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Health Benefits and Problems of Drinking Green Tea

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  • Introduction

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.

  • Aims for the dissertation

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.

  • Methodology

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.

  • Overall structure

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.

  • Background

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.

  • Green tea processing

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.

  • History of green tea

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.

  • Green tea components

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

Compound Green tea*
Phenolic compounds** 30
Fibre 26
Proteins 15
Others carbohydrates 7
Lipids 7
Minerals 5
Amino acids 4
Pigments 2
Oxidised phenolic compounds*** 0

*Data referred to dry weight of tea leaves.

**Especially flavonoids.

***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).[2] 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.

  • Tea Polyphenols

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

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. [8] 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.

  • Nutrients

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.

  • Vitamins

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.

  • Inorganic elements

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)




N3.5 - 7.1


Al420 - 3,500


P0.2 - 0.7


As0.20 - 0.42


K1.6 - 2.5


Ba1.3 - 5.1


Ca0.12 - 0.57


Br7.8 - 25.0


Mg0.12 - 0.30


F17 - 260


S0.24 - 0.48


Na20 - 33


Fe100 - 200


Ni1.3 - 5.9


Mn500 - 3,000


Pb2.2 - 6.3


Cu15 - 20


Rb8 - 44


Mo0.4 - 0.7




B20 - 30


Se1.0 - 1.8


[Source: "Standard Tables of Food Composition in Japan", Resources Council, Science and Technology Agency, Tokyo, 1991]

  • Other Components
  • Amino Acids

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

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.

  • Carbohydrates

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.

  • Lipids

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>

  • Health Benefits


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.


  • Antioxidant Effects


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. [8] 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. [23] 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


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.


  • HIV


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. [26] 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.


  • Neuroprotective Effects
  • Parkinson's Disease


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.


  • Alzheimer's Disease


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.


  • Huntington'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.


  • Prevention of Cancer


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. [8] 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. [8] 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.


  • Breast Cancer


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. [8] 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. [32] 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. [33] 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.


  • Prostate Cancer


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.


  • Leukemia


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.


  • Prevention of Cardiovascular Disease


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.


  • Other Effects
  • Hypotensive Action


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".


  • Lowering Blood Sugar levels


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.


  • Helping Digestion


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.


  • Weight Loss


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%. [44] 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. [8] 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. [45] 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.


  • Anti-bacterial Effects
  • Effects on Intestinal Flora


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


  • Prevention of Dental Caries


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.


  • Anti-viral Effects


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). [49] 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.


  • Anti-inflammatory Effects


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.


  • Longevity


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.


  • Applications


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.


  • Supplements


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. [53] 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.


  • Dosage


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. [8] 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.


  • Other Uses


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. [57]

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. [48] 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. [10]

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.[58] 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. [59] 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.


  • Potential Adverse Effects
  • Side Effects


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.


  • Caution about Caffeine


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. [38] 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. [60] That's why doctors would not recommend pregnant or lactating women to consume green tea. [55]

For some people caffeine causes irritation in the gastrointestinal tract or sleeping disorder. [18] 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. [8]

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. [8]


  • Green Tea vs Coffee


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 ma

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