea consumption would increase energy expenditure. Its active ingredient, EGCG, would reduce fat absorption in the intestine, limit the formation of adipocytes where body fat accumulates, increase fat oxidation, and inhibit their production. Moreover, by regulating blood sugar and limiting insulin sensitivity, it would promote the elimination of excess fat.
Depressive disorders
Several studies have highlighted the benefits of green tea on mood. According to a Chinese study, regular consumption of green tea would reduce the prevalence of depressive symptoms. While researchers do not know the exact reasons for these benefits, they explain that green tea would stimulate the neural circuits related to pleasure. Researchers suppose that the polyphenols contained in green tea act on dendritogenesis, that is, the way neurons connect with each other.
Anti-stress
Although it contains a bit of caffeine, green tea provides deep relaxation and soothes nervous tension. Its leaves indeed release L-theanine, an amino acid that is believed to induce the production of relaxing alpha waves in the brain. It would also help promote falling asleep.
Skin protection
Because it is ultra-concentrated in polyphenols, green tea has a positive impact on skin cells. Its catechins, particularly EGCG, neutralize free radicals responsible for premature skin aging. Its molecules would boost collagen production and help preserve skin elasticity.
Anti-cancer virtues
At the heart of scientific research, green tea is considered a valuable ally against the development of cancers. Researchers have shown the promising role of catechins, these powerful antioxidants belonging to flavanols. The four types of catechins would play an important role, but the most powerful would be EGCG. This molecule notably has the property of "suffocating tumors." Indeed, when cancer cells proliferate to form a small tumor, they must simultaneously establish a network of blood vessels to be nourished and multiply. This is called the process of angiogenesis. EGCG has the property of preventing angiogenesis, that is, the formation of the blood vessel network necessary for the formation and growth of any tumor.
How to consume green tea?
Green tea is consumed as a hot or cold beverage (infusion of the leaves) or as dietary supplements. It is used in cooking recipes for its beautiful color and subtle taste, especially in cakes, muffins, cupcakes, ice creams, or milkshakes. Cosmetics have also adopted this virtuous plant for the design of anti-aging treatments.
Sources
Beneficial Properties of Green Tea Catechins, International Journal of Molecular, Claudia Musial, Alicja Kuban-Jankowska, Magdalena Gorska, Sciences 21(5):1744, March 2020.
Green Tea and One of Its Constituents, Epigallocatechine-3-gallate, Are Potent Inhibitors of Human 11β-hydroxysteroid Dehydrogenase Type 1, Jan Hintzpeter. Claudia Stapelfeld, Christine Loerz, Hans-Joerg Martin, Plos One, January 2014.
L-Theanine reduces psychological and physiological stress responses, Kenta Kimura, Makoto Ozeki, Lekh Raj Juneja, Hideki Ohira, Biological Psychology, p-39-45, January 2007.
Effects of L-theanine or caffeine intake on changes in blood pressure under physical and psychological stresses, Ai Yoto, Mao Motoki, Sato Murao, Hidehiko Yokogoshi, Journal of Physiological Anthropology, 2012.
Antioxidant mechanism of tea polyphenols and its impact on health benefits, Zhaomong Yan, Yinzhao Zhong, Yehui Duan, Animal Nutrition, January 2020.
Anti-inflammatory Action of Green Tea, Tomokazu Ohishi a, Shingo Gotob, Pervin Monirac, Mamoru Isemura b,c, Yoriyuki Nakamurac, Anti-Inflammatory & Anti-Allergy Agents in Medicinal Chemistry, September 2016.
The Impact of Green Tea and Coffee Consumption on the Reduced Risk of Stroke Incidence in Japanese Population, Yoshihiro, Hiroyasu Iso, Isao Saito et al., The Japan Public Health Center-Based Study Cohort, 2013.
Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials, Kai Liu, Rui Zhou, Bin Wang, Ka Chen et al., The American Journal of Clinical Nutrition, August 2013.
Systematic review of green tea epigallocatechin gallate in reducing low-density lipoprotein cholesterol levels of humans, Yuko Momose, Mari Maeda-Yamamoto, Horoshi Nabetani, International Journal of Food Sciences and Nutrition, June 2016.
Neurological mechanisms of green tea polyphenols in Alzheimer's and Parkinson's diseases, Orly Weinreb, Silvia A Mandel, Tamar Amit, Moussa B Youdim, Journal of Nutritional Biochemistry, October 2004.
L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance, Simon P. Kelly, Manuel Gomez-Ramirez, Jennifer L. Montesi, John J. Foxe, The Journal of Nutrition, August 2008.
A Brief Review on Green Tea and its Effect on Weight Management, Abhinav Joseph et al., Journal of The Guajarat Research Society, 2019.
Effect of green tea on reward learning in healthy individuals: a randomized, double-blind, placebo-controlled pilot study, Qiangye Zhang, Hongchao Yang, Jian Wang et al., Nutrition Journal, June 2013.
Reduced Stress and Improved Sleep Quality Caused by Green Tea Are Associated with a Reduced Caffeine Content, Keiko Unno, Shigenori Noda, Yohei Kaeasaki et al., Nutrients, July 2017.
Protective Mechanisms of Green Tea Polyphenols in Skin, Patricia Oyetakin White, Heather Tribout, Elma D Baron, Oxidative Medicine and Cellular Longevity, June 2012.
Cancer Prevention with Green Tea and Its Principal Constituent, EGCG: from Early Investigations to Current Focus on Human Cancer Stem Cells, Hirota Fujiki, Tatsuro Watanabe, Eisaburo Sueoka et al., Molecules and cells, February 2018.
