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Green tea comes from the plant Camellia sinensis which belongs to the family Theaceae; and consists of leaves that haven’t been fermented, allowing them to retain high levels of highly beneficial phytochemicals. Despite that it does contain small amounts of caffeine; Green Tea consumption has been associated with more health benefits than even many of the healthiest foods available to us. Studies have found that the benefits of Green Tea are due to the fact Green Tea contains more healing compounds than many other herbs, spices, fruits and vegetables, truly making it a powerful “superfood”.
Green Tea contains more than 4000 bioactive compounds, of which the highest number being the polyphenols. Green Tea also contains alkaloids (caffeine, theophylline and theobromine), amino acids (L-theanine), proteins (proteins make up about 15 percent to 20 percent of the leaves dry weight), carbohydrates (cellulose, pectin, glucose, fructose and sucrose), volatile organic compounds (chemicals that readily produce vapours and contribute to the odour of tea), minerals and trace elements (calcium, magnesium, chromium, manganese, iron, copper and zinc), linoleic acid and quercetin (Namita et al., 2012). The polyphenolic compounds found in Green Tea are mostly flavonoids and catechins, with catechins being the most predominant. Major catechins are epicatechin gallate (ECG), epicatechin (EC), epigallocatechin (EGC) and epigallocatechin gallate (EGCG). EGCG is the most researched catechin; and has been demonstrated to contribute to enhanced metabolic activities that may prevent weight gain, by boosting thermogenesis (the body producing heat by using energy) and suppressing appetite (Namita et al., 2012).
Increased free radical generation and high levels of oxidative stress are the foundation for phenotypic changes associated with many metabolic, cardiovascular and neurodegenerative disorders such as atherosclerosis, stroke, diabetes, Alzheimer’s and Parkinson’s. Green Tea has potent antioxidant effect in protecting cells from oxidative damage. In 2009, King’s College researchers found that epicatechin (EC) may protect brain cells from the negative effects of beta-amyloid plaques because of its ability to cross the blood-brain barrier. On the other hand, epigallocatechin gallate (EGCG) has been shown to inhibit the beta secretase enzyme (BACE1) responsible for processing sAPP to beta-amyloid, thus preventing the production of beta-amyloid plaque all together (Jeon et al., 2003).
Coronary artery disease is associated with endothelial dysfunction and increased levels of oxidative stress. Some antioxidants are known to reverse endothelial dysfunction and numerous studies have demonstrated the cardiovascular effect of the antioxidant components in green tea, flavonoids and catechins. A study done by Miura et al. (2000) demonstrated the ability of Green Tea to lower the risk of atherosclerosis by increasing the resistance of plasma LDL (bad cholesterol). The ability of Green Tea to prevent LDL cholesterol oxidation and lower triglyceride levels was also demonstrated in a study by Riemersma et al. (2001). In a meta-analysis of observational research studies, 13 conducted in green tea drinkers and five in black tea drinkers, scientists found that people who drank the most green tea had a 28% lower risk of coronary artery disease than those who drank the least green tea (Kuriyama et al., 2006).
The flavonoids and anthocyanidins found in Green Tea are known to improve glycaemic control and help normalise blood sugar levels. Moreover, the catechins, especially EGCG, have been demonstrated to have potent antidiabetic effects (Chatterjee et al., 2012). Green Tea improves lipid and glucose metabolism, prevents sudden increases in blood sugar levels, and has a balancing effect on metabolic rate. Green Tea is also known for its anti-inflammatory properties, and because of that it is believed to be beneficial for anyone suffering, or being at risk of type 2 diabetes. A study done by Iso et al. (2006) found that people who consume six or more cups of green tea daily had a 33 percent lower risk of developing type 2 diabetes than those who consumed less than one cup per week.
There is some evidence that long-term consumption of green tea catechins, especially EGCG is beneficial for burning fat due to its ability to increase levels of fat oxidation and thermogenesis, and promote metabolic health. In a study published by Hursel et al. (2009), in the International Journal of Obesity, researchers found that catechins, or an epigallocatechin gallate (EGCG) caffeine mixture have a positive effect on weight loss and weight maintenance. Another study, explaining a 12-week randomized controlled trial with 60 obese adults demonstrated that Green Tea can significantly contribute to weight loss by increasing energy expenditure and fat oxidation (Auvichayapat et al, 2008). Matsuyama et al. (2008) investigated the effect of Green Tea on obese children and found that consumption of 576 mg green tea catechins per day for 24 weeks had a statistically significant reduction in waist circumference, blood pressure, and LDL cholesterol.
Green Tea contains L-Theanine, an important an amino acid that crosses the blood-brain barrier and has psychoactive properties. L-Theanine increases levels of gamma-aminobutyric acid (GABA), serotonin, dopamine, and alpha wave activity, and may reduce mental and physical stress and produce feelings of relaxation. One of the appealing aspects of L-theanine is that it works to relax the mind without sedating. Therefore, Green Tea can be a good choice for people who are looking to enhance their “wakeful relaxation,” without worrying about becoming sleepy and fatigued during the day. L-Theanine has also been suggested to be beneficial in preventing age related memory decline and affecting areas of the brain involved in attention and problem solving (Park et al., 2011).
BSc Herbal Medicine; MSc Pharmacology
Auvichayapat, P., Prapochanung, M. et al. (2008). Effectiveness of green tea on weight reduction in obese Thais: A randomized, controlled trial. Physiol Behav. 8 (23), 76-82.
Chatterjee, A., Saluja, M., Gunjan A. et al. (2012). Green tea: A boon for periodontal and general health. J Indian Soc Periodontol. 16 (2), 161–167.
Hursel, R., Viechtbauer W. et al. (2009). The effects of green tea on weight loss and weight maintenance: a meta-analysis. International Journal of Obesity. 33 (9), 956-961
Iso, H., Date, C., Wakai, K. et al. (2006). The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults. Annual Internal Medicine. 144 (8), 554-562.
Kuriyama, S., T. Shimazu, K. Ohmori. et al. (2006). Green tea consumption and mortality due to cardiovascular disease. JAMA. 296 (10), 1255-1265.
Matsuyama, T., Tanaka, Y. et al. (2008). Catechin safely improved higher levels of fatness, blood pressure, and cholesterol in children. Obesity. 8 (19), 231-236.
Miura,Y., T. Chiba, S., Miura, I.I. et al. (2000). Green tea polyphenols (flavan 3-ols) prevent oxidative modification of low density lipoproteins: an ex vivo study in humans. Journal of Nutritional Biochemistry. 11 (4), 216-222.
Namita, P., Mukesh, R., Vijay, K.J. (2012). Camellia Sinensis (Green Tea): A Review. Global Journal of Pharmacology 6 (2), 52-59.
Park, S.K., Jung, I.C., Lee, W.K. et al. (2011). A combination of green tea extract and l-theanine improves memory and attention in subjects with mild cognitive impairment: a double-blind placebo-controlled study. J Med Food. 14 (4), 334-343.
Riemersma, R.A., C.A. Rice-Evans. et al. (2001). Tea flavonoids and cardiovascular health. QJM. 94 (5), 277-282.
Jeon, S.Y., Bae, K., Seong, K.S. et al. (2003). Green tea catechins as a BACE1 (beta-secretase) inhibitor. Bioorganic Medicinal Chemistry Letters. 13 (22), 3905-3908.
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