Scientific Name: Camellia sinensis (L.) Kuntze, synonym: C. thea Link, formerly Thea sinensis L., T. assamica L.
Family: Theaceae
Other Common Name: Cha.
Catechins belong to the flavan-3-ol class of flavonoids and these are found in green tea leaves. . There are 4 major catechins in green tea leaves, namely (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC), all polyphenolic compounds.
Green tea catechins make up about 30% of the dry weight of green tea leaves, EGCG being the most abundant of the catechins. 2
The possible health benefits of green tea are attributed to the catechins. These polyphenolic substances act as antioxidants and EGCG is the most potent.
Thermal treatment either by roasting (Chinese process) or steaming (Japanese process) the dark green, shiny-toothed oval leaves of evergreen shrub, C. sinensis shortly after harvesting, produces green tea.
C. sinensis is cultivated mainly in India, Sri Lanka (Ceylon) and China.
Green tea contains polyphenolic catechins, which can act as antioxidants and potentially decrease risk for cardiovascular diseases.
It may have anticarcinogenic activity. EGCG may inhibit the proteolytic enzyme urokinase that cancer cells may use to invade normal tissue and form metastases.
May act as an anti-inflammatory agent, possibly also due to the catechins’ antioxidant actions.
May have antiatherogenic activity, although the exact mechanism is still unclear.
May promote thermogenesis possibly by inhibiting the enzyme catechol-O-methyl-transferase.
It may have antimicrobial activity, but the exact mechanism is unknown.
When green tea is taken in excessive doses, it can cause unwanted stimulant effects, as with any caffeine-containing product. These side effects include: anxiety, tremors, irritability, and insomnia, tachycardia, flushing and diuresis, generally lasting from 6 to 16 hours 1. These effects are mainly due to caffeine present at approximately 50mg per cup of tea-as compared to caffeine present at approximately 50mg per cup of tea-as compared to about 85 mg per cup of coffee. 3
Pregnant and lactating women should avoid green tea catechin supplements.
Contraindication:
Green tea and green tea polyphenols should not be administered to infants, as there is evidence that doses of more than 250mL of tea may interfere with iron metabolism and result in microcytic anemia. 4 No other specific contraindications have been identified.
Antioxidant: Green tea polyphenolic antioxidants have been shown to possess anticarcinogenic properties which may have inhibitory effects on tumor formation, growth, invasion and metastasis.
In a complete crossover design, 21 volunteers (10 male, 11 female), aged 18 to 65 years, were administered 6 single doses of green and black tea, with or without milk, and mineral water with or without mil. Plasma was analyzed for total catechins and antioxidant activity, using the ferric reducing ability of plasma (FRAP) assay. Plasma catechin concentrations were higher in green tea than in black tea at a ratio (5.3:1) comparable to that of the total catechin composition of the respective teas (4.6:1). Consumption of a single dose of tea, equivalent to three cups, resulted in a significant increase in plasma antioxidant activity, greater after drinking black tea – by a factor of roughly 1.5. Addition of milk to tea did not abolish the observed increases in antioxidant activity. The latter observation suggests that other flavonoids in black tea, such as theaflavins and thearubigins, may contribute to the antioxidant potential of black tea. 8Cancer/General: A Japanese population-based study, surveyed 8,552 individuals over 40 years of age on living habits and consumption of green tea. During 9 years of 71,248.5 person-years evaluation, a total of 384 cases of cancer were identified. Researchers found a negative association between green tea consumption and incidence of cancer, especially in women drinking >10 cups of green tea a day. The relative risk of cancer incidence was lower among females and males that had the highest consumption of green tea, although the preventive effects were not significant among males. Overall, green tea was found to have a potential preventative effect against cancer. 9
Breast Cancer:
A hospital-based Epidemiologic Research
Program at Aichi Cancer Center started a routine
lifestyle questionnaire from all first-visit
outpatients. Two years later, 1160 new surgical
cases of female invasive breast cancers were
found over 8 years and were followed for 16
months. During the follow-up of 5264 person-
years evaluation, 133 subjects or 12% had
recurrent breast cancer. The percentage
reduction in risk was 31% for total cases and
57% for cases restricted to stage I with
consumption of three or more daily cups of
green tea. The results suggested the possibility
that regular green tea consumption may be
preventative against recurrence of breast cancer
in its early stages. 10
Five or more cups of green tea daily was
associated with the decreased recurrence of
breast cancer at stages I and II, but not stage III,
in Japan. 11
Prostate Cancer: A study on human prostate cancer seeded DU145 cells for 2 days and incubated them with different concentrations of green tea extract or green tea catechins including EGCG, EGC, ECG, and EC. The study showed green tea extract and 3 green tea catechins decreased growth and induced apoptosis in human prostate cancer DU145 cells likely through an increase in reactive oxygen species formation and mitochondrial depolarization.12 Further investigation is needed to clarify the mechanism of induction of apoptosis.
Gastric and Stomach Cancers:
A study in China looked at green tea
consumption and the risks of chronic gastritis
and stomach cancer using 133 stomach cancer
cases, 166 chronic gastritis cases and 433
healthy controls. The number of cups of green
tea per week was categorized into nondrinker,
1-21 cups and > 21 cups; years of drinking tea
was categorized into nondrinkers, 1-13 years,
and >13 years. Researchers found that green
tea drinkers had a 48% reduced risk of stomach
cancer and a 51% lower risk of chronic gastritis
than nondrinkers after adjusting for potential
confounders. Overall, researchers found that
green tea drinking may be protective against
chronic gastritis, which may be important to
prevention strategies for stomach cancer and its
pre-malignant lesion in the high-risk
population. 13
Consumption of at least 10 cups of green tea
per day was associated with a decreased risk of
gastric cancer in Northern Kyushu, Japan.14
UV Protection: Green tea and its polyphenols may help protect against ultraviolet-induced carcinogenesis and reduce the growth rate of established tumors in skin.
A study on intact mouse and human skin and reconstituted human skin were used to assess the effect of both topical and oral (0.4 or 0.8%) administration of standardized green tea extracts against psoralen plus ultraviolet-induced photodamage. Oral administration of 0.4 or 0.8% standardized green tea extract 1 day after psoralen plus ultraviolet A treatment was effective in reducing psoralen plus ultraviolet A-induced inflammatory responses. Overall, the treatment was protective against psoralen plus ultraviolet A-induced phototoxicity possibly by inhibiting DNA damage and alleviating inflammatory effects. 15
Another study was done on areas of skin on normal volunteers treated with a 5% solution of green tea extract or one of its constituents. After 30 minutes, treated sites were exposed to minimal erythema dose solar-stimulated radiation. The application of the green tea extracts resulted in a dose-dependent inhibition of the erythema response. The authors concluded that polyphenolic extracts of green tea were effective as cheomopreventive agents and may serve as natural alternatives for photoprotection. 16
Atherosclerosis:In vitro studies have shown that flavonoids inhibit the oxidation of low-density lipoproteins. Green tea is rich in flavonoid catechins. Epidemiolgical and animal studies on green tea suggest that it may have a lowering effect on serum cholesterol concentrations.
Five hundred and twelve men and women aged 30 years or older who underwent coronary arteriography were questioned on dietary habits, clinical risk factors and lifestyle habits. Results indicated that 38.7% of men and 23.8% of women had significant stenosis of one or more coronary arteries. Consumption of green tea in men was inversely associated with coronary atherosclerosis. Overall, researchers concluded that green tea may be protective against coronary atherosclerosis, at least in men. 17
Twenty-two male volunteers between 22 and 32 years of age were assigned the same dietary regimen for 2 weeks. After a 1-week baseline period, half were given 300 mg of green tea polyphenol extract 2 times a day for 1 week, the other was a control group. Plasma concentrations of lipids, ascorbate, alpha-tocopherol, and lipid peroxides did not change before and after the experiment in either group, although betcarotene was higher in the green tea group. When incubated with Cu2+ , lag time of oxidation of LDL isolated from tea drinkers was prolonged as compared to that from nondrinkers. Results indicated that 7 to 8 cups daily of green tea may increase the resistance of LDL to in vivo oxidation, leading to reduction in the risk of cardiovascular diseases. . 18
utoimmunity: Green tea polyphenols may decrease endotoxin-induced tumor necrosis factor production and lethality. Green tea polyphenols may inhibit inflammatory responses and possibly help treat chronic inflammatory states.
A study on mice looked at whether 5 g/L of green tea polyphenols compared to water decreased disease activity in interleukin-2-deficient mice for 6 weeks. At 6 weeks the green tea polyphenols group had less severe colitis, lower plasma concentrations of amyloid A, increased weight gain and improved hematocrits. Overall, results showed that green tea polyphenols attenuated inflammation in interleukin-2-deficient mice and suggest a role for them in the treatment of chronic inflammatory diseases such as inflammatory bowel disease. 19
Neuroprotective Effect: The accumulation of eicosanoids and the formation of oxygen free radicals have been implicated in the pathogenesis of ischemia. Green tea extract may protect against ischemia or reperfusion brain injury.
Researchers gave rats gave 0.5% green tea extract orally for 3 weeks prior to induction of ischemia. Green tea extract reduced ischemia/reperfusion-induced eicosanoid concentration. Ischemia/reperfusion-induced increases in hydrogen peroxide concentrations, oxidation products and 8-oxodeoxygenanosine formation were also reduced by green tea extract. Overall, the study showed that the minimizing effect of green tea extract on eicosanoid accumulation and oxidative damage, in addition to reduction of neuronal cell death, may have a protective effect against ischemia/ reperfusion-induced brain injury and behavior deficit. 20
Fat Oxidation: Green tea supplementation may help with weight control. Plant ingredients in green tea, such as caffeine and catechin polyphenols, may increase 24-hour energy expenditure and fat oxidation in humans and help with sympathetic release of noradrenaline and management of obesity. Green tea polyphenolics have been found to inhibit the action of amylase, a carbohydrate-digesting enzyme present in saliva. 1
In a small double-blind, placebo-controlled
study with 60 middle-aged obese women (30
to 45 years old), subjects were placed on a diet
of 1,800 calories daily and randomily assigned
to either a green tea supplement group or the
placebo group. Capsule were taken at each
meal for 30 days (250 mg x8/day in 3 divided
doses). After two weeks, the green tea group
had lost twice as much weight as those on
placebo. After 4 weeks of treatment, the
women in the green tea group had lost 3 times
as much weight (2.90 kg) as those on placebo
(0.94 kg). Compared to the placebo group, the
green tea group also showed a significantly
greater reduction in waist size (-2.10±1.37 cm
vs. –0.48±0.97 cm), and in their blood
triglyceride levels compared to the placebo
group also a significant decrease
(-2.10±0.19g/L vs. –0.03±0.14g/L). No side
effect, including sleep loss, were reported. 21
Ten healthy men were given 50 mg caffeine and 90 mg of epigallocatechin gallate or 50 mg caffeine or placebo on 3 different occasions. Relative to placebo, the green tea extract resulted in an increase in 24-hour energy expenditure (4%) and a decrease in 24-hour respiratory quotient (from 0.88 to 0.85) without any change in urinary nitrogen. Twenty-four hour urinary norepinephrine excretion was 40% higher than placebo. Overall, researchers concluded that green tea extract might play a role in body composition via sympathetic activation of theromogenesis, fat oxidation or both. [~22~]
Traditionally, 4-7g of loose green tea 4; an average infusion may contain from 50 to 400mg of polyphenols per cup 5; a dose of 500mg of green tea polyphenols, three or four times daily, has been recommended.
Standardized extracts of green tea, typically containing 60 to 80% polyphenols are available on the supplement market.
In traditional Indian medicine green
tea has been regarded as astringent,
diuretic and mildly CNS stimulant. In
traditional Chinese medicine, it has
also been regarded as helpful in the
treatment of digestive problems, in
regulating temperature and improving
mental processes. 3
In modern times, green tea has been ascribed the following functions, mainly due to its constituent catechins:
EGCG has been found to completely inhibit collage-induced platelet aggregation at a concentration of 0.2mg/ml, in vitro, activity comparable to that of aspirin, suggesting an anti-coagulant potential. 6 .
.
Vitamin K in green tea may directly interfere
with the blood-thinning action of warfarin
[Coumadin], an anticoagulant agent.
Drinking large amounts of green tea may
decrease the therapeutic effects of the drug. 7Information on the relationship between substances and disease is provided for general information, in order to convey a balanced review of the scientific literature. In many cases the relationship between a substance and a disease is tentative and additional research is needed to confirm such a relationship.
The dietary supplement information contained on this site has been compiled from published sources thought to be reliable, but it cannot be guaranteed. Efforts have been made to assure this information is accurate and current. However, some of this information may be purported or outdated due to ongoing research or discoveries. The authors, editors and publishers cannot accept responsibility for errors or omissions or for any consequences from applications of the information in this site and make no warranty, expressed or implied, with respect to the contents herein.
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