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Home Green Tea Benefits Reviewed
Review
Beneficial Effects of Green Tea—A Review
Carmen Cabrera, PhD, Reyes Artacho, PhD, Rafael Gime´nez, PhD
Departamento de Nutricio´n y Bromatologı´a, Facultad de Farmacia, Universidad de Granada, Granada, SPAIN
Key words: green tea, polyphenols, catechins, antioxidant activity, human health
Tea is the most consumed drink in the world after water. Green tea is a ‘non-fermented’ tea, and contains
more catechins, than black tea or oolong tea. Catechins are in vitro and in vivo strong antioxidants. In addition,
its content of certain minerals and vitamins increases the antioxidant potential of this type of tea. Since ancient
times, green tea has been considered by the traditional Chinese medicine as a healthful beverage. Recent human
studies suggest that green tea may contribute to a reduction in the risk of cardiovascular disease and some forms
of cancer, as well as to the promotion of oral health and other physiological functions such as anti-hypertensive
effect, body weight control, antibacterial and antivirasic activity, solar ultraviolet protection, bone mineral
density increase, anti-fibrotic properties, and neuroprotective power. Increasing interest in its health benefits has
led to the inclusion of green tea in the group of beverages with functional properties. However, although all the
evidence from research on green tea is very promising, future studies are necessary to fully understand its
contributions to human health, and advise its regular consumption in Western diets, in which green tea
consumption is nowadays limited and sporadic.
Key teaching points:
• Green tea contains numerous components with antioxidant activity: polyphenols (especially catechins), minerals, vitamins.
• Green tea contains more catechins than black or oolong teas.
• The strong antioxidant potential of catechins, and especially EGCG, are widely demonstrated in vitro and in animal studies. In
addition, catechins possess antimutagenic, antidiabetic, anti-inflammatory, antibacterial and antiviral properties.
• Recent human studies suggest that green tea may contribute to reduce the risk of cardiovascular disease and cancer, and has another
beneficial effect on health.
• Although research of green tea is very promising, future studies considering dietetic, environmental and life style factors, are
necessary to fully understand its contribution to human health.
INTRODUCTION
Tea, a product made up from leaf and bud of the plant
Camellia sinensis, is the second most consumed beverage in the
world, well ahead of coffee, beer, wine and carbonated soft
drinks [1–2]. Originating from China, tea has gained the
world’s taste in the past 2000 years. The economic and social
interest of tea is clear and its consumption is part of many
people daily routine, as an everyday drink and as a therapeutic
aid in many illnesses.
Depending on the manufacturing process, teas are classified
into three major types: ‘non-fermented’ green tea (produced by
drying and steaming the fresh leaves to inactivate the polyphenol
oxidase and thus, non oxidation occurs); ‘semi-fermented’
oolong tea (produced when the fresh leaves are subjected to a
partial fermentation stage before drying); and ‘fermented’
black and red (Pu-Erh) teas which undergo a post-harvest
fermentation stage before drying and steaming, although the
fermentation of black tea is due to an oxidation catalyzed by
polyphenol oxidase, and that of Pu-Erh tea is attained by using
Address reprint requests to: Carmen Cabrera, PhD, Dpto. Nutricio´n y Bromatologı´a, Facultad de Farmacia, Campus Universitario de Cartuja, 18012-Granada, SPAIN.
E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abbreviations: CI  confidence interval, DNA  deoxyribonucleic acid, DPPH  2,2-diphenyl-l-picrylhydrazyl assay, DMPD  N,N-dimethyl-p-phenylendiamine assay,
EC  ()-epicatechin, ECG  ()-epicatechin-3-gallate, EGC  ()-epigallocatechin, EGCG  ()-epigallocatechin-3-gallate, FRAP  ferric reducing ability of
plasma assay, GA  gallic acid, GTP  green tea polyphenols, HDL  high density lipoproteins, HR  hazard ratio, LDL  low density lipoproteins, OR  odd ratio,
ORAC  oxygen radical absorbance capacity assay, PCL  photochemiluminescence assay, RR  relative risk, TEAC  Trolox equivalent antioxidant capacity assay,
TRAP  total radical-trapping antioxidant parameter assay, UV  ultraviolet.
Journal of the American College of Nutrition, Vol. 25, No. 2, 79–99 (2006)
Published by the American College of Nutrition
79
microorganisms [3– 4]. McKay and Blumberg [4] reported a
per capita mean consumption of tea in the world of 120 mL/
day. Approximately 76–78% of the tea produced and consumed
is black tea, 20–22% is green tea and less than 2% is
oolong tea [5]. Black tea is consumed principally in Europe,
North America and North Africa (except Morocco) while green
tea is widely drunk in China, Japan, Korea and Morocco;
oolong tea is popular in China and Taiwan [5– 6]. In USA, the
80% of tea consumed is black ice tea [7].
Although health benefits have been attributed to green tea
consumption since the beginning of its history, scientific investigations
on this beverage and its constituents have been
underway for less than three decades [4]. In vitro and animal
studies, and clinical trials employing putative intermediary
indicators of disease, particularly biomarkers of oxidative stress
status, provide strong evidence that green tea polyphenols
(GTP) may play a role in the risk and pathogenesis of several
chronic diseases, especially cardiovascular disease and cancer,
and related pathologies. In addition, several studies suggest a
beneficial impact of green tea intake on bone density, cognitive
function, dental caries and kidney stones, among other effects
[4 –5]. Over the last years, numerous epidemiological and clinical
studies have revealed several physiological responses to
green tea which may be relevant to the promotion of health and
the prevention or treatment of some chronic diseases. However,
the results from epidemiological and clinical studies of the
relationship between green tea consumption and human health
are mixed. For example, conflicting results between human
studies may arise in part, from ignoring socioeconomic and
lifestyle factors as well as by inadequate methodology to define
tea preparation and intake [2,4 –7].
Foodstuff can be regarded as functional if it is satisfactorily
demonstrated to affect beneficially one or more target functions
in the body, beyond adequate nutritional effects in a way which
is relevant to either the state of well-being and health or the
reduction of the risk of a disease [5,8 –9], so green tea has been
proved to have functional properties and at present, its consumption
is widely recommended.
The aim of this article is to revise the most recent studies on
green tea beneficial effects and to evaluate its potential interest
in Western diets.
Green Tea Processing
Green tea is mainly produced from Camellia sinensis var.
sinensis. The Assan type (Camellia sinensis var. assamica) has
a too high content of polyphenols, which would make green tea
taste excessively bitter [3]. The production of green tea is
characterized by an initial heating process, which kills the
enzyme polyphenol oxidase, which is responsible for the conversion
of the flavanols in the leaf into the dark polyphenolic
compounds that colour black tea. The other important process
is rolling, in which leaves are cut and twisted. The final form of
green tea depends on the particular variant being produced. The
rolling stage is very similar to the operation with the same
name in black tea production. Green tea production is restricted
mainly to China and Japan [3,6]. Fig. 1 shows the principal
differences between green and black tea processing.
Green Tea Composition
Green tea chemical composition is complex: proteins (15–
20% dry weight) whose enzymes constitute an important fraction;
aminoacids (1–4% dry weight) such as teanine or 5-Nethylglutamine,
glutamic acid, tryptophan, glycine, serine,
aspartic acid, tyrosine, valine, leucine, threonine, arginine, lysine;
carbohydrates (5–7% dry weight) such as cellulose, pectins,
glucose, fructose, sucrose; lipids as linoleic and -linolenic
acids; sterols as stigmasterol; vitamins (B, C, E); xanthic
bases such as caffeine and theophylline (Fig. 2); pigments as
chlorophyll and carotenoids; volatile compounds as aldehydes,
alcohols, esters, lactones, hydrocarbons, etc.; minerals and
trace elements (5% dry weight) such as Ca, Mg, Cr, Mn, Fe,
Cu, Zn, Mo, Se, Na, P, Co, Sr, Ni, K, F and Al. Due to the great
importance of the mineral presence in tea, many studies have
been carried out to determine their levels in green tea leaves
and their infusions. For example, Costa et al. [1] observed large
variations of the mineral content (Al, Ca, Mg and Mn) in green
tea from different origins. Ferna´ndez-Ca´ceres et al. [10] determined
the content of Al, Ba, Ca, Cu, Fe, K, Mg, Mn, Na, Sr, Ti,
and Zn in 46 tea samples, and no clear differences were found
between mineral content of green and black teas. Shu et al. [11]
observed the great variations among different tea varieties in
accumulating fluoride and aluminum. Fung et al. [12] indicated
that black tea had higher Al and F concentrations than green
tea. Xu et al. [13] reported that the content of Se in green teas
was greatly increased by foliar application of Se-enriched fertilizers;
moreover, the selenium-enriched green tea exhibited
significantly higher antioxidant activity than regular green tea.
Table 1 summarizes the mean chemical composition of green
tea leaves in comparison with black tea leaves and its infusion.
Polyphenols constitute the most interesting group of green
tea leaf components, and in consequence, green tea can be
considered an important dietary source of polyphenols, particularly
flavonoids. Flavonoids are phenol derivatives synthesized
in substantial amounts (0.5–1.5%) and variety (more than
4000 identified), and widely distributed among plants [14]. The
United States Department of Agriculture (USDA) has recently
published a Database for the Flavonoid Content of Selected
Foods [15]. The main flavonoids present in green tea include
catechins (flavan-3-ols). The four major catechins are ()-
epigallocatechin-3-gallate (EGCG), that represents approximately
59% of the total of catechins; ()-epigallocatechin
(EGC) (19% approximately); ()-epicatechin-3-gallate (ECG)
(13.6% approximately); and ()-epicatechin (EC) (6.4% approximately)
[4]. Green tea also contains gallic acid (GA) and
other phenolic acids such as chlorogenic acid and caffeic acid,
and flavonols such as kaempferol, myricetin and quercetin [15].
Green Tea: Beneficial Effects
80 VOL. 25, NO. 2
Fig. 3 shows the chemical structure of GA and the four
major catechins present in green tea. In black tea the polymerized
catechins such as theaflavins and thearubigins predominate.
Black and green teas both contain similar amount
of flavonoids, however they differ in their chemical structure;
green tea contains more catechins (simple flavonoids),
while the oxidation undergone by the leaves in order to make
black tea, converts these simple flavonoids into theaflavins
and thearubigins [15].
The relative catechin content of green tea depends on how
the leaves are processed before drying (a certain grade of
fermentation and heating of tea leaves during the manufacturing
process can result in polymerization of monopolyphenolic
compounds such as the catechins, leading to conformational
changes and thus modifying its properties. Other factors influencing
catechin content are the geographical location and
growing conditions (soil, climate, agricultural practices, fertilizers),
the type of green tea (e.g., blended, decaffeinated, instant,
. . .), and the preparation of the infusion (e.g., amount of
the product used, brew time, temperature) [5,16]. McKay and
Blumberg [5] reported that decaffeinating reduces slightly the
Fig. 1. Principal differences between green and black tea processing and its influence on the final polyphenols content.
Fig. 2. Chemical structure of caffeine and theophylline.
Table 1. Mean Composition (%) of Green Tea and Black
Tea (and Its Infusion). From Belitz and Grosh [167]
Compound Green tea* Black tea* Infusion†
Proteins 15 15 trace
Aminoacids 4 4 3.5
Fibre 26 26 0
Others carbohydrates 7 7 4
Lipids 7 7 trace
Pigments 2 2 trace
Minerals 5 5 4.5
Phenolic compounds‡ 30 5 4.5
Oxidised phenolic compounds§ 0 25 4.5
* Data refereed to dry weight of tea leaves.
† Black tea; infusion time: 3 min.
‡ Especially flavonoids.
§ Especially thearubigins and theaflavins.
Green Tea: Beneficial Effects
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 81
tea catechin content; also, instant preparations and iced and
ready-to drink teas present less content of catequins [16 –17].
The production of bottled green tea beverage has encountered
a browning problem mainly caused by the oxidation of catechins
[18].
Wu and Wei [5] indicated that a cup of green tea (2.5 g of
green tea leaves/200 mL of water) may contain 90 mg of
EGCG. Lin et al. [19] analyzed 31 commercial teas, and
detected that the levels of EGCG and total catechins were in the
following order: green tea (old leaves)  green tea (young
leaves) and oolong tea  black tea and Pu-Erh tea. Ferna´ndez
et al. [20] determined the contents of GA, EGCG, EGC, EC
and ECG, in a set of 45 tea samples, including black and green
teas from different geographical origins (i.e. China, Japan,
Kenya, Sri Lanka, and India); the GA levels were always
higher in black tea because the amount of GA increases during
the fermentation process due to its liberation from catechin
gallates [21]. The amount of catechins were always higher in
green tea; EGCG and EGC were the major catechins present
with average contents of 7.358% and 3.955%, respectively;
ECG presented values ranging between 0.910 and 3.556%. For
black tea, EGCG and ECG were the catechins present in higher
percentages, with average contents of 1.583 and 0.706%, respectively.
Cabrera et al. [22] reported the mean content of the
four major catechins (EGCG, EGC, ECG and EC) and gallic
acid in 45 samples of different types of tea including black, red,
oolong and green teas; the higher levels of EGCG appeared in
green tea samples. Results are summarized in Fig. 4. However,
Henning et al. [23] suggested that the large variation of the
catechin content in tea is not taken into consideration in most of
the epidemiological studies.
Bioavailability of Green Tea Catechins
The potential health effects of catechins depend not only on
the amount consumed but on their bioavailability which appears
to be very variable. In order to know the catechin bioavailability
and metabolism, it is necessary to evaluate their
biological activity within target tissues [24]. Following oral
administration of tea catechins to rats, the four principal catechins
(EC, ECG, EGC, and EGCG) have been identified in the
portal vein, indicating that tea catechins are absorbed intestinally
[25]. In rats given 0.6% GTP in their drinking water over
a period of 28 days, plasma concentrations of EGCG were
much lower than those of EGC or EC, even though the ratio of
EGCG to EGC was 5:1 in the GTP solution. When the same
GTP preparation was given to mice, plasma levels of EGCG
were much higher than those of EGC and EC. So, there appear
to be species differences in the bioavailability of EGCG compared
to the other catechins [26]. In humans, EGCG may be
less bioavailable than other green tea catechins. Catechin levels
in human plasma reach their peak 2 to 4 h after ingestion [27].
A recent study in humans compared the pharmacokinetics of
equimolar doses of pure EGC, ECG, and EGCG in 10 healthy
volunteers; average peak plasma concentrations after a single
dose of 1.5 mmol were 5.0 mol/L for EGC, 3.1 mol/L for
ECG, and 1.3 mol/L for EGCG. After 24 h, plasma EGC and
EGCG returned to baseline, but plasma ECG remained elevated
[28]. In humans, ECG has been found to be more highly
methylated than EGC and EGCG, and EGCG has been found to
be less conjugated than EGC and EC [29]. Unfortunately, little
published data are available on tissue distribution of catechins
in humans after green tea consumption; however, there are
some interesting data from studies with animals. Kim et al. [26]
Fig. 3. Chemical structure of gallic acid and the four major catechins in green tea. GA, gallic acid; EGCG, ()-epigallocatechin-3-gallate; EGC,
()-epigallocatechin; ECG, ()-epicatechin-3-gallate; EC, ()-epicatechin.
Green Tea: Beneficial Effects
82 VOL. 25, NO. 2
observed that when rats were given 0.6% GTP in their drinking
water over a period of 28 days, substantial amounts of EGC and
EC were found in the esophagus, large intestine, kidney, bladder,
lung, and prostate; EGC and EC concentrations were
relatively low in liver, spleen, heart, and thyroid; EGCG levels
were higher in the esophagus and large intestine, but lower in
other organs, likely due to poor systemic absorption of EGCG.
Catechins are rapidly and extensively metabolized; studies in
rats indicated that EGCG is mainly excreted through the bile,
while EGC and EC are excreted through urine and bile. Determination
of the actual bioavailability of metabolites in tissues
may be much more important than knowledge of their plasma
concentration, but data are still very scarce even in animals.
Consequently, the metabolism and bioavailability of individual
tea catechins and the pharmacokinetics of their metabolites
require further clarification.
Lu et al. [30] reported that GTP have biological activities
including modulation of key signal transduction pathways;
however, the possible significance of these activities in inhibition
of carcinogenesis in vivo depends on the polyphenol bioavailability.
These authors observed that after oral administration
of green tea to rats, about 14% of EGC, 31% of EC, and
1% of EGCG appeared in the blood; in mice, the bioavailability
of EGCG was higher, but the biological activities of the
catechin metabolites still need to be investigated. Inter-individual
variations in the bioavailability of GTP can be substantial
and may be due, in part, to differences in colonic microflora
and genetic polymorphisms among the enzymes involved in
polyphenol metabolism [31]. The effect of green tea drinking
may also differ by genotype [32]. To sum up, there appear to be
species differences in the bioavailability of EGCG compared to
other tea catechins. Further research results are largely consistent
in demonstrating that the addition of milk to tea does not
interfere with catechin absorption [33–35], but milk may affect
the antioxidant potential of tea, depending upon milk fat content,
milk volume added, and the method used to assess this
parameter [33–36]. Xu et al. [37] observed that the epimerisation
reaction occurring in manufacturing canned and bottled tea
drinks would not significantly affect antioxidant activity and
bioavailability of total tea polyphenols.
Green Tea and Human Health
Green tea has been considered a medicine and a healthful
beverage since ancient times. The traditional Chinese medicine
has recommended this plant for headaches, body aches and
pains, digestion, depression, detoxification, as an energizer and,
in general, to prolong life. Green tea leaves contain three main
components which act upon human health: xanthic bases (caffeine
and theophylline), essential oils and especially, polyphenolic
compounds. Caffeine acts mainly upon the central nervous
system, stimulating wakefulness, facilitating ideas
association and decreasing the sensation of fatigue [38]. Some
of the effects caused by caffeine are influenced by theophylline
tea content. Theophylline induces psychoactive activity, it also
has a slightly inotrope and vasodilator effect, and a much
Fig. 4. Mean content of gallic acid and catechins in different types of tea (n  45). Data refereed to dry weight of commercial samples (Source:
Cabrera et al. [22]).
Green Tea: Beneficial Effects
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 83
higher diuretic effect than caffeine. However, its most interesting
effects can be seen at the bronchopulmonar and respiratory
level. Theophylline causes a non-specific relaxation on the
bronchial smooth muscle, and respiratory stimulation is also
observed. Essential oils are in a great extent volatile and they
evaporate from the beverage after some time, thus it is not very
convenient to overextend the brewing time. Among their properties,
the one of facilitating digestion must be highlighted
[5,39]. Green tea is the type of tea with the higher percentage
of essential oils [38 –39]. However, green tea has received a
great deal of attention especially due to its content of polyphenols,
which are strong antioxidants and present important biological
properties. Numerous studies have also demonstrated
that the aqueous extract of GTP possesses antimutagenic, antidiabetic,
antibacterial, anti-inflammatory, and hypocholesterolemic
properties [21,40–44]. Beneficial effects in oral diseases
such as protection against dental caries, periodontal
disease, and tooth loss (which may significantly affect a person’s
overall health) have been also described [5]. Among all
GTP, catechins and gallic acid have been especially considered
to be the main players in the beneficial effects on human health
next detailed.
Antioxidant Activity. Green tea is considered a dietary
source of antioxidant nutrients: green tea is rich in polyphenols
(catechins and gallic acid, particularly), but it also contains
carotenoids, tocopherols, ascorbic acid (vitamin C), minerals
such as Cr, Mn, Se or Zn, and certain phytochemical compounds.
These compounds could increase the GTP antioxidant
potential. GTP present antioxidant activity in vitro by scavenging
reactive oxygen and nitrogen species and chelating redoxactive
transition metal ions; GTP can chelate metal ions like
iron and copper to prevent their participation in Fenton and
Haber-Weiss reactions [4,45–46]. They may also function indirectly
as antioxidants through 1) inhibition of the redoxsensitive
transcription factors; 2) inhibition of ‘pro-oxidant’
enzymes, such as inducible nitric oxide synthase, lipoxygenases,
cyclooxygenases and xanthine oxidase; and 3) induction
of antioxidant enzymes, such as glutathione-S-transferases and
superoxide dismutases.
The antioxidant capacity of GTP has been assessed by
several methods. For example, Cao et al. [47] using the oxygen
radical absorbance capacity (ORAC) assay found that green tea
has a much higher antioxidant activity against peroxyl radicals
than vegetables such as garlic, kale, spinach and Brussels
sprouts. Using the ferric reducing ability of plasma (FRAP)
assay. Langley-Evans [48] found that the total antioxidant
capacity of green tea is more potent than that of black tea.
Saffari and Sadrzadeh [49] investigated the antioxidant capacity
of EGCG using erythrocyte membrane-bound. ATPases as
a model, and the results indicated that EGCG is a powerful
antioxidant that is capable of protecting erythrocyte membranebound
ATPases against oxidative stress. Several studies have
shown that EGCG can act in vitro as an antioxidant by trapping
proxyl radicals and inhibiting lipid peroxidation [49–50]. However,
the antioxidant capacity of catechins determined in vitro
is dependent upon the type of assay employed and it does not
reflect factors such as bioavailability and metabolism. The fact
that catechins are rapidly and extensively metabolized emphasizes
the importance of demonstrating their antioxidant activity
in vivo to better represent the physiological impact of green tea
consumption. Frei and Higdon [51] reported that in order to
determine whether or not GTP act as effective antioxidants in
vivo, future studies in animals and humans should employ
sensitive and specific biomarkers of oxidative damage of lipids,
proteins and DNA.
Nevertheless, a substantial number of human intervention
studies with green tea demonstrate a significant increase in
plasma antioxidant capacity in humans after consumption of
moderate amounts (1–6 cups/day); there are also initial indications
which show that the enhanced blood antioxidant potential
leads to a reduced oxidative damage in macromolecules such as
DNA and lipids [2,4,23,28,37]. However, these authors indicated
that the measurement of oxidative damage through biomarkers
needs to be further established. McKay and Blumberg
[4] reported that the repeated consumption of green tea and
encapsulated green tea extracts for one to four weeks has been
demonstrated to decrease biomarkers of oxidative status. Furthermore,
Klaunig et al. [52] observed in a study with 40 male
smokers in China and 27 men and women (smokers and nonsmokers)
in the United States, that oxidative DNA damage,
lipid peroxidation, and free radical generation were reduced
after consuming 6 cups/day of green tea for seven days.
Therefore, GTP may contribute to defenses against oxidative
damages [5]. Erba et al. [53] suggest the ability of green tea,
consumed within a balanced controlled diet, to improve overall
the antioxidative status and to protect against oxidative damage
in humans.
Antimutagenic and Anticarcinogenic Potential. Lifestyle-
related diseases, including cancer, are also characterized
as aging-related diseases, where aging may be the most potent
causal factor. Therefore, prevention of lifestyle-related diseases
will depend on slowing the aging process and avoiding the
clinical appearance the disease. Dietary components that are
capable of retarding cellular aging and inhibiting the growth of
cancer cells without affecting the growth of normal cells are
receiving considerable attention for the development of novel
cancer-preventive approaches [54–56]. The role of green tea in
protection against cancer has been supported by ample evidence
from studies in cell culture and animal models [54].
Animal studies have shown that green tea inhibit carcinogenesis
of the skin, lung, oral cavity, esophagus, stomach, liver,
kidney, prostate and other organs [55,57–60]. In some studies,
the inhibition correlated with an increase in tumor cell apoptosis
and a decrease in cell proliferation [56]. Today, green tea is
accepted as a cancer preventive on the basis of numerous in
vitro, in vivo and epidemiological studies. The Chemoprevention
Branch of the National Cancer Institute has initiated a plan
Green Tea: Beneficial Effects
84 VOL. 25, NO. 2
for developing tea compounds as cancer-chemopreventive
agents in human trials [61]. The chemopreventive effects of
green tea depend on: (1) its antioxidant action; (2) the specific
induction of detoxifying enzymes; (3) its molecular regulatory
functions on cellular growth, development and apoptosis; and
(4) a selective improvement in the function of the intestinal
bacteria flora. D’Alessandro et al. [62] also indicated that an
important aspect of cancer risk is related to inflammatory
response; currently, anti-inflammatory agents are used in chemopreventive
strategies. The inflammatory response involves
the production of cytokines and proinflammatory oxidants such
as hypochlorous acid and peroxynitrite produced by neutrophils
and macrophages, respectively. These oxidants react with phenolic
tyrosine residues on proteins to form chloro- and nitrotyrosine.
Green tea catechins and soy isoflavones have also
been shown to be chemopreventive; the aromatic nature of
polyphenols makes them potential targets of hypochlorous acid
and peroxynitrite, and these reactions may create novel pharmacophores
at the site of inflammation. In addition, a major
mechanism of the anticarcinogenic activity of green tea in
animals is the impairment of the interaction of carcinogens with
DNA leading to mutations. Nevertheless, the antimutagenic
activity of green tea as well as its underlying mechanisms must
be reviewed, and the role of GTP, the postulated bioactive
components, and caffeine must be critically evaluated. EGCG
from green tea especially imparts a growth inhibitory effect on
cancer cells [56,63–64]. EGCG possesses promising anticancer
potential due to its antioxidant, antimutagenic and chemopreventive
properties [65–66].
Rosengren [67] indicated that the green tea catechins reduce
the proliferation of breast cancer cells in vitro and decrease
breast tumor growth in rodents. Furthermore, in vitro studies
have demonstrated that the combination of EGCG and tamoxifen
is synergistically cytotoxic to breast cancer cells; these
results suggest that the catechins have significant potential in
the treatment of breast cancer. Mittal et al. [56] reported that
the treatment with EGCG decreased cell viability at different
stages studied (approx. 80% inhibition) in human breast carcinoma
MCF-7 cells, but had no adverse effect on the growth of
normal mammary cells. These authors found that this treatment
inhibited telomerase activity (40–55%); telomerase is elevated
in 90% of breast carcinomas and therefore has received much
attention as a target for breast cancer therapy and cancer
diagnostic research. According to Wu et al. [68], green tea
drinkers showed a significantly reduced risk of breast cancer;
compared to women who did not drink green tea regularly (i.e.,
less than once a month). Furthermore, there was a significant
trend of decreasing risk with increasing amount of green tea
intake. Two studies in Japanese women diagnosed with breast
cancer indicate that green tea consumption is inversely associated
with the rate of recurrence, especially in the early stages of
breast cancer [69–70]. Zhou et al. [71] also reported that breast
cancer is significantly less prevalent among Asian women,
whose diets contain high intake of soy products and green tea.
These authors suggested that dietary soy phytochemical concentrate
plus green tea may be used as a potential effective
dietary regimen for inhibiting progression of estrogen-dependent
breast cancer.
Zhang et al. [72] reported that ovarian cancer risk declined
with increasing frequency and duration of green tea consumption.
Green tea is also an effective chemopreventive agent to
human prostate cancer. In the same line of research, Yu et al.
[73] reported that EGCG inhibited the growth of prostate
cancer adenoma cells and induced apoptosis. Jian et al. [74]
conducted a case-control study in China in order to investigate
whether green tea consumption has an etiological association
with prostate cancer. Prostate cancer risk declined with increasing
frequency, duration and quantity of green tea consumption.
The dose-response relationships were also significant, suggesting
that green tea is protective against prostate cancer.
Yamamoto et al. [59] reported that GTP could be applied to
enhance the effectiveness of chemo/radiation therapy to promote
cancer cell death while protecting normal cells.
On the one hand, epidemiological studies have suggested
that high consumption of green tea protects against the development
of chronic active gastritis and decreases the risk of
stomach cancer; in addition, the ingestion of green tea before
fasting protects the intestinal mucosa against atrophy [75]. On
the other hand, Borrelli et al. [76] concluded in a systematic
review, that an inverse association does not seem to exist
between green tea consumption and the risk of gastric and
intestinal cancer, although green tea did show a protective
effect on adenomatous polyps and chronic gastritis [76]. In the
same way, Hoshiyama et al. [66] and Koizumi et al. [77] found
no association between green tea consumption and the risk of
stomach cancer; these authors indicated that green tea consumption
had no protective effect against stomach cancer, and
suggested the implication of other factors such as age, smoking,
socioeconomic status, Helicobacter pylori infection, history of
pectic ulcer, and family history of stomach cancer along with
certain dietary components. Sasazuki et al. [78] reported an
inverse association between green tea consumption and distal
gastric cancer among women; however, these authors indicated
that more prospective studies with detailed information are
needed to confirm the role of green tea in the occurrence of
gastric cancer. Il’yasova et al. [7] examined the association
between black tea consumption and colon cancer in a population-
based study in North Carolina, and concluded that, contrary
to expectation, black tea drinking did not decrease the risk
of colon cancer. However, it is important to remark that major
risk factors for colorectal cancer are family history of colorectal
cancer, exposure to non-steroid anti-inflammatory drugs, certain
meat cooking practices, smoking, low physical activity and
an elevated body mass index, and elevated intake of red meat
and alcoholic beverages. Data on the effects of green tea in the
prevention of this type of cancer are not available.
Several authors have noted that some epidemiological studies
have generated inconsistent results [54,79]. Some of these
Green Tea: Beneficial Effects
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 85
Table 2. Epidemiological Studies on the Association between Green Tea Consumption and Cancer Risk
Country Type of study/subjects
Green tea
consumption
Health effects Reference
Breast cancer
Japan Prospective study
1160 female invasive
breast cancer (mean
age  51.5 y)
6 cups/day
3–5 cups/day
0–2 cups/day
A decrease of the risk of cancer recurrence is
observed with a consumption of 3 cups/
day of tea (HR  0.69, 95% CI  0.22–
0.84). This decrease is mainly in early stage
cases.
Inoue et al. [70]
USA Case-control study
Asian-american
women
501 breast cancer
patients and 594
controls
85.7 mL/day
0–85.7 mL/day
no drinkers
There is a significant trend of decreasing risk
of breast cancer with increasing amount of
tea intake, (OR  1, 95% CI  0.51–0.99;
OR  0.71, 95% CI  0.51–0.99; OR 
0.53, 95% CI  0.35–0.78) respectively, in
association with no, 0–85 mL/day and
85.7 mL/day.
Wu et al. [68]
Japan Pooled of two
prospective studies
with 35004 women
5 cups/day
1 cups/day
Tea intake is not associated with a lower risk
of breast cancer (RR for women drinking
5 cups/day compared with 1 cup/day 
0.84, 95% CI  0.57–1.24).
Suzuki et al.
[168]
Ovarian cancer
China Case-control study
254 ovarian cancer
patients and 652
controls
Validated
questionnaire
Increasing frequency and duration of tea
drinking can reduce the risk of ovarian cancer
(OR  0.39 for those drinking tea daily, OR
 0.23 for those drinking tea for 30 years,
compared with non tea drinkers).
Zhang et al. [72]
Prostate cancer
China Case-control study
130 prostate
adenocarcinoma
patients and 274
controls
Face-to-face interview
using a structured
questionnaire
(Almost all the tea
consumed is green
tea)
The prostate cancer risk declined with increasing:
frequency (non-drinkers for tea drinking OR 
0.28, 95% CI  0.17–0.47), duration (OR 
0.12, 95% CI  0.06–0.26 for drinking tea over
40 years) and quantity of tea consumption (OR
 0.09, 95% CI  0.04–0.21) for those
consuming more than 1.5 kg of tea leaves yearly
and OR  0.27, 95% CI  0.15–0.48 for those
drinking more than 1 L/day).
Jian et al. [74]
Gastro-intestinal cancer
Japan Case-control study
887 gastric cancer and
28619 control age:
20–79 y
6 cups/day
3–5 cups/day
1–2 cups/day
never
Consumption of more than 6 cups/day vs
never drinking decreased the risk of gastric
cancer.
Huang et al.
[169]
Japan Cross-sectional study
636 men and women
mean age: men: 59.2
y, women: 60.4 y
10 cups/day
0–9 cups/day
Consumption of more than 10 cups/day
reduces the risk of chronic atrophic gastritis
(OR  0.59, 95% CI  0.42–0.86).
Shibata et al.
[170]
Japan Cross-sectional study
566 men
age: 50–55 y
5 cups/day
3–4 cups/day
3 cups/day
No relationship between tea consumption and
risk of chronic atrophic gastritis (OR  0.7,
95% CI  0.5–1.2).
Kuwahara et al.
[171]
Japan Prospective cohort
study
8552 adults
10 cups/day
4–9 cups/day
3 cups/day
Consumption of more than 10 cups/day
decrease the risk of stomach cancer (OR 
0.69, 95% CI  0.23–1.88) and colorectal
cancer (OR  0.56, 95% CI  0.22–1.4).
Nakachi et al.
[88]
Japan Prospective cohort study
14873 men and 23667
women
Hiroshima atomic bomb
survivors
5 cups/day
2–4 cups/day
0–1 cups/day
No relation between tea consumption and
reduced risk of stomach cancer (OR 
0.95, 95% CI  0.76–1.2), colon cancer
(OR  1.0, 95% CI  0.76–1.4) or rectum
cancer (OR  1.3, 95% CI  0.77–2.1).
Nagano et al.
[79]
China Case-control study
166 chronic atrophic
gastritis, 133 gastric
cancer and 433
controls
21 cups/week
1–21 cups/week
never
Significant inverse association between tea
drinking and gastric cancer (OR  0.39,
95% CI  0.15–1.01) or chronic atrophic
gastritis (OR  0.52, 95% CI 
0.28–0.99).
Setiawan et al.
[172]
(Table continues)
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86 VOL. 25, NO. 2
studies related tea consumption with reduced risk of cancer. In
a similar way, other authors found that tea lacks protective
activity against certain human cancers; these results raise questions
about the actual role of green tea components in human
cancer that need to be addressed. For example, Arab and
Il’yasova [80] provided a brief synopsis of 30 studies aimed at
examining tea consumption as a factor in the incidence of colon
and rectal cancers; the 30 papers examined populations in 12
countries and provided data on consumption of both black and
green tea. These studies do not provide consistent evidence to
support the theory from animal studies and basic research of tea
being a potent chemopreventive agent. A negative association
is stronger in observational epidemiologic studies of rectal
cancer than in colon cancer. There is no consistent adjustment
for important potential confounders of any tea relationship,
such as coffee and alcohol consumption and physical activity
levels. Finally, these authors indicated that the assessment of
tea in most of these studies was based on a single question and
Table 2. Continued
Country
Type of
study/subjects
Green tea
consumption
Health effects Reference
Japan Prospective cohort
study
11902 men and
14409 women
(mean age: 46.4 y)
5 cups/day
3–4 cups/day
1–2 cups/day
1 cup/day
No association with risk of gastric cancer
men: (OR  1.16, 95% CI  0.9–2.6),
women: (OR  0.8, 95% CI  0.5–1.3).
Tsubono et al.
[173]
Japan Prospective cohort
study
30370 men and
42481 women
10 cups/day
5–9 cups/day
3–4 cups/day
1–2 cups/day
1 cup/day
No association between tea consumption and
stomach cancer death; men: (OR  1.00,
95% CI  0.5–2), women: (OR  0.7, 95%
CI  0.3–2).
Hoshiyama et al.
[174]
Japan Prospective cohort
study
18746 men and
26184 women
Every day
3 times/week
3 times/week
No association between tea consumption and
stomach cancer death; men: (OR  1.11,
95% CI  0.75–1.63), women: (OR 
1.43, 95% CI  0.78–2.62).
Fujino et al.
[175]
Japan Case-control study
157 incident stomach
cancer and 285
controls
10 cups/day
5–9 cups/day
3–4 cups/day
1–2 cups/day
1 cup/day
No inverse association between tea
consumption and the risk of stomach
cancer.
Hoshiyama et al.
[66]
Esophageal cancer
China Prospective
interventional
study
778 esophageal
precancerous
lesion
Intervention group: 5
mg/day of
decaffeinate green
tea (DGT) for 12
months.
DGT trial did not show apparent difference
between the treatment and placebo group in
alleviating the esophageal precancerous
lesions and abnormal cell proliferation.
Wang et al.
[176]
Bladder cancer
Japan Prospective cohort
study
14873 men and
23667 women
Hiroshima atomic
bomb survivors
A mail survey Tea consumption is not related to risk of
bladder cancer
Nagano et al.
[177]
Lung cancer
China Case-control study
649 lung cancer
women and 675
controls women
Face-to-face
interviews
Among non-smoking women, consumption of
green tea was associated with a reduced risk
of lung cancer (OR  0.65, 95% CI 
0.45–0.93), and the risks decreased with
increasing consumption.
Zhong et al.
[178]
Cancer incidence
Japan Prospective study
38540 people
(14.873 men,
mean age 52.8 y
and 23667 women,
mean age 58.8 y)
5 times/day
2–4 times/day
1 time/day
never
Tea consumption is unrelated to incidence of
cancers under study. (RR  1, 95% CI 
0.91–1.1, and RR  0.98, 95% CI  0.88–
1.1 for all cancer consuming tea twice to
four times per day and five or more times
per day, as compared with those consuming
tea once per day or less).
Nagano et al.
[79]
HR  hazard ratio; OR  odd ratio; RR  relative risk; CI  confidence interval.
Green Tea: Beneficial Effects
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 87
therefore may have significant measurement error compared
with more recent studies specifically aimed at assessing green
tea consumption. Table 2 summarizes some recent epidemiological
studies on the association of green tea consumption and
cancer risk.
Anti-Hypertensive Effect And Cardiovascular Disease
Risk. Green tea has long been believed to possess hypotensive
effects in popular Chinese medicine. However, conflicting results
have been shown among trials and animal studies on the
relation between tea consumption and blood pressure. Epidemiological
evidence about the long-term effect of green tea on
hypertensive risk is also inconsistent. Negishi et al. [81] observed
that both black and green tea polyphenols attenuate
blood pressure increases, through their antioxidant properties,
in stroke-prone spontaneously hypertensive rats, but the
amounts of polyphenols used in this experiment correspond
approx. to those 1L of tea. Recently, some epidemiological
studies indicated that green tea consumption slightly reduces
blood pressure. Yang et al. [82] concluded that habitual moderate
strength green tea or oolong tea consumption, 120 mL/day
or more for 1 year significantly reduces the risk of developing
hypertension in the Chinese population. Hodgson et al. [83]
reported that long-term regular ingestion of green tea may have
a favorable effect on blood pressure in older women. However,
other studies do not support a hypotensive effect of green tea
[4]. Singh et al. [84], and Murakami and Ohsato [85] reported
that dietary green tea intake preserves and improves arterial
compliance and endothelial function. Green tea consumption
has also been inversely associated with the development and
progression of atherosclerosis, which is consistent with the
former observations. Geleijnse et al. [86] in their prospective
Rotterdam study with 3454 adults, 55 years of age or older, and
with a follow-up duration ranging from two to three years,
examined aortic atherosclerosis via X-ray measurement of calcified
deposits in the abdominal aorta; the odds ratio (OR) for
drinking 125–250 mL (1–2 cups) of black tea daily was 0.54
(95% CI  0.32–0.92) and decreased to 0.31 (95% CI 
0.16–0.59) when 500 mL/day (more than four cups) were
consumed. Data on green tea are reported by Sasazuki et al.
[87] who in a cross sectional study of 512 coronary patients
(302 men and 210 women) established that green tea may be
protective against coronary atherosclerosis in men (OR  0.5,
95% CI  0.2–1.2 for consumption of 2–3 cups, and OR  0.4,
95% CI  0.2–0.9 for 4 cups per day as compared with a
consumption of one cup per day or less), but not in women.
Nakachi et al. [88] in a prospective cohort study of 8522 men
and women concluded that consuming 10 cups/day is linked
with a decreased relative risk (RR) of death from cardiovascular
disease in men (RR  0.58, 95% CI  0.34–0.99) and in
women (RR  0.82, 95% CI  0.49–1.38).
Epidemiological studies suggest that green tea consumption
is associated with a reduced cardiovascular disease risk, but the
mechanisms for these observations have remained uncertain.
Several studies have demonstrated that green tea may affect the
cardiovascular function through mechanisms of action related
to LDL-cholesterol oxidation [4,89]. The oxidation of LDLcholesterol,
associated with a risk for atherosclerosis and heart
disease, is inhibited by green tea due to EC and EGCG antioxidant
activity. The in vitro antioxidant activity of EGCG on
LDL oxidation was stronger than that of EC [90]. In accordance
with these observations, Trevisanato and Kim [91] indicated
that GTP may slow atherogenesis by reducing the oxidative
modification of LDL-cholesterol and associated events such as
foam cell formation, endothelial cytotoxicity and induction of
proinflammatory cytokines. Gomikawa and Ishikawa [90] suggested
that catechins suppressed the susceptibilities of human
LDL to oxidation by CuSO4 in vitro and plasma oxidation in
vivo after ground green tea ingestion. Recent bioavailability
studies indicate that GTP can accumulate in the body at concentrations
comparable to those employed in vitro by several
investigators [31]. Other data report that catechins have been
shown to reduce plasma cholesterol levels and the rate of
cholesterol absorption. Raederstorff et al. [92] investigated the
dose-response and the mechanism of action of EGCG on these
parameters in rats which were fed a diet high in cholesterol and
fat; after 4 weeks of treatment, total cholesterol and LDLcholesterol
plasma levels were significantly reduced in the
group fed 1% EGCG when compared to the non-treatment
group. Plasma triglycerides and HDL-cholesterol did not
change significantly. These authors suggested that one of the
underlying mechanisms by which EGCG affects lipid metabolism
is by interfering with the micellar solubilization of cholesterol
in the digestive tract, which then in turn decreases
cholesterol absorption. Yokozawa et al. [93] reported that the
administration of GTP effectively inhibited LDL-cholesterol
oxidation and elevated serum antioxidative activity. Furthermore,
GTP increased the levels of HDL-cholesterol, leading to
dose-dependent improvement of the atherogenic index. Thus,
GTP may exert an antiatherosclerotic action by virtue of its
antioxidant properties and by increasing HDL-cholesterol levels.
Consistent with these results are the data reported by
Hertog et al. [94] that demonstrated an inverse correlation
between catechin intake and coronary heart disease mortality
after a 25-year follow-up of 12763 men from seven different
countries. Similarly, another research showed that men and
women from the Boston Area Health study who consumed one
or more cups per day of green tea in the previous year had a
44% lower risk of myocardial infarction than those who drank
no tea [95]. Recently, Peters et al. [96] have provided a metaanalysis
that suggested a decrease in the rate of cardiovascular
disease outcomes with increasing green tea consumption.
Through seven studies the incidence rate of myocardial infarction
was estimated to decrease by 11% with an increase in
green tea consumption of three cups per day (RR  0.89; 95%
CI  0.79–1.019). In addition, an inverse association of green
tea intake and myocardial infarction and its genetic variation
has been found by Hirano et al. [97] and Ohmori et al. [98].
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88 VOL. 25, NO. 2
Impaired endothelium-derived nitric oxide activity contributes
to the pathogenesis of atherosclerosis, and in coronary
circulation, it has been linked with future cardiovascular disease
events. Furthermore, this endothelial dysfunction is associated
with increased oxidative stress and may be reversed by
antioxidant interventions [4]. Duffy et al. [99] observed that tea
consumption improved flow-mediated dilation, in association
with an increased plasma catechin concentration (p  0.001).
No effects were observed with an equivalent dose of caffeine
(200 mg) or on endothelium-independent nitroglycerin-mediated
dilation. As flow-mediated dilation is blunted in coronary
heart disease patients compared to healthy subjects, these results
suggest that green tea reverses endothelial vasomotor
dysfunction. Hertog et al. [100] reported no association of
catechin by tea intake with ischemic heart disease incidence in
a 14-year follow-up of 334 men, 45 to 59 years of age, conducted
in Caerphilly, Wales. According to McAnlis et al. [101],
the discrepancy between the effect of green tea in vivo and ex
vivo, on the susceptibility of LDL-cholesterol to oxidation may
be due to the inability to achieve concentrations in vivo as great
as those obtained with the former methods. The possible variations
between the different studies may be also due to their
ignorance of socioeconomic and lifestyle factors associated
with the green tea drinking (i.e., geographical differences,
social class, body mass index, healthy lifestyle, higher prevalence
of smoking, higher fat intake, alcohol intake, coffee
consumption).
Oral Health. Oral diseases including dental caries, periodontal
disease, and tooth loss may significantly impact a
person’s overall health. Among these, dental caries is a multifactorial
infectious disease in which nutrition, microbiological
infection, and host response play important roles. Earlier reports
in experimental animals and humans suggested that green
tea consumption (without added sugar) reduces dental caries
[5,102–103]. Linke and LeGeros [104] indicated that frequent
intake of green tea can significantly decrease caries formation,
even in the presence of sugars in the diet. In vivo animal studies
have shown that specific pathogen-free rats infected with Streptococcus
mutans and then fed with a cariogenic diet containing
GTP have significantly lower caries scores [105]. Supplementing
drinking water of rats with 0.1% GTP along with a cariogenic
diet also significantly reduced total fissure caries lesions
[5]. Recent findings of Okamoto et al. [106] suggest that green
tea catechins may have the potential to reduce periodontal
breakdown resulting from the potent proteinase activity of
Porphyromonas gingivalis. In addition, green tea decoctions
inhibit -amylase in human saliva, reducing maltose release by
70% and effectively lowering the cariogenic potential of starchcontaining
food [4]. Similarly, Zhang and Kashket [107] reported
that green tea extracts inhibits human salivary amylase
and may reduce the cariogenic potential of starch-containing
food such as crackers and cakes because it may reduce the
tendency of this kind of food to serve as slow-release sources
of fermentable carbohydrate. It is likely that the cariogenic
challenge in a cariogenic diet may be reduced by the simultaneous
presence of green tea in the diet.
Apart from their polyphenol content, both green and black
tea, are a natural source of fluoride and an effective vehicle for
fluoride delivery to the oral cavity. According to Simpson et al.
[108], after cleansing the mouth with tea, approximately 34%
of the fluoride is retained and shows a strong binding ability to
interact with the oral tissues and their surface integuments. This
fluoride content may have a beneficial impact on caries and
may carry out a wide range of biological activities including
prevention of tooth loss and oral cancer [106,109]. Nonetheless,
the data have suggested that GTP extract may be responsible
for the noted effects on oral health and it has been also
demonstrated that GTP rather than fluoride contribute to anticariogenic
potential [5,105] by inhibition of oral bacteria
growth such as Escherichia coli, Streptococcus salivarius, and
Streptococcus mutans. Several studies have indicated that GTP
inhibit growth, acid production, metabolism, and glucosyltransferase
enzyme activity of S. mutans and dental plaque bacteria
[5]. In consequence, green tea has been considered as functional
food for oral health and is widely used in toothpaste
formulation.
Solar Ultraviolet Protection. Epidemiological, clinical and
biological studies have shown that solar ultraviolet (UV) light
is a complete carcinogen and repeated exposure can lead to the
development of various skin disorders including melanoma and
non-melanoma skin cancers. EGCG is considered to be a topic
protector agent against some types of radiation, since it prevents
skin disease, photoaging and potential cancer problems
due to prolonged exposure [109–111]. It seems that the rest of
catechins also favour this action [5,109–110]. Katiyar [111]
indicated that topical treatment or oral consumption of GTP
inhibits chemical carcinogen or UV radiation-induced skin
carcinogenesis in different laboratory animal models. Topical
treatment of GTP or ECCG and oral consumption of GTP
resulted in prevention of UVB-induced inflammatory responses,
immunosuppression and oxidative stress, which are
the biomarkers of several skin disease conditions. Topical
application of GTP and EGCG prior to exposure of UVB
protects against UVB-induced local as well as systemic immune
suppression in laboratory animals. This fact was associated
with the inhibition of UVB-induced infiltration of inflammatory
leukocytes. The in vitro and in vivo animal and human
studies have suggested that GTP are photoprotective in nature,
and can be used as pharmacological agents for the prevention
of solar UVB light-induced skin disorders including photoaging,
melanoma and non-melanoma skin cancers [4–5,109,111].
Body Weight Control. Obesity has increased at an alarming
rate in recent years and is now a worldwide health problem.
Current interest in the role of functional foods in weight control
has focused on plant ingredients capable of interfering with the
sympathoadrenal systems [112]. The effects of long-term feeding
with tea catechins have been widely studied, and some
investigators suggest a potential role of green tea in body
Green Tea: Beneficial Effects
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 89
weight control. In addition, caffeine and theanine have been
found to strengthen polyphenol effects on body weight control
and fat accumulation in mice [113]. In vitro studies with green
tea extracts containing 25% of catechins have shown its capacity
(in conditions similar to physiological ones) to significantly
inhibit the gastric lipase, and in a lower extent also the pancreatic
lipase. Thus, the lipolysis of long-chain triglycerides is
reduced in a 37% [114]. In vitro studies have also shown that
green tea extracts interfere in the fat emulsification process,
which occurs before enzymes act, and is indispensable for lipid
intestinal absorption [114–115]. Green tea also exhibits a fatty
acid synthase inhibitor activity [116]. In addition, green tea
may have thermogenic properties not only attributable to its
caffeine content, but to the joint-effect of caffeine and catechins.
EGCG can act upon AMPc levels by increasing the
energetic expenditure [114]. Dulloo et al. [112] using a green
tea extract rich in catechins and caffeine, concluded that green
tea has thermogenic properties and promotes fat oxidation
beyond than those explained by its caffeine content per se; the
green tea extract may play a role in the control of body
composition via sympathetic activation of thermogenesis, fat
oxidation, or both. Dulloo et al. [117] indicated that the thermogenic
properties of green tea could reside primarily in an
interaction between its high content in catechins and the presence
of caffeine with sympathetically released noradrenaline;
since polyphenols are known to be capable of inhibiting catechol-
o-methyl-transferase (the enzyme that degrades noradrenaline),
and caffeine of inhibiting trancellular phosphodiesterases
(enzymes that break down noradrenaline-induced AMPc).
Such a synergistic interaction between polyphenols and caffeine
to increase and prolong sympathetic stimulation of thermogenesis
could be of value in assisting the management of
obesity. Kovacs et al. [118] reported that weight maintenance
after 7.5% of body weight loss in overweight and moderately
obese subjects was not affected by green tea treatment and that
regular caffeine consumption affected weight maintenance in
green tea treatment. According to some authors, green tea
extracts (with a 25% of catechins content) may be advisable for
overweight treatment in patients whose body mass index ranges
between 25 and 29.9 kg/m2, only if they do not present special
sensitiveness to xantic bases [118]. Wu et al. [119] indicated
that an inverse relationship may exit among regular green tea
consumption, body fat percentage, and body fat distribution,
especially for subjects who have maintained the habit of tea
consumption for more than 10 years.
Glucose Tolerance and Insulin Sensitivity. Epidemiological
observations and laboratory studies have shown that green
tea has an effect on glucose tolerance and insulin sensitivity.
Anderson and Polansky [120] reported that green tea increases
insulin activity, and that the predominant active compound is
EGCG; these same authors indicated that addition of lemon to
the tea did not affect the insulin-potentiating activity but the
addition of 50 g of milk per cup decreased the insulin-potentiating
activity similar to 90%. Wu et al. [121] examined the
effect of green tea supplementation on glucose tolerance and
insulin sensitivity in rats; rats were divided into two groups: a
control group was fed with standard chow and deionized distilled
water, while the other was fed with the same chow diet
but with green tea instead of water (0.5 g of lyophilized green
tea powder dissolved in 100 mL of deionized distilled water);
after 12 weeks of green tea supplementation, this group had
lower fasting plasma levels of glucose, insulin, triglycerides,
and free fatty acid than the control rats. In addition, GTP
significantly increased basal and insulin-stimulated glucose
uptake of adipocytes [4]. Some investigations have also shown
that EGCG does not only regulate the glucose level in blood,
but also may rehabilitate damaged beta-cells, which are responsible
for producing insulin [4,119].
Other Effects. Green tea catechins have been reported to
have antibacterial and antiviral activity. Green tea effectiveness
against any type of diarrhoea and typhoid has been known in
Asia since ancient times [4,68,119]. Nowadays it is also known
that it inhibits the reproduction and growth of many bacteria,
among which some types of Salmonella, Clostridium or Bacillus
can be named. Takabayashi et al. [122] and Yee et al. [123]
reported an inhibitory effect of green tea catechins on Helicobacter
pylori infection. Moreover, it has been shown that green
tea has not effect over intestinal flora, which is a great advantage
against other bactericide agents. Regarding its antiviral
action, green tea is well known for preventing tobacco crops
from being invaded by the ‘mosaic virus’ of tobacco. Recent
investigations have confirmed that catechins completely inhibit
its growth and reproduction [3]. Effects of green tea against the
influenza virus, especially in its earliest stage, as well as against
the Herpes simplex virus have also been demonstrated [124–
126]. Furthermore, Weber et al. [127] observed that adenovirus
infection is inhibited in vitro by green tea catechins. Hirasawa
and Takada [128] indicated the antifungal activity of green tea
catechins against Candida albicans, and the convenience of a
combined treatment with catechins and lower doses of antimycotics;
this treatment may help to avoid the side effects of
antimycotics.
Green tea consumption has also been associated with increased
bone mineral density, and it has been identified as an
independent factor protecting against the risk of hip fractures;
this fact has been considered independent of smoking status,
hormone replacement therapy, coffee drinking and the addition
of milk to tea [129]. Park et al. [130] observed the positive
effects of green tea extracts and GTP on the proliferation and
activity of bone cells. Wu and Wei [5] indicated that bone
mineral density may be influenced by several chemical compounds
that are contained in tea extracts (i.e., caffeine, phytostrogen,
fluoride, . . .).
Green tea polyphenols are known to have anti-fibrotic properties
on the skin and on the arteries. The proliferation of
hepatic stellate cells is closely related to the progression of liver
fibrosis in chronic liver diseases, and EGCG has a potential
inhibitory effect on the proliferation of these cells [131–132].
Green Tea: Beneficial Effects
90 VOL. 25, NO. 2
Green tea strengthens the immune system action since green tea
protects it against oxidants and radicals. Bayer et al. [133]
suggest that oral intake of green tea could act as an adjunctive
therapy for prevention of transplant rejection in humans. The
neuroprotective power of complex extracts rich in flavonoids
like those of Ginkgo biloba, green tea or lyophilized red wine
have been demonstrated in several studies [134–135]. Recent
studies suggest that GTP possibly protect against Parkinson’s
and Alzheimer’s diseases and other neurodegenerative diseases
[44,136]. GTP have demonstrated neuroprotectant activity in
cell cultures and animal models, such as the prevention of
neurotoxin-induced cell injury; the biological effects of GTP
may benefit patients with Parkinson’s disease, but further indepth
studies are needed to investigate the safety and effectiveness
of green tea in humans and to determine the different
mechanisms of green tea in neuroprotection [44]. In the same
way, the neuroprotective effects of the theanine contained in
green tea are a focus of considerable attention, and further
studies are warranted [134].
Finally, the following health effects of green tea consumption
have also been described. Green tea is considered to be
useful for insect stings due mainly to its antiinflammatory
effects and its capacity to stop bleeding [137–138]. Some
studies have suggested an inverse association between green
tea consumption and the risk of kidney stone formation [4,139].
In addition, green and black tea extracts led to a retardation of
the progression of lens opacity in rats with cataracts induced by
selenite [140]. Gupta et al. [141] reported that green tea acts by
preserving the antioxidant defense system of the lens. Skrzydlewska
et al. [142] indicated a beneficial effect of green tea in
alcohol intoxication. Besides all the above mentioned properties,
which have helped to the recognition of green tea as
functional food by some authors [143], it is not to forget its
current use in the preparation of a variety of food, pharmaceutical
preparations, dentifrices and cosmetics [144]. This additional
use is mainly due to its antioxidant activity, which makes
it a natural, efficient and safe preservative.
Green Tea Nutritional Value
Green tea consumption contributes to the overall daily fluid
intake, and if sugar is not added, the calories intake is insignificant;
besides, the caffeine intake is lower than in coffee,
black tea or cola soft-drinks. In addition, green tea contribution
to the dietary intake of antioxidant compounds (catechins and
other phytochemical substances, certain vitamins as vitamin C,
and minerals as Mn, Cr, Se, Zn) is very interesting to promote
human health and well being, and more relevant than that other
non-alcoholic beverages widely consumed. The Mn content is
high, and tea is considered a rich source of this essential
element [21,145]. Manganese is a constituent of three metalloenzymes
(i.e., arginase, pyruvate carboxylase, and Mn-superoxide
dismutase) and it activates a large number of enzymes, such as
glycosyl transferases, involved in mucopolysaccharide synthesis
[146]. Manganese deficiency can cause abnormalities in the metabolism
of carbohydrates, glycosaminoglycans, and cholesterol
[147]. Chromium, selenium and zinc play also an important role in
human metabolism, and interest in these elements is increasing
since there are reports relating trace element status and oxidative
diseases. Chromium is involved in carbohydrate and lipid metabolism;
the most frequent sign of Cr deficiency is altered glucose
tolerance; this nutrient has been associated with diabetes and
cardiovascular diseases [146]. Beneficial effects of dietary Cr
supplementation, particularly in groups in which deficiencies are
frequent, have been reported [147]. Garcia et al. [148] measured
through duplicate diet sampling the Cr dietary intake in Spain and
detected that the most elevated intakes are related to high consumption
of infusions, especially tea and coffee. Selenium functions
through selenoproteins, several of which are oxidant defense
enzymes; Se acts as enzymatic cofactor of glutathione peroxidase
in the elimination of peroxide radicals from the organism. Epidemiological
studies have shown the possible effects of Se in the
prevention and regression of cancer [146–147]. Most Se is ingested
in food, but food derived from vegetables has a variable Se
content depending on the zone where they have been cultivated
[149]. Zinc enzymes participate in a wide variety of metabolic
processes including carbohydrate, lipid, and protein synthesis or
degradation. This element is required for deoxyribonucleic and
ribonucleic acid synthesis; it may also play a role in stabilizing
plasma membranes [147]. Zinc has been recognized as a cofactor
of the superoxide dismutase enzyme, which is involved in protection
against oxidative processes [146]. Recently there has been a
development of terminology and change in conceptual approaches
towards setting nutrient recommendations from adequate to optimum
nutrition [150]. Regarding antioxidant minerals, the US
Food and Nutrition Board has set an Adequate Intake for Mn at 2.3
and 1.8 mg/day for adult men and women, respectively, and a
Tolerable Upper Intake Level at 11 mg/day for adults. Chromium
Adequate Intake values are 35 and 25 g/day for young men and
women, respectively. The Recommended Dietary Allowance for
Zn is 8 and 11 mg/day for adult men and women, respectively; the
Tolerable Upper Intake Level for adults is 40 mg/day. The selenium
Recommended Dietary Allowance and Tolerable Upper
Intake Level for adults is 55 and 400 g/day, respectively [151–
152]. Table 3 summarizes data on the content of minerals with
antioxidant activity in green tea.
In addition, green tea contains more vitamin C than black
and oolong teas [153]; the total content of vitamin C in tea
leaves decreased during the manufacturing process of fermented
teas [154], however bibliographical data on vitamin C
content in green tea are scarce. Due to the fact that green tea
consumption in the occidental diets (except Morocco) is scarce
and occasional, its contribution to the total antioxidant dietary
intake is low [155]. For example, Pulido et al. [156] evaluated
the contribution of the most consumed beverages to the antioxidant
intake in the Spanish diet; the intake is estimated at
1623 mg of vitamin E and 598 mg of vitamin C by FRAP
procedure. Tea only contributes to 3–5% of the total, whereas
Green Tea: Beneficial Effects
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 91
coffee and red wine are the main contributors. However, all the
above mentioned properties of green tea, demonstrate that it
can be considered an alternative to other widely consumed
drinks, which have a higher content of energy and/or caffeine,
and are richer in sugars, alcohol, CO2, etc. Besides, drinking tea
is an optimum way of fighting thirst due to its refreshing
properties, its slightly bitter taste, its low binding effect and its
fruity and agreeable smell [149,157]. Its preparation is easy,
uncomplicated and varied (lemon, mint, cinnamon, . . . can be
added to it).
Harmful Effects of Tea Over Consumption
Harmful effects of tea over consumption (black or green)
are due to three main factors: (1) its caffeine content, (2)
aluminum presence, and (3) the effects of tea polyphenols on
iron bioavailability. A day-long consumption of green tea improved
the cognitive and psychomotor performance of healthy
adults in a manner similar to coffee, but green tea (which
contains less caffeine) is less likely than coffee to disrupt sleep
quality at night [4]. Lin et al. [19] compared the caffeine
content in the same type of tea but manufactured by different
fermentation processes, and concluded that the caffeine level
presented the following order: black tea  oolong tea  green
tea  fresh tea leaf. Cabrera et al. [22] determined the caffeine
content in a total of 45 tea samples, including ‘fermented’ teas
(red and black teas), oolong tea and green tea samples; the
results showed that caffeine presence is higher in the case of
black teas (41.5– 67.4 mg/g), whereas green and oolong teas
show a mean caffeine content of 32.5 and 29.2 mg/g, respectively.
Fernandez et al. [20] also reported that caffeine content
is higher in the case of ‘fermented’ teas, showing values between
2.4 and 4.8%, whereas ‘non-fermented’ teas show caffeine
levels ranging between 1.47 and 3.86%. Table 4 includes
data on the caffeine content in beverages widely consumed.
The caffeine content in green tea may vary according to the
type of tea and the form of preparation (i.e., brewing time);
generally, bagged tea produces a higher percentage of caffeine
than tea leaves [3]. In any case, although green tea caffeine
content is low, its consumption is not advisable in cases of
special sensitiveness to xanthic bases. The negative effects
Table 3. Antioxidant Minerals Content in Green Tea Leaves (Data Referred to Dry Weight)
Mineral Content (mean; range) Class (origin) Reference
Cr 238.6 ng/g sencha (Japan) Cabrera et al. [22]
291.0 ng/g jasmine (Japan) Cabrera et al. [22]
219.8 ng/g Kokaicha (Japan) Cabrera et al. [22]
111.9 ng/g Bancha (Japan) Cabrera et al. [22]
141.7 ng/g Paimutan (China) Cabrera et al. [22]
118.4 ng/g gunpower (China) Cabrera et al. [22]
Mn 699 g/g (160–1500) A set of samples (China) Xie et al. [21]
1069.7 g/g sencha (Japan) Ferna´ndez-Ca´ceres et al. [10]
1021.5 g/g gunpower (China) Ferna´ndez-Ca´ceres et al. [10]
714.9 g/g jasmine (China) Ferna´ndez-Ca´ceres et al. [10]
500.7 g/g sencha (Japan) Cabrera et al. [22]
354.1 g/g jasmine (Japan) Cabrera et al. [22]
651.3 g/g Kokaicha (Japan) Cabrera et al. [22]
987.6 g/g Bancha (Japan) Cabrera et al. [22]
236.6 g/g Paimutan (China) Cabrera et al. [22]
518.9 g/g gunpower (China) Cabrera et al. [22]
Se 0.18* g/g (0.03–7.5) A set of samples (China) Xie et al. [21]
455  184 ng/g “high Se tea” (China) Yoshida et al. [179]
92.9 ng/g sencha (Japan) Cabrera et al. [22]
89.7 ng/g jasmine (Japan) Cabrera et al. [22]
48.5 ng/g Kokaicha (Japan) Cabrera et al. [22]
80.1 ng/g Bancha (Japan) Cabrera et al. [22]
75.1 ng/g Paimutan (China) Cabrera et al. [22]
70.2 ng/g gunpower (China) Cabrera et al. [22]
Zn 39.4* g/g (20–60) A set of samples (China) Xie et al. [21]
24.6 g/g sencha (Japan) Ferna´ndez-Ca´ceres et al. [10]
28.4 g/g gunpower (China) Ferna´ndez-Ca´ceres et al. [10]
44.3 g/g jasmine (China) Ferna´ndez-Ca´ceres et al. [10]
78.1 ng/g sencha (Japan) Cabrera et al. [22]
78.6 ng/g jasmine (Japan) Cabrera et al. [22]
76.1 ng/g Kokaicha (Japan) Cabrera et al. [22]
65.0 ng/g Bancha (Japan) Cabrera et al. [22]
75.1 ng/g Paimutan (China) Cabrera et al. [22]
57.5 ng/g gunpower (China) Cabrera et al. [22]
* Geometric mean.
Green Tea: Beneficial Effects
92 VOL. 25, NO. 2
produced by caffeine are nervousness, sleep disorders, vomits,
headaches, epigastric pain, tachycardia [38 –39]. Theophylline
negative effects are similar to those of caffeine, but they only
occur with high quantities intake. Thus, green tea should not be
taken by patients suffering from heart conditions or major
cardiovascular problems. Pregnant and breast feeding women
should drink no more than 1–2 cups/day, since it can cause an
increase in heart rhythm. It is also convenient to control the
concomitant consumption of green tea and some drugs, due to
its diuretic effects [39].
Regarding aluminum presence in black and green tea, some
studies revealed the high capacity of this plant to accumulate
Al. This aspect is important for patients with renal failures
because Al can be accumulated by the body, resulting in
neurological diseases; it is therefore necessary to control the
intake of food with high amounts of this metal [1]. The possible
connection between elevated tissue Al content and problems
such as osteomalacia and neurodegenerative disorders (i.e.,
Alzheimer’s disease) has awakened interest in Al intake via
diet [158]. Minoia et al. [159] found concentrations of Al in
green and black teas (as infusions) accounting for 431–2239
g/L, whereas in coffee they found lower concentrations (9.1–
30.8 g/L). In a study carried out in Italy, these authors
estimated the tea contribution to the total Al dietary intake as
665 g/week (considering a weekly mean consumption of 2
cups). According to several authors, Al dietary intake must not
exceed 6 mg/day in order to avoid potentially toxic levels
[160]. Lo´pez et al. [158] evaluated Al presence in food and
beverages widely consumed in Spain, and found that Al levels
in tea ranged from 43.42 to 58.04 g/g referred to dry weight
of the solid product, and from 13.91 to 27.45 g/L in the
corresponding infusions; levels in coffee samples varied between
25.6 and 29.08 g/g referred to dry weight of the solid
product, and from 7.12 to 9.14 g/L in the corresponding
infusions. Costa et al. [1] observed that black tea contains
nearly six-fold more Al than green tea, and the extraction of Al
in black teas was higher than the one observed in green teas; the
Al concentrations in the tea infusions were constant after 5 min
of extraction. These authors also indicated that the variations
between different samples may be due to different soil conditions
as well as different harvesting periods, and the influence
of the water quality. Following this line of study, several
authors considered that this element does not seem to be much
more bioavailable in tea than in other dietary sources [1,161].
Even so, it cannot be ignored that tea infusions may contain
particularly bioavailable and neurotoxic compounds such as Al
maltolate, but this is currently speculative [161]. At this respect,
Costa et al. [1] reported that the composition of Al
species could vary depending on the method of tea production,
and for non-fermented teas, most of the leached Al is mainly
found in large or small organic compounds; in organic complexes
with small molecular masses, such as citrates, the Alcomplexes
are more bioavailable than in inorganic complexes
(such as hydroxide), but generally, Al is poorly absorbed by the
body. Thus, future studies designed to accurately assess the
presence and bioavailability of Al in green tea leaves is necessary.
Several studies have demonstrated that black tea appears to
inhibit the bioavailability of non-heme iron by 79% to 94%
when both are consumed concomitantly; the impact of this
interaction depends on the iron intake and iron status of the
individual [162–163]. Likewise, green tea catechins may have
an affinity for iron, and green tea infusions can cause a significant
decrease of the Fe bioavailability from the diet [164]. On
the one hand, some authors affirm that tea should not be
consumed by patients suffering from anaemia. For example,
iron deficiency anaemia among children in Saudi Arabia and
the United Kingdom may be exacerbated by the regular consumption
of tea with meals [165–166]. On the other hand, this
effect may be of benefit to patients with genetic hemochromatosis
[4]. It is worth noting that the interaction between tea and
iron can be mitigated by the addition of lemon or consuming
tea between meals.
Conclusions
Green tea has been consumed in China and other Asian
countries since ancient times in order to maintain and improve
health. Nowadays, green tea is considered one of the most
promising dietary agents for the prevention and treatment of
many diseases and consequently, it is being studied extensively
worldwide. Numerous studies in a variety of experimental
animal models have demonstrated that aqueous extract of the
mayor GTP designed as catechins (EGCG, EGC, ECG and EC)
possess antioxidant, antimutagenic, antidiabetic, anti-inflammatory,
antibacterial and antiviral, and above all, cancer-preventive
properties. Epidemiological studies suggest that consumption
of green tea may have a protective effect against the
development of several cancers. Preclinical studies of green tea
Table 4. Caffeine Content in Food and Beverages
Product Caffeine content*
Normal coffee 80–115 mg/150 mL†
Espresso coffee 108–180 mg/150 mL
Instant coffee 65 mg/150 mL
Decaffeinated coffee 1–3 mg/150 mL
Green tea (3 min brewing time) 15–25 mg/150 mL
Black tea (3 min brewing time) 40–70 mg/150 mL
Oolong tea 18–33 mg/150 mL
Decaffeinated tea 0.6–3 mg/150 mL
Iced tea 70 mg/360 mL
Cocoa milk shake 5 mg/240 mL
Hot chocolate 4 mg/150 mL
Plain chocolate (bar) 15 mg/20 g
Milk chocolate (bar) 5 mg/20 g
Cola soft drink 38–46 mg/360 mL
* A consumption higher than 200 mg/day is not advisable.
† Quantities vary according to the beverage preparation.
Green Tea: Beneficial Effects
JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION 93
and its polyphenolic components have demonstrated antimutagenic
and anticarcinogenic activity, and inhibition of growth of
tumor cell lines and animal tumor models, including cancer.
Green tea may also have chemopreventive properties, and
enhancement of chemotherapeutic agents has been demonstrated.
In addition, several epidemiological studies with humans
have demonstrated that regular green tea consumption
has beneficial effects and it shows a significant rate of protection
against the development of some oral diseases and against
solar radiations. It also contributes to body weight control and
to the rise of bone density as well as being able to stimulate the
immune system. Furthermore, green tea consumption has been
recently reported to act positively against neurodegenerative
diseases such as Parkinson and Alzheimer disease. Catechin
antioxidant power is also strengthened by the presence of other
phenolic compounds, vitamin C and minerals such as Cr, Mn,
Se, and Zn, although specific data regarding this fact are still
scarce.
However, conflicting results between cohort studies conducted
in different countries may also arise from confusion in
the frequency and timing of intake, and the marked contrasts in
the socioeconomic and lifestyle factors associated with tea
drinkers. It is also important to consider the type of tea or its
preparation (e.g., short time vs. long brewing time and hot tea
vs. iced tea) due to the marked impact of these factors on
polyphenol content and concentration. It is also important to
draw attention on the need of further-in-depth studies on the
nature and mechanisms of the active green tea compounds, on
the bioavailability of the different catechins in humans, and
appropriate dose levels to act as functional food.
Since green tea beneficial health effects are being increasingly
proved, it could be advisable to encourage the regular
consumption of this widely available, tasty and inexpensive
beverage as an interesting alternative to other drinks, which do
not only show the beneficial effects of green tea, but are also
more energetic, do contain more caffeine (green tea contains
less caffeine than black tea, coffee or cola soft-drinks), are rich
in additives and/or CO2. While no single food item can be
expected to provide a significant effect on public health, it is
important to note that a modest effect between a dietary component
and a disease having a major impact on the most
prevalent causes of morbidity and mortality, i.e., cancer and
heart disease, should merit substantial attention. Taking all this
into account, it would be advisable to consider the regular
consumption of green tea in Western diets.
ACKNOWLEDGMENT
We thank M.J. Martinez-Vique for revising the English
grammar of the original manuscript. We thank Antiguo Tostadero
(specialized tea shop) for its cooperation and interest in
this research.
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