For centuries, this earthy, aromatic beverage, that is native to China and India, has been widely consumed and credited for an array of health benefits.
Increasing research into this area has made us stand up and take notice: in particular, of the health benefits and effects that specific compounds in green tea have been shown to have on health- and lifespan.
Green tea has been on our radar for years as a result and, following careful consideration of the ever-growing body of scientific evidence into its benefits in humans and animals, we’re beginning to see the fruits of our labour, so to speak. Using the power of green tea, we may now have more of an idea about how to tap into that dream of eternal youth. When it comes to green tea, however, it’s not a simple magic potion or elixir of life you use to extend your years on this earth… This is about living well and in good health for many years to come.
The numerous health benefits of green tea are due to its antioxidant effects
Breaking down green tea, we find it is rich in a group of beneficial bioactive compounds called polyphenols, which make up around 30% of the dry weight of the fresh leaves.
Polyphenols are found everywhere in nature and they are well-known for their antioxidant and anti-inflammatory properties; two of the most common processes involved in the development of disease and typical effects that ageing has on our bodies.
One particular group of polyphenols that can be extracted from green tea that has sparked serious interest in health and well-being are called catechins. Catechins can be further categorized into five different types where epigallocatechin gallate (EGCg) is the most potent one.
Now, let’s look at why the antioxidant, free-radical clearing properties of green tea would be of interest in health and the prevention of disease. To do so, let’s dive into the most relevant scientific research conducted about green tea and its effects on specific areas of health…
Neurological benefits of green tea
It has been known for some time that green tea has a role in reducing the risk of neurological disease.
Alzheimer’s disease, one of the most common neurodegenerative diseases associated with ageing, may be the target of beneficial green tea mechanisms where the compounds it contains may act as both a preventative measure and potentially reduce its progression. It has been suggested that the EGCG compound in green tea may alter the structures of the amyloid plaques that collect in the brain of affected people, which is a hallmark of the disease.
In a 2017 review of the evidence gathered from pre-clinical trials, researchers suggest that green tea and its catechins, through their antioxidant and anti-inflammatory mechanisms of action, may reduce oxidative stress, which has been proven to be involved in the pathogenesis and progression of Alzheimer’s disease. Despite many of the current studies having been conducted in cells and animal models, researchers have suggested that larger studies be conducted in humans to provide more relevant information of these effects. Current data obtained from small-scale huma studies suggest that discrepancies in dosage and mode of delivery of green tea and its catechins can affect the bioavailability in the brain (1).
Heart health protective properties of green tea
Cardiovascular disease (CVD) is one of the leading causes of death and it can affect anyone over the age of 20. In both preclinical and human trials, EGCG has been found to hold vast potential in the prevention and treatment of various risk factors of CVD, including atherosclerosis, hypertrophy of the cardiac muscle, heart attack, and other risks related to increased inflammation and oxidation (2).
Research into these major factors include evidence for reducing:
- High blood pressure. 56 obese individuals with high blood pressure supplementing with one capsule of green tea a day for three months showed improved blood pressure status along with improved oxidative stress markers and cholesterol (3).
- High cholesterol. It appears that EGCG has the ability to reduce the risk of cholesterol plaques building up and clogging the arteries, a process known as atherosclerosis. It’s one of the highest risk factors for CVD and research shows that EGCG inhibits LDL cholesterol, which is a major contributing factor when out of balance. A meta-analysis of green tea consumption showed significant ability to reduce LDL cholesterol as well as total cholesterol levels (4), the results of which have been replicated in other studies.
In one placebo-controlled trial that lasted 12 weeks, the effects of consuming green tea daily was studied in over 10,000 otherwise healthy volunteers who were living with high LDL levels. In confirmation with other studies, green tea appears to reduce LDL cholesterol levels and improve blood triglycerides (5). It has been shown that green tea reduces the ability of cholesterol to be absorbed back through the digestive system, where it suppresses the aggregation of cholesterol particles. Additionally, green tea reduces triglycerides by delaying the absorption of dietary fat into the lymphatic system, thereby further reducing the impact it may have on overall cholesterol balance (6).
- Stroke and heart attack. There’s also evidence to support the use of green tea in the prevention of stroke and coronary artery disease (CAD) due to its blood pressure lowering effects. Like in Alzhiemer’s disease, where EGCG alters the structure of amyloid beta plaques, research suggests it has the same effect on cholesterol plaques, which reduces the risk of heart attack and stroke (7).
Overall, the consensus is that consumption of green tea has more favourable risk profiles with regards to CVD. In a 2016 review that included 9 studies on over 259,000 people, it was found that those who drank 1-3 cups of green tea each day had a lower risk of CVD than those who drank less than a cup a day. The risk improved even more significantly for those individuals who drank more than 4 cups a day and those who drank more than 10 cups a day had even lower LDL levels than those drinking less than 3 cups a day (8).
Metabolic diseases and green tea
Metabolic syndrome is another common lifestyle disease that has serious complications and is associated with blood sugar irregularities, cholesterol imbalances, overweight or obesity and high blood sugar. We’ve already seen the health benefits of green tea in these CVD markers, but overall, there’s also evidence to support the use of green tea in metabolic syndrome, which encompasses a wider array of imbalances.
In populations that have a high consumption of tea, there is an inverse relationship to metabolic syndrome that includes the diagnosis of blood sugar imbalances, greater waist circumference, insulin resistance, high blood pressure and high cholesterol (9).
Research in mice has also shown that consumption of EGCG may improve metabolic risk factors and stabilize hormones even when eating a high fat diet, which has been shown to reduce balance of metabolic pathways. In a 2017 study, researchers fed 3-month old mice either a standard diet, high fructose diet, high fat diet or a high fat diet with the addition of EGCG in their drinking water for 16 weeks. Liver and adipose tissue was then collected from mice in each group for evaluation of metabolic function.
EGCG was shown to reduce weight gain and increased energy intake typically stimulated by a high fat diet. Additionally, insulin resistance was reduced in the EGCGC group, it offered protective effects on blood fat levels, it prevented liver dysfunction due to fat accumulation, and it improved energy balance overall. The conclusion of the study therefore suggested that EGCG would be an effective functional intervention that may help to combat obesity and reduce the risk of complications associated with metabolic syndrome (10).
Due to these multiple effects on energy metabolism and homeostasis, green tea extracts are often touted as effective weight loss supplements. Research is currently mixed on the physical weight loss mechanisms of the compound, with some studies showing weight loss may be associated with taking green tea, while others showing that the overall benefits of green tea, while improving disease risk profile, do not promote weight loss as such.
For example, a 2018 study showed that obese women, taking green tea extract for 8 weeks, had improved metabolic parameters with regards to specific beneficial genetic changes in their adipose tissue, but this did not promote weight loss within the study period (11).
In an earlier study, completed in 2015, a mini review of the literature revealed that the combination of the caffeine and catechins in green tea had a positive effect on energy expenditure through the stimulation of thermogenesis, which is a process of heat production in an organism that promotes increased fuel burning (12).
In conclusion, we have a significant level of evidence to support the use of green tea extracts for their positive benefit on metabolic processes, however, in isolation, the evidence cannot be construed as green tea being a ‘magic bullet’ for weight loss.
Cancer and antioxidants
Research suggests that those who drink more green tea are less likely to develop certain types of cancer. Studies conducted into breast, prostate and colorectal cancer have yielded promising results in this regard, with fewer studies also suggestive of positive effects in adrenal carcinoma and other types of cancers. Due to its high antioxidant potential, researchers began investigating the effects of EGCG on cancer and its potential preventative action since 1983.
In a 2018 review, the anticancer effects of EGCG were proposed and the mechanism whereby it appears to work, were explained (13).
- Apoptosis. Cell that are damaged and dysfunctional typically undergo programmed cell suicide, which is called apoptosis. It is a mechanism through which the body gets rid of these cells. Cancer cells, even though they are mutated and can be seen as being damaged, evade this mechanism and thus continue to mutate and affect other cells to do the same (14). Having tested the effects of EGCG on breast, prostate and pancreatic cancer cells, researchers have shown that the compound, through various activation pathways, can suppress the ability of cells to evade apoptosis and even stimulate pro-apoptotic proteins.
- Cell cycle arrest. One of the ways cancer cells grow and proliferate is through upregulation of the cell cycle, which is the process whereby cells progress and divide. Proteins that regulate these processes become uncontrolled in cancer cells, however, with the inclusion of EGCG, they become more regulated, which can reduce the risk of proliferation in these mutant cells (15).
- Angiogenesis. Cancer cells recruit new blood cells to increase their supply of nutrients through a process known as angiogenesis. When angiogenesis is inhibited, tumor cells die, which has been noted as one of the mechanisms through which EGCG further exhibits anticancer properties (16).
While many of the studies on green tea and its EGCG effect have been conducted in animal and cell lines, a number of smaller-scale studies have found correlation in humans. In one study, Japanese women, who consumed more than 1.2 litres of green tea throughout the day had a delayed onset of cancer of 7.3 years when compared to women who drank less than three cups a day. In another study, green tea catechins taken by mouth at a dose of 600mg a day was shown to be effective in treating the early stages of prostate cancer, before the cells become malignant. Women in yet another study on green tea consumption and breast cancer development, showed that those who drank on average 8 cups a day, had a significantly lower recurrence rate of breast cancer, with a longer disease-free period, when compared to women who drank less than 4 cups a day (17).
Healthy ageing and longevity
Researchers interested in the effect of green tea catechins and their role in expansion of lifespan used the common fruit fly, Drosophila melanogaster to determine the mechanisms by which it works. Interestingly, the fruit fly is a model organism to use in studies such as this, as this species has a genetic profile that is very easy to study and manipulate, which is pertinent to obtaining evidence on lifespan (18).
Using this model, one mechanism was found to be activated, resulting in a 21% increase in lifespan of the male species: there was a reduction of iron accumulation and subsequent toxicity, which have been implicated in the aging process of flies (19). Green tea has been previously reported to be protective against iron accumulation, where it has consistently been shown to reduce iron absorption (20).
In another animal study, this time using a type of worm called Caenorhabditis elegans, green tea extract administered daily showed a 14% increase in their lifespan. C. elegans is another species that offers us a way to study human development and disease. Due to evolutionary changes, this species actually shares some common mechanisms with humans!
With regards to lifespan and the effects of green tea extracts, even when the worms were placed under a significant amount of stress, which would typically be lethal to the species, there was a 65% survival rate in those receiving the green tea intervention (21).
Yet another study showed that this increase in lifespan as a result of green tea administration was most significant under conditions of heat and oxidative stress. In fact, under oxidative stress (strongly associated with inflammatory conditions and disease in humans, too), lifespan was seen to increase by 172%. While the researchers could not correlate these astounding effects when the worms were kept under normal physiological conditions, it is promising to note the effects of green tea extract is greatest under imbalanced conditions that cause death and disease, which goes back to our desire to promote longevity and health (22).
Mice offer another animal model to study various mechanisms that can be translated into humans.
Early research conducted on mice receiving green tea compounds showed mixed results for its benefits. One such study showed that there was a limiting factor to the benefit of lifespan. Once a 10% increase in lifespan had been achieved in the intervention group, the benefits plateaued. Another provided evidence to support that the greatest impact was on the reduction of risk of death in midlife. In a secondary study, performed to obtain correlation for this, showed no statistically significant evidence to support these effects (23,24,25). As the authors noted, the results are promising in many aspects, which warrants further research.
More research has, indeed, been done. Recent evidence suggests a stronger correlation between rats that are fed with EGCg and an increased lifespan where, compared to controls, treated rats have an average lifespan of 105 weeks versus 92.5 weeks. In fact, the authors of the study noted that death in the EGCg treated rats was delayed by 8-12 weeks due to marked reduction in age-associated inflammation, free radical damage and failure of their liver and kidney systems (26).
In addition to the benefits of green tea on longevity, research has also been conducted into the effects on enzymatic activity and how green tea extract may protect the sequencing of telomeres (27,28). Telomeres are repeating sequences of DNA at the ends of the chromosome that provides the code for different reactions to take place within the body. As we age, these telomeres shorten, which reduces the optimal functioning capacity of the body and reduces our lifespan.
In a study conducted on a sample of elderly Chinese men, telomere length was preserved in those drinking more than 3 cups of green tea a day, which translated into an average of approximately 5 years extended lifespan when compared to those in the lowest tea consumption group (29).
Green tea shows promising free-radical scavenging effects in humans
In humans, green tea extract has been widely studied for its role in free radical scavenging, particularly in populations that consume a high amount of it as part of their culture.
There is an extensive amount of evidence available to date on the effects of green tea extract and its health benefits. While we’re aware of the evidence that shows little support for this intervention, we’re monitoring the reasons why, and there is still an overwhelming number of studies that offer a strong correlation between the use of green tea extract and its positive effects on healthy ageing and lifespan (30,31,32).
One area to be observed is the potential side-effects of green tea. Studies have suggested that there may be a negative correlation with those who have thyroid function abnormalities. Green tea may block the production of these essential hormones and further exacerbate hypothyroid conditions. As mentioned earlier, research in fruit flies suggests that green tea may block iron absorption. It is important to note that those who have lower iron levels should reduce their intake of green tea (33).
When it comes to researching the benefits and potential risks of consuming large amounts of green tea, it is important to dig into the quality of each study and compare how they have used a specific green tea extract, and in what concentration it was administered in each case (34). It is of particular relevance as the ability of green tea extract to be absorbed by the human body largely depends on the nature of its preparation. In order for its full effects to be determined, it is necessary to develop formulations of the extract to improve and maximize not only its stability, but its bioavailability (35).
Success in this area allows us to begin to align with the more recent research conducted on green tea’s ability to promote health and wellbeing by targeting body systems from multiple angles to potentially reduce the impact of a variety of debilitating diseases and promote healthy living through the ages overall.
Who wouldn’t want to have an opportunity to harness these astounding health benefits of this powerful natural ingredient that 11th century Japanese Zen priest Eisai described in his writings Kissa Youjouki (Tea and Health Promotion) as (36): the elixir of care and nostrum for a long-lasting life.
Selection of studies used for this article:
- Cascella, M., et al. The efficacy of Epigallocatechin-3-gallate (green tea) in the treatment of Alzheimer’s disease: an overview of pre-clinical studies and translational perspectives in clinical practice. Infectious Agents and Cancer. 2017. 12:36.
- Eng, Q. Y., Thanikachalam, P. V., & Ramamurthy, S. (2018). Molecular understanding of Epigallocatechin gallate (EGCG) in cardiovascular and metabolic diseases. Journal of Ethnopharmacology, 210, 296–310.
- Bogdanski P, Suliburska J, Szulinska M, et al. Green tea extract reduces blood pressure, inflammatory biomarkers, and oxidative stress and improves parameters associated with insulin resistance in obese, hypertensive patients. Nutr Res 2012; 32:421–427.
- Zheng XX, Xu YL, Li SH, et al. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. Am J Clin Nutr 2011; 94:601–610
- Imbe, H., et al. “Benifuuki” green tea, containing O-methylated EGCG, reduces serum low-density lipoprotein cholesterol and lectin-like oxidized low-density lipoprotein receptor-1 ligands containing apolipoprotein B: A double-blind, placebo-controlled randomized trial. Journal of Functional Foods. 2016. 25:25-37.
- Ravindran, R., et al. EGCG exerts its protective effect by mitigating the release of lysosomal enzymes in aged rat liver on exposure to high cholesterol diet. Cell Biochemistry and Function. 2020. 38(3).
- British Heart Foundation. Green tea molecule could prevent heart attacks: Compound breaks-up potentially dangerous protein plaques in blood vessels [press release]. London: BHF; 2018a.
- Pang, J., et al. Green tea consumption and risk of cardiovascular and ischemic related diseases: A meta-analysis. International Journal of Cardology. 2016. 202(1):967-974.
- Vernarelli JA, Lambert JD. Tea consumption is inversely associated with weight status and other markers for metabolic syndrome in US adults. Eur J Nutr 2013; 52:1039–1048.
- Mi, Y., Qi, G., Fan, R., Ji, X., Liu, Z., & Liu, X. (2017). EGCG ameliorates diet-induced metabolic syndrome associating with the circadian clock. Biochimica et Biophysica Acta (BBA) – Molecular Basis of Disease, 1863(6), 1575–1589.
- Quinhoneiro, D., et al. Green tea supplementation upregulates uncoupling protein 3 expression in severe obese women adipose tissue but does not promote weight loss. International Journal of Food Sciences and Nutrition. 2018. 69(8):995-1002.
- Turkozu, D., & Tek, N. A minireview of effects of green tea on energy expenditure. Critical Reviews in Food Science and Nutrition. 2017. 57(2):254-258.
- Rady, I., et al. Cancer preventive and therapeutic effects of EGCG, the major polyphenol in green tea. Egyptian Journal of Basic and Applied Sciences. 2018. 5(1):1-23.
- Sanna, V., et al. Targeted nanoparticles encapsulating (-)-epigallocatechin-3-gallate for prostate cancer prevention and therapy. Sci Rep. 2017. 7:41573.
- Feitelson, M., et al. Sustained proliferation in cancer: Mechanisms and novel therapeutic targets. Semin Cancer Biol. 2015. 35(S2):554.
- Li, Y., et al. Epigallocatechin-3-gallate inhibits IGF-I-stimulated lung cancer angiogenesis through downregulation of HIF-1alpha and VEGF expression. J Nutrigenet Nutrigenomics 2013. 6:169-178.
- Fujiki, H., et al. Cancer Prevention with Green Tea and Its Principal Constituent, EGCG: from Early Investigations to Current Focus on Human Cancer Stem Cells. Mol Cells. 2018 Feb 28; 41(2): 73–82.
- Adams MD, Celniker SE, Holt RA, Evans CA, Gocayne JD, Amanatides PG, Scherer SE, Li PW, Hoskins RA, Galle RF, et al (2000). The genome sequence of Drosophila melanogaster. Science (New York, N.Y.), 287 (5461), 2185-95.
- Massie HR, Aiello VR, Williams TR. Inhibition of iron absorption prolongs the life span of Drosophila. Mech Ageing Dev. 1993 Apr; 67(3):227-37.
- Perron NR, Brumaghim JL. A review of the antioxidant mechanisms of polyphenol compounds related to iron binding. Cell Biochem Biophys. 2009; 53(2):75-100.
- Abbas S, Wink M. Epigallocatechin gallate from green tea (Camellia sinensis) increases lifespan and stress resistance in Caenorhabditis elegans. Planta Med. 2009 Feb; 75(3):216-21.
- Zhang L, Jie G, Zhang J, Zhao B. Significant longevity-extending effects of EGCG on Caenorhabditis elegans under stress. Free Radic Biol Med. 2009 Feb 1; 46(3):414-21.
- Kitani K, Osawa T, Yokozawa T. The effects of tetrahydrocurcumin and green tea polyphenol on the survival of male C57BL/6 mice. Biogerontology. 2007 Oct; 8(5):567-73.
- Green tea protection against age-dependent ethanol-induced oxidative stress. Łuczaj W, Waszkiewicz E, Skrzydlewska E, Roszkowska-Jakimiec W. J Toxicol Environ Health A. 2004 Apr 9; 67(7):595-606.
- Strong R., et al. Evaluation of resveratrol, green tea extract, curcumin, oxaloacetic acid, and medium-chain triglyceride oil on life span of genetically heterogeneous mice. J Gerontol A Biol Sci Med Sci. 2013 Jan; 68(1):6-16.
- Niu Y, Na L, Feng R, Gong L, Zhao Y, Li Q, Li Y, Sun C. The phytochemical, EGCG, extends lifespan by reducing liver and kidney function damage and improving age-associated inflammation and oxidative stress in healthy rats. Aging Cell. 2013 Dec; 12(6):1041-9.
- Prasad, K., et al. Telomere shortening during aging: Attenuation by antioxidants and anti-inflammatory agents. Mechanisms of Ageing and Development. Volume 164, June 2017, Pages 61-66.
- Mikhelson, V.M., Gamaley, I.A., 2012. Telomere shortening is a sole mechanism of aging in mammals. Curr. Aging Sci. 5, 203–208
- Chan, R., et al. Chinese tea consumption is associated with longer telomere length in elderly Chinese men. Br J Nutr. 2010 Jan;103(1):107-13.
- th Parkinson’s disease. J. Nutr. Health Aging 15, 277–281.
- Szebeni, A., et al. 2014. Shortened telomere length in white matter oligodendrocytes in major depression: potential role of oxidative stress. Int. J. Neuropsychopharmacol. 17, 1579–1589.
- Ma, D., et al. 2013. Association between oxidative stress and telomere length in Type 1 and Type 2 diabetic patients. J. Endocrinol. Invest. 36, 1032–1037.
- Saraswat, A. Health benefits of green tea versus black tea. International Journal of Food Science and Nutrition. 2018. 3(3):7-8.
- Naasani, I., et al. Telomerase Inhibition, Telomere Shortening, and Senescence of Cancer Cells by Tea Catechins. Biochemical and Biophysical Research Communications. Volume 249, Issue 2, 19 August 1998, Pages 391-396.
- Dekant, W., et al. Safety assessment of green tea based beverages and dried green tea extracts as nutritional supplements. Toxicology Letters. Volume 277, 5 August 2017, Pages 104-108
- Hara, Y., et al. Health benefits of green tea: An evidence-based approach. CAB International 2017.