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GREEN TEA
Green
tea has been considered a medicinal remedy in Chinese tradition
dating back over 4,000 years. The observed health benefits of this
folk remedy, now being validated by modern scientific investigation,
include: lowers total cholesterol, increases HDL cholesterol levels,
reduces blood pressure, acts as a "blood thinner" by
inhibiting platelet aggregation, reduces risk of heart attack and
stroke, reduces risk of cancer, enhances immune cell function,
improves digestion, and prevents dental cavities and gingivitis.
Green
tea catechins are definitely included in a broad brush approach to
the health benefits of flavonoids, which include potential for the
prevention and treatment of cardiovascular disease, cancer,
inflammatory conditions, asthma, periodontal disease, liver disease,
cataracts, and macular degeneration. Epidemiological studies suggest
that populations drinking 8-10 cups of Green tea daily have markedly
reduced rates of gastrointestinal cancers as well as lower rates of
cancer of the pancreas, breast, and lung. Japan, for example, has a
very low incidence of cancer which is thought secondary to their
relatively high intake of Green tea.
Laboratory
studies supporting the cancer protective effect of Green tea
demonstrate that catechins and other polyphenols inhibit free
radical precursors to cancer as well as block the effects of other
tumor promoters including estrogen, growth factors, and cancer
causing chemicals like benzopyrenes and nitrosamines.
The
anticancer effect of Green tea polyphenols, specifically catechins,
in human and animal studies has been impressive enough for the
National Cancer Institute to include Green tea polyphenols in its
"Designer Nutrient Program", a research effort to
investigate the cancer preventative and therapeutic benefits of
foods and food products.
Extensive
international research reveals that Green tea catechins have apoptic
activity in human cancer cell lines including prostate, skin,
lymphoma, ovarian, colon, adenocarcinoma, liver breast, lung, and
stomach cancers.
Green
tea consumption is protective for gastrointestinal cancers in large
studies. Green tea polyphenols have shown promise in vitro as
antineoplastic substances, due to their ability to scavenge
oxidative initiators of neoplasia (Yoshikawa, Picard).
Laboratory
and epidemiological studies indicate Green tea catechins exert a
protective effect against prostate cancer. Green tea drinkers have
lower rates of prostate cancer with the lowest rate of prostate
cancer in China with the highest consumption of tea (Gupta).
Antimutagenic
properties of catechins against tumors found in laboratory animals
were reproduced recently when tested against four human tumor cell
lines from carcinomas of the breast, colon, lung and melanoma.
Epigallocatechin gallate was the most potent catechin against all
four tumor lines. It was recommended that in vivo animal trials be
conducted prior to consideration of testing Green tea catechins
against cancer in humans.
Green
tea inhibits cancer in laboratory studies by several mechanisms
including enhanced cell-mediated immunity, increased
glutathione-S-transferase activity (increases glutathione, a
powerful intracellular antioxidant), inhibits tumor growth rate,
blocks tumor-induced inhibition of intracellular communication, and
scavenges free radicals. Green tea polyphenols specifically block
the formation of carcinogenic nitrosamines.
When
volunteers were given Green tea in combination with 300 mg of sodium
nitrate and 300 mg of proline, the formation of nitrosoproline was
strongly inhibited (Stich).
Daily
intake of Green tea polyphenols appears to have multiple health
benefits summarized below, including reduced risk of cancer and
cardiovascular disease:
-
Catechins
protect against radiation, including increased survival and
decreased incidence of radiation-induced tumors.
-
Catechins
have antimutagenic activity against both spontaneous and
chemically-induced mutations.
-
Catechins
have anti-tumor activity, inducing phase I and II metabolic
enzymes that increase the formation and excretion of detoxified
metabolites of carcinogens, slowing the rate of cell replication
and thus the growth and development of neoplasms, and preventing
spontaneous and chemically-induced cancer development.
-
Catechins
are powerful antioxidants that inhibit oxidation of LDL-cholesterol,
reduce cholesterol levels, and reduce body fat, resulting in a
decreased risk of heart disease.
-
Catechins
have regulatory effects on blood pressure and high
blood-pressure induced strokes. Individuals consuming more than
five cups a day having a 500% decrease in stroke incidence.
-
Catechins
have antibacterial activity against foodborne pathogenic
bacteria and cavity-inducing bacteria, modifying the intestinal
microflora, reducing undesirable bacteria and increasing
beneficial bacteria.
-
Catechins
have an antihyperglycemic action, lowering both blood-glucose
and normalizing insulin release.
-
Catechins
show antiviral effects, inhibiting reproduction of numerous
viruses including influenza and human immunodeficiency virus.
Additional
research is being published almost weekly on the remarkable healing
properties of Green tea catechins. Important studies are summarized
briefly below.
Green
tea also reduces oxidative stress caused by smoking, including
decreased oxidative DNA damage, reduced lipid peroxidation, and
reduced urine levels of free radicals. Green tea appears to
significantly lower risk of cardiovascular disease, even having a
protective effect in smokers. Japanese males, for example, have a
relatively low risk of heart disease despite the fact 75% of adults
smoke tobacco.
This
"Japanese Paradox" is similar to the "French
paradox" in that the polyphenols in Green tea have a protective
effect against heart disease and cancer just like the polyphenols in
red wine protect the French against cardiovascular disease in spite
of their high fat diets.
In
Japanese males over 40, the protective effects of Green tea against
heart disease and cancer increased exponentially in proportion to
average daily tea intake comparing risk in men drinking less than
three, four to nine, and more than ten cups of tea daily (Imai).
Green
tea increases thermogenesis or fat oxidation. Green tea catechins
increased 24-hour energy expenditure, decreased respiratory
quotient, and increased urinary excretion of nitrogen and
catecholamines compared to controls and those taking caffeine alone.
Green tea catechins independent of caffeine inhibit catechol O-methyltransferase,
an enzyme that degrades norepinephrine, causing a more sustained
effect of norepinephrine (adrenalin) on thermogenesis and energy
production from burning of fatty acids. This occurred without a
stimulatory increase in heart rate, distinguishing Green tea from
sympathomimetic drugs, which can have adverse cardiovascular side
effects (Dulloo).
Green
tea inhibits viral infections by a mechanism similar to elderberry
flavonoids. Catechins bind to the hemagglutinin of the influenza
virus and inhibit its absorption to the target cell, thereby
inhibiting its ability to infect the target cell (Nakayama).
Green
tea correlates inversely with total serum cholesterol in a study of
1300 Japanese males. Cholesterol level was an average of 8 mg/dl
lower in males drinking 9 or more cups of Green tea per day compared
to those consuming zero to two cups per day (Kono).
Green
tea lowers cholesterol by increasing fecal lipid excretion in lab
animals and may reduce levels in humans by a similar mechanism of
increasing bile acids (Yang).
In
summary, studies confirm that flavonoids in Green tea have
antibacterial, anti-inflammatory, antiallergic, antimutagenic,
antiviral, antineoplastic, antithrombotic, and vasodilatory
activity. Catechins from Green tea are potent antioxidants that
scavenge hydroxyl radicals, superoxide anions, and lipid peroxyl
radicals. In most experimental studies catechins demonstrate
superior antioxidant properties than Vitamin C or E.
Green
tea catechins have bacteriocidal activity at concentrations of
catechins found in a single cup of Green tea.
Green
tea catechins inhibit oxidation of LDL cholesterol, lower total
serum cholesterol levels, and increase levels of HDL cholesterol.
Green
tea also contains components unrelated to the flavonoids.
Approximately 3.5% caffeine, 6.5% lignan, 1.5% organic acids, 15%
proteins, and 2% theanine, an amino acid that has recently been
shown to reduce blood pressure. Standardized Green tea extracts
contain on average 60-80% total polyphenols, but may be as high as
over 90%.
Green
tea contains about 50-100 mg of caffeine, the principal ingredient
responsible for the social popularity of Green tea. Caffeine
stimulates the central nervous system, respiratory, cardiac, and
skeletal muscle systems. Caffeine causes coronary artery dilation,
smooth muscle relaxation, and diuresis. Long-term studies on
caffeine consumption, interesting, refute acute studies that
caffeine is harmful to the cardiovascular system and aggravates
hypertension (Robertson). Most Green tea extracts, including the
extract in Ellagic Insurance Formula, have been decaffeinated.
Studies
suggest that 200-400 mg of Green tea polyphenols approximates the
amount of catechins found in 8-10 cups of tea daily. Unfortunately,
it is difficult for most individuals to consume the 5-10 cups of
Green tea daily that research has shown to be beneficial. One option
is to take catechins concentrated in extracted supplement form as
provided in Ellagic Insurance Formula. Approximately 200 mg of Green
tea catechins in this formula corresponds to the amount of catechins
found in 5-8 cups of Green tea.
Selected
References
Ahmad
N et al. Green tea polyphenols and cancer: biologic mechanisms and
practical implications. Nutr Rev 57(3): 78-83, 1999.
Brown
MD. Green tea (Camellia sinensis) extract and its possible role in
the prevention of cancer. Altern Med Rev 4(5): 360-370, 1999.
Bushman
JL. Green tea and cancer in humans: a review of the literature. Nutr
Cancer 31(3): 151-159, 1998.
Chen
et al. Green tea epigallocatechin gallate shows a pronounced growth
inhibitory effect on cancerous cells but not on their normal
counterparts. Cancer Letters 129: 173-179, 1998.
Dulloo
AG et al. Efficacy of a green tea extract rich in catechin
polyphenols and caffeine in increasing 24-h expenditure and fat
oxidation in humans. Am J Clin Nutr 70: 1040- 1045, 1999.
Gupta
S et al. Prostate cancer chemoprevention by green tea. Semin Urol
Oncol 17(2): 70-76, 1999.
Imai
K et al. Cancer-preventive effects of drinking green tea among a
Japanese population. Prev Med 26(6):769-75, 1997.
Ji
HT et al. Green tea consumption and the risk of pancreatic and
colorectal cancer. Int J Can 7; 255-258, 1997.
Kono
S et al. Relation of green tea consumption to serum lipids and
lipoproteins in Japanese men. J Epidemiol 6(3):128-33, 1996. Lin JK
et al Cancer chemoprevention by tea polyphenols. Proc Natl Sci Counc
Repub China B 24(1):1-13, 2000.
Mukhtar
H et al. Tea polyphenols: prevention of cancer and optimizing
health. Am J Clin Nutr 71(6 Suppl):1698S-702S, 2000.
Nakayama
M et al. Inhibition of the infectivity of influenza virus by tea
polyphenols. Antiviral Res 21: 289-299, 1993.
Picard
D. The biochemistry of green tea polyphenols and their potential
application in human skin cancer. Alt Med Rev 1: 31-42, 1996.
Sasazuki
S et al. Relation between green tea consumption and the severity of
coronary atherosclerosis among Japanese men and women. Ann Epidemiol
10(6):401-8, 2000.
Stich
HF. Teas and tea components as inhibitors of carcinogen formation in
model systems and man. Prevent Med 21: 377-384, 1992.
Yang
CS et al. Tea and tea polyphenols inhibit cell hyperproliferation,
lung tumorigenesis, and tumor progression. Exp Lung Res
24(4):629-39, 1998.
Weisburger
JH. Mechanisms of action of antioxidants as exemplified in
vegetables, tomatoes, and tea. Food Chem Toxicol 37(9-10): 943-948,
1999.
Weisburger
JH. Tea and health: the underlying mechanisms. Proc Soc Exp Biol Med
2200(4): 271-275, 1999.
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