A lecture about Tea
Lecture on Tea and Chinese Herb 09.20.06Prepared for The Leaf – All things Tea
Marco Chung-Shu Lam, MS, Lic. Acupuncturist
Tea is the second most commonly drank liquid on earth after water. It has numerous medicinal benefits mainly due to its antibacterial and antioxidant properties.
• Description, origin and distribution
• Chemical constituents
• Medicinal benefits
• Possible health risks
• Further reading
• References
Many of us would agree with the ancient Chinese saying: " Better to be deprived of food for three days, than of tea for one" (Ody 1993). Tea has been consumed socially and habitually by people for so long (since ± 3000 BC), that aside from the astringent taste and boost it provides, it’s medicinal properties are often over-looked. However, traditional healers have long believed that drinking tea is a means of prolonging life (Chopra 2000).
Description, origin and distribution
Native to China, C. sinensis spread to India and Japan, then to Europe and Russia, arriving in the New World in the late 17th century (Chopra 2000). As a cultivated evergreen plant, tea is usually trimmed to below six ft. in height. However, if left to grow wild, the bush can reach 30 ft. green, Oolong and black (‘normal’) tea are all made from the leaves of the same plant species, Camellia sinensis (Ody 1993). Their chemical content and flavours are, however, very different due to their respective fermentation processes. Green tea leaves are allowed to wither in hot air then pan-fried to halt the oxidation (fermentation) processes. The leaves of Oolong tea are wilted in sunlight, bruised and allowed to partially oxidise, until reddening of the leaf edges occurs. Black teas leaves are fermented in cool, humid rooms, until the entire leaf is darkened (Chopra: 87).
Chemical constituents
Tea leaves contain many compounds, such as polysaccharides, volatile oils, vitamins, minerals, purines, alkaloids (eg.caffeine) and polyphenols (catechins and flavonoids). Although all three tea types have antibacterial and free radical capturing (antioxidising) activities, the efficacy decreases substantially the darker the variety of tea is. This is due to lower contents of anti-oxidising polyphenols remaining in the leaves (Chopra 2000).
• Flavonoids (polyphenols). Proven medicinal properties include antioxidant, anti-inflammatory, anti-allergic, antibacterial and antiviral effects. They also have the ability to strengthen veins and decrease their permeability. It is widely believed that the antioxidising effects of both black and green varieties are reduced when taken with milk.This is thought to be due to the effective binding of flavonoids by proteins (Chopra: 2000). However, a recent ex vivo study concluded that flavonols are absorbed from tea and their bioavailability is not affected by milk.7
• Tea tannins - called catechins (polyphenols). Appear to be the most potent therapeutic plant-derived chemicals, in that, aside from their antiseptic and antioxidant properties, they are able to form complexes with other molecules, thereby detoxifying the system (van Wyk et al). Catechins include gallocatechin, epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (EGC) and epigallocatechin gallate (EGCG). Catechins make up approximately one-quarter of fresh dried green tea leaves, of which EGCG comprises 60 % (Chopra 2000).
• Vitamin C. A recent study by du Toit et al, showed that Black, Green and Oolong tea are all extremely good sources of vitamin C. They found that 1 or 2 cups a day provide the equivalent of three glasses of orange juice or two capsules (200mg) of vitamin C.
Medicinal benefits
Benefits of all tea varieties
• Digestive complaints
• Infections
• Pain relief Benefits of green tea
• Skin disorders
• Guards against tooth decay
• Stems bleeding
• Boosts the immune system
• Combats various forms of cancer
• Reduces risk of cardiovascular diseases
• Digestive complaints. Tea is an old home remedy for unsettled digestive systems. All three varieties have antibacterial, antioxidant, antiseptic and detoxifying properties that make tea effective in treating infectious dysentery as well as easing inflammatory bowel disease.
• Infections. The antiseptic properties of tea are attributed to the tannins and flavonoids present. The former also have anti-inflammatory effects, while the latter act as detoxifiers (van Wyk et al). Tea has been used as an age-old home remedy for burns, wounds and swelling. A poultice of green tea eases itching and inflammation of insect bites, while a compress stems bleeding.
• Guards against tooth decay. As well as containing catechins, green tea is known to be very rich in flouride. A study using natural toothpaste (containing green tea bioflavonoid/zinc ascorbate) was conducted to determine the effect on bacterial plaque accumulation. The results showed a significant decrease in total viable plaque biomass when compared with a non-active control toothpaste19. Another in vitro experiment, using both green and black tea, showed the epicatechins to have properties that prevent bacterial adherence to teeth, inhibit human and bacterial amylases and inhibit glucosyl transferase, thereby limiting the biosynthesis of sticky glucan. The few human ex vivo clinical trials performed, suggest that regular tea drinking may decrease the incidence and severity of caries. If substantiated, tea could play a very economical role in public health 6.
• Skin disorders. Using different animal models, many laboratories have shown that green tea extract, taken orally or applied to the skin, inhibits skin tumour formation induced by chemical carcinogens or ultra-violet radiation(UVB). The extracts also possess anti-inflammatory activity that, similarly to the anti-cancer forming activity, is owed to the polyphenolic constituents present therein. The polyphenol mainly responsible for the prevention of cancer formation is epigallocatechin-3-gallate(EGCG). When applied to mouse skin, EGCG prevents UVB-induced oxidative stress and suppression of the immune system. Mouse skin models have illustrated extensive beneficial effects of green tea extracts and although only a few human skin studies have been conducted, many cosmetic and pharmaceutical companies are supplementing their skin care products with green tea extracts10.
• Immune booster. This is due to the free radical capturing (antioxidant), invigorating (caffeine),detoxifying antibacterial properties of tea, as well as the vitamins and minerals present therein.
• Combats various forms of cancer. Green tea has a reputed role in cancer prevention as tea catechins have been shown to inhibit tumour cell proliferation as well as promote the destruction of leukaemia cells 17. Laboratory studies on cultures of tumour cells and mice given carcinogenic chemicals, showed green teas' potential to inhibit cancer cell growth. Similarly, both black and green tea have been shown to suppress Deoxyribonucleic acid (DNA) reproduction and promote the demise of tumour cells (Chopra: 2000).
One study involving an in vitro plasmid DNA system and radiolytically generating reactive oxygen species (ROS) under constant scavenging conditions, showed that all four catechins (EC; EGC; ECG and EGCG), moderate free radical damage sustained by DNA - even when present in low concentrations. EGCG was the most effective of the catechins, with activity seen at micromolar concentrations. The antioxidant activity of catechins is thought to occur by the mechanism of electron transfer from catechins to ROS-induced radical sites on the DNA 1.
Inoue et al examined the association between regular green tea consumption prior to diagnosis and subsequent risk of breast cancer recurrence. The results indicated that regular intake of green tea, in the early stages of breast cancer, may prevent the recurrence thereof. Furthermore, the incidence of prostate cancer among Chinese men was found to be the lowest in the world and correlated with their tea consumption (Chopra: 2000).
Stomach cancer is the second most common form of cancer worldwide. Thus much research has gone into searching for cures and treatments thereof. One such study, conducted in China15, aimed at investigating the effect of green tea consumption on chronic gastritis and the risk of stomach cancer. Their sample included 133 stomach cancer cases, 166 chronic gastritis cases and 433 healthy controls. Results showed an inverse association between green tea drinking and both diseases. Furthermore, dose-response relationships were observed, with years of green tea consumption being more effective in combating both stomach cancer and chronic gastritis.
A study11 using 8552 residents, representative of Japan’s population, tested whether or not Green tea was an effective anti-carcinogenic. Results showed a decreased relative risk of cancer incidence for those consuming over ten cups, compared with those consuming below three cups of green tea per day. The risks decreased by 57 % for women, 54 % for men and 59 % for both sexes. In addition, increased consumption was associated with a significant delay in the onset of cancer.
• Decreases risk of cardiovascular disease. Coronary artery disease is associated with increased oxidative stress and dysfunction of the endothelium(cells lining the heart, blood and lymphatic vessels and various other cavities). Some antioxidants are known to reverse endothelial dysfunction4. Thus numerous studies have aimed at determining whether or not the antioxidant polyphenols (flavonoids and catechins) present in tea, can perform the same function. Although results tended to be equivocal, several findings were quite common. Various case studies show that tea does not decrease blood pressure, nor plasma lipids (cholesterol) ex vivo 13 and while tea catechins do inhibit the peroxidation of LDL (low density lipoprotein) cholesterol in vitro, the effect ex vivo is small12,13.
Catechins are absorbed from tea but low plasma concentrations are attained and easily excreted, unless they are rapidly absorbed or metabolised 18. This may explain why other studies only revealed effectiveness at high dosages. A study on 8 552 residents, representative of Japan’s population, revealed a decreased relative risk of death from coronary disease as 82 % for women, 58 % for men, and 72 % for both sexes consuming over ten cups of green tea per day11.
Amongst other findings, a study by Riemersma et al concluded that although the plasma antioxidant potential increases post green tea consumption, this is not so for black tea. However, a more recent (July 2001) paper4 revealed increased plasma flavonoids after short- and long-term black tea consumption and improved vasomotor functioning (endothelium-dependant flow-mediated dilation) of the brachial artery.
While mild cholesterol lowering has been documented in mice and green tea consumption has been shown to reduce the development of aortic atherosclerosis (hardening, thickening and elasticity-loss of arteries) in rabbits, it is more difficult to show in humans and results are inconsistent. While most epidemiological studies support the suggested role of tea in decreasing the risk of coronary artery disease, there is much debate as to the mechanisms of benefit. However, the potential benefits of tea consumption are worthy of confirmation by more human trials.
Possible health risks
• Although all tea varieties possess far less caffeine than both coffee and coke cola (with green having the least), it can induce insomnia and nervousness in sensitive and over-indulgent individuals.
• It should also be noted that the antioxidant action of (phenolic-rich) tea extracts has been shown to reduce the ability of humans to utilise dietary iron. Thus excessive intake of tea should be avoided by people who are prone to anaemia14.
While the exact origin of tea's discovery is not known, the most widely accepted version recounts the tale of a man who lived in China many thousands of years ago. The man was standing under a tea tree holding a cup of boiling water when a few tea leaves fell into his cup. He tasted the water and found it to be quite agreeable. Hence, the birth of tea.
As early as 700 AD, tea houses became centers for social and philosophical discourse, and the drink itself was favored among poets, royalty, educators, martial artists, and doctors. Tea has remained a staple in Chinese households today. In recent years, tea has made significant cultural and scientific inroads. With gaining demand, the United States is now China's second largest importer of Chinese tea. The popularity of tea lies not only in its many flavors but also in its medicinal properties, which are well known to practitioners of traditional Chinese medicine (TCM). According to an ancient TCM medical text called Essentially Treasured Prescriptions for Emergencies, "tea makes people energetic and pleased." Another text, Tea Manual from the Ming dynasty, teaches that "drinking tea helps quench thirst, digest food, dissolve phlegm, refresh the mind, produce diuresis, promote vision, relieve irritability, and remove greasiness. One cannot go without tea even for a single day."
Types of Tea
The Chinese word for tea is cha . One should not confuse cha with chai served in cafés. As tea spread to the Middle East, people began adding spices to it and the name became chai. This article will use the standard TCM terminology for tea, cha. All teas come from an evergreen plant, Camellia sinensis , which produces many types of tea. These plants, when grown in the wild, can reach up to 50 ft in height. However, most tea plants are cultivated and are kept as shrubs that are 3- to 5-ft tall. Various types of tea are created by the fermentation/oxidation process, which is considered an art in Chinese culture. Approximately 300 different varieties of cha are produced in China alone. Tea comes in five basic types:
Black Teas : These teas (also known as hong cha, or red teas, in Chinese) have been fully fermented, giving them a full, smoky flavor. As the leaves are picked, they are spread on a screen and dried by exposure to hot air or the sun. The leaves are rolled and tossed, causing an enzyme reaction called oxidation to occur. Once brewed, black tea will range in color from red to dark brown. Black tea is more yang (the active principle in TCM; refer to "Role of Nutrition and Dietary Therapy in TCM" in the July 2003 U.S. Pharmacist for a full definition) in nature and is best consumed during colder months because of its warming properties. For this reason, black tea is beneficial for people with other conditions related to cold weather, such as pain in the extremities, poor circulation, arthritis due to dampness, or coughs caused by a cold.
Most often, black tea is consumed after desserts, sweets, or salty foods, or it may be served between meals, as its flavor is too strong to go with meals. Keemun, lapsang souchong, and pu-er are well-known varieties of black tea from the Yunnan province in China. Pu-er black tea is the most effective for keeping weight, triglycerides, and cholesterol levels down. It is used in Chinese nutritional medicine to decrease risk of stroke, atherosclerosis, and obesity.
Oolong Teas : Oolong teas, translated as dark dragon, are half fermented. These tea leaves undergo oxidation and fermentation so that the outside edges of the leaves are darkened, leaving the middle green in color. Oolong teas have a flavor between a black tea and a green tea. Once brewed, the tea is light brown to dark yellow; it is the type usually served in Chinese restaurants in this country. Thus, oolong teas are often served with meals or dim sum brunch, a finger-food brunch that consists of several small portions of various dishes. Ti kuan yin is a popular oolong tea that comes from the Fujian province of China.
Oolong teas can aid digestion as well as decrease the absorption of fats and bad cholesterol from big meals such as Thanksgiving dinner or meals heavy in meat or high in carbohydrates. Oolong tea is an excellent choice for hypertensive patients. It is also beneficial for patients who have skin problems such as rashes or acne.
Green Teas : Lu cha (the Chinese collective term for all green teas) is a green- to yellowish-colored tea that has a light, fresh, grassy flavor. These tea leaves are not fermented at all. Instead, they are steamed or baked immediately after being picked. Lu cha is considered the most yin (the opposite of yang) of all the teas and therefore has a weaker ability to boost overall metabolism as compared to more yang teas such as black or oolong. Green teas are popular during summer because of their cooling properties and have higher antioxidant contents than all other types of tea. Gunpowder tea is the green tea with the highest antioxidant content.
Genmai is another green tea. It is mixed with unpolished brown rice and provides the body with extra fiber and vitamin B. Lungjing, also known as dragon well, is another popular green tea. Green tea is used in TCM for patients suffering from menopause, sore throat, fever, allergies, and anxiety, and it is also used as a prevention of cancer.
Flower, Fruit, and Scented Teas : These are black, green, or oolong teas scented with a flower such as jasmine, hibiscus, or rose or scented with a fruit such as lychee. The purpose of such additions is primarily for aromatherapy and to enhance flavor. This type of tea is often served as a dessert tea because of its fragrant scent. In addition, a scented tea is used when serving fish, lamb, or other strong-tasting food. Some of these teas may contain only flowers, with no black, green, or oolong tea leaves. An example is ju hua, which is chrysanthemum flowers. It is a popular drink during the summer because of its ability to minimize effects of summer heat, such as excessive sweating, dehydration, headaches, irritability, sinus allergies, and eye problems.
Teas used in TCM may also contain only fruit, such as chen pi (dried orange peel). Fruit teas are beneficial for those suffering from intestinal or stomach problems such as bloating, gas, indigestion, and heartburn.
White Teas : These teas are emerging as a new favorite among tea consumers. White teas, like green teas, are not fermented. White tea comes from the white fuzzy, hair-like fur that exists on the leaves or buds of the branch tips. These tips are only plucked once a year, so white teas are not readily available. Since only the small leaves from the tips of the branch are used, this tea is lighter in color and aroma, and has a delicate flavor.
Health Benefits
There is a famous quote from the ancient Chinese herbal pharmacopoeia called Ben Cao Gan Mu that states, "Tea is better than water for it does not carry diseases; neither does it act like poison as water does when the wells contain foul and rotten matter."
Besides the health benefits already mentioned, scientific research proves that tea also has antibacterial, antiviral, and antifungal properties. It lowers blood sugar, combats osteoporosis, prevents tooth decay, boosts the immune system, replenishes vitamins, alleviates exposure to radioactivity, and activates qi (the moving force that flows through all living things, according to Chinese medicine, or life energy) and blood flow. Tea can also decrease plaque buildup in the blood vessels.
In general, tea contains 20 amino acids, 12 sugars, six organic acids, polyphenolic compounds, essential oils, magnesium, fluoride, theophylline, and vitamin C. The polyphenols in tea are a powerful antioxidant that aids in cancer prevention. It is no wonder that the "Father of Tea," Lu Yu of the Tang dynasty, said, "I would rather drink no wine for my entire life than drink no tea every day."
Modern science is just beginning to explore the possibilities of the medicinal properties of teas, and the following are some of the areas where it is gaining significant recognition.
Alzheimer's Disease : Both black and green teas inhibit the activity of acetylcholinesterase and butyrylcholinesterase, which are brain enzymes linked to Alzheimer's disease. Green tea also inhibits beta-secretase, an enzyme that appears to be directly involved in the early development of Alzheimer's disease.
Cancer : Heavy smokers who drank at least four cups of green or black tea each day had a 31% reduction in 8-hydroxydeoxyguanosine, a chemical that is released in response to DNA damage, compared to no reduction in a similar group who drank no tea, as reported by the American Association for Cancer Research.
Green tea has been associated with an increased survival rate of patients diagnosed with epithelial ovarian cancer. Three years after diagnosis, 77.9% of 104 green tea-drinking patients were still alive, compared to 47.9% of 140 non-tea drinkers.
In a study using mice, results suggested that polyphenols in green tea are able to battle prostate cancer. They can restrict the amount of blood and nutrients to the tumor and reduce the expression of proteins known to cause the cancer to spread.
HIV : A compound found in tea appears to prevent HIV from latching on to T cells. This is significant because current AIDS drugs target only active infection.
Hypertension : Habitual tea drinkers (defined in this study as consuming 6 to 16 oz. of tea per day for one year) who consumed a dark tea such as oolong showed a decrease in both systolic and diastolic blood pressure. Study authors noted several substances in tea that may reduce blood pressure: caffeine, antioxidants, amino acids, and a compound that relaxes smooth muscles.
External Uses of Tea
There are other uses for tea besides drinking it. Tea is known for its germicidal activity. Many Chinese restaurant patrons have been shocked to discover their leftover tea was used to wipe tabletops. If no medicine or ointment is available, washing a cut in tea can prevent the spread of infection. Research shows that washing with tea proves useful for treating athlete's foot and putting dry tea leaves in socks prevents them from gathering moisture. Tea in the Orient is sometimes placed in pillowcases and used as an air freshener because of its deodorizing properties. Tea can also be used as mouthwash to eliminate foul breath.
Tea Used in TCM Nutritional Medicine
Although Chinese teas used as beverages are rarely blended, tea leaves are sometimes used in combination with other foods in Chinese diet therapy. Here is an example of one such recipe for headache, fever, cough, and/or rhinitis due to cold or influenza:
ï walnuts, 25 g
ï bulb of green onions, 25 g
ï fresh ginger, 25 g
ï tea leaves, 15 g
Simmer crushed walnuts, crushed bulbs, and crushed ginger with tea leaves in 3 cups water for 10 minutes. Strain off liquid. Drink this decoction and allow body to sweat lightly. Avoid exposure to drafts. Consult an acupuncturist or a TCM practitioner for a holistic diagnosis and prescription if illness persists or exacerbates.
Tea Used in TCM Herbal Medicine
Tea has the following herbal properties: It is bitter, sweet, and cool in nature. The mechanism of actions of herbs was explained in a previous U.S. Pharmacist article titled, "The Art and Science of Chinese Herbal Medicine" (March 2003). Tea also acts on the heart, lung, and stomach meridians. To understand the meridian system, refer to the article, "A Clinical Guide to Acupuncture" (May 2003). One classical herb prescription that involves tea leaves is called Chuan Xiong Cha Tiao San, which consists of the following herbs:
ï Chuan xiong ( ligusticum rhizome), 120 g
ï Jing jie ( Herba schizonepetae), 120 g
ï Bai zhi ( Radix angelicae dahuricae), 60 g
ï Qiang huo ( Rhizoma seu radix notopterygii), 60 g
ï Gan cao ( Radix glycyrrhizae, licorice root), 60 g
ï Xi xin ( Herba asari), 30 g
ï Fang feng ( Radix ledebouriellae), 45 g
ï Bo he ( Herba menthae), 8 g
Grind all ingredients into powder. Mix 2 qian (6 grams) of the powder with a green tea beverage after meals three times daily. A TCM doctor or acupuncturist may prescribe this herbal prescription for a patient with exopathic wind/cold conditions, such as sinus allergy symptoms, nasal congestion, frontal headaches, sneezing, chills, and watery and itchy eyes. Using this information to self-medicate is not recommended. Please consult an acupuncturist for a proper TCM diagnosis before using any herbs.
Various Tea Products
As tea grows in popularity, it may be difficult to decide which tea to buy. The Chinese like to use loose-leaf tea; it is a higher grade than tea sold in teabags. Loose tea is less processed and therefore retains more of its original flavor as well as its therapeutic value. In the tea industry, tea in teabags is often referred to as tea dusts or shavings, since most of it comes from what is left when the leaves are gone. Chinese tea connoisseurs refer to tea used in teabags as tea "picked up from the floor" during production.
Tea crystals are lower in quality than bulk or loose tea. Products that contain tea crystals have little tea content and are mostly sugar. Tea capsules or tablets, although powerful, are not recommended because they are extremely concentrated and have drug-like properties that may interfere with other medication.
Tea Storage
Tea leaves should be stored in a dry box, tin container, or paper bag at room temperature away from direct sunlight. Since tea is a deodorizer, the leaves should be stored away from items with strong odors (e.g., soaps, mothballs) to prevent the tea from absorbing the smells of other substances. Tea Preparation When brewing tea, there are some basic steps to follow:
1. Put 1/2 to 1 tsp. of tea leaves into a teapot or tea strainer.
2. Pour boiling water into the teapot. Always use clear cold water for boiling. If using a strainer, place it over a cup and pour the boiling water through.
3. Steep tea for a few minutes before serving. For stronger preparation, steep tea longer or add more tea leaves.
The Chinese do not add milk and sugar to their tea, but the natural, slightly bitter taste of tea is difficult for some to enjoy. However, drinking tea without sugar and milk is a healthy habit to start, according to TCM, because it is being consumed in a more natural form.
Caffeine Content
A common misconception about caffeine is that it is inherently bad. This is not the case. In TCM, everything that exists in nature, in our food and drink, has its purpose for mankind. Teas are caffeinated, but because they are less yang than coffee, they have less of a moving energy. Therefore, unlike coffee, which releases caffeine all at once, leading to an instant "boost," the caffeine in tea is released slowly throughout the day. Overall, the caffeine content in tea is significantly lower than that of coffee. Patients sensitive to caffeine are unlikely to have a problem with tea, especially if it is infused lightly. To compare caffeine content of beverages, see table 1.
Conclusion
The use of cha to treat specific conditions in TCM dates back thousands of years. The far-reaching benefits of tea are just gaining acceptance in modern medicine. Culturally, tea has an important role in Chinese society; tea is served during business meetings, family gatherings, formal state dinners, Sunday brunches, casual meetings, or after tai chi exercises. Shen Nung, who lived around 3500 bc and is recognized as the father of natural medicine as well as the first pharmacist in TCM, gave this recommendation: "Tea gives vigor to the body, contentment to the mind, and determination of purpose." So, have a cup of tea and drink to your health.
[Marco Chung-Shu Lam is a licensed Acupuncturist and Chinese herb specialist. He has studied in China and now is practicing in Boulder, Colorado.]
Disclaimer: The benefits of tea are based on the thousands of years of human practices. However, please consult your doctors for any scientific approves. Teas are not the substitues of your medicinces.