The Science and Art of TeaForHealth™
Background | The Science and Art of Tea Drinking | The Practical Considerations to Tea Drinking
Precautions | References | Printer-friendly file

Background

Aqueous extract of the dried leaves of tea trees, Camellia sinensis, which is generally referred to as tea, has been used as a favorite beverage in certain societies for almost 5,000 years for its soothing taste and for its potential health benefits to humans. But only in the past few decades has scientific data clearly demonstrated a positive relationship between regular tea drinking and the prevention of certain human diseases. This trend of medical and scientific research began in Japan where the scientists first noticed that the tea drinkers experienced less radiation sickness than the non-tea-drinkers after the two atomic bomb explosions in 1945.

Now we all know that tea drinking is associated with a wide range of health benefits, including lowering the total blood cholesterol and the low-density-lipid cholesterol level, increasing the high-density-lipid blood cholesterol level, reducing blood pressure, acting as blood thinner, reducing the risk of heart attack, reducing the death rate after a heart attack, decreasing the risk of stroke, reducing the risk of cancer, enhancing the immune system of the body and preventing dental cavities. These health benefits are supported by a large volume of recently published experimental and clinical research data.

For example, results from studies in animals showed that tea consumption protects against lung, stomach, esophagus, duodenum, pancreas, liver, breast, colon, and skin cancers induced by chemical carcinogens. Regular consumption of green tea has a preventive effect against atherosclerosis, hypercholesterolemia, and hypertension.¹ The growth of certain types of high-grade human non-Hodgkin’s lymphoma cells can be inhibited by green tea extracts in animal models, apparently by inhibition of angiogenesis and induction of endothelial and tumor cell apoptosis. Green tea extracts were found to be more effective than the chemotherapeutic drug, cyclophosphamide, in preventing lymphoma recurrence.² Tea extracts also appear to have antiviral effects by interference with virus adsorption to target cells, and have been recommended as a beverage to reduce the incidence of influenza and other viral infections.^3,4

Extracts of green tea have been shown to reverse methicillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) and also, to some extent, penicillin resistance in b-lactamase-producing S. aureus by preventing bacterial synthesis of a penicillin binding protein (PBP2') and by inhibition of the secretion of beta-lactamase.⁵ Epicatechin gallate, a constituent of green tea extract, has been found to lower the minimum inhibitory concentration (MIC) of beta-lactams in methicillin-resistant S. aureus. ⁶

The green tea constituent (-)-epigallocatechin-3-gallate has been shown to inhibit the activity of a DNA topoisomerase in human colon carcinoma cells and has been suggested as being a potential supplement to the conventional topoisomerase inhibitor for the treatment of colonic cancer.⁷ The quinolone antibiotics (such as ciprofloxacin and ofloxacin) are also known to inhibit the growth of mammalian cancer cells by targeting DNA topoisomerases in the malignant cells^7-12 and by interfering with key cell division steps.⁸ Quinolones have been proposed as an adjunct for the treatment of human bladder cancer because anticancer concentration of the drugs can be achieved more readily in the urine or intravesically ¹³. Since many currently used anticancer drugs, such as doxorubicin, also target a topoisomerase (topoisomerase II), the combination of green tea extracts and quinolones, or doxorubicin, i.e. DNA topoisomerase inhibitors from different sources, may have a synergistic cytotoxic effect on the cancer cells.¹³

In addition, a special amino acid, theanine, extracted from green tea has been found to enhance the anticancer effects of adriamycin¹⁴ or doxorubicin.^15,16 In vitro studies showed that theanine inhibits the efflux of adriamycin from the cancer cells selectively, raising its intracellular toxic concentration in the malignant cells, but not in the normal tissues. A combined administration of theanine and DNA topoisomerase inhibitors^14-16 from various sources may allow a reduction of the required doses of the chemotherapeutic agents. Other important ingredients of tea beneficial to human health may be as yet to be identified.¹⁷

Patients who are regular heavy tea drinkers have a much better chance to survive a potentially fatal heart attack, with a 44% lower death rate.¹⁸ Cancer onset in patients who had consumed over 10 cups of green tea per day was 8.7 years later among females and 3.0 years later among males, compared with patients who had consumed under three cups per day.¹⁹ Patients with stage I and II breast cancer who consumed over five cups of green tea per day experienced a lower recurrence rate and longer disease-free period than those consuming less than four cups per day.²⁰

Most of the first-generation members of the Politburo of the Communist Party of China from the 1920's to the 1990's were cigarette chain smokers, notably Mao Ze-dong and Deng Xiao-ping, and practically all were heavy tea drinkers partly because tea was the only beverage available in the revolutionary years. All of them apparently lived to old age without developing lung cancer. In comparison, the Chinese living in Hong Kong who have adopted a westernized life-style and drink little tea have one of the highest lung cancer rates in the world, which may be caused by cigarette smoking (active or passive) while living in crowded quarters without the benefits of tea protection. Lung cancer, especially the adenocarcinoma type, was already a major malignancy among the Chinese living in Hong Kong prior to 1961 before Hong Kong became an economic and industrial world center with the associated heavy air pollution.²¹

The Science and Art of Tea Drinking

The published research data indicate that the major health-protective active ingredients in the tea leaves belong to a family of chemicals, functionally referred to as “antioxidants” which also exist in many plant foods loosely labeled as “flavonoids”. Most researchers have identified the health-beneficial antioxidants in tea leaves to be polyphenols, known in chemical terms as (-)epigallocatechin gallate (EGCG), (-)epigallocatechin (EGC), (-)epicatechin gallate (ECG), and (-)epicatechin (EC) (referred to hereafter collectively as catechins). These active polyphenolic compounds may account for 30-40 % of the extractable solids of green tea leaves.²²

One of the most important discoveries in medical research of recent years is the finding of the toxic effects of the so-called free radicals in human body. Free radicals, which are often reactive oxygen species, are highly reactive molecules that can damage the cells of the human body and contribute to many diseases and to the aging process. A free radical takes an electron from another molecule, turning the latter molecule into an electron-deficient free radical that will rob an electron from yet another molecule. In such a chain reaction, some of normal cellular structures reacting with the free radicals may be damaged. These damages may be apparent immediately or may be latent.

The harmful effects of free radicals on the human cells include causing oxidation of the fats and proteins of the cell membranes, damaging the mitochondria, interference with normal cellular functions by inactivating enzymes and hormones and damaging the DNA code leading to irreversible mutation and development of cancer.

Free radicals are being created constantly in the human body as part of the normal living process, or can be introduced from the environment in the form of nitrogen dioxide and other potentially harmful chemicals in the air pollutants, toxic wastes and pesticides. Ultraviolet radiation from the sun, cigarette smoking (active or passive) and various medications also induce generation of free radicals or introduce them into the human body. Therefore, there is no way to avoid free radicals completely in life. However, some nutrient supplements are known to help the body to minimize the harmful effects of free radicals. For example, the flavonoids can prevent the formation of free radicals, and protect vitamin C which can neutralize free radicals in the extracellular and intracellular fluids. Vitamin E can protect the cell membranes from the oxidation damage induced by free radicals. The carotenoids can scavenge singlet oxygen molecules and prevent the oxidation of fats which are essential components of cell membranes.

The tea polyphenols as antioxidants in the flavonoid family are capable of preventing the formation of free radicals or interrupting the chain reaction of free radical formation by donating their loosely attached electrons to the free radicals, making the latter inactive and harmless without becoming free radicals themselves. Therefore, tea polyphenols are ready electron donors and their antioxidative function must be maintained or preserved in the dried tea leaves and in the tea extracts for the latter to be effective as a health-protective herbal beverage.

Exposure to oxygen may reduce the contents of tea polyphenols. For example, the process of fermentation which is actually an oxidative treatment of the tea leaves for 60 to 120 minutes in preparing black tea has been shown to cause more than 80% degradation of the tea catechins in the tea leaves with no decrease in caffeine contents.²³ Therefore, the majority of the published medical and scientific research data were based on studies using the unfermented green tea extracts as the active substance.

The antioxidative activities of tea catechins, especially EGCG, the most abundant and most active catechin in tea extracts, are influenced by the pH and metal ions in the aqueous extracts, remaining high and constant at near neutral pH, but decreasing in acidic and strong alkaline solutions. While copper ions increase the antioxidative activity of EGCG, ferrous ions (iron) inhibit this activity.²⁴

The EGCG contents in the dry tea leaves vary greatly not only with the types of dry tea leaves processed with different methods, but are also known to vary between leaves plucked from different parts of the same tea tree. The first young leaf has been shown to have the highest concentration of EGCG, and the concentration of EGCG decreases with aging of the leaves on the same tea tree.²⁵

Khokhar and Magnusdottir ²⁶ studied the efficiency of aqueous extraction of tea catechins from dry tea leaves. The results showed that a high temperature of 100ºC for 5 minutes is necessary for the most efficient extraction of the tea catechins. At a lower temperature, for example, at 80ºC, the extraction efficiency for EGCG is reduced by more than one third (1/3). Therefore, for the most effective extraction, boiling water at or close to 100ºC in temperature should be used for filling the steeper for tea brewing. Any additional gadgets or devices which may contribute to lowering of the initial temperature of the hot water in the tea steeper or which may restrict the free unfolding of the dry tea leaves during the initial phase of the hot water extraction should not be put into the tea steeper.

Degradation of the green tea catechins in tea drinks has also been studied.²⁷ The results showed that the green tea catechins, namely (-)epigallocatechin gallate (EGCG), (-)epigallocatechin (EGC), (-)epicatechin gallate (ECG) and (-)epicatechin (EC) are generally stable at room temperature. However, at high temperature in the presence of oxygen, especially during autoclaving at about 120ºC with addition of sucrose, citric acid, and ascorbic acid, unpredictable degradation of the tea catechins will take place. As a result, a person will ingest 400-500 mg of green tea catechins if one cup of tea drink is properly brewed in the “traditional manner”. In contrast, a person will ingest only 3-60 mg of green tea catechins when one canned or bottled tea drink of 250 ml is consumed. Oxidation and epimerization of EGCG to (-)gallocatechin gallate during the heating process required for sterilization appear to be the mechanisms of green tea catechin degradation in the preparation of canned or bottled tea drinks. (Epimers are stereoisomers of a sugar or sugar derivative that differ in the arrangement of the hydrogen atom and the hydroxyl group on the last asymmetric carbon of a chain. The process of going from one epimer to another is called epimerization. Epimerization can occur as the result of a physical treatment, like heating, or an enzymatic activity.) In aqueous solutions, EGCG has been shown to be stable at 4ºC for 24 hours at pH 3-9. However, it degrades to a level below 80% of the initial concentration in 24 hours at 50ºC and pH 5. This process of degradation was further accelerated when the pH was above 5.²⁸ At pH 9 and 50ºC, all active catechins in the tea extracts had practically vanished in 24 hours, due to accelerated oxidation in the alkaline solution. When pure green tea catechins were heated to 98ºC for 15 minutes in distilled water in the presence of oxygen, about 15% of the catechins were lost. This heat-induced degradation of catechins may be markedly reduced when oxygen is excluded from the solution or has been exhausted.²⁷

One source has suggested that the dose of polyphenols needed for effective health protection is at least 300 to 400 mg of polyphenols per day, usually taken in the form of a green tea extract that may be standardized up to 97% polyphenols, with up to 67% being EGCG.²⁹ This amount of tea catechins is usually present in one cup of tea drink if the latter is properly brewed in the “traditional manner”, using high quality dry tea leaves. However, a daily consumption of three to ten (3-10) cups a day is necessary to achieve the maximum health benefits of tea drinking, dependent on the quality of the tea and the methods of tea brewing. As mentioned above, cancer onset in life can be delayed by regular tea consumption.¹⁹ Tea drinking may lower the recurrence rate and prolong disease-free period in patients with breast cancer.²⁰ These two series of clinical studies indicate a dose-dependent relationship between tea drinking and cancer prevention in humans. In order to achieve the maximum benefits of tea drinking, the authors recommended that an adult consume 10 cups of green tea, 180 ml per cup, per day.

Naturally, the volume of this herbal beverage to be consumed daily for the purpose of health protection depends on the levels of the active tea catechins and other effective ingredients in the final tea extract, which in turn vary as the result of many factors, including where the tea plant was grown, the age of the tea leaves when plucked, how the tea leaves were processed, how the dried tea leaves were stored and how the tea was brewed. The EGCG contents in the loose green tea leaves available on the Hong Kong market have been found to range from a low of 4.7 to a high of 10.44 g/100 g in dry weight.²⁷ Even the traditional methods of tea brewing differ from location to location in countries with a long history of tea-drinking culture. In order to maximize the benefits of drinking tea as a herbal beverage for health protection, it is best to select young leaves from the tea trees grown in a reputable plantation (for example, the use of insecticides should be prohibited), to choose a drying process with the maximum preservation of the tea catechins and other active ingredients, to store the dried tea leaves properly to avoid oxidation, and to brew the aqueous tea extracts under conditions with minimal catechin degradation for maximum preservation of its antioxidative activities. Since oxidation is the major mechanism of tea catechin degradation, especially at high temperature, the contents of molecular oxygen in a hot tea extract should be reduced to a minimal level during tea brewing.

The traditional methods of tea brewing have not taken proper measures to prevent oxidation of the “antioxidants” during tea extraction. The common practice of brewing tea leaves in a pot of hot water exposed to atmospheric oxygen, then pouring the tea extract into cups and sipping the tea from the cups when the liquid cools down to ambient temperature exposes the hot tea to free oxygen molecules in the air through the entire process. A significant and uncontrollable proportion of the tea catechins extracted would have been rendered inactive by oxidation during the brewing and cooling process. Another common practice of tea drinking is to continuously add more hot water into the tea pot for the second and third infusion of the same tea leaves after the first extraction has been consumed. Based on the current understandings, the second and third aqueous extractions of the tea leaves left in pot would yield little active tea catechins because almost 100% of the active ingredients beneficial for health protection would have been extracted out from the tea leaves in the first 5-10 minutes if the water is hot enough. A prolonged extraction in hot water only draws out more caffeine and other bitter substances from the tea leaves which offer little health benefits.

↑top | >>next page>>

Dr. Lee's dog, Marty:
Canine lymphoma survivor and TeaForHealth™ patient