Green Tea Health Benefits

The Japanese custom of drinking green tea came from China around 800 AD. The use of tea started when Buddhist monks, who had gone to China for study, returned to Japan bringing tea with them as a medicinal beverage. In the Kamakura era (1191-1333), the monk Eisai stressed the beneficial effects of tea in his book Maintaining Health by Drinking Tea (1211):

“Tea is a miraculous medicine for the maintenance of health. Tea has an extraordinary power to prolong life. Anywhere a person cultivates tea, long life will follow. In ancient and modern times, tea is the elixir that creates the mountain-dwelling immortal”.

From this passage we can see that green tea has from early times been highly valued as a powerful medication. But in recent years research into the effects of green tea has progressed so far it can now provide scientific confirmation for the legendary saying that “Tea is a miraculous medicine for the maintenance of health”. It is becoming increasingly clear that green tea has a broad efficacy in preventing disease. The remainder of this text will introduce you to the main point of the research summarised in “The Components and Healthy Effects of Green Tea” below (1).

Cancer mortality statistics on Japanese people indicate that the death rate from cancer is significantly lower, for both men and women, in Shizuoka Prefecture. This fact stimulated our interest in cancer prevention and led us to calculate the death rate (Standardised Mortality Ratio) by cancer type for every city, town and village in Shizuoka Prefecture. Based on these death ratio statistics, we created a cancer distribution map of the Prefecture and examined it in details for trends. We found that areas devoted to green tea production in central and western regions of Shizuoka Prefecture exhibit a significantly lower death rate for all types of cancer in general and for gastrointestinal cancers such as stomach, oesophagus and liver cancer in particular². We then made a survey to see how the residents of the green tea producing regions, which have such low cancer death rates, drink their tea. The results showed that those who live in area where green tea is the staple crop tend to drink it daily in rather strong concentrations by frequently refreshing the tea leave in their pots^{2, 3}. From these results we theorised that green tea must be connected in some wat with cancer prevention, and we decided to continue our research with animal experiments.

Mice were first inoculated with cancer cells and then studied for the growth of malignancies. One group was given an extract of green tea while another control group was not given such an extract. Comparison of the two groups showed a marked reduction in the growth of tumours among the group receiving green tea (Table 2)⁴. In further joint research with Prof. Shu-Jun Cheng of the Cancer Institute, Chinese Academy of Medical Science (Beijing), mice were given substances which when transformed in the body to cancer causing chemicals, generate carcinoma in both the oesophagus and the fore stomach. The researchers then proceeded to check if green tea has the ability to inhibit the development of these cancers. Administration of green tea extract did indeed reduce the incidence of cancer to less than 50% (Table 3)⁵. In addition, research at the National Cancer Institute (Tsukiji, Tokyo) has demonstrated that the administration of catechin (the main component of green tea tannin) to mice previously given chemicals that induce duodenal cancer can also significantly lower the incidence of cancer. Green tea and its component catechin have, therefore, been shown to reduce the growth as well as the actual generation of cancer.³

2) I.Oguni et al., Japanese J. of Nutrition, 47, 31 (1989).

3) I.Oguni, Metabolism and Disease, 29, 453, (1992).

1. a) The means ±S.E. b) p<0.05 c) p<0.01

The crude extracts of green tea leaves were daily administered to ICR mice orally for 4 days after subcutaneous inoculation of sarcoma 180 cells (1X10⁷ cells / mouse). Mitomycin C was used as a positive control. Tumor weight was compared with that of the control (10 mice / group) on the 21st day after inoculation.

1. a) p < 0.05 GTE : Green Tea Extract

Green tea extract (5mg/mouse/day) was incubated to mice (Tientsin II, female) 6 times a week, for 14 weeks. From the second week, mice of both Group I and II were incubated with sarcosine ethyl ester hydrochloride (2g/kg) and sodium nitrite (0.3g/kg) 3 times a week, for total 5 weeks. The animals were sacrificed at the 14th week.

From our previous epidemiological research we can estimate that the inhabitants of the Midwestern region of Shizuoka Prefecture, where green tea is the staple product and main beverage, consume as much as 1.0-1.5g of crude green tea catechins daily in their green tea. This strongly suggests that green tea catechins plays a role in their low SMR (Standardised Mortality Ratio) for stomach cancer.

We do not yet fully understand the mechanism underlying the generation of cancer, but it involves at least the following two stages (Fig. 1). This is called the “Two-stage theory of cancer development”. A substance capable of causing mutations (initiator) first damages the DNA in the cell and renders it subject to cancer (initiation). This condition then remains unchanged for some time until another substance, which activated cancer (promoter), leads to the actual growth of a malignancy (promotion). It is clear from recent research that extract of green tea and catechin can markedly inhibit both stages of development^6.

Even though these results have gained from animal studies or pure laboratory tests, we think it highly significant that green tea and its component catechin have the ability to prevent cancer. When taken together with the survey that indicates a striking reduction in the cancer death rate in the tea producing regions where the residents are accustomed to drinking quite strong tea by frequent changes of the tea leaves, they support the conclusion that green tea may also be a factor in the prevention of human cancer.

Cholesterol is always indicted as the “bad guy” for causing a wide range of diseases in adults. But it is a chemical present in all animals and crucial in human bodies for such important processes as the manufacture of cell membranes and the adhesion of cells. There are two types of cholesterol: one is the so-called “bad” cholesterol (LDL and VLDL-Cholesterol) that accumulates in tissues and the other is the “good” cholesterol (HDL-Cholesterol) that collects excessive cholesterol from the tissues. If the amount of bad cholesterol in the blood increases too much, it is deposited on the walls of blood vessels and can lead to atherosclerosis. Atherosclerosis in conjunction with high blood pressure can cause myocardial infarction and cerebral infarction. Good cholesterol, however, prevents atherosclerosis and must exist in a proper balance with bad cholesterol for proper health.

Prof. Muramatsu has demonstrated in experiments with rats that green tea catechin restricts the excessive build-up of blood cholesterol⁷. When rats were fed a diet high in fat, the amount of bad cholesterol in the blood increased rapidly. But the addition of only 1% catechin to the food checked the increase of bad cholesterol (LDL) with only minimal effect on the amount of good cholesterol (HDL) (Fig. 2). In another series of experiments, rats fed normal food with catechin exhibited no decrease in blood cholesterol and remained unaffected by the supplement. We can see from these results that green tea catechin acts to limit the excessive rise in blood cholesterol. In 1991 Dr. Goto⁸ reported similar results for human blood cholesterol.

Fig. 2 Hypocholesterolemic effect of “crude catechins”

High blood pressure places a serious burden on the vascular system and contributes to atherosclerosis. Atherosclerosis will in turn precipitate heart diseace, strokes and other cardiovascular diseases. The cause of high blood pressure is not yet fully understoon, but it is clear that a chemical called angiotensin II plays a role in high blood pressure due to essential hypertension and to arterial stenosis of the kidneys. Blood contains the substance antiotensiogen which is transformed to angiotensin I under action of the enzyme rennin in the kidneys. Another enzyme called the “Aniotensin Converting Enzyme” (ACE) then changes angiotensin I to angiotensin II, which is an extremely strong vascular constrictor. It is the constriction of the blood vessels caused by this constrictor that leads to high blood pressure.

Dr. Hare⁹ has shown that green tea cateshin impedes the action of ACE and suppresses production of anogiotensin II. He has also demonstrated that administration of catechin to Spontaneously Hypertensive Rat (SHR) could limit increases in the rats’ blood pressure. SHR are rats used as models for human high blood pressure expriments, and their blood pressure at the start of the experiment (when they were five weeks old) was 130 – 140mmHg. By the age of about 10 weeks, after a diet of normal feed, their blood pressure had risen to more than 200mmHg. But the blood pressure of those rats raised with 0.5% catechin added to their feed remained below 200mmHg. Exchanging the feed of the two rat groups at 16 weeks of age led to a reversal in blood pressure between the two groups (Fig. 3). These results indicate that green tea catechin has the ability to prevent a rise in blood pressure. If the amount of catechin used in this experiment is converted to the amount of green tea normally drunk by humans, it is equivalent to drinking about 10 moderately large cups of tea per day. These are surely quite significant results in suggesting, as they do, that the daily consumption of green tea can prevent high blood pressure.

About 60 years ago, Dr. Minowada of Kyoto University noticed that sugar in the urine of patients of hospitalised for diabetes fell markedly during periods when they participated in chanoyua (Tea Ceremony). He reported that powdered tea of the types used in the traditional Tea Ceremony (Matcha) had the capability of lowering blood sugar. Unfortunately, however, this important report was ignored due to the outbreak of World War II and the subsequent post-war food shortages. But the arrival of the “gourmet era” in recent years in Japan has led to heightened interest in diabetes and the ability of green tea to reduce blood sugar.

The sugars and carbohydrate in our food are digested mainly in the duodenum, converted there to glucose and then absorbed into the blood. The agent that regulates that intake of blood sugar into the tissues is insulin, a chemical secreted from Lange Hans islets on the pancreas. Diabetes is a disease characterised by insufficient secretion or improper functioning of insulin, which hinders the proper absorption of glucose into the tissues and leads to high concentration of blood sugar that must eventually be excreted into the urine. If this high concentration of blood sugar should continue for a long period, it will affect the vascular system and cause a number of quite serious diseases including atherosclerosis and retinal hemorrhages. Dr. Hara¹⁰ gave dried green tea catechin in edible form to mice that were subject to hereditary diabetes and verified a lowering of blood sugar. In parallel experiments, Dr. Shimizu¹¹ gave an extract of green tea to mice and demonstrated that it had the ability to lower blood sugar (Table 4). It has also been shown that the polysaccharides in green tea possess the same ability. Although these results come from animal tests, the evidence that green tea catechin and polysaccharides can lower blood sugar in mice may also, in light of Dr. Minowada’s old report, apply to humans.

1) Synthetic blood glucose-lowering drug

2) Blood sugar reduction ratio greater than 35% = + +, 30 ~ 35% = +, 20 ~ 30% = ±, less than 20% = –

Oxygen is necessary for human life. But oxygen has two aspects, One beneficial and one malign. The oxygen we breathe is conveyed to every part of the body where it plays a key role in metabolism. But it can also be a very harmful agent in the form of active or free radical oxygen is a problem because it can combine with anything in the body and oxidise it – with consequent destruction of cell membranes, damage to DNA and oxidation of lipids (fats). All of these can lead to diseases cancer. Here we shall focus on the process by which active oxygen combines with lipids (fats) in the body to create lipid peroxide, that is, lipid with an excessive amount of oxygen. Lipid peroxide is thought to be a harmful substance which can trigger the diseases such as cancer, cardio-vascular disease and diabetes. Since lipid peroxide is more easily generated and less easily purged as age advances, it tends to accumulate in the body. Lipofuscin, called the “aging pigment”, also accumulates in the body in proportion to age and is considered to be an index of aging. But lipofuscin is itself created by lipid peroxide, which suggests a connection between aging and lipid peroxide. One way to slow aging may, therefore, be to prevent the producing and accumulation of active oxygen and lipid peroxide in the body. It has been shown, for example, that the higher the concentration of the powerful antioxidants vitamins E and C in the bodies of animals, the longer the live. This suggests that active consumption of agents that are effective antioxidants will restrain the aging process.

We already know that green tea is rich in those vitamins that possess this anti-oxidising capability. In addition, Prof. Okuda¹² has recently demonstrated that catechin in green tea is a far stronger antioxidant than vitamin E (about 20 times stronger in fact). These results come from laboratory tests only, and we much wait for further research to confirm a direct cause and effect – relationship between the anti-oxidising function of green tea and the retardation of aging. But the very fact that green tea contains a powerful antioxidant is a strong foundation for believing it can help control aging.

Tea contains caffeine which, when taken in the proper quantity, stimulates every organ in the body. It has a particularly strong effect on the central nervous system, heart and liver. This reaction is even more pronounced when one is sleep or tired. A cup of tea or coffee will help clear a dull mind after rising in the morning or after a prolonged period without sleep. The power to stimulate and awaken the mind comes from caffeine. It is also said that the amount of caffeine contained in normal servings of green tea can stimulate the skeletal muscles and facilitate muscular contraction. For this reason, it is quite helpful to drink tea or coffee in the middle of work to refresh the mind and restore the body. We find it noteworthy that there is some scientific support for such old customs as the afternoon snack, coffee break or tea time ritual

The caffeine in green tea is mostly extracted in the first infusion of the leaves, but the quantities in subsequent infusions will still be greater than coffee. Also, since green tea caffeine combines with catechin in the brewing water, its action is said to be rather milder that other caffeine-containing beverages. Even so, some people are sensitive to caffeine and cannot sleep if they drink green tea before going to ben. It is safer for such individuals to drink a weak green tea after dinner.

Why not treat yourself to a zestful day by enjoying the positive effects of mild caffeine with the sweet aroma of green tea?

It has long been known from experience that green tea has the ability to kill bacteria. Consumption of strong green tea, for example, is often recommended as a good treatment for diarrhoea.

Dr. Hara¹³ has shown in his research that catechin is a powerful sterilising agent for many types of bacteria that cause food poisoning (Table 5). He checked the Minimum Inhibitory Concentration (MIC, ppm) of green tea catechin necessary to stop the growth of various types of food poisoning and bacteria and found that (a) Staphylococcus aureus, (b) Vibrio parahaemolyticus, (c) Clostridium perfringens, (d) Bacillus Cereus, (e) Plesiomonas shigelloides, (f) Aeromonas sobria and (g) Clostridium botulinum cannot grow in the 1/10-1/2 of 0.1% of catechin in the green tea normally drunk by the Japanese people. But even fairly high concentrations of catechin has no negative effect on the bifidus bacillus, which is necessary for proper function on the intestinal tract. In addition to this evidence, Prof Shimamura¹⁴ has reported that green tea is a very strong sterilant of cholera vibrioand has a strong antitoxic effect on toxins produced by bacteria other than cholera.

ECG : (–) -epigallocatechin gallate

EC : (–) -epicat-chin.

EGCg : (–) -epigallocatechin gallate

ECG : (–) -epicatechin gallate

These results indicate the antibacterial function of green tea catechin and suggest that it may be effective in preventing food poisoning. Every year throughout the world there are countless incidents of food poisoning.

Wouldn’t it have been a good idea, given the facts, to enjoy one’s meals with several cups of green tea?

Dental techniques have improved greatly in the past few years, but once teeth have been damaged by cavities they can never be restored to their original condition. It is of the highest priority, therefore, to prevent cavities from developing in the first place. By the end of the 19^th century, it had been determined the cavities are caused by cariogenic bacteria. The cariogenic bacteria first produce non-water-soluble glucan from sugar or other foods, and this glucan adheres to the tooth enamel as hard plaque. Next, they feed on sugar to generate acids such as lactic acid in the plaque. There acids then dissolve the tooth enamel. That in brief is the mechanism of cavity production. To prevent cavities it is necessary, then, to keep plaque off the teeth by brushing – an important tool in good dental hygiene. But according to experiments by Dr. Hattori¹⁵ green catechin can suppress the process (glucosyl transferase) by which cariogenic bacteria create glucan (Table 6). Other experiments by Dr. Sakanaka¹⁶ have verified that green tea catechin can destroy cariogenic bacteria (Table 7). That is, it is antibacterial. Clearly, then, green tea catechin not only suppresses the formation of plaque by cariogenic bacteria but also kills the bacteria themselves.

It has been known for some time that small amounts of fluorine can strengthen teeth and help prevent cavities. For this reason, many cities add fluorine to their drinking water. Green tea, however, contains natural fluorine and is thought to help prevent cavities. That may explain those reports that show a reduction in cavities among grade school children who drank green tea after lunch.

Halitosis or bad breath embarrasses many people. It is caused by a number of bacteria that flourish in the mouth. Green tea can also kill other oral bacteria besides those causing cavities. It has, therefore, some ability to prevent bad breath by destroying the cause of bad breath.

Why not enjoy gleaming white teeth and a fresh breath by drinking green tea?

1. 1. a) GTase-I and GTase-S synthesized insoluble and soluble glucan, respectively
   2. b) Test compounds : C, (+) -catechin; EC, (–) -epicatechin; GC, (+) -gallocatechin; EGC, (–)-epigallocatechin; ECg, (–) -epicatechin gallate; GCg, (–) -gallocatechin gallate; EGCg, (–) -epigallocatechin gallate

1) BHI agar medium

2) Sensitive meat extract agar medium

3) Test compounds : C, (+) -catechin; EC, (–) -epicatechin; GC, (+) -gallocatechin; EGC, (–) -epigallocatechin; ECg, (–) -epicatechin gallate; EGC, (–) -epigallocatechin gallate

Dr. Okada¹⁷ has noted the fact that tobacco growers use exudates of green tea to prevent damage to the tobacco mosaic virus and verified that green determined that green tea catechin and suppresses the growth of this virus. In addition, Prof. Shimamura¹⁸ has determined that green tea catechin and theaflavin (an oxidised form of catechin) present in black tea have a strong effect on the influenza virus. Green tea catechin and black tea theaflavin directly act on the influenza virus and inactivate it. It appears, therefore, that gargling with green or black tea is very effective in preventing influenza. This effect is increased by keeping the green tea catechin and the virus in contact as long as possible.

It is also hoped that the antiviral capability of green tea catechin may have some beneficial effect on the AIDS (Acquired Immune Deficiency Syndrome) virus, which is now the world’s most feared infectious disease. Dr. Nakane and Dr. Oso¹⁹ at the Aichi Cancer Institute have verified the fact that green tea catechin can inhibit the activity of the AIDS virus in laboratory tests (Table 8). Although this research is just in its nascent stage, it provides a slight ray of hope that a treatment may someday be found to combat the now unstoppable AIDS virus. Future research advances in this field are expected.

People feel a great peace of mind when sipping a cup of high quality Japanese Green Tea. Why does high quality Japanese Green Tea make people relax although tea contains caffeine, which stimulates the central nervous system? Components in tea must have a key to the settlement of this contradiction. Theanine is the most abundant amino acid in Japanese Green Tea and it affects the quality of the taste of tea. Its chemical structure is similar to glutamine and glutamic acid, which are both neurotransmitters. So, Theanine may exert a physiological function in the brain.

According to recent research, Theanine is absorbed in the intestine and goes to the brain. Theanine in the brain gives a boost in releasing dopamine, which plays an important role in the action of neurotransmitters. Also, some chemical components, which control the blood pressure at the peripheral nervous system, are increased by the intake of Theanine.

Theanine is proved to diminish the risk of hypertension, since spontaneous hypertensive rate show a reduced blood pressure after a Theanine intake.

Fig, 2. Dose-dependent Theanine Stimulation of Dopamine Striatal

Fig. 3. Theanine Administration of the Decrease on Systolic and Diastolic Blood Pressure of Conscious Wistar Kyoto (WKY) and Spontaneously Hypertensive Rats(SHR)

On the other hand, Theanine also directly affects the functions of the neurotransmitters. So called α-brain waves, which are emitted in a relaxing human brain, are observed frequently and for a long period of time after a Theanine intake. Furthermore, scientist found that Theanine strengthens the memory ability.

Tea of higher qualities such as Gyokuro, Match and high quality Sencha, contains high amounts of Theanine. Tea leaves for Gkyokuro and Matcha are grown under shaded gardens, and high quality Sencha are picked very young. This is done in order to reduce the loss of Theanine in tea leaves, since Theanine changes into Cathechins by sunlight.

So, all these positive effects of Theanine should show us, why we would better choose Japanese Green Tea of higher qualities.

Discussions of food normally were focused on its nutritional content and its flavour. Recently, however, more attention is being paid to the role of food in bio-regulating functions. Foods that possess this regulatory function are called “functional food”. Dr. Inaba²⁰ classifies food by function as shown in table 9. If we classify green tea and green tea catechin according to this table, they possess the following functions:

1. 1. 1. Bio-defencing function by preventing cancer through fortification of the immune system
      2. Disease-preventing function by preventing high blood pressure or diabetes
      3. Disease-recovery function by inhibiting the rise of cholesterol
      4. Physical rhythm-controlling function by stimulating the central nervous system with caffeine
      5. Aging-suppressing function by providing the body with antioxidants

Green tea is, therefore, rich in possibilities as a functional food and should prove a popular beverage among the new health conscious generation.

Green tea, with its sweet aroma and eternally fresh taste, has been loved and continuously drunk since its introduction to Japan centuries ago. But modern research has finally started to remove the veil concealing some of its true power as a functional food. Green tea is truly a “miraculous medicine” with an “extraordinary power to prolong life”.