Green tea: Potential health benefits

Department of Family Medicine, Maine Medical Center, Portland, Maine 04102, USA.
American family physician (Impact Factor: 2.18). 05/2009; 79(7):591-4.
Source: PubMed
ABSTRACT
Green tea has been used widely and in high doses for centuries as a health tonic in many societies. Evidence suggests that green tea is effective for treating genital warts. There is some supportive evidence for the use of green tea in cancer prevention. Drinking green tea is associated with a decrease in all-cause mortality, but not in cancer-related mortality. Small clinical studies have found that green tea may also be helpful in losing and managing weight, and lowering cholesterol. Epidemiologic evidence suggests that green tea may prevent stroke and cardiovascular disease. Green tea appears to be safe, although there have been case reports of hepatotoxicity possibly related to a specific extract in pill or beverage form. Green tea seems to be a low-risk complementary therapy for a number of conditions, but more studies are needed.

Full-text

Available from: Craig Schneider, Feb 05, 2014
April 1, 2009
Volume 79, Number 7 www.aafp.org/afp American Family Physician 591
Green Tea: Potential Health Benefits
CRAIG SCHNEIDER, MD, Maine Medical Center, Portland, Maine
TIFFANY SEGRE, MD, Gorham Family Medicine, Gorham, Maine
T
ea is the most frequently con-
sumed beverage in the world
after water, and the fourth most
frequently consumed beverage
in the United States. The average American
drinks 155 cups of tea annually,
1
and green
tea extracts are a rapidly growing dietary
supplement in the United States.
Legend has it that drinking tea originated
when leaves from a nearby Camellia sinen-
sis plant landed in a Chinese emperor’s
pot of boiling water.
2
Green tea is made by
lightly steaming and drying the leaves from
C. sinensis. Green tea, black tea, and oolong
tea are all distinct preparations of this plant.
Pharmacology
Multiple substances in green tea may contrib-
ute to its health benefits. Caffeine, theanine,
theaavins, theobromine, theophylline, and
phenolic acids are found in green tea.
3
In
vitro, animal, and human studies suggest
that the polyphenols in green tea are potent
antioxidants with antimutagenic, antidia-
betic, antibacterial, anti-inammatory, and
hypocholesterolemic properties.
3
Green tea
is 20 to 45 percent polyphenols by weight, of
which 60 to 80 percent are catechins. Green
tea contains more catechins than oolong or
black tea,
3
although catechin content may
vary because of processing and growing con-
ditions. Epigallocatechin gallate (EGCG) is
the most prevalent catechin in tea, and the
most researched.
Uses and Effectiveness
Green tea polyphenols may play a beneficial
role in several conditions. They are most
commonly studied in genital warts, cancer,
weight management, and cardiovascular
disease. The results from epidemiologic and
clinical studies are mixed.
3
GENITAL AND PERIANAL WARTS
The U.S. Food and Drug Administration has
approved a topical ointment (sinecatechins
15% [Veregen]) for the treatment of external
genital and perianal warts caused by human
papillomavirus (HPV). The active ingredient
is a defined mixture of catechins extracted
from green tea that acts as an immunomod-
ulator and inhibits major viral functions.
4,5
Preliminary trials also suggest a possible
role for sinecatechins, alone or in combina-
tion with an oral extract, in treating cervical
lesions caused by HPV.
6
CANCER
Many studies suggest an inverse relation-
ship between green tea intake and the risk of
a variety of cancers, although other studies
have found no association.
7
Clinical trials
have been small and heterogenous with con-
tradictory results. Dietary, environmental,
and population differences may account for
these inconsistencies.
A 2006 meta-analysis of epidemiologic
studies found that high intake of green tea
was associated with a 20 percent reduction
Green tea has been used widely and in high doses for centuries as a health tonic in many societ-
ies. Evidence suggests that green tea is effective for treating genital warts. There is some sup-
portive evidence for the use of green tea in cancer prevention. Drinking green tea is associated
with a decrease in all-cause mortality, but not in cancer-related mortality. Small clinical studies
have found that green tea may also be helpful in losing and managing weight, and lowering cho-
lesterol. Epidemiologic evidence suggests that green tea may prevent stroke and cardiovascular
disease. Green tea appears to be safe, although there have been case reports of hepatotoxicity
possibly related to a specific extract in pill or beverage form. Green tea seems to be a low-risk
complementary therapy for a number of conditions, but more studies are needed. (Am Fam
Physician. 2009;79(7):591-594. Copyright © 2009 American Academy of Family Physicians.)
COMPLEMENTARY AND
ALTERNATIVE MEDICINE
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592  American Family Physician www.aafp.org/afp Volume 79, Number 7
April 1, 2009
in the risk of breast cancer (odds ratio [OR] = 0.78;
95% confidence interval [CI], 0.61 to 0.98).
8
The stron-
gest association was in the U.S. Asian population. Large
Japanese cohort studies did not reveal a reduction in
breast cancer diagnoses with green tea intake, although
the studies were confounded by pervasive green tea con-
sumption among participants (i.e., 98 percent of Japa-
nese adults drink green tea).
8
A second meta-analysis by the same authors found
that high consumption of green tea was associated
with an 18 percent reduction in the risk of colorectal
cancer (summary OR = 0.82; 95% CI, 0.69 to 0.98).
9
Another large prospective cohort study of more than
40,000 Japanese adults found that green tea beverage
consumption was inversely associated with all-cause
mortality at 11 years, but not specically with cancer-
related mortality.
10
Some data are available on green tea and its effect on
stomach and esophageal cancers. One Chinese study
of more than 18,000 men found that those who drank
green tea were about one half as likely to develop stom-
ach or esophageal cancer as men who drank little tea.
11
The authors reported an inverse relationship between
EGCG intake and the risk of gastric cancer, or gastric
and esophageal cancers combined (OR = 0.52; 95% CI,
0.28 to 0.97, and OR = 0.58; 95% CI, 0.34 to 0.90).
11
Other studies have examined the relationship between
green tea and prostate cancer. A small controlled trial
followed 60 patients with high-grade prostate intraepi-
thelial neoplasia.
12
Patients were grouped randomly to
receive green tea catechins extract (200 mg three times
a day) or placebo for one year.
12
Nine cancers were found
in the placebo group, whereas only one cancer was
detected in the green tea group.
12
Another small clinical
trial found no benefit from the use of green tea extract
(500 mg per day for two to four months)
13
; however, a
recent epidemiologic study of nearly 50,000 Japanese
men found a dose-dependent relationship between green
tea consumption and a reduction in the risk of advanced
prostate cancer.
14
WEiGht manaGEmEnt
Several small clinical trials have investigated the effect
of green tea on weight loss and weight management.
15,16
Some controlled trials suggest a benefit from green tea,
whereas others do not. None of the studies demonstrate
persistent effects.
In one randomized placebo-controlled double-blind
trial, investigators tracked the effects of green tea in
76 men and women who were overweight or obese.
17
The
effects of a green tea/caffeine mixture (two capsules, each
containing 45 mg of EGCG and 25 mg of caffeine, taken
before meals) on persons who habitually consumed large
amounts of caffeine (more than 300 mg per day) were
compared with the effects on those who consumed small
amounts of caffeine. There appeared to be no effect on
the high consumers, but the low consumers regained sig-
nificantly less weight (P < .01) than participants receiv-
ing placebo.
17
A 12-week double-blind controlled trial compared the
effects of a green tea extract beverage high in catechins
with a lower catechin placebo beverage in 240 Japanese
adults who were obese.
18
The results showed that the
active treatment group had greater reductions in body
weight, body mass index, body fat ratio, body fat mass,
and waist and hip circumference (P < .05).
18
CardiovasCUlar FUnCtion
Epidemiologic studies suggest that green tea intake is
associated with a reduced risk of cardiovascular disease,
but the mechanisms remain uncertain. Clinical trials
show inconsistent results in the effect of green tea on
lipid levels, blood pressure, and coronary artery disease.
A prospective cohort study of more than 40,000
Japanese adults found that green tea consumption was
inversely associated with cardiovascular disease mor-
tality.
10
Women who consumed five or more cups per
day had a 31 percent lower risk of dying from cardio-
vascular disease.
10
Participants who consumed five or
more cups per day had a significantly reduced incidence
of stroke.
10
sort: KEy rECommEndations For PraCtiCE
Clinical recommendation
Evidence
rating References
Ointment derived from green tea appears to be effective in the treatment of genital warts. B 4, 5
Drinking green tea may help prevent cancer of the breast, gastrointestinal tract, and prostate, but results
are mixed.
B 8, 9, 11, 12, 14
Green tea beverages may be effective for short-term weight loss, although studies are inconsistent. B 17, 18
Drinking green tea is associated with decreased risk of stroke and cardiovascular disease, although the
evidence is conflicting.
B 10
A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-
oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.
org/afpsort.xml.
Page 2
April 1, 2009
Volume 79, Number 7 www.aafp.org/afp American Family Physician 593
A cross-sectional study of nearly 1,000 Japanese adults
in their 40s found no association between green tea
intake and total cholesterol level.
19
However, a double-
blind randomized placebo-controlled trial of 240 Chi-
nese adults with mild to moderate hypercholesterolemia
(low-density lipoprotein [LDL] cholesterol = 130 to
190 mg per dL [3.36 to 4.91 mmol per L]) who received a
once-daily theaavin-enriched green tea extract reduced
their LDL by 16.4 percent ± 1.1 percent (P < .01) and
their total cholesterol by 11.3 percent ± 0.9 percent com-
pared with placebo.
20
Participants’ high-density lipopro-
tein cholesterol and triglyceride measurements were not
changed significantly.
20
Dosing, Adverse Effects, Interactions,
and Contraindications
Green tea is available in various formulations. Typical
consumption is about three cups per day (1 teaspoon of
tea leaves in 8 oz of boiling water), which provides 240 to
320 mg of polyphenols. Green tea in extract form should
be taken in recommended doses and with a meal. The
cost of green tea varies by quality, type, and preparation
(Table 1).
Green tea is safe for most adults when used in mod-
erate quantities. The most common adverse effects of
consuming green tea orally are gastrointestinal upset
and central nervous system stimulation from caffeine
content (Table 2
4-21
). There are several case reports of
hepatotoxicity linked to green tea extract products in pill
or beverage form. The mechanism for this is unknown.
21
Allergic reactions have been reported with topical green
tea ointment, which may cause cervical and vaginal
inflammation, irritation, and vulvar burning.
6
Green tea contains a small amount of vitamin K. There
are conflicting reports about whether green tea interferes
with anticoagulant or antiplatelet medications. In one
case report, large amounts of green tea (0.5 to 1.0 gallon)
antagonized the effects of warfarin (Coumadin).
22
Because catechins seem to inhibit dihydrofolate reduc-
tase, there is concern that consuming large amounts of
green tea might cause antifolate activity, which could
potentially increase the risk of birth defects related to
folic acid deficiency.
23
Bottom Line
The National Cancer Institute is actively exploring tea
compounds as cancer-chemopreventive and adjuvant-
treatment agents in human trials. Although further studies
are needed, green tea appears to be a low-risk, inexpensive
complementary therapy for a number of conditions.
Table 1. Commonly Studied Dosages and Formulations of Green Tea
Use* Formulation Dosage Cost
Treatment of external genital and
perianal warts caused by human
papillomavirus
Sinecatechins
15% ointment
(Veregen)
0.5 cm per wart three times per day
for 16 weeks
15-g tube ranges from $250 to
$300
Reduction of breast cancer risk Green tea beverage Three or more cups per day Green tea ranges from $5 for 30
tea bags to $23 for 240 tea bags;
loose green tea leaves range
from $7 to $45 for 75 servings of
average to good quality tea
Reduction of colorectal cancer risk Green tea beverage Five to 10 cups per day
Weight reduction and
management
Capsules or
beverage
Two capsules three times a day
before meals (45 mg of EGCG plus
25 mg of caffeine per capsule)
340 mL (one cup) of green tea
containing 600 mg of catechins
and 70 mg of caffeine
Extracts with 45 mg EGCG and
25 mg caffeine are roughly $5 to
$10 for 100 capsules
Reduction of cholesterol Theaflavin-enriched
green tea extract
(Teaflavin)
375-mg capsule daily (75 mg of
theaflavins, 150 mg of green tea
catechins, and 150 mg of other
tea polyphenols)
30-day supply ranges from
$18 to $25
Green tea beverage 10 or more cups per day
Reduction of cardiovascular risk Green tea beverage Five or more cups per day
EGCG = epigallocatechin gallate.
*—Independent testing of green tea dietary supplements is available at http://www.consumerlab.com.
More condition-specific dosing recommendations are available at National Medicines Comprehensive Database (http://www.naturaldatabase.
com) and National Standard (http://www.naturalstandard.com).
—These costs are estimates based on a search of commonly used Internet sites (http://www.amazon.com, http://www.inpursuitoftea.com,
http://www.naturesstore.com, http://www.vitacost.com, and http://www.vitaminshoppe.com).
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594 American Family Physician www.aafp.org/afp Volume 79, Number 7
April 1, 2009
Members of various family medicine departments develop articles for
“Complementary and Alternative Medicine.” This is one in a series
coordinated by Sumi Sexton, MD, and Benjamin Kligler, MD, MPH.
The Authors
CRAIG SCHNEIDER, MD, is director of integrative medicine in the Depart-
ment of Family Medicine at Maine Medical Center in Portland. He received
his medical degree from the Columbia University College of Physicians and
Surgeons in New York, NY. Dr. Schneider completed a family medicine resi-
dency at Maine Medical Center and a fellowship in integrative medicine at
the University of Arizona in Tucson.
TIFFANY SEGRE, MD, practices family and integrative medicine in Gorham,
Maine. At the time the article was written, Dr. Segre was completing a
fellowship through the combined integrative medicine program at Maine
Medical Center and the University of Arizona in Tucson. She received her
medical degree from the Temple University School of Medicine in Philadel-
phia (Pa.). She completed a family medicine residency at Maine Medical
Center in Portland.
Address correspondence to Craig Schneider, MD, Maine Medical Cen-
ter, 22 Bramhall St., Portland, ME 04102. Reprints are not available
from the authors.
Author disclosure: Nothing to disclose.
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3. Cabrera C, Artacho R, Giménez R. Beneficial effects of green tea
a review. J Am Coll Nutr. 2006;25(2):79-99.
4. Gross G, et al. A randomized, double-blind, four-arm parallel-group,
placebo-controlled Phase II/III study to investigate the clinical ef-
cacy of two galenic formulations of Polyphenon E in the treatment
of external genital warts. J Eur Acad Dermatol Venereol. 2007;21(10):
1404-1412.
5. U.S. Food and Drug Administration. Veregen (Kunecatechins) ointment,
15%. http://www.fda.gov/cder/foi/label/2006/021902lbl.pdf. Accessed
December 22, 2008.
6. Ahn WS, Yoo J, Huh SW, et al. Protective effects of green tea extracts
(polyphenon E and EGCG) on human cervical lesions. Eur J Cancer Prev.
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7. Bushman JL. Green tea and cancer in humans: a review of the literature.
Nutr Cancer. 1998;31(3):151-159.
8. Sun CL, Yuan JM, Koh WP, Yu MC. Green tea, black tea and breast
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2006;27(7):1310-1315.
9. Sun CL, Yuan JM, Koh WP, Yu MC. Green tea, black tea and colorectal
cancer risk: a meta-analysis of epidemiologic studies. Carcinogenesis.
2006;27(7):1301-1309.
10. Kuriyama S, Shimazu T, Ohmori K, et al. Green tea consumption and
mortality due to cardiovascular disease, cancer, and all causes in Japan:
the Ohsaki study. JAMA. 2006;296(10):1255-1265.
11. Sun CL, Yuan JM, Lee MJ, et al. Urinary tea polyphenols in relation to
gastric and esophageal cancers: a prospective study of men in Shang-
hai, China. Carcinogenesis. 2002;23(9):1497-1503.
12. Bettuzzi S, Brausi M, Rizzi F, Castagnetti G, Peracchia G, Corti A. Che-
moprevention of human prostate cancer by oral administration of green
tea catechins in volunteers with high-grade prostate intraepithelial neo-
plasia: a preliminary report from a one-year proof-of-principle study.
Cancer Res. 2006;66(2):1234-1240.
13. Choan E, Segal R, Jonker D, et al. A prospective clinical trial of green tea
for hormone refractory prostate cancer: an evaluation of the complemen-
tary/alternative therapy approach. Urol Oncol. 2005;23(2):108-113.
14. Kurahashi N, Sasazuki S, Iwasaki M, Inoue M, Tsugane S, for the
JPHC Study Group. Green tea consumption and prostate cancer risk
in Japanese men: a prospective study. Am J Epidemiol. 2008;167(1):
71-77.
15. Kovacs EM, Lejeune MP, Nijs I, Westerterp-Plantenga MS. Effects of
green tea on weight maintenance after body-weight loss. Br J Nutr.
2004;91(3):431-437.
16. Diepvens K, Kovacs EM, Vogels N, Westerterp-Plantenga MS. Meta-
bolic effects of green tea and of phases of weight loss. Physiol Behav.
2006;87(1):185-191.
17. Westerterp-Plantenga MS, Lejeune MP, Kovacs EM. Body weight loss
and weight maintenance in relation to habitual caffeine intake and
green tea supplementation. Obes Res. 2005;13(7):1195-1204.
18. Nagao T, Hase T, Tokimitsu I. A green tea extract high in catechins
reduces body fat and cardiovascular risks in humans. Obesity (Silver
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19. Tsubono Y, Tsugane S. Green tea intake in relation to serum lipid
levels in Middle-aged Japanese men and women. Ann Epidemiol.
1997;7(4):280-284.
20. Maron DJ, Lu GP, Cai NS, et al. Cholesterol-lowering effect of a theafla-
vin-enriched green tea extract: a randomized controlled trial. Arch
Intern Med. 2003;163(12):1448-1453.
21. Gloro R, Hourmand-Ollivier I, Mosquet B, et al. Fulminant hepatitis dur-
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Table 2. Key Points About Green Tea
Effectiveness
Effective for treatment of genital warts
4,5
Conflicting evidence for prevention and treatment of cancer
7-14
Conflicting evidence for weight loss
15-18
Possibly effective for prevention of stroke
10
Conflicting evidence for decreasing risk of cardiovascular
disease
10,19,20
Adverse effects
Central nervous system stimulation; gastrointestinal upset; case
reports of hepatotoxicity involving green tea extract in pill or
beverage form
21
Topical ointment may cause local irritation
6
Interactions
Additive effect with stimulants (caffeine component)
Dosage
Available as tea, liquid and solid extracts, and ointment
Cost
Prices vary widely for tea and extracts by brand and quality,
but potentially as low as $5 to $18 for one-month supply;
ointment pricing varies by pharmacy, currently in $250 range
or higher for 15-g tube
Bottom line
Safe alternative to treat genital warts; inconsistent evidence for
use in cancer prevention, cardiovascular disease and stroke
prevention, and weight management
Information from references 4 through 21.
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  • Source
    • "10 mg/kg administration of Coenzyme Q10 and 400 mg/kg administration of fish oil combination has protective effect against to alimunium chloride-induced testicular dysfunction in the rats [29]. Green Tea: Green tea has a potential health-promoting properties due to its catechins and it has an ability to scavenge reactive oxygen species including strong antioxidant activity [30,31]. 300 mg/kg green tea and 0,4 mg/kg vitamin E combination had a protective effect in the testicular tissue in diabetic rats which were induced by streptozotocin [32]. "
    Preview · Article · Jan 2016
  • Source
    • "So, it will be important in these studies to determine the effects of caffeine consumption on the efficacy of these drugs [29]. The phenolic compounds (especially epigallocatechin- 3-gallate, EGCG) in green tea may help prevent cancer when consumed in moderation [26,30]. The US FDA has approved a topical ointment (sinecatechins 15%, Verege®) for the treatment of external genital and perianal warts caused by the human papillomavirus. "
    Full-text · Article · Sep 2015
  • Source
    • "Tea plants also have the ability to produce flowers and seeds depending on seasons and stress levels. Phyto-chemicals use is not only limited to foods but also used to manufacture drugs [9] [10] . Residues from the extraction can be utilized as manure and animal feeds accordingly [5] . "
    [Show abstract] [Hide abstract] ABSTRACT: Tea (Cammelia sinensis) is the most widely consumed beverage in the world and has been reported to have unlimited health benefits due to its antioxidant properties. There is a high correlation between polyphenol compounds with antioxidant properties. Tea leaves are a major source of polyphenols. The aim of the present investigation was to determine the approximate level of po-lyphenols in different other parts of the tea plant to give comparative data on obtaining extracts that can be used to design products through value addition to assist in the prevention of diseases associated with oxidative stress. Twenty-one selected region specific tea varieties were used to obtain roots, flowers, leaves and barks. Leaves were prepared by microwaving and the remaining portions processed as green non-aerated teas and black aerated tea. Roots, barks, flowers were sun-dried and milled. Total polyphenol content was determined by calorimetric method using Fo-lin-Ciocalteu reagent. The obtained results suggest that different parts of tea plant have varying numbers of total polyphenols with microwaved leaves having mean levels at 23.1%, steamed leaves (non-aerated green tea) at 22.37%, aerated leaves at 15.51%, barks at 14.92%, flowers at 10.62% and roots at 1.48%.
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