Web site: "Information
About Herbs, Botanicals and Other Products"
URL: http://www.mskcc.org/aboutherbs
© 2003 Memorial Sloar-Kettering Cancer Center (Monograph)
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Full Text |
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Barrie Cassileth
and K. Simon Yeung
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Green
Tea
(Camellia sinensis)
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| Clinical Summary |
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Derived
from the leaf of the plant. Patients use this as a dietary beverage and to
prevent and treat cancer, hyperlipidemia, hypertension, and
atherosclerosis. The principal active constituent in green tea is
epigallocatechin-3-gallate (EGCG), which accounts for 40% of the total
polyphenol content of green tea extract. Caffeinated green tea may cause
insomnia and nausea. Use of decaffeinated products may be preferred due to
lower incidence of adverse events, but data are inconsistent regarding the
relative efficacy of caffeinated versus decaffeinated teas. Tannins in
green tea may reduce absorption and bioavailability of codeine, atropine,
and iron supplements. Studies of the chemopreventive activity of green tea
indicated some positive results. Green tea polyphenols may reduce risk of
prostate, breast, esophageal, lung, skin, pancreatic, and bladder cancers
and oral leukoplakia. Research evaluating the effectiveness of green tea
extracts to treat cancer is currently underway. Cardiovascular protection
from constituents in green tea is not established in large-scale human
studies. Moderate intake of green tea appears safe.
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| Scientific Name |
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Camellia
sinensis
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| Also Known As |
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Chinese
tea, tea, green tea extract, green tea polyphenols, epigallocatechin
gallate (EGCG), Camellia thea, Camellia theifera, Thea sinensis,
Thea bohea, Thea
viridis
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| Purported Uses |
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• Cancer
prevention
• Cancer
treatment
• Cardiovascular
disease
• Cognitive
improvement
• GI
disorders
• Hypertension
• Weight
loss
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Constituents
[9] |
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• Caffeine
• Flavonoids •
Methylxanthines:
Theophylline, theobromine, and theanine
• Polyphenols:
Gallic acid and catechins: gallocatechin (GC), epigallocatechin (EGC),
epicatechin (EC), and epigallocatechin gallate (EGCG)
• Polysaccharides
• Proanthocyanidins
(tannins)
• Vitamins:
Ascorbic acid, tocopherol
• Other:
Fluoride, chlorophyll, organic acids
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Mechanism Of Action
[1], [2], [3], [4], [5], [6], [7], [13], [14], [15], [16], [17], [18],
[19], [21], [24], [25], [26] |
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The
anticancer activity of green tea is thought related to its polyphenol
content. Its chemopreventive attributes are associated with catechin
epigallocatechin-3-gallate (EGCG), which is thought to induce apoptosis
and tumor antiangiogenesis. EGCG may inhibit enzymes involved in cell
replication and DNA synthesis by interfering with cell-to-cell adhesion or
via inhibition of intracellular communication pathways required for cell
division. In vitro data indicate that concentrations of 30 mcg/mL EGCG and
(-)-epigallocatechin (EGC) inhibit LOX-dependent arachidonic acid
metabolism by 30-75% in normal human colon mucosa and colon cancers. In
vitro studies in human colon cancer cell lines suggest that EGCG inhibits
topoisomerase I, but not topoisomerase II. EGC also inhibits DNA
replication in vitro in three leukemia cancer cell lines, Jurkat T, HL-60
and K562. Topical EGCG may be useful as chemoprevention for skin cancer,
but additional research and formulation are necessary.
Green tea's antioxidant activity may repair oxidative damage to cells, but
its role in protection against cancer is unclear. Mechanism of action is
not fully known, as the biological activity of its polyphenols may act
synergistically with other constituents of the plant. Administration of
green tea before and during carcinogen treatment reduces the incidence and
number of stomach and esophageal tumors in mice.
The tannins in green tea may have antibacterial properties and can produce
anti-diarrhea effects. Green tea is thought to confer cardiovascular
protection by increasing HDL cholesterol, decreasing LDL cholesterol and
triglycerides, as well as by blocking platelet aggregation. Flavonoids
present in green tea may reduce lipoprotein oxidation, although more
research on green tea constituents and cardiovascular disease is required.
Green tea also contains caffeine, which has stimulatory effects and is
responsible for the majority of adverse effects and drug interactions. It
is unknown whether removing caffeine alters green tea's activities.
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Pharmacokinetics
[8], [9], [10], [11], [15] |
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Catechins
from green tea are absorbed rapidly; the addition of milk does not impair
bioavailability of tea catechins in green tea. Following
ingestion of steeped green tea leaves or catechin extract, polyphenol can
be measured in blood, urine, saliva, and feces. This indicates that
ingested polyphenols and their metabolites may provide localized tissue
action in addition to indirect gastrointestinal effects.
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Warnings
[7] |
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Although
the U.S. Food and Drug Administration (FDA) includes tea on their list of
"Generally Recognized As Safe" substances, pregnant women and
women who breast feed should limit their intake of green tea because of
caffeine content.
Because tea can pass into breast milk, it may cause sleep disorders in
nursing infants. Green tea ingestion in infants has been linked to
impaired iron metabolism and microcytic anemia.
Individuals with peptic ulcers may want to avoid drinking green tea
because it can stimulate the production of gastric acid.
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| Adverse Reactions
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Reported (Oral): Nausea and GI upset, possibly due to
tannin content. Insomnia, irritability, and nervousness can occur due to
caffeine content.
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Drug Interactions
[7], [12], [20] |
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Adenosine:
The caffeine content in green tea may inhibit the hemodynamic effects of
adenosine.
Anticoagulants / Antiplatelets: Theoretically, consumption
of large amounts of green tea (.5-1 gallon/day) may provide enough vitamin
K to antagonize the effects of anticoagulants and antiplatelet agents,
though this effect has not been reported in humans.
Atropine: The tannin content in green tea may reduce the
absorption of atropine.
Iron supplements: The tannin content in green tea may reduce
the bioavailability of iron. Green tea should be taken either 2 hours
before or 4 hours following iron administration.
Codeine: The tannin content in green tea may reduce the
absorption of codeine.
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| Lab Interactions |
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Caffeine
in green tea may increase PT / PTT. Check labels for caffeine-free
product.
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| Literature Summary And Critique |
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Pisters
KM, et al. Phase
I trial of oral green tea extract in adult patients with solid tumors. J
Clin Oncol 2001;19:1830-8.
A phase I trial to determine the maximum-tolerated dose, toxicity,
and pharmacology of oral green tea extract (GTE) administered once or
three times daily to patients with refractory solid tumors. Each cohort
consisted of three or more adult cancer patients with dose ranges of 0.5
to 5.05 g/m2 once daily and 1.0 to 2.2 grams/m2
three times daily with water after meals for 4 weeks, to a maximum of
6 months. Pharmacokinetic analyses were encouraged but optional. A total
of 49 patients were studied. Patient characteristics: median age, 57 years
(range, 27 to 77 years); 23 patients were women (47%); 21 were diagnosed
with non-small-cell lung, 19 with head and neck cancer, three with
mesothelioma, and six had other cancers. No major responses were noted.
Mild to moderate toxicity was related to caffeine content of GTE and
promptly reversed upon discontinuation. Dose-limiting toxicities included
neurologic and gastrointestinal effects. The maximum-tolerated dose was
4.2 g/m2 once daily or 1.0 g/m2 three times daily
(approximately 2.5 liters brewed green tea/day). Additional studies are
recommended.
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Sun
CL, et al. Urinary
tea polyphenols in relation to gastric and esophageal cancers: a
prospective study of men in Shanghai, China. Carcinogenesis
2002;23:1497-503.
A
prospective cohort study examining the relationship between tea
polyphenols and cancer risk. The Shanghai Cohort consists of 18,244 men
aged 45-64 with up to 12 years of follow-up. Validated biomarkers of tea
polyphenols (epigallocatechin (ECG), epicatechin (EC), and their
metabolites M4 and M6) were measured in urine collected at the
introductory interview. Tea intake was not assessed at the
interview. One hundred and ninety cases of gastric cancer and 42 cases of
esophageal cancer developed; these cases were compared to 772 cohort
control subjects matched for age, month/year of sample
collection, and neighborhood of residence, but not for risk factors. When
adjusted for risk factors (smoking, alcohol intake, H. pylori
seropositivity, and serum carotene level), tea polyphenols were not
associated with a decreased risk of gastric cancer. After exclusion
of cases diagnosed under 4 years follow-up, which the authors justify by
proposing that data from patients with advancing disease may have been
inappropriate for dietary studies, a protective effect of ECG alone
on gastric cancer was found. This effect was primarily seen among
subjects with low serum carotenes. It is not likely that a
one-time measurement of urine tea polyphenols is an adequate indicator of
average long-term tea consumption.
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Tsubono
Y, et al. Green tea and the risk of gastric cancer in Japan. N
Engl J Med
2001;344:632-6.
A prospective population survey conducted in the Miyagi Prefecture of
Japan assessing green tea intake and various health habits. A total of
26,311 resident surveys were included equaling nearly 200,000 person-years
of follow-up. No association was found between consumption of green tea
(range <1 to >5 cups per day) and risk of gastric cancer
development. Adjustments were made for cigarette and alcohol use, age,
health insurance, and other dietary intake. While results cannot be
extrapolated to other populations, it appears that green tea is not
related to an increase or decrease in risk of gastric cancer.
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| References |
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[1] Hamilton-Miller
JM. Anti-cariogenic properties of tea (Camellia sinensis). J Med
Microbiol 2001;50:299-302.
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[2] Tosetti
F, Ferrari N, De Flora S. Angioprevention: angiogenesis is a common and
key target for cancer chemopreventive agents. FASEB J
2002;16:2-14.
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[3] Wang
ZY, et al. Inhibitory
effect of green tea on the growth of established skin papillomas in mice. Cancer
Res
1992;52:6657-65.
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[4] Kada
T, et al. Detection
and chemical identification of natural bio-antimutagens. A case of the
green tea factor. Mutat
Res
1985;150:127-32.
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[5]
Liao
S, et al. Growth
inhibition and regression of human prostate and breast tumors in athymic
mice by tea epigallocatechin gallate. Cancer
Lett
1995;96:239-43.
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[6]
Dulloo
AG, et al. Efficacy
of a green tea extract rich in catechin polyphenols and caffeine in
increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutr
1999;70:1040-5.
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[7]
LaValle
JB, et al. IN: Natural Therapeutics Pocket Guide 2000-2001;452-4.
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[8]
Graham
HN. Green tea composition, consumption, and polyphenol chemistry. Prev
Med
1992;21:334-50.
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[9]
Yang
CS, et al. Blood
and urine levels of tea catechins after ingestion of different amounts of
green tea by human volunteers. Cancer Epidemiol Biomarkers Prev
1998;7:351-4.
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[10]
He
YH, Kies C. Green and black tea consumption by humans: impact on
polyphenol concentrations in feces, blood, and urine. Plant Foods Hum
Nutr 1994;46:221-9.
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[11]
van
het Hof KH, et al. Bioavailability
of catechins from tea: the effect of milk. Eur
J Clin Nutr
1998;52:356-9.
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[12]
Brinker F. Herb Contraindications and Drug Interactions, 3rd
ed. Sandy (OR): Eclectic Medical Publications; 2001.
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[13]
Huang
MT, et al. Effects
of tea, decaffeinated tea, and caffeine on UVB light-induced complete
carcinogenesis in SKH-1 mice: demonstration of caffeine as a biologically
important constituent of tea. Cancer
Res
1997;57:2623-9.
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[14]
Yang
CS, et al. Prevention
of carcinogenesis by tea polyphenols. Drug
Metab Rev
2001;33:237-53.
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[15]
Yang
CS, et al. Human
salivary tea catechin levels and catechin esterase activities:
implications in human cancer prevention studies. Cancer Epidemiol
Biomarkers Prev 1999;8:83-9.
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[16]
Hong
J, et al. Effects
of purified green and black tea polyphenols on cyclooxygenase- and
lipoxygenase-dependent metabolism of arachidonic acid in human colon
mucosa and colon tumor tissues. Biochem
Pharmacol
2001;62:1175-83.
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[17]
Berger
SJ, et al. Green
tea constituent (--)-epigallocatechin-3-gallate inhibits topoisomerase I
activity in human colon carcinoma cells. Biochem Biophys Res Commun
2001;288:101-5.
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[18]
Smith
DM, et al. Green tea polyphenol epigallocatechin inhibits DNA replication
and consequently induces leukemia cell apoptosis. Int J Mol Med
2001;7:645-52.
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[19]
Proniuk
S, et al. Preformulation study of epigallocatechin gallate, a promising
antioxidant for topical skin cancer prevention. J Pharm Sci
2002;91:111-6.
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[20]
Taylor
JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann
Pharmacother
1999;33:426-8.
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[21]
Sartippour
MR, et al. Green
tea inhibits vascular endothelial growth factor (VEGF) induction in human
breast cancer cells. J
Nutr
2002;132:2307-11.
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[22]
Hoshiyama
Y, et al. A
prospective study of stomach cancer death in relation to green tea
consumption in Japan. Br J Cancer 2002;87:309-13.
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[23]
Chen
PC, et al. A
green tea-derived polypheol, epigallocatechin-3-gallate, inhibits IkappaB
kinase activation and IL-8 gene expression in respiratory epithelium. Inflammation
2002;26:233-41.
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[24]
Kinjo
J, et al. Activity-guided fractionation of green tea extract with
antiproliferative activity against human stomach cancer cells. Biol
Pharm Bull 2002;25:1238-40.
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[25]
Hsu
SD, et al. Chemoprevention
of oral cancer by green tea. Gen
Dent
2002;50:140-6.
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[26]
Sun
CL, et al. Urinary
tea polyphenols in relation to gastric and esophageal cancers: a
prospective study of men in Shanghai, China. Carcinogenesis 2002;23:1497-503. |
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| Written |
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03/21/2002 |
| Updated |
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11/24/2002
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Source: http://www.mskcc.org/mskcc/print/11571.cfm?RecordID=500 |
