Green tea was originated from China and has been consumed for thousands of years. It was initially used as a natural remedy and in religious ceremonies before it became a beverage. Heavy green tea drinkers like the monks and Japanese have been known to live longer than average people. It is believe that regular consumption of tea is good because it helps to relax one's mind, decrease his need for sleep, and lightens his weight by reducing fat in the body system. These observations have been gradually proven by scientists. Today, several billion cups of green tea are consumed daily by people around the world. It has become one of the most widely consumed drinks and popular even among younger generations who are health conscious. Although the majority of drinkers are Asians, it is gaining popularity in the West as more people hear how beneficial it can be to human health. Many people who used to drink coffee or black tea with milk are now joining the trend of drinking green tea. Those who do not enjoy drinking green tea but want its health benefits can take green tea extracts in the form of supplements.
A lot of studies and research have been done on green tea extracts and their effects on health the past few decades. While most scientists confirmed the goodness of green tea, some experts expressed concerns about the potential health risks of consuming too much green tea extracts. The objective of this paper is to look at the benefits and drawbacks of consuming green tea. It also attempts to find out whether green tea is really so good and as safe as so many people claim or think it to be.
There are now many books about green tea, websites designed to inform and update visitors on green tea, as well as thousands of scientific articles, research studies and media reports on the health benefits and potential risks. This paper was based on information and data from secondary source, mainly literature review of books, journal articles searched from the Internet database and newspaper reports. Updates from government and official websites were also used.
This dissertation looks at the history of green tea, its composition, applications and uses. It then discusses the health benefits and potential risks of the green tea extracts, as well as the controversy about some of the health claims.
There are different varieties of the tea plants and as many as 500 existing species of tea grown in around 50 different countries, with China having the most species than the others. Most tea specialists prefer to cultivate the species Camellia sinensis which almost all green tea comes from. Green teas are made exclusively from the young leaves and buds of the Camellia sinensis plant. This plant is a slow-growing evergreen perennial tree of the genus Camellia, which survives in tropical or sub-tropical rainforest climates and thrives at altitudes of 2,100 meters above sea-level. The two parent strains were originated in Darjeeling, Assam and China. In order to harvest them more easily and conveniently, the trees are kept short as shrubs. There is no uniform grading for green tea. Good quality green tea consists of a leaf and a bud. The eight criteria to determine good green tea are the appearance, shape, colour, completeness, aroma, liquor, flavour and wet leaf.
Teas are classified into three major types, depending on how they are processed: green, black and oolong. Green teas are made from unfermented leaves. They are steamed, roasted, or pan-fried almost immediately after being picked. Since there is no time for them to ferment, no chemical change occurred. This is why it tends to be lighter in color and have the delicate 'green' character. Oolong teas are produced when the fresh leaves are subjected to a partial fermentation stage before drying. Black teas undergo post-harvest fermentation stage before drying and steaming. As a result of the fermentation and oxidation, many of the components in the tea leaves that are beneficial for health are destroyed during the production of black tea. Green tea is considered better than black tea or oolong tea for health reasons because it does not go through fermentation or oxidation during its production. It is the purest form of all teas.
In China, green tea leaves are allowed to dry naturally before they are roasted or pan-fried. Such treatments prevent fermentation and soften the leaves which will then be rolled and twisted to remove additional moisture. The Japanese use a steaming method before rolling, twisting and drying the leaves. China's green tea is known to be the most delicate of all with a sweet and mild grassy taste. Some of the best Chinese green tea like fine Dragonwell could result in five or more infusions. The best green teas are those picked during early spring around the time of the Qing Ming Festival. Modern tea masters could list 500 or more green teas which could be plucked and processed slightly differently to give slightly different taste.
Green tea has been used by people as a healthy and medicinal drink for thousands of years. There are many different stories about how it was first discovered. The most popular one from China dated as far back as 2737 B.C. The Chinese legend described how Shen Nong accidentally discovered the soothing taste of the beverage after a leaf dropped from a tea plant into a pot of boiling water while he was in the garden. He became very interested in the infusion and began to study about its various healing properties. Other stories of tea link it with Zen Buddhism. Whichever is true, there is no doubt that tea was originated from China. Anthropologists have reasons to believe that prehistoric humans living in the area of Yunnan chewed on the leaves of tea trees to increase their alertness when hunting. Fresh green tea leaves were gradually used by people for medicinal properties such as to treat depression, digestive and nervous conditions. During the Han dynasty, tea plants were known to be grown by monasteries in Sichuan. Some people started to steam tea leaves and then compressed them into cakes. These tea bricks would be baked and hardened so that they could be prevented from spoiling and be kept for a longer time. By the Tang Dynasty, as tea cultivation improved and trade increased, tea drinking became very popular in the upper class. Tea rules and ceremony were developed during this golden age of tea. Gradually, tea was consumed as a common healthy drink for all levels of society in China and Tibet instead of mainly used as a remedy to treat different health complaints for certain groups of people.
Around A.D. 780, a book dedicated to tea called Ch'a Ching (Tea Classics) written by Lu Yu was published. He described in great details how tea was grown, cultivated and processed. He even wrote about the utensils and proper way of tea consumption. It was Lu Yu who transformed the process of tea drinking into a form of art, which would eventually be passed to Japan by monks who travelled around Asia. As the popularity of drinking tea continued to grow in China, a tea culture began to develop in Zen ceremonies and secular society in Japan, where the tea plant was able to adapt very well. The tradition of drinking green tea involves a wide range of green tea and is still an important part of their society.
By the 12th century, tea plants were already exported to Japan on a large scale. It was until the 14th century when the culture of drinking tea was first introduced to Europe via the Silk Road and soon spread to other parts of the world. During the 1600's a Chinese ambassador brought tea to Moscow which led to a flourishing tea trade to Russia. The Manchus were in power when China was the most important trading country in the world and tea trade was a monopoly. The Portuguese were the first traders to bring tea to Europe in large scale. China was able to be a sole exporter of tea by keeping the knowledge of tea cultivation technique for a long time. It was the British, eager to learn how to cultivate tea, who uncovered the secret of growing tea outside China in the 1800s. They sent a man to China who disguised himself as a merchant. The seeds he collected in China were brought to India but efforts to cultivate them failed. However, experiments using the Chinese techniques to grow local India tea plant were successful. Since the 19th century, the British began to cultivate tea on plantations in the colonies of India and Sri Lanka. It was only then when black tea, mass-produced and sold in packets, became more popular in the rest of the world.
Nowadays, the tea plant is cultivated in many countries around the world, with China, Japan, India and Sri Lanka being the greatest producers. About 3.1 million tons of dried tea is produced every year, 20% of which is green tea.
Although green tea has been consumed by the Chinese and Japanese for such a long time, its popularity increased only gradually in the West as the health benefits became more widely known. This is because green tea research has been widely conducted only in recent years by scientists. In fact, well-publicized results of research on green tea have been available only since the early 1990s. Green tea is now one of the most popular beverage consumed by people besides water. In some places, brewed tea steeped from carefully harvested green tea leaves of delicately grown tea tree is treated like prized wine or rare coffee. As studies continue to show evidence of its benefits, green tea will continue to be sought after by more and more people everywhere. The use of green tea and its extracts by manufacturers will continue to increase as green tea's reputation keeps growing.
While the history of green tea is long and interesting, its chemistry is complex and studied by scientists only quite recently. To understand more about green tea extracts and their effects on health, it is necessary to look at the composition as well as chemical and biochemical properties of green tea.
The composition of green tea leaf is very similar to that of other fresh leaf since green tea, being the most natural form of tea, is made from unfermented leaves from the tea plant. Only a few changes to the enzymes of the leaves occur right after they are plucked from the plant and some new volatile substances are produced when they are dried.
The buds and leaves of the tea plant contain carbohydrates, proteins, lipids, enzymes and the genetic material necessary for growth and photosynthesis. The main constituents of the leaves are polyphenols, the catechin and catechin-derived antioxidants; caffeine; theobromine; theophylline; and theanine. Other compounds in green tea that affect the human health are fluoride, minerals, vitamins such as B1, B2 and C, and trace elements such as chromium and manganese.
Table 1 - Mean Composition (%) of Green Tea
|Oxidised phenolic compounds***||0|
*Data referred to dry weight of tea leaves.
***Especially thearubigins and theaflavins.
[Sources: Belitz DH, Grosch W(1997), "Qu?mica de los Alimentos." Zaragoza: Acribia]
The amount of these ingredients differs according to where the green tea is cultivated and age of the leaves. Young leaves and buds contain more caffeine while older leaves have larger amount of tannin (flavonols). Fresh green tea buds and leaves contain 75-80% water while the polyphenol components make up the remaining 20-25% of solid matter. Careful drying could prevent changes to the active ingredients of the green tea leaves whereas fermentation and oxidation that occur when black tea is processed would cause chemical changes. This leads to the major difference in the effects and taste between black tea and green tea.
Green tea extracts are herbal derivatives from green tea leaves which are used or taken orally by people. The extracts can be divided into 4 categories: a) Strong infusions - Green tea leaves are processed by soaking in alcohol solution; b) Soft extracts - the solution made by strong infusion is concentrated to 20 - 25%; c) Dry extracts - the solution from strong infusion is further concentrated to 40 - 50% solids and turned into dehydrated extract powder; d) Partly purified extracts - techniques such as solvent extraction, column chromatography, membrane extraction and separation are used to acquire more purified derivatives of green tea in order to produce supplements like green tea tablets and capsules.
The color of green tea is partly due to chlorophyll and partly due to a kind of naturally occurring compound in it, called polyphenols. These compounds are responsible for the pungency and unique flavor of green tea. They are antioxidants which is a type of phytochemical compounds found in most plants, vegetables and fruits as well as coffee, cocoa, wine and tea. Polyphenols are the most biologically active group among the tea components, with antioxidative, antimutagenic and anticarcinogenic effects. Exposure to oxygen during enzymatic process reduces polyphenols levels. Green tea has unaltered polyphenols because unlike oolong or black tea, they do not undergo oxidation. Because of this, green tea has the greatest effect on health among all teas. In green tea, polyphenols are in the form of flavonoids. The main flavonoids present in green tea are the green tea catechins (GTC) which comprise four major derivatives: (-)-epigallocatechin-3-gallate (EGCG) (represents approximately 59% of the total of catechins); (-)-epigallocatechin (EGC) (19% approximately); (-)-epicatechin-3-gallate (ECG) (13.6% approximately); and (-)-epicatechin (EC) (6.4% approximately). Catachins have a carbon structure C6-C3-C6 composed of two aromatic rings.
[Source: V. Jane, et al. (Jan 2003), "Tea Catechins and Polyphenols: Health Effects, Metabolism, and Antioxidant Functions", Critical Reviews in Food Science and Nutrition, 43(1):89-143]
The catechin content of green tea depends on how the leaves are processed, the geographical location and growing conditions (e.g. soil, climate, agriculture, practices and fertilizers), the type of green tea and the infusion (e.g. brew time, temperature) Green tea polyphenols are important for their ability to halt the damaging effects of oxidation which is a process of molecular DNA damage caused by the formation of toxic molecules called free radicals that develop in the human body. Individual catechins have different antioxidative and health properties.
Other compounds found in different plants also have antioxidative action. Catechins found only in green tea however have been proved to be more effective than many well-known antioxidants. Professor Catherine Rice-Evans of the Guy's Hospital in London carried out tests and determined that green tea catechins have greater effects as antioxidants than the same quantity of Vitamin C and E, or beta-carotene. She also ranked the catechins according to the proportion of their presence in green tea. According to her study, EGCG was the most active of the catechins, responsible for 32% of the antioxidant property of green tea. The order from most antioxidative to least antioxidative are: 1) EGCG 2) EGC 3) ECG and 4) EC.
Caffeine is a central nervous system stimulant belonging to the family of chemicals called methylxanthines. It can be found in more than sixty different plants.  Most of them have been utilized as foods or beverages by people since ancient times. Caffeine is a trimethyl derivative of purine 2,6-diol. It was first discovered in coffee by Runge in 1820 and later isolated from tea by Nakabayashi. Caffeine content is usually 2.5-4.5% in dry green tea leaves. The amount of caffeine in green tea drink is about 1/10 to 1/5 of that in brewed coffee.
[Source: V. Jane, et al. (Jan 2003), "Tea Catechins and Polyphenols: Health Effects, Metabolism, and Antioxidant Functions", Critical Reviews in Food Science and Nutrition, 43(1):89-143]
Caffeine has a strong effect on the brain and muscles which is why drinker will experience a mental boost shortly after drinking tea. The amount of caffeine varies among different types of tea. Black tea has the greatest amount whereas green tea contains only one-third the caffeine of black tea. It has been shown in many studies that caffeine improves cognitive performance and certain aspect of memory. Besides mental health, caffeine may also helps to enhance one's emotional health, for example, making the drinker feel energized and motivated to work. Caffeine is known to be a cardiac stimulant and a diuretic. It also stimulates the cerebral cortex, causing excitation in the central nervous system. However, it may have adverse effects on some people and its intake could cause health risks instead of benefits. Because of that, this component is often removed and excluded when green tea is extracted for applications such as health supplements.
Besides polyphenols and caffeine, the two most commonly known components, green tea also actually contains many nutrients, including different kinds of vitamins and inorganic compounds.
Commercial green tea leaves contain about 280mg of Vitamin C (VC, ascorbic acid) per 100g of dried leaves. The content of Vitamin C in green tea can be ten times that in black tea because the vitamin is partly destroyed during fermentation, which green tea does not undergo. Other vitamins found in green tea in different amounts are Vitamin B2, Vitamin D, Vitamin K, and carotenoids.
There are many minerals in green tea such as calcium, iron, copper, sodium, zinc and potassium. Green tea can also be a rich source of selenium if it is grown in a soil rich in this essential mineral. Another important mineral found in green tea is manganese which is used by the body in digesting protein as well as maintaining healthy bones and connective tissue. Green tea also contains a lot of fluoride - the mineral known for fighting dental cavities.
The amounts of aluminum in green tea leaves are higher than any other plants. Fortunately, the tea plant is able to biochemically neutralize the toxicity of aluminum, which exists mainly in a chelate form, which is less absorbable than the ionic form, with less potential to cause adverse effect on health. Experiments on animals and people also confirm that tea catechins can prevent the damage caused by accumulation of aluminum in the bones.
"Some specific inorganic compounds in the tea plant are aluminum, fluorine, and manganese."
Table 2 Inorganic Elements and their contents in green tea leaves (per 100g dried leaves)
|N||3.5 - 7.1
|Al||420 - 3,500
|P||0.2 - 0.7
|As||0.20 - 0.42
|K||1.6 - 2.5
|Ba||1.3 - 5.1
|Ca||0.12 - 0.57
|Br||7.8 - 25.0
|Mg||0.12 - 0.30
|F||17 - 260
|S||0.24 - 0.48
|Na||20 - 33
|Fe||100 - 200
|Ni||1.3 - 5.9
|Mn||500 - 3,000
|Pb||2.2 - 6.3
|Cu||15 - 20
|Rb||8 - 44
|Mo||0.4 - 0.7
|B||20 - 30
|Se||1.0 - 1.8
[Source: "Standard Tables of Food Composition in Japan", Resources Council, Science and Technology Agency, Tokyo, 1991]
The content of total nitrogen in green tea extracts ranges from 4.5 to 6%. Half of that are free amino acids, which are the building blocks of protein. The amount of amino acids in tea leaves harvested during spring time is larger than that during other seasons. Green tea contains some common amino acids like aspartic acid, glutamic acid, glycine, tyrosine etc. as well as an amino acid that is unique to it: theanine.
Green tea has four basic tastes: sweet, sour, salty and bitter. There is in fact a fifth taste known as unami which is contributed by the amino acid l-theanine. This constituent was only identified in 1949, by a Japanese who discovered that theanine makes up about 50% of the free amino acids present in tea. Young tea buds harvested in early spring contain a lot more theanine than tea leaves harvested later in the year because the theanine are converted into catechins as the leaves mature. Green tea experts rate the unami taste most highly and consider it to be the most important factor in determining the quality of the tea. High grade green tea is more soothing to drink than lower grade ones because the l-theanine can decaffeinates tea naturally, making it taste less bitter. Scientific studies using electroencephalography show that if 8 times more theanine is present than caffeine, the effect of caffeine will be blunted. Studies have also shown that theanine increases production of dopamine in the brain, giving the drinker the sense of alertness while feeling relaxed.
Aromatic oils play a major role in determining the fragrance of green tea. The oils accumulate as the tea leaf grows and evaporate during and after harvest of the leaf. For green tea, some aromatic oils remain in the final tea product, contributing to the taste of the tea. About 500 different aromatic oils have been identified in tea leaves.
Total carbohydrates in green tea leaves are about 40%, one third of which is cellulosic fiber. Starch is also contained in green tea. Tea leaves harvested in the morning when there is less starch are considered to be better in quality.
Green tea leaves has an average of 4% oil by weight. The seeds of tea also contain oil of around 20-40% by weight. The oil is nondrying and has a solidifying temperature of -5 to + 15?C.>/p>
Since the 1990's, scientists in different countries, particularly Japan, have almost suggested that every system of the body can be benefited by green tea consumption. The polyphenols are known to reduce the risk of cancer before genetic mutations occur by neutralizing free radicals, prevent cardiovascular disease by preventing LDL cholesterol from changes that promote heart disease, and protect the body from various other illnesses. As more people around the world hear about these benefits, it has become increasingly popular for those who want a healthy life style to drink green tea as beverage or take green tea extracts as supplements.
Free radicals are highly reactive molecules that could damage the body and lead to many diseases if left alone. They take an electron form another molecule, turning it into another electron-deficient free radical that can take an electron from a third molecule and so on, leading to a chain reaction. The human body has a number of antioxidant molecules that help to defend it against degenerative diseases, but sometimes they may be overwhelmed by the free radicals. Antioxidants are substances that patrol the body and quench free radical reactions.  The antioxidant property of green tea extract is the most basic of all the health benefits of green tea.
Many plant foods provide an abundant source of antioxidant nutrients. Polyphenols in green tea are among the most effective. Gramza Anna et al. examined the antioxidative activity of several biologically active components from plants to find which are safe for people and showing high antioxidant activities if added to food with lipids such as lard. Results show that the 1000ppm green tea ethanol extract inhibited the oxidation process most strongly among samples of green and black tea leaves. It was observed that the antioxidant activity was higher in tea extracts containing high levels of ECG, EC and C.
The US Department of Agriculture (USDA) analysed nearly 400 foods for their EGCG content and published a report in 2007. It showed that regular green tea contains the highest concentration of antioxidants, followed by decaffeinated green tea, flavored green tea and instant or bottled green tea. That USDA study also showed why green tea is the best way to ingest antioxidants. One gram of green tea steeped in 100 millimeters of water yields 127 milligrams of catechins whereas 100 grams of dark chocolate contains only 54 milligrams, blueberries 52 milligrams and black grapes just 22 milligrams.
Since tea contains higher levels of antioxidants than many fruits and vegetables, green tea consumption can protect the cells in the human body from damage caused by free radicals. Flavonoids, act as antioxidants, through four possible mechanisms: "1) as reducing agents, disarming free radicals. 2) by donating hydrogen molecules to prevent the formation of free radicals. 3) by quenching singlet oxygen that would otherwise act as a free radical in the body. 4) by binding with metals that could otherwise initiate the creation of free radicals."
Among the four polyphenols in green tea, EGCG has been found to be particularly effective as an antioxidant. Researchers from Rutgers University concluded that "the strong antioxidant activities of green tea are mainly due to the higher content of EGCG" after comparing the antioxidant effect of various polyphenols in green tea and oolong tea.  Studies of the effects of tea consumption in people confirm evident that green tea is the most effective scavenger of free radicals among the different types of tea. In one study, five adults each drank two cups of green tea while five others drank the same amount of black tea. Both green and black teas improve the antioxidant capability of the blood, but green tea was found to be six times more powerful. Scientists also found that fresh green tea extracts is a better scavenger of singlet oxygen than stale green tea extract. Green tea polyphenols are also effective in quenching other free radicals such as hydrogen peroxide and superoxide.
Diabetes mellitus is known to affect the structure and function of myocardium, causing increased collagen in the heart and reducing cardiac function. Babu and his team from India found that the antioxidant enzymes of diabetic rats are not sufficient and efficient enough to reduce the oxidative stress caused by hyperglycemia. In 2006, their investigation showed that green tea treatment is effective in controlling the antioxidant system in the heart and aorta by alleviating lipid peroxidation. In 2007, their studies suggested that administration of green tea extract may improve myocardial collagen changes in diabetic rats. They believe that the antioxidant, antihyperglycemic, and hypolipidemic effects of green tea catechins may be responsible and concluded green tea may provide a therapeutic option for the treatment of cardiovascular complications in diabetes.
The majority of the world's 33 million HIV cases were infected through heterosexual sex with 96% of new infections occurring in developing countries. Therefore ways to fight the spread of HIV in poor countries are extremely necessary. Previously, scientists have carried out lab tests and reported that EGCG may prevent HIV from binding to the T-cells in the immune systems protecting them from HIV's damage. Although they knew that EGCG inhibited HIV in test tubes, they did not know if the findings would be useful beyond the lab.  Just recently, researchers in Germany have found a practical way to use EGCG to help prevent the spreading of AIDS. The researchers found that EGCG was capable of neutralizing a protein in sperm that served as a vector for the transmission of the virus that causes AIDS during sex. They say that the use of green tea in vaginal creams could provide a simple and affordable way to reduce cases of HIV infection.
Parkinson's disease is a progressive, degenerative disorder of the central nervous system resulting from loss of dopamine-producing brain cells. A research team led by Professor Zhao affiliated to the Chinese Academy of Sciences Institute of Biophysics using an animal model of Parkinson's disease discovered that green tea polyphenols can protect dopamine neurons. He hopes that green tea polyphenols may eventually be developed into a safe drug for Parkinson's disease in humans.
In an article published by the Journal of Neuroscience, researchers from University of South Florida reported that EGCG prevented Alzheimer's-like damage in the brain of mice genetically programmed to develop the neurodegenerative disease process. They work by decreasing production of the Alzheimers'-related protein called beta-amyloid which causes nerve damage and memory loss when accumulated abnormally in the brain. The researchers think that a new generation of dietary supplements containing pure EGCG might be beneficial for treating Altheimer's disease.
Like Alzheimer's and Parkinson's, Huntington's disease is also a type of neurodegenerative disease caused by protein misfolding characterized by jerky and uncontrolled movements. Mutant proteins are accumulated in the brain of sufferers and become toxic to the nerve cells in the brain. A research in Germany found that EGCG could interfere with the early events of this process by inhibiting the aggregation of mutant huntington protein.
Cancer is one of the greatest causes of death for both man and women, killing more than six million lives worldwide every year. It develops in three stages: 1) Initiation - a substance called a mutagen or carcinogen alters a healthy cell. 2) Promotion - a substance called a promoter encourages abnormal cell to multiply. 3) Progression - the abnormal cell growth, now called a tumor, increases in size and may spread to other parts of the body.
70% to 90% to all cancer cases are initiated or promoted by factors in one's diet and lifestyle as well as the environment. Approximately two thirds of all cancer cases could be prevented if all the risk factors were avoided. For example, reducing total fat intake, stop smoking and avoiding too much sun exposure.
Many years ago, epidemiologists and scientists who studied the risk of disease and death among different groups of people discovered that Asians have a lower risk of getting certain diseases that are common in the West. Even within Asian countries, something in the diet seem to affect disease rates. For example, in Japan, the tea producing region called Shizuoka where people drink more cups of green tea than the average Japanese, have much lower cancer rates. Results from other studies seem to indicate that green tea in some way lowers the risk of cancer. Green tea reduces cancer risks by increasing a person exposure to certain cancer fighting compound called anti-carcinogens. These chemo preventive agents are generally extracted so that they can be administered more conveniently. Compared with pharmaceutical drugs, green tea extracts have one big advantage in cancer treatment. It is less potent and safer to use.
The anticancer properties of green tea during various stages of cancer development have been studied by many scientists. Cancer researchers believe that cancer is a result of the accumulation of cell damage which is often caused by free radicals. Intake of external free radical quenchers such as Vitamin C or the antioxidants found in green tea would help the body defense system greatly.  Cancer occurs because of mutagenesis caused by different physical, chemical and biological causes in cell's DNA. Scientists believed that tea polyphenols have a strong radical scavenging and reducing property. They scavenge radicals produced by cancer promoters, making them harmless. In the digestive tract, they could prevent the production of cancer causing nitroso-amine by reducing nitrite. They also tend to form strong bonds with proteins which at low concentrations could inactivate enzymes and viruses including some cancer causing viruses. These are the reasons why green tea is promoted as a healthy way of preventing cancer.
A study published in the Journal Food & Chemical Toxicology described how green tea extracts may prevent cancer by inhibiting the activation of carcinogens.  High levels of green tea intake may provide some benefits in preventing cancer of the digestive tract, especially gastric cancer. The green tea catecheins expecially EGCG have been found to inhibit carcinogenesis of the skin, lung, esophagus, stomach, liver, small intestine, colon, bladder, prostate, and mammary glands in animal models.
Many women suffer from breast cancer due to different risk factors, for example, family history of breast cancer, onset of menstruation before twelve and beginning of menopause at a late age etc. A relationship between green tea and lower risk of breast cancer was first discovered when epidemiologists noticed that Japanese women who have adopted an American diet after moving to US quickly changed from having low breast cancer risk to higher risk like the average American women. Some people began to study whether including green tea in the diet of American women could lower their chances of developing breast cancer.  Laboratory studies indicate that green tea extracts particularly EGCG inhibit growth of cancer cells in mice by interacting with tumor promoters, hormones, and growth factors to stop the spreading of cancer cells.  At Nagoya City University Medical School in Japan, scientists found that green tea polyphenols is the best among naturally occurring antioxidants in preventing breast cancer.  In Australia, researchers compared diets of women who had breast cancer with those who do not. The data show that drinking green tea regularly seems to be useful in breast cancer prevention.
Just recently in June 2009, researchers in US conducted a study testing polypehnon E effects in green tea. The study involves 26 men taking four capsules a day for a month before they had suggery to remove their prostate glands. The results show of decrease of up to 30% in the levels of proteins that tumors use to grow. It was not exactly clear if the green tea extract really can shrink tumors but the team was certain that it helped to keep cancer from growing very fast.
Very recently in May 2009, researchers at Mayo Clinic suggest that EGCG may increase the survival chance of patients with chronic lymphocytic leukaemia (CLL). In the clinical trial, 33 patients with the aggressive form of the disease were given 8 different doses of Polyphenon E. The majority of the participants with enlarged lymph nodes saw a reduction in the size of swollen lymph glands and decline in lymphocyte count (the number of white blood cells). The trial show that the patients could tolerate green tea extract at very high doses, and many of them saw regression to some degree. The researchers hope that EGCG may stabilize CLL for patients in the early stage or improve the effectiveness of treatment by combining it with other therapies.
Cardiovascular diseases include different conditions affecting the heart and blood vessels, such as heart attack, stroke and hardening of the arteries. According to the National Cholesterol Education Program, the risk of cardiovascular disease varies with the person's blood cholesterol levels. For example, if one's total cholesterol level is 200 and HDL-cholesterol is 50, then this person has a ratio of 4.0 to 1, which means "a low to moderate risk of developing cardiovascular disease".
Table 3 Risk levels associated with cholesterol levels
|Low Risk||Moderate Risk||High Risk|
|Total cholesterol||Less than 200||200 to 239||More than 240|
|LDL-Cholesterol||Less than 130||130 to 159||More than 160|
|HDL-Cholesterol||More than 50||40 to 50||Less than 35|
|Ratio of Total to HDL||Below 3.5 to 1||4.5 to 1||5 to 1|
*All measures are in milligrams per deciliter of blood. These categories apply to adults age 20 and above.
[Source: Report of the National Cholesterol Education Program Expert Panel on detection, evaluation, and treatment of high blood cholesterol in adults. Achieves of Internal Medicine. 148: 36-69, 1988]
Green tea has been shown to lower Low-density lipoprotein (LDL) cholesterol and serum triglyceride levels. The antioxidant effect of green tea inhibits oxidation of LDL cholesterol in the arteries. Green tea inhibits abnormal blood clot formation (thrombosis) which is the leading cause of heart attack and stroke. It works by specifically inhibiting platelet aggregation and adhesion. Green tea also raises levels of High-density lipoprotein (HDL), the good cholesterol that helps the body remove atherosclerotic plague from walls of arteries.
In Japan, the Ohsaki National Health Insurance Cohort Study conducted studies involving 40,530 adults over a period of 7 years. It was found that women who consumed 5 or more cups of green tea per day had a 31% lower risk of dying from cardiovascular disease than those who drank less than one cup a day. For man who drinks much more green tea, a reduced risk of 22% was observed. The researchers also concluded that green tea-loving groups are also less likely to develop clot-related strokes.
Many research findings strongly suggest a relationship between the flavonoids in green tea and reduction of heart disease. For example, a Japanese epidemiologist did a survey interviewing 1,371 men aged 40 and above to collect data related to their diet lifestyle and average daily consumption of green tea. It was found that men who drank ten or more cups per day had significantly lower levels of cholesterol in their blood. Those who drank the most green tea had low levels of LDL-cholesterol and high levels of HDL-cholesterol. Additionally, those who smoke heavily but were dedicated green tea drinkers had lipid peroxide profiles similar to those who do not smoke, indicating that green tea was able to counteract the damaging effects of tobacco in cigarettes.
Chinese doctors treating patients with various cardiovascular diseases have reported favorable results using green tea supplements to lower the rate of occurrence of heart disease. After substituting anti-clotting medications with daily supplements of polyphenols, all of the 40 patients showed reductions in their tendency to form blood clots and thus had reduced risk of heart attack or stroke. Another group of patients in China diagnosed with symptom of atherosclerosis (hardening of the arteries) was given green tea polyphenols in addition to their medication for one month. It was reported afterwards that the symptoms of attacks of chest pain were controlled in 71% of the patients involved.
The loss of arterial elasticity is one cause of high blood pressure. Green tea inhibits thromboxane production which is one cause of arterial constriction. Another cause of hypertention is an enzyme secreted by the kidneys. Green tea is a natural inhibitor of this enzyme.
In the olden days when manometer was not yet invented to measure blood pressure, some people seem to have already noticed that tea consumption could alleviate symptoms of hypertensive circulation in the brain. For example, a seventeenth century tea house in London described the benefits of drinking tea as follows: "It helpth the headache, giddiness and heavyness thereof".
When starch is consumed, the enzyme amylase breaks it down into simple sugars. Sugar is the primary culprit in the accumulation of body fat. High blood level of glucose and insulin are some of the causes of diabetes and cardiovascular disease. Green tea catechins have been shown to inhibit amylase activity.
Throughout history, people from different cultures like to have a cup of tea during or after a meal. Besides enjoying the pleasant taste of the beverages, the habit of drinking tea has also been known to help digestion. The digestive system of the human body includes the esophagus, stomach, small intestine, pancreas, gallbladder, liver and large intestine. Most of the breakdown of the food occurs in the stomach and intestine. Green tea polyphenols affect carbohydrate metabolism by first inhibiting the function of the enzyme in the saliva. They then inhibit the enzymes necessary for carbohydrate digestion in the small intestine. Thirdly, green tea extracts alter the mechanism that brings glucose across the intestinal wall. As a result absorption of carbohydrates is reduced and blood glucose levels are reduced. This function would be beneficial for people who have conditions like diabetes or obesity.
Tea polyphenols are believed to be able to control body weight without affecting the drinker's appetite. Weight loss experts claim that green tea can reduce the rate and amount of carbohydrates absorbed by the body without the risk of malnutrition because slow release of carbohydrates caused by green tea can prevent sharp rise in blood insulin levels. This would lead to fat burning instead of fat storage. After reviewing several experimental and clinical studies, Shixian Q et al. concluded that green tea extract rich in EGCG is associated with increased weight loss due to diet-induced thermogenesis. They reported that in vitro, green tea extract excert a stimulation of thermogenesis while in human studies there was significant increase of energy expenditure lowering of body weight decrease in waist circumference, and no change in heart rate for blood pressure.
Previous study have shown that green tea consumption promote fat oxidation in humans at rest. It also prevent obesity and improve insulin sensitivity studies using mice. Venables et al. decided to look at the effects of acute ingestion of GTE on glucose tolerance and fat oxidation during exercise in humans. They found there was indeed an increase possibly through the increase in lipolysis, leading to increased availability of fat as a fuel. They also concluded that acute GTE ingestion can improve insulin sensitivity and glucose tolerance in health young men.
In France, researchers gave green tea extract supplements to a group of moderately obese individuals for a period of time and later found that their body weight dropped by 4.6%.  The results were even more impressive when some of a group of obese middle-aged women who were dieting took green tea supplements with their meals for one whole month. Those who took the green tea supplements were found to have lost weight 3 times than those who were simply dieting without taking the supplement. The Coca-Cola Company recently introduced a green tea drink that contains both EGCG and Caffeine, as well as other plant extracts. This drink called Enviga is claimed to be able to speed up metabolism and promote weight loss.  In Japan, there is also a new Coca-Cola with green tea flavor and has no calories. It targets health-conscious women in their 20s and 30s.  However, drinking a cup of green tea directly will probably get the same effect and cost less.
Furthermore, green tea can protect the digestive tract by preventing carcinogens from harming the stomach, intestine and colon. Dr. John H. Weisburger from the American Health Foundation reported that adding green tea to meats or fish during cooking may be a way of blocking the formation of certain carcinogens formed during preparation process such as by frying the food.
Many people suffer from indigestion once in a while as a result of eating too much, eating too quickly or after eating certain foods. Besides avoiding such conditions or foods, drinking green tea may also ease the symptoms of indigestion such as heartburn, bloating and gas as well as upset stomach.
Many factors can cause diarrhea other than upset stomach after eating too much oily food, for example infections of the intestines. Green tea is also known to promote friendly bacteria necessary for healthy intestine. In the human intestine, there are 100 trillion viable bacteria of 100 different species. A balance between the beneficial and detrimental kinds of bacteria in the intestinal flora could be achieved by a well-balanced diet. Green tea catechins have been shown to have anti-bacterial effects against floral bacteria and most tea polyphenols are thought to remain in the intestine. Therefore intake of green tea could have beneficial effects on intestinal flora and reduction of fecal odor.
Fecal odor is one of the major problems faced by nursing homes. The ordor of the residents' feces can be very unpleasant and lessening that would improve the living environment for everyone. In a series of experiments, Japanese scientists found that more than 50% of the catechins ingested orally are excreted via feces which shows that most of tea catechins past through the intestinal flora. In one study, the effects of green tea catechins on fecal flora were investigated in elderly patients. All subjects in the study received the same daily diet of liquid alimentation, supplemented with different doses of tea catechins for a continuous period of time. The amount of tea catechins given to them was equivalent to the quantity contained in 5-6 cups of green tea. Fecal specimens were collected after one week. Favorable results were obtained with much reduction of fecal odor and increase of feces volume. In the follow-up studies, catechins tablets were given to the elderly residents. Identical results were achieved, and confirming the previous findings of beneficial effects of tea catechins on fecal conditions.
In another study, a group of 37 volunteers were given catechin capsules to ingest daily for 12 weeks. Before the experiments, 50% of the group said they have regular bowel movements. After the experiment, 80% of them reported to have regular bowel movements. All of those interviewed afterwards reported favorable improvement in their bowel conditions.
In the 1990s, Ishihara examined the effect of green tea extract on farm-raised calves suffering from diarrhea caused by bacterial infection and parasites infection, viruses etc. They found that green tea extracts has a distinct effect in curing and suppressing diarrhea. As a result of that study, use of green tea polyphenols as a remedy for diarrhea is now not only for calves but also for milking cows
There is a traditional saying "Drinking green tea makes our mouth clean." As green tea has antibacterial property, it is often consumed after meals to kill bacteria in the mouth that cause cavities and bad breath. Many years ago in Japan, a group of scientists first observed that drinking green tea after school lunch could result in a decrease of dental caries problems in children. It was originally thought that the fluoride in green tea was responsible for the anti-caries effect. Later, several green tea polyphenols were found by other scientists to be responsible for preventing dental caries and periodontal diseases induced by the bacteria cariogenic streptococci Streptococcus mutans.
The antiviral activities of EGCG have also been reported in many studies. After many tests and clinical trials, the U.S. Food and Drug Administration (FDA) approved in 2006 an Ointment produced from partially purified water extract of green tea leaves as a prescription drug for the treatment of genital warts, one of the most common and fastest spreading venereal diseases caused by human papilloma viruses (HPV).  A more recent study indicated that GTE are efficient Hepatitis B virus (HBV) inhibitors and suggest that GTE could be a candidate agent in treating HBV infection.
For people suffering from rheumatoid arthritis, their own immune system attacks the body's movable joints causing inflammation, swelling and pain, even deforming the joint area, often making simple daily activities difficult. Dr. Salah-uddin Ahmed from the University Michigan Medical School recently reported that EGCG is a potent anti-inflammatory molecule which can inhibit production of several immune system molecules responsible for inflammation and joint damage. The compound was also found to be able to suppress the inflammatory products in their connective tissue. More tests are being done to see how the green tea compound can be used in therapy for people with the condition.
One major goal for most people would be to age healthily and be free from diseases. To achieve this, a healthy lifestyle including good food, lots of exercise and minimal stress is being promoted by many health experts. Nutritionists would say that what one eats and drinks during one's lifetime would influence the person's life span. There has been a lot of evidence showing that drinking green tea may promote longevity. Preventing the production and accumulation of active oxygen and lipid peroxides in the body is one way to slow down the aging process. Besides people who are active or those who spend a lot of time outdoors, the elderly tend to be dehydrated when exposed to hot temperatures. Studies on the benefits of green tea by various groups including the elderly are necessary and ongoing.
As more and more people realize that green tea has so many beneficial health properties, new products and uses are being introduced in the market, even in different forms for those who do not like to drink tea but want to get its benefits.
There are different types of supplements: 1) Green tea diet patch, which manufacturer claim can be worn to melt fat away. However, green tea is not fat soluble, so skin absorption is extremely inefficient. 2) Green tea fat burner, these are administered orally to give weight loss effects. But since tea supplements are not considered drugs and do not protected by FDA, manufacturers are not required to do any testing. These products may contain inferior ingredients. 3) Liquid green tea extract is a new idea with convenience as its main attraction. Manufacturers claim that a drop of the liquid extract into a water bottle would create a beverage with chemical composition resembling that of a real green tea. 4) Green tea powder was first developed in the 1930s to produce instant tea but it was until the late 1950s when they were commercialized with flavors added. Although convenient and tasty, instant green tea may lack antioxidants and may have a high level of fluoride. 5) Matcha green tea is produced by grinding tea leaves into fine powder and added to a cup of water then whisking it to frothy perfection. True matcha is made from the best Japanese green tea called gyokuro.  Matcha green tea seems to be the safest among the five types and most popular in the market. Many products have matcha green tea as a food flavor while restaurants offer varies matcha food and drinks such as matcha icecream and milkshake.
Consumer awareness of the benefits of green tea and its extracts continues to rise as the number of studies showing the benefits of catechins keeps growing. There were only 430 papers in 2000. By 2003 there were almost 1500. The demand of green tea extracts in Europe has also been great, reaching 500 metric tonnes in 2003. Many manufacturers of catechin supplements have gained a strong position in the supplement market.
One cup of green tea typically has 142milligrams of EGCG, 65 milligrams of EGC, 28milligrams of ECG and 17milligrams of EC. Supplements of green tea extract often provide the consumer with amount of polyphenol equivalent to 4 cups of tea or even more. Usually caffeine is removed from the supplement.  To be cautious, some experts suggested people to take daily dose of supplement that is approximately equal to two cups of green tea per day or the equivalent of 200-400mg EGCG per day. Green tea extract varies among different brands. It is important for consumer to read the labels carefully when choosing their products and make sure that the recommended dosage is not exceeded.
Because of the antioxidant properties of tea polyphenols, green tea has caught the attention of food industry. It is used as a healthier natural additive in food with high water content as well as cooked products due to their water solubility and resistance to heat degradation.
Two categories of green tea extracts are used industrially for different purposes: 1) Polyphenons which are extracts of green tea made up of tea catechins only, without other constituents; and 2) Sain-catechins, polyphenons diluted in large quantity of liquid, water or oils.
Polyphenons are sometimes used to suppress the fading of natural food colors, such as beta-carotene in corn oil. Some polyphenons which have bactericidal potency, are also useful in preventing PET (Polyethylence Terephthallate) bottled soft drinks of neutral pH from being contaminated. The addition of less than 100ppm of polyphenons into mouthwash or chewing gum could act as deodorizer against the compound that causes bad breath; Sain-catechins are mainly used to help preserve various foods and cosmetics. It is used widely in Japan's fish industry to prolong the shelf life of fish fillets. Polyphenons and sain-catechins are also used in other products such as antiflu air purifier, soap, kitchen deodorizer etc.
Many researchers have tried to use tea catechins in various ways, but sometimes not successful. Wang et al. tried to incorporate green tea extract into bread to see if it is possible to turn bread from a traditional staple food into a source of the beneficial catechins. Unfortunately after doing many experiments and trials, they concluded that adding GTEs to bread made from the unfrozen dough process have significantly adverse effects on the quality, producing a bread with reduced volume and firm crumb texture. 
Because tea polyphenols can prevent dental caries, they are now added to many food products such as chewing gums, candies, caramels, jelly beans, beverages etc as a dental carries prevention agent.  Besides food for humans, tea catechins are also added to pet foods to promote good health and to reduce fecal odor and caries in animals. 
All kinds of green tea soft drinks with different flavours are also appearing in bottles, and sold at supermarkets as well as convenient stores everywhere. Like the new Coca-Cola with green tea flavor mentioned earlier, the bottled green tea drinks target the younger generations and consider it trendy and healthy to drink green tea softdrinks. Many commercials for these green tea beverages often use teenagers' idols as their spokesmen to increase sales. However, a stability study done have shown that GTC was stable in water at room temperature. When GTC was added into commercial soft drinks or sucrose solutions containing citric acid and ascorbic acid, it exhibited varying stability. This find suggested that other ingredients used in the production of green tea soft drinks might interact with GTC, affecting its stability and biological activities. People may probably get more health benefits by drinking traditional green tea, which cost much less.
Few years ago the Hong Kong Consumer Council looked at the content of 30 different brands of popular bottled green tea soft drinks after mainland reported that some bottled green tea drinks contained less than one-thirtieth of the polyphenols needed to make them considered as healthy drinks. The Consumers Council found that the polyphenol content was in 25 of the samples was below 0.1% of the drink whereas a traditionally brewed cup of green tea should have 0.2% to 0.27%. The drinks may also be containing more sugar than people expected.  So, the consumers who bought the green tea bottled dinks, wanting to have a healthy beverage with a green tea soothing taste, may not get any health benefits as they intended.
It has been noted by researchers and warned by experts that while green tea has many health benefits, it also has some drawbacks and potential risks for certain people. Consuming too much green tea can cause some side effects which can be classified into three main types: 1) Those related to caffeine; 2) Those related to EGCG; 3) Those related to supplements.
Ordinary healthy people do not have to worry about the content of caffeine in the recommended dose of 250-mg of green tea extract per day. For patients with cancer or hepatitis, a daily intake of 5 to 8 times the normal dosage might be needed for the green tea extract to be effective. However, such a dosage might contain too much caffeine for people to tolerate, especially cancer patient who should avoid caffeine. This is why many manufacturers would offer decaffeinated green tea extract.  Although green tea extract have been shown to have healthy benefits and medicinal properties, it should not be used in place of professional medical care. Some studies found that females who drink more coffee during pregnancy are likely to give birth to babies that tend to be nervous and restless because caffeine causes anxiety. Even green tea should be avoided.  That's why doctors would not recommend pregnant or lactating women to consume green tea. 
For some people caffeine causes irritation in the gastrointestinal tract or sleeping disorder.  Several other negative effects have also been attributed to caffeine intake, e.g. diarrhea, anxiety, heart burn and irritability. Since tea contains much less caffeine than coffee, it is less likely to produce the adverse effects. To completely avoid caffeine intake, it is often removed by various methods to produce caffeine free green tea supplements. 
Some experts also recommend females with fibrocystic breast disease to stay away from drinking coffee and tea, including green tea. Green tea is not the culprit itself, the caffeine it contains is believed to be indirectly linked with symptoms of painful lumpy breasts. For these women, drinking decaffeinated tea or taking caffeine-free green tea supplements might still be recommended for the intake of the cancer-fighting polyphenols. Women who have premenstrual syndrome (PMS) like mood changes, weight gain, swelling, and cravings several days before menstruation are also advised to avoid caffeine. A team of researchers from US and China investigated the green tea drinking habits of 188 young Chinese women. Tea was the only source of caffeine. The ones who drank green tea more frequently were found to be more likely to suffer from PMS. 
Green tea and coffee, being two of the most widely consumed beverages in the world, are often compared for their properties and benefits. Both tea and coffee plants belong to the evergreen family that could develop into fairly large trees if allowed to grow. Both are kept at a height of a shrub in order to be harvested more easily. Both plants produce a drink that contains caffeine and their methods of preparation are very similar.
While green tea has catechins, potent antioxidants that neutralize free radicals, coffee contains mainly chlorogenic acids. In some studies, coffee has been shown to reduce the risk of diabetes, Parkinson's, colon cancer, asthma and depression, green tea is effective in preventing all these and many more. Many of the benefits of coffee come from caffeine. However, too much caffeine can make people nervous and jittery. Green tea allows the drinker to enjoy the benefits of caffeine without the jitters. This is because theanine in green tea but not found in coffee, relaxes and soothes the drinker while the caffeine causes the energy boost. Also, tea catechins are capable of combining with caffeine in hot water to make it less active. According to Mayo Clinic, caffeine can act as a moderate appetite suppressant. But because people usually drink coffee with milk and sugar to improve the taste, they are adding calories. On the other hand, good quality green tea has a naturally sweet taste and special fragrance, so sugar is not needed and therefore green tea consumption is less fattening. Green tea can stimulate metabolism much more than coffee because EGCG and caffeine can work better together.
To study the safety of green tea catechins, samples were given orally to mice to find out their LD50 (50% lethal dose). It was found that EGCG when taken orally in its pure form has an LD50 of more than 1g/kg body weight whereas Polyphenon 60- a kind of commonly used polyphenons, which have amount of tea catechins equivalent to more than 1000 cups of green tea, has an LD50 of 2856 mg/kg. For human, that would be around 143g/50kg body weight of Polyphenon 60. Yukihiko concluded that oral intake of tea catechins will not have any acute or lethal toxicity.  In another experiment, in order to look at the safety of tea catechin intake on the lifetime basis, rats were fed catechins continuously for a long period of time. Some of them were given the equivalent of 100 cups worth of catechins intake every day for almost a quarter of a lifespan in human beings. The rats were then killed after 6 months and various organs were studied. Overall results showed that there was only light degeneration in the liver of catechin fed groups was observed and there was no fibrosis or necrosis. It was concluded that huge amount of catechin intake over a lifetime will not harm human beings.  Hara believed that it would be safe to say that catechins intake in daily amount less than that contained in 20 cups of tea (1-2g catechins a day) will not be toxic for humans.
There have been some experiments showing EGCG causing liver, kidney and gastrointestinal toxicities in rodents and dogs giving high doses in the laboratory. Researchers from the Rutgers University in US reviewed available information on the toxic potential of polyphenols and looked into the hepatic and intestinal toxicities of high doses of tea catechins as well as the potential DNA damaging effects and leukemiogenic activities of flavonoids. They noted that in reports of people with liver toxicity after having overdose of green tea supplements, the symptoms disappear when the parients stop taking the pills and reappeared they started to take the supplements again. They warn that people with liver diseases such as hepatitis or cirrhosis may be at greater risk of getting the toxic side effects of green tea polyphenols when taking in large doses. They concluded that while the polyphenols in green tea may be beneficial in preventing heart disease and cancer, they can cause liver and kidney damage if consumed in very large quantities. Further studies on potential adverse effects of green tea polyphenols are necessary.
Particularly in China and Japan, some people have been reported to consume more than 10 cups of green tea a day. These heavy tea drinkers are taking almost 1g of tea catechins every day. Since green tea catechins are also used widely for consumption in capsules, tablets and in foodstuff, it is important to determine the safe use of green tea. 
Green tea extracts have been used as health supplements and sold around the world. The quality of green tea supplement is an important factor to take note of.  There are good and bad tea extract, for some people, a high quality tea supplement may provide an excellent way to get the maximum health benefits of green tea conveniently. Unfortunately, green tea supplement are not regulated by the FDA, so there are many sub-standard products in the market everywhere around the world. 
In the United States, companies that produced medicinal drugs are required to provide results from tests to the FDA to show their products are safe and effective before they can be sold. Companies that make supplements on the other hand do not have to produce evidence of safety or health benefits to the FDA before selling their products. Many of the green tea supplements may not have been tested to find out whether there will be harmful effects when they are combined with medicines and foods. Moderate intake of green tea and its extracts should be safe in general. However, for some people allergic reactions or other problems may occur when huge amounts are consumed. 
While there are numerous epidemiologic studies on the health benefits of green tea supplements, the numbers of studies on the toxicity of green tea polyphenols are relatively fewer. Supplements of l-theanine are believed to be very safe with no side-effect or adverse reaction. Their benefits include lowering blood pressure, improving learning ability and even boosting the immune system.  As for the catechins, some scientists have warned consumers about EGCG supplements after studies conducted on test tube seem to indicate that too much EGCG can cause cancer. Others however believed EGCG supplements are safe because studies using rats showed that EGCG is excreted through the bile while human trials have shown that when too much EGCG is consumed, EGCG may be metabolized into simpler compounds by colonic bacteria, absorbed, and eventually excreted in the urine. 
In 2005, Schmidt et al. were interested in the possible mechanism of hepatotoxicity of green tea extracts after reading reports of cases of liver disorders following ingestion of green tea dietary supplements, and conducted tests using rats. They concluded that their results suggest high concentration of EGCG can cause acute toxicity in rat liver cells.  There also have been case reports of green tea associated with hepatotoxicity in humans. For example, a Canadian woman became seriously ill after taking weight loss products containing high levels of green tea extracts everyday for about six months. The products caused damage to her liver and test results showed that she was suffering from toxic hepatitis. A liver transplant was required. The experts who reported the case of acute liver dysfunction caused by consumption of green tea extract supplements supported the hypothesis that they can cause serious side effects. Although this kind of extreme adverse cases maybe infrequent, they suggested doctors to take a careful history of herbal products such as green tea extracts when treating patients with acute hepatitis or liver failure. 
Herbal remedies including green tea have become popular among cancer patients to deal with side effects from chemotherapy. However, these supplements are unregulated and the patients should be cautious. A study by researchers at the University of Mississippi think the idea of taking huge amount of green tea per day is something that needs to be careful with, especially for patients with cancer. Because they found that very high doses of green tea extracts may actually help certain tumors to survive and grow through genetic mechanisms.  For example, researchers at the University of Southern California recently found a surprising side effect of green tea consumption for people being treated with the drug Velcade for multiple myeloma and mantle cell lymphoma. They strongly advise such patients to avoid green tea and in particular concentrated green tea products because it is very likely to make the drug completely ineffective in treating their cancer. They found that combining GTE or EGCG with Velcade can be "dangerously detrimental". 
In the past when green tea was mainly popular in Asia and not many people in the US were aware of its benefits, green tea was not evaluated by FDA for safety, effectiveness or purity. The potential risks of using green tea as a supplement were not studied widely and there were no regulated standards for the manufacture of green tea supplements. As the health-conscious in the West became interested in the benefits of green tea consumption and the manufacturers began to publicize the therapeutic properties of green tea extracts, scientists around the world began to take a closer look at green tea and its effects. Hundreds of research and studies were conducted within the past 10 years, some confirming the health claims while others raising alert. Even the health authorities do not seem to have made a conclusion.
There was a petition dated January 27, 2004 submitted to FDA which requested that the agency authorize a qualified health claim acknowledging the relationship between the consumption of green tea and reduce risk of cancer. The company submitting the claim proposed that "Daily consumption of 40 ounces of typical green tea containing 710µg/ml of natural EGCG may reduce the risk of certain forms of cancer." A year later, based on the scientific evidence and other information submitted by the petitioner, FDA concluded that "there is no credible evidence to support qualified health claims for green tea consumption and a reduced risk of gastric, lung, colon/rectal, esophageal, pancreatic, ovarian, and combined cancers." However, FDA thought there is some limited credible evidence regarding the health claims specifically for breast cancer and prostate cancer. 
Then in June 2005, the FDA received another petition, this time from a Japanese company which is one of the world's largest green tea manufacturers, requesting the agency to authorize a qualified health claim linking consumption of green tea with reduction of a number of risk factors associated with CVD for use in labeling food and dietary supplements. The company claimed that: "Daily consumption of at least 5 fluid ounces (150ml) of green tea as a source of catechins may reduce a number of risk factors associated with cardiovascular disease." One year later in May 2006, the FDA said it had reviewed the 105 articles and publications submitted as petition and stated that it has determined that "the evidence is supportive but not conclusive for this claim." FDA concluded that "there is no credible evidence to support qualified health claims for green tea or green tea extracts and a reduction of a number of risk factors associated with CVD." 
FDA's conclusion was released in a detailed report, attracting a lot of attention from the media and scientists because after all there have been numerous published studies with evidence on the health benefits of green tea. Some experts criticized FDA for the negative findings. For example, one magazine think FDA has omitted important studies because they did not meet their rigid criteria. The magazine also pointed out that the National Library of Medicine's database has over 600 studies related to green tea and cancer. The National Library of Medicine is in fact part of the US Department of Health and Human Services, which is the same parent agency as the FDA.  Other experts believe that both the FDA and the Japanese green tea company had faults in causing all the confusion. It was pointed out by Nadine Taylor that the Japanese company claim of just 5 ounces of daily intake of green tea is irresponsible, because most studies have shown that green tea reduces certain CVD risk factors with a daily intake of 4-5 cups [74,75] and improves cholesterol at about 10 cups per day.  Taylor also felt that FDA's has narrowed the definition of a CVD risk factor too much, excluded many studies as a result. Also FDA ignored all the research using animals, considering only those using human participants. Because of a lot of restrictions and criteria, FDA based their conclusion on only 11 of the 105 articles and papers submitted by the petitioners. 
In 2007, the US Pharmacopeia (USP), an official public standards-setting authority for all medicines, dietary supplements, and other health care products manufactured or sold in the US,  proposed to require manufacturers to have a cautionary label statement on all dietary supplements containing green tea extracts after reviewing reports linking a relationship between green tea extracts and liver damage.
Then in 2008, USP reviewed the safety of green tea products in order to re-evaluate the current safety classification. A total of 216 case reports were analyzed, including 34 on liver damage. 27 reports relating to liver damage were categorized as possible and 7 as probable. Clinical pharmacokinetic and animal toxicological studies indicated potential adverse effects is increased when concentrated extracts are consumed, particularly on an empty stomach.  In February 2009, USP updated their safety review for green tea extracts with new information gathered during the past few years and re-classified green tea extracts as falling within Class A, which does not require a caution/warning statement be included in the labeling section when publishing its Powdered Decaffeinated Green Tea monograph. It said it would continue to review reports and act accordingly if there are safety issues that make a cautionary statement necessary. 
FDA's rejection to the petitions few years ago has been criticized by some people as being unfair to green tea, ignoring a lot of evidence concerning its health benefits. Others think it is being too political because the people in FDA are not scientists but government officials who may have other concerns besides potential health risks. For example, they may worry about opening up a huge market for overseas importers of green tea products in US. However I think on one hand, FDA is being over-cautious, on the other hand, I think it is right for FDA to be extra careful on this issue because many governments around the world including Hong Kong, are using FDA's recommendations as reference when making important decisions concerning public health. There are really a lot of green tea products on the market. Green tea extracts may be beneficial to health, but some manufacturers seem to be exaggerating the good effects and a bit misleading consumers when selling their products.
The wordings for food labeling must be considered carefully. Nowadays many consumers will really read the labels when they buy a product as simple as a beverage. So if FDA allow manufacturers to claim certain things, it must be very sure those claims are 100% true with no hidden risks or uncertainties. Lee Sin Hang understands FDA's concerns although the petition he helped to submit was rejected in 2005. In his article "Re-introducing Tea to the West- This time to fight Cancer", he explained that FDA does not prefer using the word "prevention" in health claims for food labeling to prevent people from being misled that consuming certain things or taking certain supplements could prevent health problems that are complicated, such as cancer. 
I think that if green tea extracts are as safe as the manufacturers and some scientists think they are, perhaps there should be more tests using humans as subjects to prove those claims because rats and humans are very different after all. Maybe they should spend more on appointing scientists to prove the health claims first rather than spending huge sum of money on marketing unproven claims. Also majority of the studies and surveys on green tea involving human participants were done in Japan. There might be physiological differences between people in Asia and those in the West due to different ethnic background. FDA is supposed to look after the health of the American public. So I find it understandable for them to be so careful about green tea and its extracts, which are from the east.
The general public should know that there are real health benefits related to green tea and its extracts as well as some health claims that are not scientifically proven yet. There are genuine green tea producers who really want to tell the world that drinking green tea is good for the health as well as bad manufacturers who are taking advantage of this trend and add the green tea flavor to their products just to boost sales. Slogans like "Green tea is the most natural miracle curer" and "Green tea is the king of all remedies" might be too exaggerating.
I believe green tea products including supplements should be somehow regulated to monitor the bad manufacturers who have only profit in their mind. If it is a fact that consumers looking for health benefits should drink traditional green tea rather than getting tiny amount of the useful extracts from some products, then maybe consumers should be given more choices of real quality green tea to consume. However, in this commercial world, this may not be so easy because the green tea extracts in supplement forms can attract more people who prefer convenience and do not want to spend time brewing tea. Also, the profit from selling extracts is probably much higher than selling plain green tea.
Having read many articles and news about green tea, I think it is generally agreed that drinking traditionally brewed green tea is basically safe. One would need to drink many many cups everyday for a long period before any toxic effects will occur. The most common bad effects from drinking green tea is being over stimulated by the caffeine in it, causing the drinker difficulty in sleeping. More serious problems involve special groups who should avoid caffeine such as women who are pregnant, who suffer from fibrocystic breast disease or PMS. They should not drink any coffee or tea, including green tea.
Although green tea has a soothing taste with a special fragrance, not all people enjoy that. They would prefer taking green tea extract in supplement forms. Many scientists and experts have already agreed on recommended daily dose. Problems would arise when people have an overdose of green tea extracts, for example after taking supplements produced by unprofessional manufacturers. There have been cases of people suffering from conditions like liver damage as a result of taking too many dietary supplements without supervision. I think the manufacturers should take up more responsibilities in preventing people from overdose like educating people about the possible risks. Governments should keep reminding people to be more responsible for their own health and learn more about a product before taking it, especially in great amount for long period of time.
As a famous physician and alchemist said, "All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy." A substance can be very useful when you take small amount, but the same food could harm you if you take in too large amount. We should not take high quantities of any one substance no matter how good it is supposed to be for our health. Just because something is good in small doses does not mean that it will be even better for us in higher doses. Anything, even healthy food, moderation is the principle. And the dosage recommended for any remedy must be followed and not be exceeded in order to be effective.
There is a saying "An ounce of prevention is worth a pound of cure". This is especially true when it comes to people's health. Prevention is the most effective way in practicing medicine. Since ancient times Chinese physicians have been using food as medicine for the prevention of diseases for thousands of years. The famous Greek physician Hippocrates also emphasized the importance of food as medicine.  Eating a balanced diet and consuming moderate amount of a natural healthy drink like green tea should be good for most people.
Prevention of diseases should also be everyone's responsibility in a modern society because the doctors and other healthcare providers already have a great burden treating existing patients. In many places, the pressure on the healthcare system will continue to increase as the populations continue to age. The future trend of health care is to encourage preventive medicine by individuals because the society will not be able to sustain the current demand for health care services in the long term. Everyone should seek reliable scientifically proven information to manage their own health properly instead of getting help from healthcare professionals when they become ill. 
In a busy city like Hong Kong, people are facing all kinds of pressure everyday. For health reasons they should develop a lifestyle that will allow them time to relax and be away from all the stress. One way to calm down is sipping a cup of green tea during or after meals. Green tea is a gentle beverage that requires time to prepare and sip. Because the beverage is soothing, people who drink green tea tend to slow down their pace and enjoy the tea in calm and peaceful environment. Furthermore, green tea has many health benefits that have been known for thousands of years. Like the Chinese monks and the Japanese who drink green tea regularly as part of a healthy balanced diet, other people should be able to live longer with a healthier lifestyle.
After thousands of years as a traditional beverage, green tea is now regarded as a healthy drink with ingredients that are an important source of antioxidant. It has also become a useful product with beneficial health properties being consumed or applied in various ways. As its popularity grows, the number of experimental studies investigating the benefits as well as toxicity of green tea constituents continues to rise.
In conclusion, drinking traditionally brewed green tea regularly is safe and healthy for most people. Those who prefer to take green tea supplements to get the beneficial effects should be careful with what the manufacturers claim and follow the instruction on dosage in order not to turn green tea extracts, which is naturally good, into a poison that causes damage to one's health.
Many of the research on green tea are still using animal subjects at this stage. It is hoped that there could be more evidence from human studies appearing soon, showing the benefits to human health. Scientists need to confirm that the cases of toxicity occur only under extreme situations, for example, over-dosing huge amount of dietary supplements causing liver damage. When the evidence from human studies is available, green tea can be more widely recommended to people; and regular consumption of green tea could be introduced to the western people's diet. This is a non-expensive way to improve health of the general public.