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Review on green tea constituents and its negative effects

February 2015
A capillary micro-reactor as a tool to study pressurised reactions The influence of pressure on the stereoselectivity of the Diels-Alder reaction of 2-and 3-Furylmethanol with maleimides

Authors:

Najaf Farooq

Jinnah University for Women

Amber Nawab

Jinnah University for Women

Objective: to review and discuss the negative effects of green tea. Green tea is obtained from Camellia sinensis and belongs to the family theaceae and is used most popularly as beverage all over the world. Although there are beneficial effects of green tea, but it has also side effects. We have search different research articles and found that by consuming large amounts of green tea nausea, vomiting, dehydration, lethargy, central nervous system stimulation such as dizziness, insomnia, tremors, restlessness, confusion, diuresis, heart rate irregularities and psychomotor agitation may occur. Most side effects are due to high consumption of caffeine. Epigallocatechin-3-gallate (EGCG) has anti-folate activity so to prevent folate deficiency it should not used in excessive quantity and it may reacts with some drugs like aspirin and MAOI so used with caution if high level of green tea is used.

: Principle components of green tea [28]

…

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The Pharma Innovation Journal 2015; 4(1): 21-24

ISSN: 2277- 7695

TPI 2015; 4(1): 21-24

www.thepharmajournal.com

Received: 30-11-2014

Accepted: 07-02-2015

Amber Nawab

Faculty of Pharmacy

Jinnah University for Women,

Pakistan

Najaf Farooq

Faculty of Pharmacy

Jinnah University for Women,

Pakistan

Correspondence:

Amber Nawab

Faculty of Pharmacy

Jinnah University for Women,

Pakistan

Review on green tea constituents and its negative

effects

Amber Nawab, Najaf Farooq

Abstract

Objective: to review and discuss the negative effects of green tea.

Green tea is obtained from Camellia sinensis and belongs to the family theaceae and is used most

popularly as beverage all over the world. Although there are beneficial effects of green tea, but it has also

side effects. We have search different research articles and found that by consuming large amounts of

green tea nausea, vomiting, dehydration, lethargy, central nervous system stimulation such as dizziness,

insomnia, tremors, restlessness, confusion, diuresis, heart rate irregularities and psychomotor agitation

may occur. Most side effects are due to high consumption of caffeine. Epigallocatechin-3-gallate

(EGCG) has anti-folate activity so to prevent folate deficiency it should not used in excessive quantity

and it may reacts with some drugs like aspirin and MAOI so used with caution if high level of green tea

is used.

Keywords: Green tea, side effects, caffeine, drug interactions, anti-folate activity

1. Introduction

Tea is one of the most popular beverages, which are commonly used all over the world. Tea is

mostly used in countries such as China and Japan, and green tea accounts for 20% of tea

consumption worldwide

[1]. Today, green tea is cultivated commercially in Asia, Africa and

South America [2].

Green tea is derived from Camellia sinensis, an evergreen plant of the Theaceae family.

Dissimilar black tea, which is fermented, green tea is produced in a non-fermented procedure.

Green tea may be used in the form of a brewed drink or capsular extract. Tea may be used as

dietary supplements. In China, consumption of green tea and the medicinal use of green tea

was begun more than 4,700 years ago. Presently, there is no proper dose suggested for green

tea extract. Researchers examined the effects of consistently green tea drinking on cancer

prevention; however, evidence has not been corroborated [3-5].

The main active ingredients of green tea include polyphenolic compounds such as epicatechin

(EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC) and epigallocatechin-3-gallate

(EGCG), all of which may be responsible for the anti-carcinogenic and anti-mutagenic

activities of green tea. Other polyphenols in green tea include flavanols and their glycosides

and depsides such as chlorogenic acid, quinic acids, carotenoids, trigalloylglucose, lignin,

protein, chlorophyll, minerals (aluminum or manganese, depending on the soil content),

caffeine and a very small amount of methylxanthines [6]. The constituents of green tea have a

broad array of biological activities [7]. EGCG is one of the major components in green tea [8],

and its pharmacology has been intensively studied [9, 10, 11, 12, 13, 14, 15].

Drinking green tea has several benefits, but there are potential side effects associated with

excessive use of green tea.

Green tea contains about 30 to 60 mg of caffeine per 6 to 8 oz. cup. This is normal and less

than the average 100 mg caffeine contained in a cup of coffee. But green tea is generally

consumed in greater amounts when used for weight loss and this increases the consumption of

caffeine. And if more than five cups of tea per day are used, it will raise caffeine intake to

unsafe levels, and may increase risk for insomnia, restlessness, tremors, and upset stomach.

Tannins are present in large quantities in a green tea Tannins bind with non-heme iron in the

body. Nonheme iron is the type of iron that is contained in plants and iron-fortified foods. It is

not as easily absorbed in the body as heme iron, however most iron in the diet is typically

nonheme iron. Tea specialist Lindsey "Vee" Goodwin of Vee Tea comments that “the tannins

in green tea can form irresolvable bonds with iron in the body, rendering the iron hard to

digest. According to Goodwin, "The typical reduction in iron absorption from a food with a

cup of tea in clinical studies is approximately 30-60 percent."

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This hindrance with iron absorption can lead to iron deficit

anemia. Iron deficiency anemia can account feelings of

weakness, shortness of breath, irritability, headaches and alter

heartbeat.

American Association of Cancer Research study on the anti-

folate activity of tea showed that EGCG can interfere with

folate use in cells. Folate is needed to make DNA and prevent

negative changes to DNA from cancers. Folate also helps to

make red blood cells, protect against heart disease and prevent

anemia. It is important to be aware of green tea intake to

prevent folate deficiency. According to the website World's

Healthiest Foods, one cup of green tea supplies 20 to 35 mg of

EGCG.

Green tea is a natural diuretic so; by drinking extreme amounts

of green tea (more than five cups /day) it can cause excessive

urination leading to dehydration and electrolyte disproportion.

Dehydration can also leads to headaches, lethargy, changed

heart rate and distress.

According to the University of Maryland Medical Center,

green tea can interfere with the absorption and effects of

certain medications. This can lessen or intensify the effects of

medications, which could put your health at risk. Some

medications that might be affected include MAOI inhibitors,

lithium, adenosine and blood thinners [16].

A Cochrane review on green tea preparations and weight loss

has showed a non significant loss of weight in obese or

overweight adults likely not of clinical relevance [17].

In diabetic patients green tea may lower the fasting glucose

levels, but no significant HbA1c changes are observed [18].

A cohort study of 8, 552 people with nine years of follow-up

showed a negative association of green tea consumption with

cancer incidence, especially among Japanese women drinking

more than ten cups a day (RR 0.59; 95% CI, 0.35–0.98) [19, 20].

However, a larger cohort study with 38,540 people in Japan

did not show an association between green tea consumption

and the sum incidence of all cancers (RR 1.0; 95% CI, 0.91–

1.1 for those drinking two to four times per day; RR 0.98;

95%CI, 0.88–1.1 for those drinking five times or more per

day, both compared with those drinking one time or less per

day) [21].

Depending on the brand, two to three cups of green tea per day

(for a total of 240–320 mg polyphenols) or 100–750 mg per

day of standardized green tea extract is recommended [22].

.There is evidence that dietary components rich in polyphenols

may cause tooth staining [23].

Herbs contain active substances that can trigger side effects

and interact with other herbs, supplements, or medications.

However, pharmacological and toxicological evidence does

indicate that green tea polyphenols can in fact cause oxidative

stress and liver toxicity in vivo at certain concentrations.

Patients on Warfarin should not take green tea because green

tea having vitamin K. Green tea must not to be delivering with

aspirin in light of the fact that it keeps platelets from

coagulation. Too much amount of caffeine (including caffeine

from green tea), may cause nausea, vomiting, diarrhea,

headache, and loss of appetite, and so it should be skipped [22].

Utilization of high dosages of green tea or green tea extract

(i.e. 5–6 liters for /day) may causes, nausea, spitting, stomach

bloating/ache, dyspepsia, flatulence and diarrhea [24, 25].

Excessive consumption of caffeine from green tea may also

cause central nervous system stimulation such as dizziness,

insomnia, tremors, restlessness, confusion, diuresis (i.e.

increasing urine output), heart rate irregularities and

psychomotor agitation [25].

Inoueetal reported that a diet containing high dose green tea

polyphenols disrupts renal function in both mice with dextran

sulfate sodium-induced colitis and normal mice [26]. They

assumed that high-dose green tea polyphenols down-adjust

antioxidant enzymes, prompting kidney impairment. In any

case, in human subjects, as far as anyone is concerned, there is

no robust proof reporting valuable impacts of green tea

utilization on renal capacity. A clinical trial reported that green

tea consumption does not increase GFR in19 healthy young

adults, while coffee consumption increases it [27].

2. Results and discussion

Green tea is obtained from Camellia sinensis, and belongs to

the Theaceae family. Green tea mostly consists of

polyphenolic compounds such as epicatechin (EC),

epicatechin-3-gallate (ECG), epigallocatechin (EGC) and

epigallocatechin-3-gallate (EGCG) (shown in Fig.1), all of

which may be responsible for the anti-carcinogenic and anti-

mutagenic activities of green tea. It also contains flavanols and

their glycosides and depsides such as chlorogenic acid, quinic

acids, carotenoids, trigalloylglucose, lignin, protein,

chlorophyll, minerals (aluminum or manganese, depending on

the soil content), caffeine and a very small amount of

methylxanthines.

Green tea has beneficial effects, but there are potential side

effects which are showed on high consumption of green tea.

Caffeine is a major constituent and if more than five cups of

green tea are consumed daily it may cause insomnia,

restlessness and upset stomach. It has been observed that for

reducing weight, green tea is consumed so if high levels of

caffeine is used it may cause severe side effects. It is necessary

to used green tea for this purpose cautiously. Tannins present

in green tea like catechin, epicatechin etc. bind with non heme

iron in the body. This interferes with iron absorption, which

can lead to iron deficiency anemia. Iron deficiency anemia can

cause feelings of weakness, shortness of breath, irritability,

headaches and irregular heartbeat. So anemic patient should

use it cautiously, if taken in high amount. Epigallocatechin-3-

gallate (EGCG) has anti-folate activity so to prevent folate

deficiency it should not used in excessive quantity. Since

green tea is a diuretic and it can cause excessive urination

which may lead to dehydration and electrolyte imbalances. If

severe dehydration occurs, it may cause headaches, lethargy,

altered heart rate and shock. Green tea contains poly phenols;

the researchers showed that it may stain the teeth.

Nausea, vomiting, loss of appetite, abdominal bloating/pain,

dyspepsia, flatulence and diarrhea are other side effects

reported that are caused by the use of green tea. Excessive

consumption of caffeine from green tea may also cause central

nervous system stimulation such as vertigo, insomnia, tremors,

impatience, distraction, agitation and psychomotor agitation

[25]. It also contain vitamin k that’s why should be avoided

excessive intake of green tea, patient who on warfarin, aspirin

and anticoagulants may prevent clotting of blood.

3. Conclusion

We have studied the side effects of green tea through literature

and research papers and observed that green tea is beneficial

for health, but it has side effects which are found on excessive

consumption of green tea. Possible side effects include nausea,

vomiting, dehydration, lethargy, central nervous system

stimulation such as dizziness, insomnia, tremors, restlessness,

confusion, diuresis, heart rate irregularities and psychomotor

agitation. Polyphones present in green tea may stain the teeth.

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So, peoples who are consuming green tea in large amounts or

peoples who are using it to reduce weight should use it

cautiously to prevent the side effects associated with green tea.

Large consumption of green tea should be avoided in patients

who taken anticoagulants.

Fig 1: Flavonoids founds in green tea

Fig 2: components of green tea

Fig 3: structure of catechin.

Table 1: Principle components of green tea [28]

Components Green Tea

(% weight of extract solids)

Catechins 30-42

Flavonols 5-10

Other flavonoids 2-4

Theogallin 2-3

Other depsides 1

Ascorbic Acid 1-2

Gallic Acid 0.5

Quinic acid 2

Other organic acids 4-5

Theanine 4-6

Other amino acids 4-6

Methylxanthines 7-9

Carbohydrates 10-15

Minerals 6-8

Volatiles 0.02

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Purpose: The purpose of this present study is to determine the effect of single cup of green tea on the tear film stability and the quantity of tears production. Methodology: A prospective observational study was carried out at the Department of Optometry and vision sciences, The University of Lahore. 30 participants were enrolled in this study. The subjects who had fulfill the inclusion criteria were examined for baseline measurement half an hour before the green tea intake. The tear film stability and the quantity of tears production were accessed by using tear breakup time and schirmer test respectively. After the initial baseline investigation, a cup of green tea was given to the participant and the measurements was taken again after 1 hour of green tea consumption under same examination room at same room temperature. Results: A 30 normal healthy subjects were enrolled in this study. Out of 30 participant there were 18 (60%) females and 12 (40%) of males of age ranges 20 − 40 years. The mean age of the patients was 28.1 ± 5.06. The mean of baseline tear breakup time of right eye was 14.63 ± 2.06 sec and after 1 hour of green tea consumption was 13.06 ± 1.76sec. Similarly, the baseline means value of quantity of tear production of right eye by using scheimer test was 18.06 ± 1.96 and after 1 hour of green tea consumption was 15.9 ± 2.41. The mean baseline measurement of quantity of tear production (Schirmer test) of left eye before 30 mint green tea consumption was 18.06 ± 1.42mm and after 1 hour of drinking green tea was 16.1 ± 1.62mm respectively. Similarly, the stability of tear film (TBUT) was assessed before 30 mint of green tea consumption and after the 1-hour green tea consumption of initial baseline measurement of left eye was 15.4 ± 1.96sec and 13.9 ± 0.98sec respectively. Paired Sample t test shows a significant association of stability of tear film and tear production after the consumption of green tea. Conclusions: There was a significant effect of green tea on tear film stability and the quantity of tears production. The quantity of tears production reduced significantly.

Effect of Green Tea Consumption on the Tear Film Stability and Quantity of Tear Production in Normal Subjects

Article

Full-text available

Jan 2022

Green tea influence on iron overload in thalassemia intermedia patients: A randomized controlled trial

Article

Full-text available

Sep 2020

Background: Although iron chelation therapies have been available for many years for thalassemia intermedia patients, iron accumulation remains the major cause of death. Therefore, the need for additional chelation options is in demand. This randomized controlled study aimed to understand the effects of green tea on iron balance in thalassemia intermedia patients. Methods: Using a random selection method, 141 thalassemia intermedia patients were initially screened for inclusion in this trial; only 68 patients included after applying exclusion criteria. Two equal groups were generated (n=34/group): green tea (three cups/day after meals) + usual treatment (deferasirox iron chelator and on demand blood transfusion); and control (only usual treatment). The study lasted for a period of 12 months. Patients failing to comply to the trial methodology were excluded, leaving a final total of 29 patients in the green tea group and 28 patients in the control group. Liver iron concentration, and serum ferritin were assessed at baseline and 12 months, while hemoglobin levels were assessed monthly. Results: At baseline, both groups were matched regarding general demographics. At 12 months, the net drop of liver iron concentration in the green tea group (7.3 mg Fe/g dry weight) was significantly higher than the control group (4.6 mg Fe/g dry weight) (p<0.05). This was also seen with serum ferritin; net reduction in green tea and control groups were 1289 ng/ml and 871 ng/ml, respectively (p<0.05). Hemoglobin levels were slightly higher in the green tea group compared with the control group, but this was not significant. Conclusions: Regular green tea consumption had a significant capability to improve iron deposition in thalassemia intermedia patients who already undergo deferesirox iron chelation therapy. Trial registration: UMIN-CTR Clinical Trials Registry, UMIN000040841 (retrospectively registered June 21, 2020).

Human Clinical Studies of Tea Polyphenols in Allergy or Life Style-related Diseases

Article

Full-text available

Feb 2013
CURR PHARM DESIGN

Mari Maeda-Yamamoto

Many previous epidemiological studies have revealed that green tea or green tea catechins contributed to the preveintion of lifestyle-related diseases. Several cohort studies on the relationship between green tea consumption and cardiovascular disease (CVD) risk/type 2 diabetes mellitus risk have been conducted. The results showed that green tea consumption (5 or more cups/day) was inversely associated with mortality from CVD and all causes. Within CVD mortality, the strongest inverse association was observed for stroke mortality. Furthermore, consumption of green tea, coffee, and total caffeine was associated with a reduced risk for type 2 diabetes. On the other hand, the analysis of randomized clinical trial (RCT) studies showed that the administration of green tea beverages or extracts resulted in significant reductions in serum total cholesterol and LDL-cholesterol concentrations, but had no apparent effect on HDL-cholesterol. Green tea reduced fasting blood glucose levels in a small intervention trial, although no improvements in HbA1c levels were seen. Continuous intake of green tea containing catechins and caffeine (5 or more cups per day) may be beneficial for body weight management, vascular disease risk reduction via LDL-cholesterol improvement, and type 2 diabetes risk reduction through the lowering of fasting blood glucose levels.

Green tea for weight loss and weight maintenance in overweight or obese adults

Article

Full-text available

Dec 2012

Preparations of green tea are used as aids in weight loss and weight maintenance. Catechins and caffeine, both contained in green tea, are each believed to have a role in increasing energy metabolism, which may lead to weight loss. A number of randomised controlled trials (RCTs) evaluating the role of green tea in weight loss have been published; however, the efficacy of green tea preparations in weight loss remains unclear. To assess the efficacy and safety of green tea preparations for weight loss and weight maintenance in overweight or obese adults. We searched the following databases from inception to specified date as well as reference lists of relevant articles: The Cochrane Library (Issue 12, 2011), MEDLINE (December 2011), EMBASE (December 2011), CINAHL (January 2012), AMED (January 2012), Biological Abstracts (January 2012), IBIDS (August 2010), Obesity+ (January 2012), IPA (January 2012) and Web of Science (December 2011). Current Controlled Trials with links to other databases of ongoing trials was also searched. RCTs of at least 12 weeks' duration comparing green tea preparations to a control in overweight or obese adults. Three authors independently extracted data, assessed studies for risk of bias and quality, with differences resolved by consensus. Heterogeneity of included studies was assessed visually using forest plots and quantified using the I(2) statistic. We synthesised data using meta-analysis and descriptive analysis as appropriate; subgroup and sensitivity analyses were conducted. Adverse effects reported in studies were recorded. Due to the level of heterogeneity among studies, studies were divided into two groups; those conducted in Japan and those conducted outside Japan. Study length ranged between 12 and 13 weeks. Meta-analysis of six studies conducted outside Japan showed a mean difference (MD) in weight loss of -0.04 kg (95% CI -0.5 to 0.4; P = 0.88; I(2) = 18%; 532 participants). The eight studies conducted in Japan were not similar enough to allow pooling of results and MD in weight loss ranged from -0.2 kg to -3.5 kg (1030 participants) in favour of green tea preparations. Meta-analysis of studies measuring change in body mass index (BMI) conducted outside Japan showed a MD in BMI of -0.2 kg/m(2) (95% CI -0.5 to 0.1; P = 0.21; I(2) = 38%; 222 participants). Differences among the eight studies conducted in Japan did not allow pooling of results and showed a reduction in BMI ranging from no effect to -1.3 kg/m(2) (1030 participants), in favour of green tea preparations over control. Meta-analysis of five studies conducted outside Japan and measuring waist circumference reported a MD of -0.2 cm (95% CI -1.4 to 0.9; P = 0.70; I(2) = 58%; 404 participants). Differences among the eight studies conducted in Japan did not allow pooling of results and showed effects on waist circumference ranging from a gain of 1 cm to a loss of 3.3 cm (1030 participants). Meta-analysis for three weight loss studies, conducted outside Japan, with waist-to-hip ratio data (144 participants) yielded no significant change (MD 0; 95% CI -0.02 to 0.01). Analysis of two studies conducted to determine if green tea could help to maintain weight after a period of weight loss (184 participants) showed a change in weight loss of 0.6 to -1.6 kg, a change in BMI from 0.2 to -0.5 kg/m(2) and a change in waist circumference from 0.3 to -1.7 cm. In the eight studies that recorded adverse events, four reported adverse events that were mild to moderate, with the exception of two (green tea preparations group) that required hospitalisation (reported as not associated with the intervention). Nine studies reported on compliance/adherence, one study assessed attitude towards eating as part of the health-related quality of life outcome. No studies reported on patient satisfaction, morbidity or cost. Green tea preparations appear to induce a small, statistically non-significant weight loss in overweight or obese adults. Because the amount of weight loss is small, it is not likely to be clinically important. Green tea had no significant effect on the maintenance of weight loss. Of those studies recording information on adverse events, only two identified an adverse event requiring hospitalisation. The remaining adverse events were judged to be mild to moderate.

Coffee Consumption and Cystatin-C-Based Estimated Glomerular Filtration Rates in Healthy Young Adults: Results of a Clinical Trial

Article

Full-text available

Jan 2011
J Nutr Metab

Recently it has been reported that the estimated glomerular filtration rate (eGFR) is higher in habitual coffee consumers than in noncoffee consumers. However, the causality remains unclear. Therefore, we conducted a clinical trial to investigate the effects of coffee consumption on kidney function. Nineteen asymptomatic nonsmokers aged 21-27 years old participated in this study. They consumed coffee (18 g coffee beans/450 mL per day) or green tea as a comparator for 2 weeks in a crossover design. Although creatinine-based eGFR was not affected after consuming either beverage, all cystatin-C-based eGFRs determined using five different equations were significantly increased after coffee consumption (means: 5.0-7.7%), but not after green tea consumption (means: 0.1-1.6%). Serum adiponectin and magnesium levels increased significantly after coffee consumption (means: 13.6% and 4.3%, resp.), but not after green tea consumption. These findings suggest that even a short period of coffee consumption may increase cystatin-C-based eGFR, along with favorable changes in serum adiponectin, in healthy young adults.

High-dose green tea polyphenols induce nephrotoxicity in dextran sulfate sodium-induced colitis mice by down-regulation of antioxidant enzyme and heat-shock protein expressions

Article

Full-text available

Jul 2011
CELL STRESS CHAPERON

Previously, we reported that oral feeding of 1% green tea polyphenols (GTPs) aggravated the dextran sulfate sodium (DSS)-induced colitis in mice. In the present study, we assessed the toxicity of 1% GTPs in several organs from normal and DSS-exposed mice. Sixty-two male ICR mice were initially divided into four groups. Non-treated group (group 1, n = 15) was given standard diet and water, GTPs (group 2, n = 15) received 1% GTPs in diet and water, DSS (group 3, n = 15) received diet and 5% DSS in water, and GTPs + DSS group (group 4, n = 17) received 1% GTPs in diet and 5% DSS in water. We found that group 4 significantly increased (P < 0.05) kidney weight, the levels of serum creatinine and thiobarbituric acid-reactive substances in both kidney and liver, as compared with those in group 3. The mRNA expression levels of antioxidant enzymes and heat-shock proteins (HSPs) in group 4 were lower than those of group 3. For instance, heme oxygenase-1 (HO-1), HSP27, and 90 mRNA in the kidney of group 4 were dramatically down-regulated as compared with those of group 3. Furthermore, 1% GTPs diet decreased the expression of HO-1, NAD(P)H:quinone oxidoreductase 1 (NQO1) and HSP90 in kidney and liver of non-treated mice. Taken together, our results indicate that high-dose GTPs diet disrupts kidney functions through the reduction of antioxidant enzymes and heat-shock protein expressions in not only colitis but also non-treated ICR mice.

Blood and urine levels of tea catechins after ingestion of different amounts of green tea by human volunteers

Article

Full-text available

May 1998

The inhibitory activity of tea against tumorigenesis has been demonstrated in many animal models and has been suggested by some epidemiological studies. Such activity has generally been attributed to tea catechins. To understand the bioavailability of tea catechins in humans, we gave 18 individuals different amounts of green tea and measured the time-dependent plasma concentrations and urinary excretion of tea catechins. After taking 1.5, 3.0, and 4.5 g of decaffeinated green tea solids (dissolved in 500 ml of water), the maximum plasma concentration (Cmax) of (-)-epigallocatechin-3-gallate (EGCG) was 326 ng/ml, the Cmax of (-)-epigallocatechin (EGC) was 550 ng/ml, and the Cmax of (-)-epicatechin (EC) was 190 ng/ml. These Cmax values were observed at 1.4-2.4 h after ingestion of the tea preparation. When the dosage was increased from 1.5 to 3.0 g, the Cmax values increased 2.7-3.4-fold, but increasing the dose to 4.5 g did not increase the Cmax values significantly, which suggested a saturation phenomenon. The half-life of EGCG (5.0-5.5 h) seemed to be higher than the half-life of EGC or EC (2.5-3.4 h). EGC and EC, but not EGCG, were excreted in the urine. Over 90% of the total urinary EGC and EC was excreted within 8 h. When the tea dosage was increased, the amount of EGC and EC excretion seemed to increase, but a clear dose-response relationship was not observed. The present study provides basic pharmacokinetic parameters of green tea catechins in humans; these parameters may be used to estimate the levels of these compounds after drinking tea.

Green tea polyphenols for prostate cancer chemoprevention: A translational perspective

Article

Jan 2010

Every year nearly 200,000 men in the United States are diagnosed with prostate cancer (PCa), and another 29,000 men succumb to the disease. Within certain regions of the world population based studies have identified a possible role for green tea in the prevention of certain cancers, especially PCa. One constituent in particular, epigallocatechin-3-gallate also known as EGCG has been shown in cell culture models to decrease cell viability and promote apoptosis in multiple cancer cell lines including PCa with no effect on non-cancerous cell lines. In addition, animal models have consistently shown that standardized green tea polyphenols when administered in drinking water delay the development and progression of PCa. Altogether, three clinical trials have been performed in PCa patients and suggest that green tea may have a distinct role as a chemopreventive agent. This review will present the available data for standardized green tea polyphenols in regard to PCa chemoprevention that will include epidemiological, mechanism based studies, safety, pharmacokinetics, and applicable clinical trials. The data that has been collected so far suggests that green tea may be a promising agent for PCa chemoprevention and further clinical trials of participants at risk of PCa or early stage PCa are warranted.

Chemoprotective Mechanism of the Natural Compounds, Epigallocatechin- 3-O-Gallate, Quercetin and Curcumin Against Cancer and Cardiovascular Diseases

Article

Feb 2009

Cancer and cardiovascular disease (CVD) chemoprevention can be achieved by the use of natural, synthetic, or biologic compounds to reverse, suppress, or prevent the development of diseases. Chemoprevention is a potential anti-cancer approach, which has reduced secondary effects in comparison to classical prophylaxis. Natural compounds such as flavonoids reduce oxidative stress, which is the most likely mechanism in the protective effects of these compounds. Even though the exact mechanisms of action are not well understood another central action mechanism of polyphenolic flavonoids seems to be an induction of apoptosis as demonstrated in numerous cellular systems. Moreover, flavonoids may modulate protein and lipid kinase signaling pathways. Understanding the mechanism of these natural products will contribute to the development of more specific preventive strategies against cancer and CVD. Much of the research in the field is focused on epigallocatechin-3-O-gallate (EGCG), quercetin and curcumin, which were found to have beneficial effects against cancer and CVD. We review the chemoprotective mechanisms through which these natural compounds exert their beneficial effects against cancer and CVDs.

Green tea composition, consumption, and polyphenol chemistry

Article

Jun 1992

Harold N. Graham

Tea is grown in about 30 countries but is consumed worldwide, although at greatly varying levels. It is the most widely consumed beverage aside from water with a per capita worldwide consumption of approximately 0.12 liter per year. Tea is manufactured in three basic forms. Green tea is prepared in such a way as to preclude the oxidation of green leaf polyphenols. During black tea production oxidation is promoted so that most of these substances are oxidized. Oolong tea is a partially oxidized product. Of the approximately 2.5 million metric tons of dried tea manufactured, only 20% is green tea and less than 2% is oolong tea. Green tea is consumed primarily in China, Japan, and a few countries in North Africa and the Middle East. Fresh tea leaf is unusually rich in the flavanol group of polyphenols known as catechins which may constitute up to 30% of the dry leaf weight. Other polyphenols include flavanols and their glycosides, and depsides such as chlorogenic acid, coumarylquinic acid, and one unique to tea, theogallin (3-galloylquinic acid). Caffeine is present at an average level of 3% along with very small amounts of the other common methylxanthines, theobromine and theophylline. The amino acid theanine (5-N-ethylglutamine) is also unique to tea. Tea accumulates aluminum and manganese. In addition to the normal complement of plant cell enzymes, tea leaf contains an active polyphenol oxidase which catalyzes the aerobic oxidation of the catechins when the leaf cell structure is disrupted during black tea manufacture. The various quinones produced by the enzymatic oxidations undergo condensation reactions which result in a series of compounds, including bisflavanols, theaflavins, epitheaflavic acids, and thearubigens, which impart the characteristic taste and color properties of black tea. Most of these compounds readily form complexes with caffeine. There is no tannic acid in tea. Thearubigens constitute the largest mass of the extractable matter in black tea but their composition is not well known. Proanthocyanidins make up part of the complex. Tea peroxidase may be involved in their generation. The catechin quinones also initiate the formation of many of the hundreds of volatile compounds found in the black tea aroma fraction. Green tea composition is very similar to that of the fresh leaf except for a few enzymatically catalyzed changes which occur extremely rapidly following plucking. New volatile substances are produced during the drying stage. Oolong tea is intermediate in composition between green and black teas.

Cancer-Preventive Effects of Drinking Green Tea among a Japanese Population

Article

Nov 1997

Laboratory studies have revealed the cancer preventive effects of green tea, so the association between green tea consumption and cancer was examined in a human population. The association between green tea consumption and cancer incidence was studied in our prospective cohort study of a Japanese population. We surveyed 8,552 individuals over 40 years of age living in a town in Saitama prefecture on their living habits, including daily consumption of green tea. During the 9 years of follow-up study (71,248.5 person-years), we identified a total of 384 cases of cancer in all sites. We found a negative association between green tea consumption and cancer incidence, especially among females drinking more than 10 cups a day. The slowdown in increase of cancer incidence with age observed among females who consumed more than 10 cups a day is consistent with the finding that increased consumption of green tea is associated with later onset of cancer. Age-standardized average annual incidence rate was significantly lower among females who consumed large amounts of green tea. Relative risk (RR) of cancer incidence was also lower among both females (RR = 0.57, 95% CI = 0.33-0.98) and males (RR = 0.68, 95% CI = 0.39-1.21) in groups with the highest consumption, although the preventive effects did not achieve statistical significance among males, even when stratified by smoking and adjusted for alcohol and dietary variables. Our epidemiological study showed that green tea has a potentially preventive effect against cancer among humans.

Green tea (Camellia sinensis) extract and its possible role in the prevention of cancer

Article

Nov 1999
ALTERN MED REV

M D Brown

The American Cancer Society estimates that in the 1980s more than 4. 5 million Americans died of cancer. In addition, there were nearly nine million new cases and about 12 million people were under medical care for cancer. With cancer being the second most common cause of death in the United States population, the possibility that readily-available natural substances may be beneficial in the prevention of cancer warrants closer examination. A growing body of research has demonstrated green tea polyphenols to be powerful antioxidants with anticarcinogenic properties. These polyphenolic compounds, specifically the catechins epigallocatechin-3-gallate (EGCG), epigallocatechin (EGC), and epicatechin-3-gallate (ECG), which account for 30-40 percent of the extractable solids of green tea leaves, are believed to mediate many of the cancer chemopreventive effects. Mechanisms of action may include antioxidant and free-radical scavenging activity, and stimulation of detoxification systems through selective induction or modification of phase I and phase II metabolic enzymes. In addition, green tea may inhibit biochemical markers of tumor initiation and promotion, including the rate of cell replication and thus inhibition of the growth and development of neoplasms. Current studies are hopeful, as they show an inverse association between green tea consumption and cancer risk, supporting a possible chemopreventive effect of green tea. Based on the knowledge that green tea is inexpensive, non-toxic, and is a popular beverage consumed worldwide, clinical trials should be conducted to evaluate the in-vivo effectiveness of green tea polyphenols on the inhibition and chemopreventive treatment of cancer.