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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