The Health Benefits of Green Tea: Research Data
|Fresh green tea plant(Camellia sinensis) leaves|
The tea plant has been used in the traditional Asian medicine for its therapeutic qualities for thousands of years. Today, clinical and basic science research confirms and specifies its preventive and curative properties . Consumed in larger quantities, green and black tea decrease the levels of cholesterol in the blood.
The green tea has an additional advantage, because it seems that it can prevent certain types of cancers.
We know about the “French paradox” attributed to the the phenolic molecules contained in the wine, the polyphenols. Now here is the “Chinese paradox ” or “Asian paradox“, according to which the phenolic compounds of green tea seem to protect the body not only of cardiovascular diseases, like wine does, but also prevents the occurrence of cancers.
A Chinese proverb says: “When you have tea and rice wine you have a lot of friends”. It would seem, according to recent studies, that you would also be in better health.
There are numerous ways and types of preparation and cultivation/processing of the green tea plant (Camellia sinensis), but we are going to mention the most common and well known ones below.
First used as a medicinal plant, green tea was imposed in the ceremonies of Chinese dynasties and in various forms of preparation. It’s the glorious Tang dynasty (618-907) that develops the true art of tea. During this dynasty, the poet Lu-Yu wrote in the Eighth century, the Code of the tea known under the name of “Tchaking”. The first book is about the complete and thorough process of tea manufacturing, from the picking of the leaves to the preparation of the drink.
Green tea is then object of the very active and flourishing trade and the imperial government is not hesitant to introduce a tax, called tribute tea. For centuries, green tea is consumed in the form of sheets or “bricks” as we now call them, which were pressed and dried in the form of a cake. It was also used for cooking, often boiled with rice, spices, milk and onions.
Prepared as a decoction in the Song dynasty (960-1279), the tea is often grind to a powder and served as a foamy emerald green drink, which we now know as matcha green tea. This practice continues even to this day, with some refinements used mainly in the art of tea ceremonies in Japan. Finally, it is probably under the Ming dynasty (1368-1644) when green tea replaces the coffee as a main stimulating drink and the tea leaves began to be consumed primarily as tea.
Europe discovered this drink at the beginning of the 17th century and was causing a real craze in England, in fact its currently their national drink. Today, tea is the second most consumed beverage in the world after water.
From a few thousand years, the tea leaves are used in traditional medicine throughout Asia. For the traditional chinese medicine, tea clears the head and eyes, aids digestion, promotes urination, and neutralizes toxins. It relates to the meridians of the heart, lungs and the stomach. In addition, chewing tea leaves would be used as a method to cure bad breath.
Finally, it’s recommended not to throw away the leaves of the tea: used as a pillow, they would supposedly provide an incomparable deep sleep.
Cultivation and production of green tea and black tea
In its wild form, the tea plant Camellia sinensis is a shrub from five to ten metres high. But in most of the plantations it is pruned to approximately 1.20 m to facilitate the collection of the leaves. In plantations they harvest the leaf buds, or “green pekoe” in chinese. from the first flush in the spring up to the third flush depending on the quality of the tea they are producing. There are three categories of tea:
– non-fermented or green tea, accounting for 80 to 90 % of the chinese production;
– semi-fermented tea, which is called Oolong,
– and fermented tea, or black tea, called red in China, represents 90 % of the indian production.
To produce green tea, the leaves are subjected to a stabilization process by drying or steaming, depending on what type of tea is needed. This operation has the effect of destroying the enzymes, especially polyphenol oxidases, which, as their name indicates, oxidize the polyphenols. It is traditionally done by roasting in pans of cast iron. Then the leaves are rolled by hand or machine, and are subject to a new roast. In modern production processes, especially in Japan, the stabilization is carried out with steam.
The production of black tea requires several steps: withering is to let the leaves cool on the trays for about two hours. Thus relaxed, they are then rolled by hand or machine, helping the release of the polyphenols oxidases in the leaves. Then starts the fermentation in a humid atmosphere, which lasts three to five hours. This treatment leads to a profound modification of the chemical composition of the leaves, which get a brown to black color and that is the result of this enzymatic oxidation. Finally, the leaves are dried with hot air.
Ingredients and chemical content of green tea
The most active and essential ingredients in green tea are the caffeine and the polyphenols. The content of caffeine in the leaves is 2% to 4%. Long called theine, the caffeine alkaloid is in fact the same molecule as in coffee. Phenolic compounds are represented by substances from the group of flavanols, called catechols: epicatechol, epigallocatechol and a derivative, Epigallocatechin gallate (EGCG) see diagram.
The EGCG are large part of the tea content, representing approximately 25 % of the weight of the dried tea leaves. It’s important to note that in the black tea fermentation causes a transformation of these active polyphenolic compounds in more complex thearubigines and theaflavins, which are responsible for the red color of the infusion. Vitamin C is also quite abundant in the fresh tea leaves with 0.6 % of the total content. It is found in the green tea, but is almost completely destroyed in the black tea. Finally, the fluorine ( not to be confused with fluoride (?) ) content of tea leaves is sufficient to prevent tooth decay naturally.
Green tea is a well-known stimulant of the central nervous system. This effect, is due to the caffeine, which stimulates both brain function and physical activity. Caffeine is also responsible for the diuretic properties of the tea and its ability to stimulate the cardio-respiratory system.
In coffee, caffeine is partially combined with the phenolic compounds found in green tea such as theanine, which is another extremely beneficial phenol tea has to offer. For this reason that the caffeine is released into the body more slowly and steadily, when you drink the tea, and its stimulating action is more gentle than that ingested from coffee.
Researches show evidence that green tea fights cancer, atherosclerosis, free radicals and aids in weight loss
Research on the beneficial effects of green tea on atherosclerosis and cardiovascular disease prevention
In recent years, numerous works published in international scientific journals have reported on the preventive or curative properties of tea on atherosclerosis. Specifically, the Japanese researchers K. Imai and K. Nakachi, from the Saitama Cancer Center Research Institute, have carried out epidemiological studies, concerning 1 371 men over 40 years and is divided into three groups according to their consumption of tea. They have shown that regular intake of green tea decreased significantly the levels of lipids circulating in the blood and in particular that of the cholesterol. They also found that when consumption is higher, cholesterol levels are lower, especially among consumers, drinking ten or more cups of tea.
Thus, the prevalence of cardiovascular disease would be 26 per 1,000 for this group, compared to almost 40 per 1 000 among the drinkers of three cups or less. Qualitatively, the rate of HDL for high density lipoprotein , the lipoprotein carrying the “good” cholesterol, was significantly increased and the rate of LDL low density lipoprotein, corresponding to ” bad ” cholesterol implicated in cardio-vascular diseases, decreases at the same time. These results have been corroborated by tests in animals subjected to high fat food regimes.
A Dutch study called “the Zutphen study,” and this time the studied tea is black, was conducted by the National Institute of Public Health and Environmental Protection in Bilthoven. For more than fifteen years, the researchers followed 552 men over 50 years of age and showed that the subjects drinking more than five cups of tea had a risk of stroke reduced by 69 % compared to those drinking less than two cups. However, not all studies go in the same direction, as the results of these epidemiological observations are based on samplings and statistical calculations that are quite complex to follow.
Research on the beneficial effects of green tea on cancers prevention
Several recent studies suggest that green tea may prevent the onset of certain types of cancers. Epidemiological studies of the ministry of Health in Japan have shown that the rate of mortality by cancer, including stomach cancer and colon cancer, was significantly lower in the green tea growing regions such as Shizuoka, located south-east of Tokyo. In the same way, the statistics of the ministries of Health indicate that the rate of lung cancer would be smaller in Japan than in the United States, while the consumption of cigarettes is much higher.
These results are obviously to be interpreted with caution, especially as the “tea drinkers” often have healthier dietary habits that are very different than that of most people in the western world and a consumption of alcohol much lower than the average.
Research on the beneficial effects of green tea on tumors prevention
Experimental work in vivo are currently being carried out on induced tumors in animals. In general, the administration of green tea provides protection against certain tumors of the skin and lungs. Thus the work of Zhi Wang, and Hasan Mukhtar, of the Veterans Administration Medical Center in Cleveland, clearly show the inhibitory activity of green tea when it is applied in mice having a skin lesion in addition to ultraviolet rays, B7. The control group receives only water, the groups tested will receive the green tea one week prior to treatment with UVB and during the week of treatment. The surface, the intensity and severity of lesions were significantly lower in animals consuming green tea.
In a similar experimental study, the treatment with UVB rays is followed a week later by the application of a compound that causes the development of tumors. The number of skin tumors is much lower in mice consuming green tea and the time in which the tumors fully develop and worsen is much longer. Another interesting study by D. Hoffmann, of the American Health Foundation in New York, reveals the preventive action of green tea and its active ingredient, EGCG, on a type of a lung tumor(cancer). In these last two cases the number of tumors is reduced significantly, by about 50%.
Research on the beneficial effects of green tea on neutralizing and decreasing free radicals
The green tea fights free radicals, which might in part explain its preventive effect in the occurrence of cancers. Its detoxifying effect was evaluated with a special purple colored molecule: the test is done with the DPPH 1,1-diphenyl-2-picrylhydrazyl. This is a stable compound and a free radical, which fade out under the action of chemicals and molecules that destroy free radicals, thus enabling an assessment of a inhibiting properties with a simple colorimetric measurement. The infusion of green tea shows effects comparable to that of rutoside( rutin ), a natural polyphenol used as a reference, and is superior to that of vitamin E. This activity is dramatically increased when using an EGCG green tea extract.
Finally, a recent article by a team of Toledo in Ohio shows that EGCG blocks the urokinase, an enzyme degrading protein that is overexpressed in many human cancers and appears to be involved in the dissemination of these cancers. The research approach is quite interesting: the authors have modeled a three-dimensional structure of the active site of the urokinase, and then they have queried the data banks for sculpting in this mold protein molecules that may be blocking the site.
The EGCG would have precisely the geometry required for binding to this enzyme, thereby inhibiting its biological activity. In the meantime to validate this property of green tea and use it as an adjuvant in the treatment of cancers, it can be emphasized that the absence of side effects of EGCG makes it a serious candidate in the chemo-prevention of cancers.
In the United States, the National Cancer Institute has deemed all of these results interesting enough to start phase I clinical studies on the activity of the green tea in the prevention of cancers, including colon cancer.
With regard to their effect on fat metabolism, black tea and green tea are very similar, at least in animal models. For the prevention of cancer, the green tea is, without a doubt, at the present time the right and better choice. In Europe, tea drinkers prefer mostly variations of black tea, though green tea is increasing its popularity in recent years there too. To take advantage of the chinese paradox mentioned in the beginning of this article you will have to go with green tea.
Anyway, no matter which is your favorite, whether it be green tea or black tea, they both offer excellent health benefits, so whichever you choose you can’t go wrong.
Enjoy your cup of tea!
Which type of tea you like the most? Is is black tea or green tea? Do you notice and feel any health benefits when you drink green or black tea? Share your thoughts with us in the comments below.