Native to eastern Asia, tea was originally grown in China at least 5,000 years ago. Today, tea is widely cultivated in Asia and parts of the Middle East and Africa. Green tea is unfermented, while black tea is fermented. Oolong tea is semifermented. In green tea the fresh leaves are slightly steamed and then quickly dried. This process inactivates enzymes that oxidize polyphenols to derivative compounds.

Polyphenols have antioxidant and anticancer activities, but their conversion products do not. Green tea polyphenols (GTP) surpass vitamins C and E in their antioxidant protective properties. In black teas, the leaves are dried slowly, allowing them to ferment. The polyphenol conversion products in black tea have no significant therapeutic benefits.

Green tea is used in traditional Chinese medicine to promote digestion, counter flatulence, stimulate mental function, improve eyesight, and regulate body temperature. It is also thought to strengthen the arteries, reduce excess fats, clear phlegm, and neutralize poisons. The tannins in green tea have antidiarrhea activity. The longer tea leaves are brewed, the greater the tannin content.

The tea plant is a large shrub with evergreen leaves that can reach a height of 30 feet. However, it is usually pruned to two to three feet. The flowers have five or six white petals and multiple yellow stamens. The branches are smooth and covered by shiny, dark green, hairy leaves. The age of the leaf can be determined by its position on the harvested stem. The leaf buds, young leaves, and stem are the preferred plant parts for making teas.

• Leaves
• Leaf buds

Purine alkaloids (caffeine [2.9 to 4.2%], theophylline [0.02 to 0.04%], theobromine [0.15 to 0.2%]; polyphenols, including (+)catechin, d-catechin, (+)catechin, (–)epicatechin (EC), (–)epicatechin gallate (ECG), (–)epigallocatechin (EGC), (–)epigallocatechin-gallate (EGCG), and other catechin derivatives; phenolic acids; terpenoids; indole; anorganic ions.

Commercial preparations consist of dried leaf tea as well as extracts made from the leaves and leaf buds. The leaves are harvested, immediately heated, and then rolled and crushed to prevent enzymatic changes from altering the color and natural constituents. Green tea has 300 to 400 mg polyphenols and 50 to 100 mg caffeine per cup. Decaffeinated products contain concentrated polyphenols (60% to 89% total polyphenols). Both the epigallocatechin and total polyphenol content should be considered when purchasing commercial products.

Traditional herbal actions: astringent, bronchodilator, antiviral, antiarteriosclerotic, anticholesterolemic

Current clinical applications: cancer prevention, coughs, colds, asthma, diarrhea, bacterial dysentery, and adjunct to radiation treatment (reduces tissue damage).

Green tea taken as a beverage has antioxidant, anticancer, antimutagenic, antibacterial, antifungal, and antiviral properties. Population studies show that green tea use correlated with lowered serum cholesterol totals and triglyceride levels, lowered LDL levels, and increased HDL levels. Green tea probably prevents atheroslerosis by blocking the oxidation of LDL. Purine alkaloids isolated from green tea have a relaxing effect on bronchial smooth muscle. Purine alkaloids also enhance cornary blood flow and simulate cardiac muscle. They may even account for the diuretic effects of green tea. One of the catechins in green tea, EGCG, had an antiplatelet aggregation effect comparable to aspirin.

Other population studies suggest that green tea taken daily as a beverage prevents cancer. Black tea consumption, on the other hand, correlated with increased risk of cancers of the rectum, gallbladder, and endometrium. GTP suppressed the activation and formation of cancer-causing substances. The cancer-prevention effects of green tea are strongest against cancers of the gastrointestinal tract, lung, and breast.

In in vitro experiments, GTP blocked the growth of mammary cancer cell lines. Green tea apparently disrupts interactions among tumor promoters, hormones, growth factors, and their receptors. In animal models, green tea extracts administered to mice in doses comparable to the amount consumed by humans blocked the formation of ultraviolet B (UVB)-induced sunburn lesions and skin tumors. And in both animal and human investigations, green tea beverages ingested with meals inhibited the formation of carcinogenic nitrosamines.

In vivo research revealed that GTP enhanced the catalytic activity of key enzymes involved in the synthesis of glutathione and quinone in the liver, small intestine, and lungs. EGCG showed potent anti-tumorigenesis in skin. In human investigations, GTP had significant anti-mutagenic properties against carcinogens formed through the process of cooking meats and fish. Polyphenols also scavenged free radicals such as hydrogen peroxide and superoxide anions. In other research, epicatechin derivatives decreased lipid peroxidation in epidermal microsomes. And GTP significantly decreased dental caries by inhibiting Streptococcus mutans, the bacterium that causes dental cavities.

Green tea is not usually prescribed as a medication even though it has therapeutic benefits.

Recommended dosage:

• Tea beverage: 3 cups/day (3 g soluble components, or 240 to 320 g polyphenols)
• Standardized green tea extract (80% total polyphenols and 55% epigallocatechin): 300 to 400 mg/day.
• Capsules and liquid preparations are also available.

Quantities of greater than 5 cups of tea consumed as a beverage (equivalent to more than 300 mg caffeine taken daily) are considered overdoses. Intake above this level can produce side effects of restlessness, tremor, and heightened reflex excitability. Long-term daily dosage beyond 1.5 g of caffeine can induce irritability, insomnia, palpitation, vertigo, vomiting, diarrhea, loss of appetite, and headache. Vomiting and abdominal spasm are indications of potential caffeine overdose.

Individuals who have sensitive stomachs should limit their intake of green tea. The chlorogenic acid and tannins in tea can cause hyperacidity, gastric irritation, reduced appetite, and diarrhea. Tea should also be used with caution by people who have cardiovascular complications, kidney disorders, overactive thyroids, and a tendency toward spasm. Because caffeine overdoses can lead to anxiety attacks, persons prone to panic or other similar psychiatric disorders should exercise caution in drinking tea.

Pregnant women should avoid caffeine. At the very least, they should limit their intake to a maximum of 200 mg/day, or 3 cups taken at evenly spaced intervals during the day. Nursing mothers who drink tea put their infants at risk for sleep disorders.

In an in vitro study, epicatechin gallate, a catechin constituent of green tea leaves, was shown to markedly lower the minimum inhibitory concentration of beta-lactam antibiotics against methicillin-resistant Staphylococcus aureus (MRSA) (Shiota et al. 1999). Epicathechin gallate may restore the effectiveness of beta-lactam antibiotics against MRSA, a major cause of nosocomial infections in hospitals that is resistant to many antibacterial agents including beta-lactams.

Theanine, a water-soluble amino acid from green tea leaves, has been shown to enhance the anti-tumor activity of doxorubicin in mice. In one study, the combination of theanine (10 mg/kg/day) with doxorubicin (2 mg/kg/day) reduced the tumor weight to 30% of the control level and inhibited hepatic metastasis of M5076 ovarian sarcoma (Sugiyama and Sadzuka 1999). In another study, administration of green tea powder (1 g/kg/day po for 4 days) to Ehrlich ascites carcinoma tumor-bearing mice enhanced the inhibitory effects of doxorubicin on tumor growth 2.5-fold (Sadzuka et al. 1998). Coadministration of doxorubicin with green tea increased the concentration of doxorubicin in the tumor, but not in normal tissue. Patients undergoing chemotherapy may benefit from drinking green tea, although clinical trials are needed to confirm these results.

In one study, a combination of green tea extract and tamoxifen significantly enhanced induction of apoptosis by (-)-epigallocatechin gallate (EGCG) in vitro (Suganuma et al. 1999). Drinking green tea may enhance the cancer-preventive activity of tamoxifen, requiring smaller doses with potentially fewer side effects.

Drinking large amounts of green tea may decrease the effectiveness of warfarin. Green tea contains vitamin K (approximately 0.03 microgram of vitamin K/100 g of brewed tea), which is known to inhibit the effects of warfarin (Taylor and Wilt 1999). In one case study, green tea consumption was reported to cause a fall in INR from a high of 3.79 to a low of 1.14 in a man treated with warfarin. He had begun drinking one-half to one gallon of green tea daily during his course of therapy with warfarin. The INR increased to 2.55 after discontinuation of the tea.

The U.S. FDA classifies green tea as a dietary supplement. Green tea is not usually sold as an herbal medicine. It is approved as a nonprescription traditional diuretic in Belgium.

Ali M, et al. A potent thromboxane inhibitor in green tea. Prostaglandins Leukot Essent Fatty Acids. 1990;40:281-283.

Blumenthal M, ed. The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, Mass: Integrative Medicine Communications; 1998:47, 132.

Bradley P, ed. British Herbal Compendium. Vol. 1. Dorset, England: British Herbal Medicine Association; 1992:1:96-98.

Heinerman J. Heinerman's Encyclopedia of Fruits, Vegetables and Herbs. Englewood Cliffs, NJ: Prentice Hall; 1988:112-113.

Imai K, Nakachi K. Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases. BMJ. 1995;310:693-696.

Murray M. The Healing Power of Herbs: The Enlightened Person's Guide to the Wonders of Medicinal Plants. Rocklin, Calif: Prima Publishing; 1995.

Poppel Piet A, van den Brandt. Consumption of black tea and cancer risk: a prospective cohort study. J Natl Cancer Inst. 1996;88:93-100.

Sadzuka Y, Sugiyama T, Hirota S. Modulation of cancer chemotherapy by green tea. Clin Cancer Res. 1998;4:153-156.

Shim JH, Kang MG, Kim YH, Roberts C, Lee IP. Chemopreventive effect of green tea (Camellia sinensis) among cigarette smoke. Cancer Epidemio Biomarkers Prev. 1995; 4(4):387-91.

Shiota S, Shimizu M, Mizushima T, Ito H, et al. Marked reduction in the minimum inhibitory concentration (MIC) of ß-lactams in methicillin-resistant Staphylococcus aureus produced by epicatechin gallate, an ingredient of green tea (Camellia sinensis). Biol. Pharm. Bull. 1999;22(12):1388-1390.

Sirving K. Drinking black tea may cut risk of stroke. AMA Arch Intern Med. March 25, 1998.

Snow J. Camellia sinensis (L.) Kuntze (Theaceae). Protocol J Botan Med. 1995;1:47-51.

Suganuma M, Okabe S, Kai Y, Sueoka N, et al. Synergistic effects of (-)-epigallocatechin gallate with (-)-epicatechin, sulindac, or tamoxifen on cancer-preventive activity in the human lung cancer cell line PC-9. Cancer Res. 1999;59:44-47.

Sugiyama T, Sadzuka Y. Combination of theanine with doxorubicin inhibits hepatic metastasis of M5076 ovarian sarcoma. Clin Cancer Res. 1999;5:413-416.

Tamozawa H, et al. Natural antioxidants I. Antioxidant components of tea leaf (Thea sinensis L.). Chem Pharm Bull. 1984;32:2011-2014.

Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann Pharmacother. 1999;33:426-428.Tyler V. Herbs of Choice: The Therapeutic Use of Phytomedicinals. Binghamton, NY: Pharmaceutical Products Press; 1994.

Wang Z, et al. Antimutagenic activity of green tea polyphenols. Mutation Research. 1989;223:273-285.

Windridge C. The Fountain of Health. An A-Z of Traditional Chinese Medicine. London: Mainstream Publishing; 1994:259.