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Health Benefits of Green Tea For centuries,
doctors, healers and tea drinkers have known that green tea possesses
remarkable healing properties. Today, after decades of research, it’s
become apparent that green tea truly is a "steaming cup of medicine."
The results of hundreds of studies performed by top scientists at
leading universities and research centers demonstrate that green tea,
even in moderate amounts, may help ward off or combat a variety of
ailments by:
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Boosting the
immune system
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Regulating
cholesterol levels
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Fighting the
build-up of sticky plaque in the arteries
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Interfering with
the cancer process
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Assisting in
weight loss
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Fighting harmful
bacteria and viruses
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Protecting the
body against free radical damage
What is Green Tea?
Tea is a hot water
infusion made from the leaves of the camellia sinensis bush. The
way the leaves are processed determines whether the result is green,
black or oolong tea. For green tea, the leaves are steamed or pan-fired
immediately after picking to prevent them from fermenting. For black
tea, the leaves are crushed and left to wither to encourage
fermentation. For oolong, the leaves are withered for a shorter time, so
they become only partially fermented.
Unfermented tea
leaves contain large amounts of catechins, which are the powerful
antioxidants and disease fighters responsible for green tea’s many
health benefits. And while you can find some catechins in black and
oolong tea, they’re found in much larger quantities in green tea. It’s
the quick processing of green tea that keeps the catechins in place.
When tea leaves are allowed to ferment, the catechins convert to another
form that doesn’t have nearly as many health benefits. There are five
types of catechins, but the most potent is epigallocatechin gallate
(EGCg, for short).
Most studies
have concluded that you need 3-10 cups of green tea per day, or up to
1,000 mg. of catechins for maximum health benefits. (The average 6-ounce
cup of green tea contains between 50 and 100 mg catechins.)
What Can Green Tea Do For Your Health?
A wealth of laboratory,
animal and human studies has provided evidence that green tea can help
promote heart health, ward off cancer, fight obesity, lessen free
radical damage to the cells, and even slow the progression of
age-related cognitive impairment and Alzheimer’s disease. Samples of
some interesting findings:
Green Tea and Cholesterol
Many researchers believe that green tea helps reduce cholesterol by
lowering its absorption in the digestive tract and increasing its
excretion.
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Italian
researchers studying two groups of volunteers following a controlled
diet found that those who drank two cups of green tea (about 250 mg of
catechins) per day for 6 weeks reduced their LDL "bad" cholesterol by
an average of 13 mg/dl.1
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A double
blind, randomized, placebo-controlled study involving 240 people with
mildly to moderately-elevated cholesterol found that taking 375 mg of
theaflavin-enriched green tea extract daily for 12 weeks caused a
reduction in total cholesterol of 11.3% and in LDL cholesterol of
16.4%, while the HDL "good" cholesterol increased by 2.3%.2
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Animal studies
have shown that even when consuming a diet rich in lard and
cholesterol, rats who receive green tea catechins have much lower
cholesterol levels than those who don't receive the catechins.3
Green Tea and Cardiovascular Disease
Green tea is
associated with a reduction in many risk factors for cardiovascular
disease. Besides improving cholesterol values, it may also help lower
blood pressure, decrease blood stickiness, and prevent of LDL oxidation
(a crucial beginning step in the atherosclerotic process). And while no
one has actually proven that green tea can prevent heart disease, some
recent findings are exciting:
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A study of
nearly 400 people scheduled for coronary angiography found that those
who drank at least 1 cup of green tea per day were 42% less likely to
have a heart attack than those who didn’t drink green tea.4
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Green tea may
also reduce a person’s risk of dying of a heart attack. Researchers
interviewed 1900 people four days after having a heart attack. Four
years later, those who consumed tea in moderate amounts (about 2 cups
per day) decreased their risk of dying by 31%, while those who drank
more than 2 cups per day decreased their risk by 39%.5
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Green tea
seems to be particularly protective against stroke-induced deaths. In
a 2006 study, researchers who had been tracking 40,530 Japanese age 40
or older over an 11-year period reported that women who drank five or
more cups of green tea daily were 42% less likely to die of a stroke
than those who drank less than one cup.6
Green Tea and Obesity
Green tea has recently
become the latest weapon in the war on weight. But does it really work?
The results of some new studies are promising, finding that green tea
can increase the rate of calorie burning, reduce body fat levels and
even prevent excess weight gain. Although most tests have been performed
on laboratory animals, at least one with humans showed that taking in
the equivalent of 3 cups of green tea per day burned an additional 80
calories per day.
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In a study of
energy expenditure in men, those who took green tea extract containing
EGCg plus caffeine three times daily burned about 80 more calories per
day than those who didn't take the extract. (Taking caffeine with EGCg
didn't have the same effect.) They took in roughly the amount of EGCg
found in 3 cups of green tea a day.7
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In another
study, green tea extract actually helped prevent obesity. Two groups
of mice were placed on a high-fat diet that ensured weight gain, and
one group also received green tea extract, while the other did not.
The mice that got the green tea extract gained 47% less weight than
those who didn't get the extract.8
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Finally, green
tea extract helped to reverse established obesity. Rats that had
become obese through deliberate overfeeding had their obesity reversed
by supplementation with EGCg, which markedly decreased the amount of
adipose tissue.9
Green tea is
believed to help prevent obesity by revving up the fat-burning effects
of brown fat, sending glucose to muscle tissue where it’s more likely to
be burned, rather than to fat tissue, and inhibiting the action of
fat-digesting enzymes so the fat that you eat is less available to the
body.
Green Tea and Cancer
Animal studies have
clearly shown that green tea can help prevent the growth of tumors in
the breast, prostate, lung and skin. And many studies of large
populations have linked green tea to a reduction of cancer of the
stomach, lung, pancreatic, breast, colon, esophageal, prostate and skin.
Green tea’s
catechins (particularly EGCg) appear to inhibit the cancer process at
all stages. Specifically, they protect the body from free radical damage
by acting as an antioxidant, lower the toxicity of certain carcinogens,
interfere with the binding of carcinogens to the DNA of healthy cells,
inhibit cancer activation, slow tumor growth and spread, inhibit the
growth of blood vessels to feed the tumor, and encourage cancer cells to
“commit suicide” (programmed cell death). Some of the more interesting
studies of green tea’s effects on cancer include:
Stomach Cancer
Researchers from Shanghai,
China compared 206 people newly diagnosed with stomach cancer to 415
healthy control subjects. After studying the volunteers’ health, diet
and lifestyle habits, the researchers concluded that drinking green tea
reduced the risk of developing stomach cancer by as much as 41%.10
Lung Cancer
The diet and lifestyle
habits of 649 nine women with lung cancer were compared to those of 675
healthy women. The researchers found that drinking green tea reduced the
risk of developing green tea by as much as 35% (in the nonsmokers only),
and that the more green tea consumed, the greater the protection.11
Breast Cancer
A study of 1,100
Asian-American women, half of whom had breast cancer, showed that those
in the non-cancer group were much more likely to be green tea drinkers.
The researchers concluded that "green tea drinkers showed a
significantly reduced risk of breast cancer..." and the more green tea
consumed, the greater the protection.12
The combined
results four studies (a meta-analysis) showed a 12% reduction in risk of
developing breast cancer for those drinking the most green tea compared
to those drinking the least.13
Pancreatic Cancer
A case-control study of
cancer of the pancreas involving over 200 people found a significantly
decreased risk of developing the disease in those who consumed green
tea.14
Another study
found that those who drank 2 or more cups of green tea per day had a 60%
lower risk of developing pancreatic cancer.15 In test-tube
studies, green tea has been shown to fight pancreatic cancer by damaging
the mitochondria of the cancer cells and inhibiting cancer activation.16
Prostate Cancer
A double-blind,
placebo-controlled study of green tea’s ability to fight prostate cancer
was published in Cancer Research in 2006. Sixty men with HG-PIN,
a condition that can quickly progress to prostate cancer, were divided
into two groups. One group received 600 mg of green tea catechins per
day; the other did not. After one year, only one prostate tumor was
found among the green tea group compared to 9 in the control group.17
Skin Cancer
Much of the research of
green tea’s effects on skin cancer has been done on hairless mice since
their skin is very similar to human skin. And it’s been found that green
tea extract, whether taken internally or painted on the skin, does help
prevent skin cancer at both the induction and promotion phases. Mice
given green tea extract in their drinking water for 50 days, then
injected with a powerful skin cancer-inducing substance, got 44% fewer
skin tumors than rats that hadn’t been given the extract.18
In another study, mice exposed to UVB rays who received green tea
catechins through their water supply developed 41% fewer skin tumors
than mice treated in the same manner, who didn’t get green tea. The
tumors that they did develop were smaller.19 And recent
test-tube studies have found that EGCg inhibits the growth and spread of
the deadly skin cancer melanoma.20
Green Tea, the Health Elixir
Perhaps the Japanese Buddhist monk
Eisai was right when he wrote circa 1211 that “Tea is a miraculous
medicine for the maintenance of health.” Countless studies have shown
that not only can green tea aid in heart health, interfere with the
cancer process and help ward off obesity, it can also fight deadly
bacteria, including the kind that cause tuberculosis21, guard
against dental cavities22,23, inhibit the action of viruses24,
fight free radical damage to the cells25 and preserve the
freshness of foods26,27 and cosmetics.
How Much Do You Need?
Most experts agree
that a daily intake of 3-10 cups of green tea (the equivalent of
300-1,000 mg of catechins) is ideal for maximum health benefits. In
extract form, to get 300 mg of catechins you’d need to take about 480 mg
of a 50:1 extract containing 60% catechins (60% of 480 mg = 300 mg).
But even a
single cup of green tea per day can be beneficial (just this small
amount confers powerful protection against dental cavities and breast
cancer). So pour
yourself a steaming cup of medicine and enjoy! It could be the beginning
of a life-long love affair with a potent and delightful health-enhancer.
Footnotes:
1)
Erba D, Riso P, Bordoni A, et al. Effectiveness of moderate green tea
consumption on antioxidative status and plasma lipid profile in humans.
J Nutr Biochem 2005;16(3):144-9.
2)
Maron DJ, Lu GP, Cai NS, et al. Cholesterol-lowering effect of a
theaflavin-enriched green tea extract: a randomized controlled trial.
Arch Intern Med 2003;163(12):1448-53.
3)
Muramatsu K, Fukuyo M, Hara Y. Effect of green tea catechins on
plasma cholesterol level in cholesterol-fed rats. J Nutr Sci
Vitaminol (Tokyo) 1986;32(6):613-22.
4)
Hirano R, Momiyama Y, Takahashi R, et al. Comparison of green tea
intake in Japanese patients with and without angiographic coronary
artery disease. Am J Cardiol 2002;90(10):1150-53.
5)
Mukamal
KJ, Maclure M, Muller JE, et al. Tea consumption and
mortality after acute myocardial infarction. Circulation
2002;105(21):2476-81.
6)
Kuriyama S, Shimazu T, Ohmori I, et al. Green tea consumption and
mortality due to cardiovascular disease, cancer and all causes in Japan:
the Ohsaki study. JAMA 2006;296(10):1255-65.
7)
Dulloo AG, Duret C, Rohrer D, 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 Dec;70(6):1040-5.
8)
Shimotoyodome A, Haramizu S, Inaba M, et al. Exercise and green tea
extract stimulate fat oxidation and prevent obesity in mice. Med Sci
Sports Exerc 2005;37(11):1884-92.
9)
Wolfram S, Raederstorff D, Wang Y, et al. TEAVIGO (epigallocatechin
gallate) supplementation prevents obesity in rodents by reducing adipose
tissue mass. Ann Nutr Metab 2005;49(1):54-63. Epub 2005 Feb 25.
10)
Mu LN, Lu QY, Yu SZ, et al. Green tea drinking and mutagenetic index
on the risk of stomach cancer in a Chinese population. Int
J Cancer 2005;116(6):972-83.
11)
Zhong L, Goldberg MS, Gao YT, et al. A population-based case-control
study of lung cancer and green tea consumption among women living in
Shanghai, China. Epidemiology 2001;12(6):695-700.
12)
Wu AH, Yu MC, Tseng CC, et al. Green tea and risk of breast cancer
in Asian Americans. International Journal of Cancer
2003;106(4):574-9.
13)
Sun CL, Yuan JM, Koh WP, et al. Green tea, black tea and breast
cancer risk: a meta-analysis of epidemiological studies.
Carcinogenesis 2006;27(7):1310-5.
14) Goto R, Masuoka H, Yosida K, et al. Gan No Rinsho 1990;Spec
No:344-50.
15)
Shibata A, Mack TM, Paganini-Hill AN, et al. A prospective study of
pancreatic cancer in the elderly. Int J Cancer 1994;58(1):46-49.
16)
Qanungo S, Das M, Haldar S, et al. Epigallocatechin-3-gallate
induces mitochondrial membrane depolarization and caspase-dependent
apoptosis in pancreatic cancer cells. Carcinogenesis
2005;26(5):958-67.
17)
Bettuzzi S, Brausi M, Rizzi F, et al. Chemoprevention of human
prostate cancer by oral administration of green tea catechins in
volunteers with high-grade prostate intraepithelial neoplasia: A
preliminary report from a one-year proof-of-principle study. Cancer
Research 2006;66(2):1234-40.
18)
Wang Z, Khan W, Bickers D, et al. Protection against polycyclic
aromatic hydrocarbon-induced skin tumor initiation in mice by green tea
polyphenols. Carcinogenesis 1989;10:411-15.
19)
Mukhtar H, Wang Z, Katiyar S, et al. Tea components: antimutagenic
and anticarcinogenic effects Prev Med 1992;21:351-360.
20)
Nihal M, Ahmad N, Mukhtar H, et al. Anti-proliferative and
proapoptotic effects of (-)-epigallocatechin-3-gallate on human
melanoma: possible implications for the chemoprevention of melanoma.
Int J Cancer 2005;114(4):513-21.
21)
Anand PK, Kaul D, Sharma M. Green tea polyphenol inhibit
Mycobacterium tuberculosis survival within human macrophages. Int J
Biochem Cell Biol 2006;38(4):600-09.
22)
Otake S, Makimura M, Kuroki T, et al. Anticaries effects of
polyphenolic compounds from Japanese green tea. Caries Res
1991;25(6);438-43.
23)
Kada T, Kaneko K, Matsuzaki S, et al. Detection and chemical
identification of natural bioantimutagens. A case of the green tea
factor. Mutation Res 1985;150:127-132.
24)
Song JM, Lee KH, Seong Bl. Antiviral effect of catechins in green
tea on influenza virus. Antiviral Res 2005;68(2):66-74.
25)
Erba D, Riso P, Bordoni A, et al. Effectiveness of moderate green
tea consumption on antioxidative status and plasma lipid profile in
humans. J Nutr Biochem 2005;16(3):144-49.
26)
Stapleton PD, Gettert J, Taylor PW. Epicatechin gallate, a component
of green tea, reduces halotolerance in Staphylococcus aureus. Int J
Food Microbiol 2006;111(3):276-79.
27)
Tanaka K, Hayatsu T, Negishi T, et al. Inhibition of N-nitrosation
of secondary amines in vitro by tea extracts and catechins. Mutat Res
1998;412(1):91-98.
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Nadine Taylor, M.S., R.D. presents
GreenTeaLibrary.com,
the most comprehensive collection of scientific information
describing the health benefits of green tea.
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