Drinking green tea may help you live longer, reduces breast and prostate cancer risk

Green tea comes from the plant Camellia Sinensis. The two main varieties of tea plants are Camellia sinensis, a small-leaf variety native to China, and Camellia sinesis assamica, a large-leaf variety that was first discovered in the Assam district of India.

Hundreds of cultivars and hybrid plants have evolved from these two plant varieties over time.

There are various types of teas made from the Camellia sinensis plant. Four well-known types are white tea made from young leaves and buds that have not yet turned green.  The only processing for this tea is drying. The next is green tea which is made from mature leaves of the plant with minimal processing that involves only drying. Then there is black tea which is made from partially fermented mature leaves and oolong Tea, produced from fully fermented mature leaves.

Green tea is produced by harvesting the leaves from the Camellia sinensis plant, quickly heated by pan frying or steaming, and dried to prevent too much oxidation from occurring. Oxidation turns the green leaves brown and alters their flavor. Brewed green tea is typically green, yellow, or light brown.

Green tea which originates from China traces back to 2737 B.C.  It was accidentally discovered by the Chinese Emperor Shennong  in the Yunan province of China when fresh tea leaves from a nearby Camellia sinensis tea tree fell into his cup of just boiled water. It was originally costly and only available to the highest tiers of Chinese society but became accessible to the general public for enjoyment and medicinal purposes in the 14th century. “The Classic of Tea”  is the first written work to explain green tea culture and art around 800 A.D., by Lu Yu of China. Green tea is said to be mainstreamed in Japan around the 12th century and to this day, China and Japan are said to be the top exporting countries of Green tea in the world. Green tea traveled to the West in the 19th century with European explorers.

Processing

Green tea undergoes the following processes:

The withering process involves reducing moisture in the leaves by using the air-blown method for 12 to 24 hours. This is followed by pan frying or steaming also known as fixing. This is done to reduce or stop the enzymatic activities in the leaf that leads to oxidation and fermentation. This helps to retain the green color of the leaves. After fixing the leaves undergo the first drying stage in a drum which is swiveled for nearly 30 minutes to further reduce the moisture content of the leaves. This is followed by rolling to crush the leaves into smaller particles. After rolling, there is further drying before packaging.

Constituents

Green tea has a high vitamin and mineral content and 5 cups of green tea will provide 5 to 10% of the daily requirements of riboflavin, niacin, folic acid, and pantothenic acid and also about 5% of the daily requirement of magnesium, 25% of potassium and 45% of the requirement for manganese (Shukla, 2007). It also contains the active ingredient polyphenol, with the subgroup catechins – A powerful antioxidant. There are four main catechins in green tea. They are (EC)    -epicatechin, (ECG) -epicatechin-3-gallate, (EGC) –epigallocatechin and (EGCG)-epigallocatechin-3-gallate. Of these four, EGCG is present in the largest quantity, and so has been used in much of the research. As the main constituent, green tea polyphenols were documented for their antioxidant, anti-inflammation, anticancer, anti cardiovascular, antimicrobial, antihyperglycemic, and antiobesity properties.

Recent reports demonstrate that green tea may exert a positive effect on the reduction of medical chronic conditions such as cardiovascular disease, cancer, Alzheimer’s disease, Parkinson’s disease, and diabetes. The health benefits of green teas, in particular EGCG, are widely investigated, and these effects are known to be primarily associated with the structure and compositions of its polyphenols. (Xing et. al., 2019).

Recent reports demonstrate that green tea may exert a positive effect on the reduction of medical chronic conditions such as cardiovascular disease, cancer, Alzheimer’s disease, Parkinson’s disease, and diabetes. (Zing et.al., 2019).

Green Tea: Supporting Literature

Live Longer

Studies have found that some compounds in green tea may help you live longer.  For instance, Kuriyama et al.(2006) studied 40,530 Japanese adults over 11 years. Those who drank the most green tea — 5 or more cups per day — were significantly less likely to die during the study period. The study found that:

• Death of all causes: 23% lower in women, 12% lower in men
• Death from heart disease: 31% lower in women, 22% lower in men
• Death from stroke: 42% lower in women, 35% lower in men

A previous study( Suzuki et al.2009) examined over 14,001 older Japanese individuals and found that those who drank the most green tea were 76% less likely to die during the 6-year study period.

Improves Brain function

Green tea does more than just keep you alert, it may also help boost brain function. The key active ingredient is caffeine, which is a known stimulant. Though green tea doesn’t contain as much as coffee,  however, it has more to produce a response without causing the nervous effects associated with taking in too much caffeine.

Two studies(Nehlig et al. 1999; Fredholm, B.B, 1995) found that caffeine affects the brain by blocking an inhibitory neurotransmitter called adenosine.  When this happens, it increases the shooting of neurons and the concentration of neurotransmitters like dopamine and norepinephrine.

Another, Ruxton, C(2008) found that caffeine could support many areas of brain function, including mood, vigilance, reaction time, and memory. Apart from caffeine, Nobre et al.(2008) found that green tea also contains the amino acid L-theanine, which can cross the blood-brain barrier.

More studies (Nobre et al. 2008; Nathan et al. 2006; Egashira et al. 2007) explained that L-theanine increases the activity of the inhibitory neurotransmitter GABA, which has anti-anxiety effects. It also increases dopamine and the production of alpha waves in the brain.

This means that two important energy-boosting compounds in green tea combinations could have synergistic effects. This means that the combination of the two can have particularly powerful effects in improving brain function(Kelly et al. 2008; Dodd et al. 2015). This also means that due to the L-theanine and the small dose of caffeine, green tea may give you a much milder and different kind of resistance than coffee. It has been reported that people experienced having more stable energy and being much more productive when they drink green tea, compared with coffee.

Cancers

Boehm et. al. (2009) conducted a systematic review of fifty-one studies with more than 1.6 million participants in studies that looked for associations between green tea consumption and cancer of the digestive tract, gynecological cancer including breast cancer, urological cancer including prostate cancer, lung cancer and cancer of the oral cavity. The result of the review was conflicting with the evidence that the consumption of green tea might reduce the risk of cancer.

Another observation studies review (Ogunleye and Michels, 2009) found that women who drank the most green tea had an approximately 20–30% lower risk of developing breast cancer, one of the most common cancers in women 

However, Reygaert (2017) found that case-control studies gave the most consistent results and were positive for reduced cancer risk in breast, cardiac, colorectal, esophageal, gastric, lung, ovarian, pancreatic, and prostate cancers. He conducted a review of research that focused primarily on using human subjects to investigate the health benefits of green tea. In his review, he also found a relationship between breast cancer risk and tea consumption, with the risk being highest in the groups that did not consume tea and lowest in the groups that consumed the most cups per day.

On Prostate cancer,  Kurahashi et al.(2008) study found that men drinking green tea had a lower risk of advanced prostate cancer.

On colorectal cancer, Chen et al.(2017) examined 29 studies and found that those drinking green tea were around 42% less likely to develop colorectal cancer.  An old study(Litt et al. 1997; Yuan. J.M, 2013) found that  green tea drinkers are less likely to develop several types of cancer, but more high-quality research is needed to confirm these effects

Finally, studies have found that adding milk to green tea reduces its antioxidant ability(Ryan and Petit, 2010).

Cardiovascular Disease

Two studies from Japan that included nearly 50,000 people found a decreased mortality rate due to CVD based on the consumption of various numbers of cups per day(Nakachi et.al., 2000, Kuriyama et. al., 2006).

Other studies in Japan using a green tea extract found that, after 12 weeks, the subjects had reductions in body fat (10%), blood pressure (6.5%), and low-density lipoprotein (LDL) levels (2.6%), suggesting a reduced risk of CVD.

 A large meta-analysis of 17 studies from over 30 years, including data from Europe, the UK, and the U.S., found that increasing the consumption of green tea by three cups per day decreased the risk of myocardial infarction (MI) death by 11%  (Peters et. al, 2001).

Another study showed a decreased risk of mortality in patients who had an acute MI and a history of regular green tea consumption for at least a year before the MI. Participants who did not drink green tea had a 14% rate of death due to MI; participants who drank up to 14 cups per week had an 11% rate of MI death; and participants who drank more than 14 cups per week had a 10% rate of MI death (Mukamal et. al,2002).

Another study, by Hartley et al.(2013) found that green tea may improve some of the main risk factors for these diseases, which includes improving total cholesterol and LDL (bad) cholesterol levels.

An old study( Yang and Koo, 2000; Yokozawa and Dong, 1997) also found that green tea also increases the antioxidant capacity of the blood, which protects the LDL particles from oxidation, which is one part of the pathway toward heart disease.

On the other hand, a meta-analysis of tea consumption concerning stroke, myocardial infarction, and all coronary heart diseases based on 10 cohort studies and seven case-control studies by Peters et. al.(2022), showed an interesting geographical effect of green tea consumption.

According to their study, the geographic region where the studies were conducted appeared to explain much of the heterogeneity among coronary heart disease, myocardial infarction, and probably stroke results. With increasing tea consumption, the risk increased for coronary heart disease in the United Kingdom and stroke in Australia, whereas the risk decreased in other regions, particularly in continental Europe.

Finally,  (Kuriyama, S, 2008; Shimazu et al. 2007; Miller et al. 2017) studies acknowledge that those who drink green tea have up to a 31% lower risk of dying from cardiovascular disease.

Diabetes

Several human- and animal-based studies suggested that green tea and its flavonoids have antidiabetic effects (Wu, 2004; Iso, 2006; Wolfram, 2006). Green tea flavonoids were also shown to have insulin-enhancing activity (Anderson, 2002). After two months, diabetic patients taking green tea had reduced fasting blood glucose levels (from 135 to 128.8 mg/dL), and hemoglobin A1c (HBA1c) levels (from 6.2% to 6.0%) (Nagao et. al., 2007 and Fukino et. al., 2005).

 A study by Waltner-Law et al.  (2002) provided compelling in vitro evidence that EGCG decreases glucose production of H4IIE rat hepatoma cells. The investigators showed that EGCG mimics insulin, increases tyrosine phosphorylation of the insulin receptor and the insulin receptor substrate, and reduces gene expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase. Green tea and green tea extracts were demonstrated to modify glucose metabolism beneficially in experimental models of type II diabetes mellitus (Wu, 2004).

Another study, by Liu et al.(2013)  found that green tea may improve insulin sensitivity and reduce blood sugar levels. In the case of Iso et al.(2006), the authors noted that Japanese individuals who drank the most green tea had an approximately 42% lower risk of type 2 diabetes.

 Huxley et al.(2009) reviewed 7 studies with a total of 286,701 individuals, tea drinkers had an 18% lower risk of diabetes.

Weight Loss, fat burning

Catechins have been found to influence intestinal and cell metabolism in several ways. Among the many effects on intestinal and cell metabolism are:

• Inhibiting intestinal lipases
  • Decreasing fat absorption
  • Increasing fat excretion
  • Increasing uncoupling proteins
  • Increasing thermogenesis
  • Decreasing lipogenic enzymes
  • Suppressing appetite

Data from human studies indicate that the consumption of green tea and green tea extracts may help reduce body weight, mainly body fat (Boschmann and Thielecke, 2007).

Another study(Auvichayapat et al. 2008; Wang et al. 2012) studies found that green tea may help reduce body fat, especially in the abdominal area.  One of these studies was a 12-week randomized controlled study involving 240 people with obesity.

One study ( Nagao et al. 2012) found that green tea drinkers had significant decreases in body fat percentage, body weight, waist circumference, and belly fat, compared with those in the control group.

Finally, Stendell-Hollis et al.(2010) found no evidence of weight loss with green tea, so researchers need to perform further studies to confirm this effect.

Additionally, in the area of fat-burning, it has been established that most fat-burning supplements contain green tea. This is because one study(Diepvens et al. 2007) found green tea can increase fat burning and boost metabolic rate.

In older studies(Dulloo et al. 1999; Venables et al. 2008) involving 10 healthy men, taking green tea extract increased the number of calories burned by 4%. In another involving 12 healthy men, green tea extract increased fat oxidation by 17%, compared with those taking a placebo.

Another study(Gregersen et al. 2009) found that green tea has no effect on metabolism, so the effects may depend on the individual and how the study was designed.

Alzhiemers & Parkinsons

A systematic review of observational studies that examined the association between green tea intake and dementia, Alzheimer’s disease, mild cognitive impairment, or cognitive impairment in the PubMed database seems to support the hypothesis that green tea intake might reduce the risk for dementia, Alzheimer’s disease, mild cognitive impairment, or cognitive impairment. (Kakutani et. al. ,2019)

However, Klaus et. al (2022) state that clinical results demonstrating efficacy in humans are scarcely making the clinical evidence regarding the preventive or therapeutic effects of green tea and its bioactive components in neuro-protection unsatisfactory.

With regards to Parkinson, Malar et. al, (2020)  concludes from a review that even though in vivo studies have suggested that the consumption of green tea protects against free radicals, inflammation, and neuro-damages aiding the understanding of the overall mechanism of green tea, doses used may not be sufficient in humans to elicit similar effects due to complex physiological, social, and cultural development.

Bad breath

The catechins in green tea also have benefits for oral health. Some test-tube studies, (Steinmann et al. 2013; Sakanaka et al. 2000; Lee et al. 2012; Song et al. 2005) found that catechins can suppress the growth of bacteria, potentially lowering the risk of infections.

Some studies (Chatterjee et al. 2012; Anita et al. 2014; Naderi et al. 2011; Narotzki et al. 2012) suggest that the catechins in green tea can inhibit the growth of oral bacteria in the lab, but no evidence shows that drinking green tea has similar effects.

Lodhia et al. 2008; Morin et al. 2015) studies established that green tea may reduce bad breath.

Side Effects of Green Tea

EGCG of green tea extract is cytotoxic, and higher consumption of green tea can exert acute cytotoxicity in liver cells, a major metabolic organ in the body ( Schmidt et. al. 2005) A study found that higher intake of green tea might cause oxidative DNA damage of hamster pancreas and liver (Takabayashi et. al., 2004). At a high dose (5% of the diet for 13 wk), green tea extract induced thyroid enlargement (goiter) in normal rats (Sakamoto Y et. al., 2001)

Green tea can cause side effects due to caffeine. These can include anxiety, tremors, irritability, and sleeping problems. This is more likely if you’re sensitive to caffeine or take large doses, Green tea extracts may cause liver problems. Symptoms can include yellowing of your skin or the whites of your eyes, nausea, and stomach pain. The negative effects of green tea extract on the liver may depend on how much green tea extract you consume each day.

Interactions

Green tea may change the effects of medicines such as nadolol, a beta-blocker used for high blood pressure and heart problems. It may keep nadolol from lowering your blood pressure as much as it should. Green tea contains small amounts of vitamin K. This means it may decrease how well blood thinner medicines work. Since green tea acts as a mild stimulant, you shouldn’t use it with other stimulants. It may change the effects of other medicines.

Conclusion

Green tea is widely consumed worldwide for its health benefits. Many retrospectives and few recent studies attest to that fact. Its effect on cancer, diabetes, and cardiovascular diseases are well documented in both human and animal studies. Its impact on neurodegenerative disease in human beings however needs more human randomized clinical control trials. Drinking three to five cups of green tea per day seems to be optimal to reap the most health benefits. Try to choose a higher quality brand of green tea, because some of the lower quality brands can contain excessive amounts of fluoride (Lu et al. 2004).

That being said, even if you choose a lower-quality brand, the benefits still outweigh any risk.

NB:

Prof. Nyarkotey has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations to justify his write-ups.  My articles are for educational purposes and do not serve as Medical advice for Treatment. I aim to educate the public about evidence-based scientific Naturopathic Therapies.

The writers are a Professor of Naturopathic Healthcare, President, of Nyarkotey College of Holistic Medicine & Technology (NUCHMT)/African Naturopathic Foundation, and final year Naturopathic Medicine student, and a trained Medical Journalist at Nyarkotey College of Holistic Medicine & Technology. E-mail: collegeofholisticmedicine@gmail.com

References

1. https://www.teatulia.com/tea-101/what-is-green-tea.htm

2. https://www.hackberrytea.com/blogs/tea-education/the-history-of-green-tea
3. Shukla Y. Tea and Cancer Chemoprevention. A Comprehensive Review. Asian Pacific Journal of Cancer Prevention (2007);8:155‐66
4. Boehm, K., Borrelli, F., Ernst, E., Habacher, G., Hung, S. K., Milazzo, S., & Horneber, M. (2009). Green tea (Camellia sinensis) for the prevention of cancer. The Cochrane database of systematic reviews, (3), CD005004. https://doi.org/10.1002/14651858.CD005004.pub2
5. Reygaert, W. (2017). An Update on the Health Benefits of Green Tea. Beverages, 3(4), 6. https://doi.org/10.3390/beverages3010006
6. Nakachi, K.; Matsuyama, S.; Miyake, S.; Suganuma, M.; Imai, K. (2000) Preventive effects of drinking green tea on cancer and cardiovascular disease: Epidemiological evidence for multiple targeting prevention. Biofactors, 13, 49–54.
7. Kuriyama, S.; Shimazu, T.; Ohmori, K.; Kikuchi, N.; Nakaya, N.; Nishino, Y.; Tsubono, Y.; Tsuji, I. (2006) Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: The Ohsaki study. JAMA , 296, 1255–1265.
8. Mukamal, K.J.; Maclure, M.; Muller, J.E.; Sherwood, J.B.; Mittleman, M.A. (2000) Tea consumption and mortality after acute myocardial infarction. Circulation, 105, 2476–2481.
9. Peters, U.; Poole, C.; Arab, L. (2001) Does tea affect cardiovascular disease? A meta-analysis. Am. J. Epidemiol. , 154, 495–503.
10. Wu LY, Juan CC, Ho LT, Hsu YP, Hwang LS: (2004),  Effect of green tea supplementation on insulin sensitivity in Sprague-Dawley rats. J Agric Food Chem. 52: 643-648. 10.1021/jf030365d.
11. Iso H, Date C, Wakai K, Fukui M, Tamakoshi A. (2006): The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults. Ann Intern Med., 144: 554-562.
12. Wolfram S, Raederstorff D, Preller M, Wang Y, Teixeira SR, Riegger C, Weber P (2006): Epigallocatechin gallate supplementation alleviates diabetes in rodents. J Nutr., 136: 3512-3518.
13. Anderson RA, Polansky MM (2002): Tea enhances insulin activity. J Agric Food Chem., 50: 7182-7186. 10.1021/jf020514c.
14. Nagao, T.; Hase, T.; Tokimitsu, I. A (2007) Green tea extract high in catechins reduces body fat and cardiovascular risks in humans. Obesity (Silver Spring) , 15, 1473–1483.
15. Fukino, Y.; Shimbo, M.; Aoki, N.; Okubo, T.; Iso, H. (2005) Randomized controlled trial for an effect of green tea consumption on insulin resistance and inflammation markers. J. Nutr. Sci. Vitaminol. (Tokyo) , 51, 335–342.
16. Waltner-Law ME, Wang XL, Law BK, Hall RK, Nawano M, Granner DK (2002): Epigallocatecin gallate, a constituent of green tea, represses hepatic glucose production. J Biol Chem., 277: 34933-34940. 10.1074/jbc.M204672200.
17. Wu LY, Juan CC, Hwang LS, Hsu YP, Ho PH, Ho LT (2004) : Green tea supplementation ameliorates insulin resistance and increases glucose transporter IV content in a fructose-fed rat model. Eur J Nutr., 43: 116-124. 10.1007/s00394-004-0450-x.
18.  Boschmann M, Thielecke F (2007): The effects of epigallocatechin-3-gallate on thermogenesis and fat oxidation in obese men: a pilot study. J Am Coll Nutr., 26 (4): 389S-395S.
19. Kakutani, S., Watanabe, H., & Murayama, N. (2019). Green Tea Intake and Risks for Dementia, Alzheimer’s Disease, Mild Cognitive Impairment, and Cognitive Impairment: A Systematic Review. Nutrients, 11(5), 1165. https://doi.org/10.3390/nu11051165
20. Klaus W. Lange, Katharina M. Lange, Yukiko Nakamura (2022), Green tea, epigallocatechin gallate and the prevention of Alzheimer’s disease: Clinical evidence, Food Science and Human Wellness, Volume 11, Issue 4, Pages 765-770, ISSN 2213-4530, https://doi.org/10.1016/j.fshw.2022.03.002. (https://www.sciencedirect.com/science/article/pii/S2213453022000064)
21. Malar, D. S., Prasanth, M. I., Brimson, J. M., Sharika, R., Sivamaruthi, B. S., Chaiyasut, C., & Tencomnao, T. (2020). Neuroprotective Properties of Green Tea (Camellia sinensis) in Parkinson’s Disease: A Review. Molecules, 25(17), 3926. https://doi.org/10.3390/molecules25173926
22. Schmidt M, Schmitz HJ, Baumgart A, Guedon D, Netsch MI, Kreuter MH, Schmidlin CB, Schrenk D (2005): Toxicity of green tea extracts and their constituents in rat hepatocytes in primary culture. Food Chem Toxicol.  43: 307-314. 10.1016/j.fct.2004.11.001.
23. Takabayashi F, Tahara S, Kanerko T, Harada N (2004): Effect of green tea catechins on oxidative DNA damage of hamster pancreas and liver induced by N-nitrosobis (2-oxopropyl) amine and/or oxidized soybean oil. Biofactors. , 21: 335-337. 10.1002/biof.552210165.
24. Sakamoto Y, Mikuriya H, Tayama K, Takahashi H, Nagasawa A, Yano N, Yuzawa K, Ogata A, Aoki N (2001): Goitrogenic effects of green tea extract catechins by dietary administration in rats. Arch Toxicol. , 75: 591-596. 10.1007/s00204-001-0286-6.
25. Xing, L., Zhang, H., Qi, R. , Tsao, Rong and Mine, Y. (2019 ) Recent Advances in the Understanding of the Health Benefits and Molecular Mechanisms Associated with Green Tea Polyphenols Journal of Agricultural and Food Chemistry 67 (4), 1029-1043  DOI: 10.1021/acs.jafc.8b06146
26. https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=19&contentid=greenteaextract
27. https://www.healthline.com/nutrition/how-much-green-tea-per-day
28. Shinichi Kuriyama, The Relation between Green Tea Consumption and Cardiovascular Disease as Evidenced by Epidemiological Studies, The Journal of Nutrition, Volume 138, Issue 8, August 2008, Pages 1548S–1553S, https://doi.org/10.1093/jn/138.8.1548S
29. Ogunleye AA, Xue F, Michels KB. Green tea consumption and breast cancer risk or recurrence: a meta-analysis. Breast Cancer Res Treat. 2010 Jan;119(2):477-84. doi: 10.1007/s10549-009-0415-0. Epub 2009 May 13. PMID: 19437116.
30. Norie Kurahashi, Shizuka Sasazuki, Motoki Iwasaki, Manami Inoue, Shoichiro Tsugane for the JPHC Study Group, Green Tea Consumption and Prostate Cancer Risk in Japanese Men: A Prospective Study, American Journal of Epidemiology, Volume 167, Issue 1, 1 January 2008, Pages 71–77, https://doi.org/10.1093/aje/kwm249
31. Taichi Shimazu, Shinichi Kuriyama, Atsushi Hozawa, Kaori Ohmori, Yuki Sato, Naoki Nakaya, Yoshikazu Nishino, Yoshitaka Tsubono, Ichiro Tsuji, Dietary patterns and cardiovascular disease mortality in Japan: a prospective cohort study, International Journal of Epidemiology, Volume 36, Issue 3, June 2007, Pages 600–609, https://doi.org/10.1093/ije/dym005
32. Miller PE, Zhao D, Frazier-Wood AC, Michos ED, Averill M, Sandfort V, Burke GL, Polak JF, Lima JAC, Post WS, Blumenthal RS, Guallar E, Martin SS. Associations of Coffee, Tea, and Caffeine Intake with Coronary Artery Calcification and Cardiovascular Events. Am J Med. 2017 Feb;130(2):188-197.e5. doi: 10.1016/j.amjmed.2016.08.038. Epub 2016 Sep 15. PMID: 27640739; PMCID: PMC5263166.
33. Kai Liu, Rui Zhou, Bin Wang, Ka Chen, Lin-Ying Shi, Jun-Dong Zhu, Man-Tian Mi, Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials, The American Journal of Clinical Nutrition, Volume 98, Issue 2, August 2013, Pages 340–348, https://doi.org/10.3945/ajcn.112.052746
34. Huxley R, Lee CMY, Barzi F, et al. Coffee, Decaffeinated Coffee, and Tea Consumption in Relation to Incident Type 2 Diabetes Mellitus: A Systematic Review With Meta-analysis. Arch Intern Med. 2009;169(22):2053–2063. doi:10.1001/archinternmed.2009.439
35. Stendell-Hollis NR, Thomson CA, Thompson PA, Bea JW, Cussler EC, Hakim IA. Green tea improves metabolic biomarkers, not weight or body composition: a pilot study in overweight breast cancer survivors. J Hum Nutr Diet. 2010 Dec;23(6):590-600. doi: 10.1111/j.1365-277X.2010.01078.x. Epub 2010 Aug 27. PMID: 20807303; PMCID: PMC2966548.
36. Steinmann J, Buer J, Pietschmann T, Steinmann E. Anti-infective properties of epigallocatechin-3-gallate (EGCG), a component of green tea. Br J Pharmacol. 2013 Mar;168(5):1059-73. doi: 10.1111/bph.12009. PMID: 23072320; PMCID: PMC3594666.
37. Lee HJ, Lee YN, Youn HN, Lee DH, Kwak JH, Seong BL, Lee JB, Park SY, Choi IS, Song CS. Anti-influenza virus activity of green tea by-products in vitro and efficacy against influenza virus infection in chickens. Poult Sci. 2012 Jan;91(1):66-73. doi: 10.3382/ps.2011-01645. PMID: 22184430.
38. Song JM, Lee KH, Seong BL. Antiviral effect of catechins in green tea on influenza virus. Antiviral Res. 2005 Nov;68(2):66-74. doi: 10.1016/j.antiviral.2005.06.010. Epub 2005 Aug 9. PMID: 16137775.
39. Chatterjee A, Saluja M, Agarwal G, Alam M. Green tea: A boon for periodontal and general health. J Indian Soc Periodontol. 2012 Apr;16(2):161-7. doi: 10.4103/0972-124X.99256. PMID: 23055579; PMCID: PMC3459493.
40. Anita P, Sivasamy S, Madan Kumar PD, Balan IN, Ethiraj S. In vitro antibacterial activity of Camellia sinensis extract against cariogenic microorganisms. J Basic Clin Pharm. 2014 Dec;6(1):35-9. doi: 10.4103/0976-0105.145777. PMID: 25538470; PMCID: PMC4268628.
41. Naderi NJ, Niakan M, Kharazi Fard MJ, Zardi S. Antibacterial activity of Iranian green and black tea on streptococcus mutans: an in vitro study. J Dent (Tehran). 2011 Spring;8(2):55-9. Epub 2011 Jun 30. PMID: 21998809; PMCID: PMC3184736.
42. Narotzki B, Reznick AZ, Aizenbud D, Levy Y. Green tea: a promising natural product in oral health. Arch Oral Biol. 2012 May;57(5):429-35. doi: 10.1016/j.archoralbio.2011.11.017. Epub 2012 Jan 5. PMID: 22226360.
43. Lodhia P, Yaegaki K, Khakbaznejad A, Imai T, Sato T, Tanaka T, Murata T, Kamoda T. Effect of green tea on volatile sulfur compounds in mouth air. J Nutr Sci Vitaminol (Tokyo). 2008 Feb;54(1):89-94. doi: 10.3177/jnsv.54.89. PMID: 18388413.
44. Morin MP, Bedran TB, Fournier-Larente J, Haas B, Azelmat J, Grenier D. Green tea extract and its major constituent epigallocatechin-3-gallate inhibit growth and halitosis-related properties of Solobacterium moorei. BMC Complement Altern Med. 2015 Mar 10;15:48. doi: 10.1186/s12906-015-0557-z. PMID: 25880992; PMCID: PMC4415245.
45. Kuriyama S, Shimazu T, Ohmori K, Kikuchi N, Nakaya N, Nishino Y, Tsubono Y, Tsuji I. Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study. JAMA. 2006 Sep 13;296(10):1255-65. doi: 10.1001/jama.296.10.1255. PMID: 16968850.
46. Abdul G Dulloo, Claudette Duret, Dorothée Rohrer, Lucien Girardier, Nouri Mensi, Marc Fathi, Philippe Chantre, Jacques Vandermander, Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans, The American Journal of Clinical Nutrition, Volume 70, Issue 6, December 1999, Pages 1040–1045,
47. Michelle C Venables, Carl J Hulston, Hannah R Cox, Asker E Jeukendrup, Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans, The American Journal of Clinical Nutrition, Volume 87, Issue 3, March 2008, Pages 778–784, https://doi.org/10.1093/ajcn/87.3.778
48. Gregersen NT, Bitz C, Krog-Mikkelsen I, Hels O, Kovacs EM, Rycroft JA, Frandsen E, Mela DJ, Astrup A. Effect of moderate intakes of different tea catechins and caffeine on acute measures of energy metabolism under sedentary conditions. Br J Nutr. 2009 Oct;102(8):1187-94. doi: 10.1017/S0007114509371779. Epub 2009 May 18. PMID: 19445822.
49. Nehlig A, Daval JL, Debry G. Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects. Brain Res Brain Res Rev. 1992 May-Aug;17(2):139-70. doi: 10.1016/0165-0173(92)90012-b. PMID: 1356551.
50. Nathan PJ, Lu K, Gray M, Oliver C. The neuropharmacology of L-theanine(N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent. J Herb Pharmacother. 2006;6(2):21-30. PMID: 17182482.
51. Egashira N, Hayakawa K, Osajima M, Mishima K, Iwasaki K, Oishi R, Fujiwara M. Involvement of GABA(A) receptors in the neuroprotective effect of theanine on focal cerebral ischemia in mice. J Pharmacol Sci. 2007 Oct;105(2):211-4. doi: 10.1254/jphs.scz070901. Epub 2007 Oct 6. PMID: 17928735.
52. Simon P. Kelly, Manuel Gomez-Ramirez, Jennifer L. Montesi, John J. Foxe, L-Theanine and Caffeine in Combination Affect Human Cognition as Evidenced by Oscillatory alpha-Band Activity and Attention Task Performance, The Journal of Nutrition, Volume 138, Issue 8, August 2008, Pages 1572S–1577S, https://doi.org/10.1093/jn/138.8.1572S
53. Dodd FL, Kennedy DO, Riby LM, Haskell-Ramsay CF. 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). 2015 Jul;232(14):2563-76. doi: 10.1007/s00213-015-3895-0. Epub 2015 Mar 13. PMID: 25761837; PMCID: PMC4480845.
54. Lu Y, Guo WF, Yang XQ. Fluoride content in tea and its relationship with tea quality. J Agric Food Chem. 2004 Jul 14;52(14):4472-6. doi: 10.1021/jf0308354. PMID: 15237954.
55. Chen Y, Wu Y, Du M, Chu H, Zhu L, Tong N, Zhang Z, Wang M, Gu D, Chen J. An inverse association between tea consumption and colorectal cancer risk. Oncotarget. 2017 Jun 6;8(23):37367-37376. doi: 10.18632/oncotarget.16959. PMID: 28454102; PMCID: PMC5514915.
56. Yuan JM. Cancer prevention by green tea: evidence from epidemiologic studies. Am J Clin Nutr. 2013 Dec;98(6 Suppl):1676S-1681S. doi: 10.3945/ajcn.113.058271. Epub 2013 Oct 30. PMID: 24172305; PMCID: PMC3831544.
57. Ryan L, Petit S. Addition of whole, semiskimmed, and skimmed bovine milk reduces the total antioxidant capacity of black tea. Nutr Res. 2010 Jan;30(1):14-20. doi: 10.1016/j.nutres.2009.11.005. PMID: 20116655.