Green tea contains large amounts of tea polyphenols (catechins and flavonoids), which are between 30% and 40% water-extractable, while black tea (green tea that has been oxidised by fermentation) contains between three percent and 10%.
The four primary polyphenols found in fresh green tea leaves - epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC) - have been shown to stimulate thermogenesis and exert heart-protective effects through multiple mechanisms, including antioxidative (1), anti-inflammatory (2); antiproliferative, increasing the plasma antioxidant capacity; and antithrombogenic effects (3) and lipid lowering effects (4,5).
As a result, numerous large and small studies, as well as laboratory and animal studies, have found green tea to have strong cardio-protective properties and to reduce overall mortality and mortality from and number of strokes and heart attacks.
It has also been demonstrated that the catechins found in green teas can inhibit the development of atherosclerosis in both laboratory animals and humans (6) and reduce the size of developing lesions in the arteries (6). These catechins have even been found to reverse endothelial (artery wall) dysfunction, which is an early marker of atherosclerosis (6). Other known benefits of consumption of green tea include a lower risk of certain cancers, improved heart health, weight loss, and protection against Alzheimer's.
Huge drop in heart disease
Compared to people who drink less than one cup a day, seven or more cups of green tea a day may reduce the risk of dying from heart disease by a huge 75%. In a study of 12,251 elderly residents in Japan, compared to people who drank less than one cup per day, drinking seven or more cups of green tea a day was associated with a 55% and 75% lower risk of all-cause and CVD mortality, respectively.
The study also found green tea consumption was associated with a 31% reduction in colorectal cancer mortality. In a study of 82,369 Japanese (aged 45–74 years, without cardiovascular disease or cancer) compared with seldom-drinking green tea, higher green tea and coffee consumption was associated with inverse risks of CVD and strokes (7). A similar large study of 76,979 Japanese adults reported a strong inverse relationship between the intake of more than six cups of green tea daily and CVD mortality (8).
Compared with less than one cup per day of green tea, five or more cups per day had a15% and 26% reduced risk of all-cause and CVD mortality, respectively (9).
Green tea consumption has also been associated with a reduced risk of incidence of all strokes (10). A study on Japanese women found that there was a reduced incidence of stroke among those who regularly consumed green tea (11). Similar results have been obtained from other studies and it is believed that the antioxidant properties of tea may also contribute to its effectiveness at preventing stroke (6). One study followed 5,910 Japanese women who neither smoked nor drank alcohol for four years. The incidence of stroke was significantly lower in women who consumed at least 1.5 cups per day of green tea.
Moderate consumers of green tea are less likely to develop hypertension (12) and epidemiological studies in China and Japan have found that habitual green or oolong tea drinkers have a significantly reduced risk of developing hypertension (6). When compared to those who do not or only occasionally drink tea, individuals who drink between 120 and 599 millilitres per day have a 46% reduced risk of developing hypertension and those who drink over 600 millilitres per day have their risk of developing hypertension reduced by 65% (13). Reduced blood pressure in tea drinkers has been attributed to the antioxidant activities of catechins, which prevent the build-up of plaque in the arteries (6).
Green tea was also found to produce statistically significant reductions in total cholesterol and LDL cholesterol. Green tea has been found to lower cholesterol levels in the liver and serum in laboratory animals (14). This reduction in cholesterol levels has been attributed to an increase in the amount of faecal bile acids and cholesterol excreted, however the mechanisms by which this is achieved are still unclear (14). A review examining green tea consumption and its antioxidant effects in 31 controlled intervention studies found that regular green tea consumption of at least 0.6 - 1.5 L/day reduced lipid peroxidation and increased antioxidant capacity (15).
Green tea even has short-term benefits straight after you drink the tea. Green tea consumption has an acute beneficial effect on endothelial function, the cells that in the arteries can produce nitric oxide, which relaxes the artery wall. In clinical studies, green tea increased FMD (flow-mediated dilation, the measure of a blood vessel's healthy ability to relax) by 3.9 percent 30 minutes after consumption, while no changes in FMD were observed following consumption of caffeine or the hot water placebo (16).
Valuable tool against diabetes
Antioxidants in green tea, particularly EGCG, are able to reduce blood glucose levels. Green tea has "antidiabetic activity" and is regarded as a valuable tool in the treatment and prevention of diabetes. Studies on "aged" rats found that EGCG may have properties to reverse the agerelated increase to glucose intolerance (17). The manner in which polyphenols are able to minimise serum glucose is by inhibiting the action of starch, digesting the enzyme amalyse. (Amalyse breaks starch down into sugar.) The tea prohibits intestinal and salivary amalyse, resulting in starch being broken down at a slower rate. Consequently, the increase in serum glucose is reduced (18). It is also believed that green tea lowers blood lipids (fats) such as cholesterol (19).
Cells of regular tea drinkers may have a younger biological age than cells of non-drinkers. The Chinese researchers reported that the telomeres (the most common way of measuring cell ageing) of people who drank an average of three cups of tea per day were about 4.6 kilobases longer than those of people who drank an average of a quarter of a cup a day, which corresponds to a difference of approximately five years of life (20).
The benefits of tea consumption in relation to preventing the onset of degenerative neurological diseases like Alzheimer's and dementia may be related to the antioxidants in green tea, as well as the chelating properties of catechins, as the accumulation of metal ions in the brain has been associated with these conditions (21,22).
Epidemiological studies in areas of Asia where green tea is widely consumed have revealed a five- to ten-fold reduction in the incidence of Parkinson's disease in comparison to nontea drinking populations (22).
Prevents Weight Gain
A number of studies have also shown consumption of green tea is beneficial in the prevention of weight gain and obesity (6). It has been demonstrated that tea consumption reduces the absorption of lipids and sugars, effectively reducing the amount of energy that is absorbed into the body and subsequently stored as fat (22,23).
Overall green tea should make up a part of every one's healthy lifestyle and the more the healthier. Green tea plays a critical role in chronic disease prevention, particularly for our biggest killer, heart disease. I have around two litres of green tea a day and despite what you may believe the growing body of scientific research shows that it does not dehydrate the body.
DISCLAIMER: Dr Peter Dingle is a researcher, educator and public health advocate. He has a PhD in the field of environmental toxicology and is not a medical doctor.
References:Khan and Mukhtar. 2007;Lee, et al 2005Babu and Liu 2008Babu and Liu 2008; Oppliger 1998Cheng 2006Kokubo, et alMineharu et al. 2010Kuriyama, 2006Tanabe. 2008Sato et al. 1989Hodgson, 2005Yang et al. 2004Yang and Koo 2000Ellinger 2011Alexopoulos et al. 2008Crespy and Williamson 2004Yang 1998Ausmus 2003Suzuki et al, Annals of Epidemiology, Volume 19Yang et al. 2006; Zaveri 2006Koo and Cho 2004;
Dr Peter Dingle (PhD) has spent the past 30 years as a researcher, educator, author and advocate for a common sense approach to health and wellbeing. He has a PhD in the field of environmental toxicology and is not a medical doctor. He is Australia’s leading motivational health speaker and has 14 books in publication.