||Green Tea (English)|
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
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
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.
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-gallate (EGCG), and other catechin
derivatives; phenolic acids; terpenoids; indole; anorganic
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,
Current clinical applications: cancer prevention, coughs, colds, asthma,
diarrhea, bacterial dysentery, and adjunct to radiation treatment (reduces
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
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
|Dosage Ranges and Duration of
Green tea is not usually prescribed as a medication even though it has
- Tea beverage: 3 cups/day (3 g soluble components, or 240 to 320 g
- 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
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
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
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.
|Regulatory and Compendial
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.
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Shiota S, Shimizu M, Mizushima T, Ito H, et al. Marked reduction in the
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(-)-epigallocatechin gallate with (-)-epicatechin, sulindac, or tamoxifen on
cancer-preventive activity in the human lung cancer cell line PC-9. Cancer
Sugiyama T, Sadzuka Y. Combination of theanine with doxorubicin inhibits
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Copyright © 2007 Drugs Area
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