The Effects of Green Tea Consumption on Incidence of Breast Cancer and Recurrence of Breast Cancer: A Systematic Review and Meta-analysis

Tea and cancer prevention: epidemiological studies

Experimental studies have consistently shown the inhibitory activities of tea extracts on tumorigenesis in multiple model systems. Epidemiological studies, however, have produced inconclusive results in humans. A comprehensive review was conducted to assess the current knowledge on tea consumption and risk of cancers in humans. In general, consumption of black tea was not associated with lower risk of cancer. High intake of green tea was consistently associated with reduced risk of upper gastrointestinal tract cancers after sufficient control for confounders. Limited data support a protective effect of green tea on lung and hepatocellular carcinogenesis. Although observational studies do not support a beneficial role of tea intake on prostate cancer risk, phase II clinical trials have demonstrated an inhibitory effect of green tea extract against the progression of prostate pre-malignant lesions. Green tea may exert beneficial effects against mammary carcinogenesis in premenopausal women and recurrence of breast cancer. There is no sufficient evidence that supports a protective role of tea intake on the development of cancers of the colorectum, pancreas, urinary tract, glioma, lymphoma, and leukemia. Future prospective observational studies with biomarkers of exposure and phase III clinical trials are required to provide definitive evidence for the hypothesized beneficial effect of tea consumption on cancer formation in humans.

Is green tea drinking associated with a later onset of breast cancer?

BACKGROUND

Studies have found that tea polyphenols inhibit aromatase. Because of the substantial difference in levels of estrogens between premenopausal and postmenopausal women, the relationship between tea consumption and breast cancer risk may depend on menopausal status.

METHODS

We examined this hypothesis in the Shanghai Women's Health Study, a population-based cohort study of 74,942 Chinese women.

RESULTS

We found a time-dependent interaction between green tea consumption and age of breast cancer onset (p for interaction, 0.03). In comparison with non-tea drinkers, women who started tea-drinking at 25 years of age or younger had a hazard ratio (HR) of 0.69 (95% confidence interval [CI]: 0.41-1.17) to develop premenopausal breast cancer. On the other hand, compared with non-tea drinkers, women who started tea drinking at 25 years of age or younger had an increased risk of postmenopausal breast cancer with an HR of 1.61 (95% CI: 1.18-2.20). Additional analyses suggest regularly drinking green tea may delay the onset of breast cancer.

CONCLUSIONS

Further studies are needed to confirm our findings.

Urinary polyphenols and breast cancer risk: results from the Shanghai Women's Health Study

Polyphenols, the most abundant dietary antioxidants, also possess many other anticarcinogenic activities. Urinary metabolites of polyphenols could complement dietary assessment of the bioavailability of these nutrients. We conducted a study of 353 incident breast cancer cases and 701 individually matched controls nested within the Shanghai Women's Health Study cohort of women aged 40-70 years at baseline. Liquid chromatography photo-diode array electrospray mass spectrometry was used to measure tea polyphenols (epicatechin, epigallocatechin, and their metabolites) and flavonols (e.g., quercetin and kaempferol). Multivariate conditional logistic regression analyses were used to assess associations between breast cancer risk and urinary excretion rates of polyphenols. Urinary excretion of tea polyphenols increased with increasing tea leaves consumed among controls, but not among breast cancer cases. Compared with cases, controls had higher levels of urinary total polyphenols and tea polyphenols, particularly epicatechin. In contrast, we did not find any dose-response relationship between urinary polyphenols and breast cancer risk. Urinary excretion of epicatechin was inversely associated with breast cancer risk [odds ratio (OR) and 95% confidence interval (CI) of 0.59 (0.39-0.88) for the intermediate tertile]. In spline regression, we found an overall dose-response relationship between epicatechin level and risk of breast cancer, although it was not apparent in low and middle urinary excretion range. In conclusion, high epicatechin may be related to a reduced risk of breast cancer. Further studies are warranted to confirm our findings.

Can green tea do that? A literature review of the clinical evidence

OBJECTIVE

Habitual green tea consumption has long been associated with health benefits including chemoprevention and cardiovascular protection. This non-systematic literature review presents the clinical evidence to date.

METHOD

A literature review of peer-reviewed articles on observational and interventional studies was conducted to include green tea, its extract or its purified polyphenol (-)-epigallocatechin-3-gallate (EGCG). Electronic databases searched included PubMed (1966-2009) and the Cochrane Library (Issue 4, 2008).

RESULTS

Observational studies are inconclusive on the benefits of habitual consumption of green tea in the prevention of most cancers. However, there are trends towards prevention in breast and prostate cancers. Interventional studies have demonstrated reduction in relapses following surgical resection in colorectal adenomas and increased survival rates in epithelial ovarian cancer. Observational studies indicate that green tea may provide protection against hypertension and reduce the risk for stroke, and interventional studies are providing biochemical and physiological evidence.

CONCLUSION

Although the overall clinical evidence is inconclusive, habitual green tea consumption may be providing some level of chemoprevention in prostate and breast cancer. Green tea may also attenuate the risk factors association with the development of atherosclerosis thus reducing the incidence of cardiovascular events and stoke.

Green tea (Camellia sinensis) for the prevention of cancer

BACKGROUND

Tea is one of the most commonly consumed beverages worldwide. Teas from the plant Camellia sinensis can be grouped into green, black and oolong tea. Cross-culturally tea drinking habits vary. Camellia sinensis contains the active ingredient polyphenol, which has a subgroup known as catechins. Catechins are powerful antioxidants. It has been suggested that green tea polyphenol may inhibit cell proliferation and observational studies have suggested that green tea may have cancer-preventative effects.

OBJECTIVES

To critically assess any associations between green tea consumption and the risk of cancer incidence and mortality.

SEARCH STRATEGY

We searched eligible studies up to January 2009 in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, Amed, CancerLit, Psych INFO and Phytobase and reference lists of previous reviews and included studies.

SELECTION CRITERIA

We included all prospective, controlled interventional studies and observational studies, which either assessed the associations between green tea consumption and risk of cancer incidence or that reported on cancer mortality.

DATA COLLECTION AND ANALYSIS

At least two review authors independently applied the study criteria, extracted data and assessed methodological quality of studies. Due to the nature of included studies, which were mainly epidemiological, results were summarised descriptively according to cancer diagnosis.

MAIN RESULTS

Fifty-one studies with more than 1.6 million participants were included. Twenty-seven of them were case-control studies, 23 cohort studies and one randomised controlled trial (RCT).Twenty-seven studies tried to establish an association between green tea consumption and cancer of the digestive tract, mainly of the upper gastrointestinal tract, five with breast cancer, five with prostate cancer, three with lung cancer, two with ovarian cancer, two with urinary bladder cancer one with oral cancer, three further studies included patients with various cancer diagnoses.The methodological quality was measured with the Newcastle-Ottawa scale (NOS). The 9 nested case-control studies within prospective cohorts were of high methodological quality, 13 of medium, and 1 of low. One retrospective case-control study was of high methodological quality and 21 of medium and 5 of low.Results from studies assessing associations between green tea and risk of digestive tract cancer incidence were highly contradictory. There was limited evidence that green tea could reduce the incidence of liver cancer. The evidence for esophageal, gastric, colon, rectum, and pancreatic cancer was conflicting. In prostate cancer, observational studies with higher methodological quality and the only included RCT suggested a decreased risk in men consuming higher quantities green tea or green tea extracts. However, there was limited to moderate evidence that the consumption of green tea reduced the risk of lung cancer, especially in men, and urinary bladder cancer or that it could even increase the risk of the latter. There was moderate to strong evidence that green tea consumption does not decrease the risk of dying from gastric cancer. There was limited moderate to strong evidence for lung, pancreatic and colorectal cancer.

AUTHORS' CONCLUSIONS

There is insufficient and conflicting evidence to give any firm recommendations regarding green tea consumption for cancer prevention. The results of this review, including its trends of associations, need to be interpreted with caution and their generalisability is questionable, as the majority of included studies were carried out in Asia (n = 47) where the tea drinking culture is pronounced. Desirable green tea intake is 3 to 5 cups per day (up to 1200 ml/day), providing a minimum of 250 mg/day catechins. If not exceeding the daily recommended allowance, those who enjoy a cup of green tea should continue its consumption. Drinking green tea appears to be safe at moderate, regular and habitual use.

Green tea (Camellia sinensis) for the prevention of cancer

BACKGROUND

Tea is one of the most commonly consumed beverages worldwide. Teas from the plant Camellia sinensis can be grouped into green, black and oolong tea. Cross-culturally tea drinking habits vary. Camellia sinensis contains the active ingredient polyphenol, which has a subgroup known as catechins. Catechins are powerful antioxidants. It has been suggested that green tea polyphenol may inhibit cell proliferation and observational studies have suggested that green tea may have cancer-preventative effects.

OBJECTIVES

To critically assess any associations between green tea consumption and the risk of cancer incidence and mortality.

SEARCH STRATEGY

We searched eligible studies up to January 2009 in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, Amed, CancerLit, Psych INFO and Phytobase and reference lists of previous reviews and included studies.

SELECTION CRITERIA

We included all prospective, controlled interventional studies and observational studies, which either assessed the associations between green tea consumption and risk of cancer incidence or that reported on cancer mortality.

DATA COLLECTION AND ANALYSIS

At least two review authors independently applied the study criteria, extracted data and assessed methodological quality of studies. Due to the nature of included studies, which were mainly epidemiological, results were summarised descriptively according to cancer diagnosis.

MAIN RESULTS

Fifty-one studies with more than 1.6 million participants were included. Twenty-seven of them were case-control studies, 23 cohort studies and one randomised controlled trial (RCT).Twenty-seven studies tried to establish an association between green tea consumption and cancer of the digestive tract, mainly of the upper gastrointestinal tract, five with breast cancer, five with prostate cancer, three with lung cancer, two with ovarian cancer, two with urinary bladder cancer one with oral cancer, three further studies included patients with various cancer diagnoses.The methodological quality was measured with the Newcastle-Ottawa scale (NOS). The 9 nested case-control studies within prospective cohorts were of high methodological quality, 13 of medium, and 1 of low. One retrospective case-control study was of high methodological quality and 21 of medium and 5 of low.Results from studies assessing associations between green tea and risk of digestive tract cancer incidence were highly contradictory. There was limited evidence that green tea could reduce the incidence of liver cancer. The evidence for esophageal, gastric, colon, rectum, and pancreatic cancer was conflicting. In prostate cancer, observational studies with higher methodological quality and the only included RCT suggested a decreased risk in men consuming higher quantities green tea or green tea extracts. However, there was limited to moderate evidence that the consumption of green tea reduced the risk of lung cancer, especially in men, and urinary bladder cancer or that it could even increase the risk of the latter. There was moderate to strong evidence that green tea consumption does not decrease the risk of dying from gastric cancer. There was limited moderate to strong evidence for lung, pancreatic and colorectal cancer.

AUTHORS' CONCLUSIONS

There is insufficient and conflicting evidence to give any firm recommendations regarding green tea consumption for cancer prevention. The results of this review, including its trends of associations, need to be interpreted with caution and their generalisability is questionable, as the majority of included studies were carried out in Asia (n = 47) where the tea drinking culture is pronounced. Desirable green tea intake is 3 to 5 cups per day (up to 1200 ml/day), providing a minimum of 250 mg/day catechins. If not exceeding the daily recommended allowance, those who enjoy a cup of green tea should continue its consumption. Drinking green tea appears to be safe at moderate, regular and habitual use.

Polyphenols from green tea and pomegranate for prevention of prostate cancer

Prostate cancer (PCa) is the most common non-cutaneous cancer diagnosed in North America with similar trends in many Western countries. Geographic, epidemiological and laboratory studies suggest a role for dietary constituents in the etiology as well as prevention of PCa. The rising incidence of PCa in several countries appears to be coincidental with adoption of western lifestyle. Increase in the incidence of PCa has also been found in Asian populations migrating to the west. These facts give numerous leads to explore testable PCa prevention strategies. There is growing evidence in support of use of dietary ingredients in prevention and treatment of PCa. While substantial data exists in favor of use of polyphenols from tea as PCa chemopreventive agent, interest in anti-cancer properties of polyphenols from pomegranate has recently emerged. This review summarizes current literature on the effects of polyphenols from green tea and pomegranate against PCa.

Tea polyphenols decrease serum levels of prostate-specific antigen, hepatocyte growth factor, and vascular endothelial growth factor in prostate cancer patients and inhibit production of hepatocyte growth factor and vascular endothelial growth factor in vitro

The purpose of this study was to determine the effects of short-term supplementation with the active compounds in green tea on serum biomarkers in patients with prostate cancer. Twenty-six men with positive prostate biopsies and scheduled for radical prostatectomy were given daily doses of Polyphenon E, which contained 800 mg of (-)-epigallocatechin-3-gallate (EGCG) and lesser amounts of (-)-epicatechin, (-)-epigallocatechin, and (-)-epicatechin-3-gallate (a total of 1.3 g of tea polyphenols), until time of radical prostatectomy. Serum was collected before initiation of the drug study and on the day of prostatectomy. Serum biomarkers hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF)-I, IGF binding protein-3 (IGFBP-3), and prostate-specific antigen (PSA) were analyzed by ELISA. Toxicity was monitored primarily through liver function enzymes. Changes in serum components were analyzed statistically using the Wilcoxon signed rank test. Cancer-associated fibroblasts were treated with EGCG, and HGF and VEGF protein and mRNA levels were measured. HGF, VEGF, PSA, IGF-I, IGFBP-3, and the IGF-I/IGFBP-3 ratio decreased significantly during the study. All of the liver function tests also decreased, five of them significantly: total protein, albumin, aspartate aminotransferase, alkaline phosphatase, and amylase. The decrease in HGF and VEGF was confirmed in prostate cancer-associated fibroblasts in vitro. Our results show a significant reduction in serum levels of PSA, HGF, and VEGF in men with prostate cancer after brief treatment with EGCG (Polyphenon E), with no elevation of liver enzymes. These findings support a potential role for Polyphenon E in the treatment or prevention of prostate cancer.

Green tea consumption and breast cancer risk or recurrence: a meta-analysis

Green tea is a commonly consumed beverage in Asia and has been suggested to have anti-inflammatory and possible anti-carcinogenic properties in laboratory studies. We sought to examine the association between green tea consumption and risk of breast cancer incidence or recurrence, using all available epidemiologic evidence to date. We conducted a systematic search of five databases and performed a meta-analysis of studies of breast cancer risk and recurrence published between 1998 and 2009, encompassing 5,617 cases of breast cancer. Summary relative risks (RR) were calculated using a fixed effects model, and tests of heterogeneity across combined studies were conducted. We identified two studies of breast cancer recurrence and seven studies of breast cancer incidence. Increased green tea consumption (more than three cups a day) was inversely associated with breast cancer recurrence (Pooled RR = 0.73, 95% CI: 0.56-0.96). An analysis of case-control studies of breast cancer incidence suggested an inverse association with a pooled RR of 0.81 (95% CI: 0.75, 0.88) while no association was found among cohort studies of breast cancer incidence. Combining all studies of breast cancer incidence resulted in significant heterogeneity. Available epidemiologic evidence supports the hypothesis that increased green tea consumption may be inversely associated with risk of breast cancer recurrence. The association between green tea consumption and breast cancer incidence remains unclear based on the current evidence.

Drinking green tea modestly reduces breast cancer risk

Green tea is a commonly consumed beverage in China. Epidemiological and animal data suggest tea and tea polyphenols may be preventive against various cancers, including breast cancer. Catechol-O-methyltransferase (COMT) catalyzes catechol estrogens and tea polyphenols. The COMT rs4680 AA genotype leads to lower COMT activity, which may affect the relationship between green tea consumption and breast cancer risk. We evaluated whether regular green tea consumption was associated with breast cancer risk among 3454 incident cases and 3474 controls aged 20-74 y in a population-based case-control study conducted in Shanghai, China during 1996-2005. All participants were interviewed in person about green tea consumption habits, including age of initiation, duration of use, brew strength, and quantity of tea. Odds ratios (OR) and 95% CI were calculated for green tea consumption measures and adjusted for age and other confounding factors. Compared with nondrinkers, regular drinking of green tea was associated with a slightly decreased risk for breast cancer (OR, 0.88; 95% CI, 0.79-0.98). Among premenopausal women, reduced risk was observed for years of green tea drinking (P-trend = 0.02) and a dose-response relationship with the amount of tea consumed per month was also observed (P-trend = 0.046). COMT rs4680 genotypes did not have a modifying effect on the association of green tea intake with breast cancer risk. Drinking green tea may be weakly associated with a decreased risk of breast cancer.

Green tea intake, MTHFR/TYMS genotype and breast cancer risk: the Singapore Chinese Health Study

The tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) has been reported to act as a cancer preventive agent through folate pathway inhibition in experimental studies. We hypothesized that if folate pathway inhibition is the mechanism of cancer preventive activities of EGCG, then the protective effect against breast cancer would be stronger among women with low dietary folate intake and the high-activity methylenetetrahydrofolate reductase (MTHFR) and thymidylate synthase (TYMS) genotypes. In a nested case-control study of 380 women with incident breast cancer and 662 controls within the Singapore Chinese Health Study, we found no association between either green tea intake or gene polymorphisms of MTHFR (C677T and A1298C) and TYMS (1494 ins/del) and breast cancer risk. However, among women with low folate intake (<133.4 microg/day), weekly/daily green tea intake was inversely associated with breast cancer risk compared with less green tea intake [odds ratio (OR) = 0.45, 95% confidence interval (CI) = 0.26-0.79, P for interaction = 0.02]. Among women with high folate intake (>or=133.4 microg/day), green tea intake was not associated with breast cancer. Similarly, among women possessing the high-activity MTHFR/TYMS genotypes (0-1 variant allele), weekly/daily versus less frequent green tea intake was associated with lower breast cancer risk (OR = 0.66, 95% CI = 0.45-0.98), which was observed even more strongly among those who also had low folate intake (OR = 0.44, 95% CI = 0.22-0.89) than high folate intake (OR = 0.92, 95% CI = 0.55-1.54). This association was not observed among women possessing the low-activity genotypes (2-4 variant alleles). Our findings suggest that folate pathway inhibition may be one mechanism through which green tea protects against breast cancer in humans.

The sensitization of glioma cells to cisplatin and tamoxifen by the use of catechin

Telomerase expression strongly correlates with the grade of malignancy in glioma with inhibition illustrating a definite increase in chemosensitivity. This study was designed to investigate the effects of a green tea derivative, epigallocatechin-3-gallate (EGCG); together with either cisplatin or tamoxifen in glioma, and to investigate whether these effects are mediated through telomerase suppression. EGCG showed a significant cytotoxic effect on 1321N1 cells after 24 h and on U87-MG cells after 72 h (P < 0.001) without significantly affecting the normal astrocytes. Treatment with EGCG inhibited telomerase expression significantly (P < 0.01) and enhanced the effect of cisplatin and tamoxifen in both 1321N1 (P < 0.01) and U87-MG (P < 0.001) cells. EGCG, as a natural product has enormous potential to be an anti-cancer agent capable of enhancing tumour cell sensitivity to therapy.

Precancerous carcinogenesis of human breast epithelial cells by chronic exposure to benzo[a]pyrene

To understand carcinogenesis of human breast epithelial cells induced by chronic exposure to environmental pollutants, we studied biological and molecular changes in progression of cellular carcinogenesis induced by accumulated exposures to the potent environmental carcinogen benzo[a]pyrene (B[a]P). Increasing exposures of human breast epithelial MCF10A cells to B[a]P at picomolar concentrations resulted in cellular transformation from a noncancerous stage to precancerous substages, in which cells acquired the cancerous abilities of a reduced dependence on growth factors, anchorage-independent growth, and disruption in acini formation on reconstituted basement membranes. Using cDNA microarrays, we detected seven upregulated genes related to human cancers in B[a]P-transformed MCF10A cells. Using this model, we verified that green tea catechin significantly (P < 0.05) suppressed B[a]P-induced carcinogenesis. Our studies indicate that this cellular model may serve as a cost-efficient, in vitro system, mimicking the chronic carcinogenesis of breast cells that likely occurs in early stages of carcinogenesis in vivo, to identify agents that inhibit cellular carcinogenesis.

Tea or coffee? A case study on evidence for dietary advice

The present paper explores the level of evidence required to justify giving dietary advice to the public. There are important practical differences between the development of public health nutrition guidelines and guidelines for clinical practice. While the gold standard for evidence for clinical practice guidelines is a meta-analysis of a number of randomised controlled trials, this is often unrealistic and sometimes unethical for the evaluation of public health nutrition interventions. Hence, epidemiological studies make up the bulk of evidence for nutrition guidelines. Tea and coffee are an interesting case study in relation to this issue. They are two of the most commonly consumed beverages worldwide, yet there is little dietary advice on their use. The evidence for a relationship between coffee or tea consumption and several diseases is discussed. The available studies, predominantly epidemiological, together with animal and in vitro studies, indicate that coffee and tea are both safe beverages. However, tea is the healthier option because it has a possible role in the prevention of several cancers and CVD. While the evidence for such relationships is not strong, the public will continue to drink both tea and coffee, and will continue to ask nutritionists to make recommendations. It is therefore argued that advice should be given on the best available data, as waiting for complete data to become available could have severe consequences for public health.

The prevalence of intrinsic subtypes and prognosis in breast cancer patients of different races

A recent report indicated that a high prevalence of basal-like breast tumors (estrogen receptor [ER]-negative, progesterone receptor [PR]-negative, human epidermal growth factor receptor [HER] 2-negative, and cytokeratin 5/6-positive and/or HER1-positive) could contribute to a poor prognosis in African American women with breast cancer. It has been reported that Japanese women with breast cancer have a significantly better survival rate than other races in the USA. These findings suggest that breast cancers in Japanese women have favorable biological characteristics. To clarify this hypothesis, we conducted a cohort study to investigate the prevalence of intrinsic subtypes and prognosis for each subtype in 793 Japanese patients. This study revealed a very low prevalence (only 8%) of basal-like breast tumors with aggressive biological characteristics in Japanese patients. Survival analysis showed a significantly poorer prognosis in patients with basal-like tumors than in those with luminal A tumors (ER- and/or PR-positive, and HER2-negative) with favorable biological characteristics. These findings support the hypothesis that breast cancers in Japanese women have more favorable biological characteristics and a better prognosis than those in other races. In conclusion, the prevalence of basal-like breast tumors could influence the prognosis of breast cancer patients of different races. The prevalence of intrinsic subtypes should be taken into account when analyzing survival data in a multi-racial/international clinical study.

Diet and breast cancer: a review of the prospective observational studies

The role of diet for the risk of breast cancer is of great interest as a potentially modifiable risk factor. The evidence from prospective observational studies was reviewed and summarized on selected dietary factors, gene-diet interactions, and breast cancer incidence. Dietary factors were considered that, based on their nutritional constituents, are of particular interest in the context of breast cancer: fat intake, biomarkers of fat intake, fruit and vegetable consumption, antioxidant vitamins (vitamins A, C, E, and beta-carotene), serum antioxidants, carbohydrate intake, glycemic index and glycemic load, dairy consumption (including vitamin D), consumption of soy products and isoflavones, green tea, heterocyclic amines, and adolescent diet. The PubMed database was searched for all prospective studies that relate these dietary items to the incidence of breast cancer or consider gene-diet interactions. Among the prospective epidemiologic studies conducted on diet and breast cancer incidence and gene-diet interactions and breast cancer incidence, to date there is no association that is consistent, strong, and statistically significant, with the exception of alcohol intake, overweight, and weight gain. The apparent lack of association between diet and breast cancer may reflect a true absence of association between diet and breast cancer incidence or may be due to measurement error exceeding the variation in the diet studied, lack of sufficient follow-up, and focus on an age range of low susceptibility. The risk of breast cancer can be reduced by avoidance of weight gain in adulthood and limiting the consumption of alcohol.

Inhibition of carcinogenesis by tea constituents

The possible cancer preventive activity of tea has received much attention in recent years. The inhibitory activities of tea and tea constituents against carcinogenesis at different organ sites have been demonstrated in many animal models. The effect of tea consumption on human cancers, however, remains inconclusive. The mechanisms of action of tea polyphenols, especially EGCG, the most abundant and active catechin, have been extensively investigated. Most of the studies, however, were based on cell culture systems, and these mechanisms need to be evaluated and verified in animal models or humans in order to gain more understanding on the effect of tea consumption on human cancer. Human intervention trials are warranted to determine the possible prevention of cancer of specific sites by preparation of tea constituents.

Reading the tea leaves: anticarcinogenic properties of (-)-epigallocatechin-3-gallate

Green tea is an extremely popular beverage worldwide. Derivatives of green tea, particularly (-)-epigallocatechin-3-gallate (EGCG), have been proposed to have anticarcinogenic properties based on preclinical, observational, and clinical trial data. To summarize, clarify, and extend current knowledge, we conducted a comprehensive search of the PubMed database and other secondary data sources, as appropriate, regarding the chemopreventive potential of EGCG. Apparently, EGCG functions as an antioxidant, preventing oxidative damage in healthy cells, but also as an antiangiogenic agent, preventing tumors from developing a blood supply needed to grow larger. Furthermore, EGCG may stimulate apoptosis in cancerous cells by negatively regulating the cell cycle to prevent continued division. Finally, EGCG exhibits antibacterial activity, which may be implicated in the prevention of gastric cancer. Although in vitro research of the anticarcinogenic properties of EGCG seems promising, many diverse and unknown factors may influence its in vivo activity in animal and human models. Some epidemiological studies suggest that green tea compounds could protect against cancer, but existing data are inconsistent, and limitations in study design hinder full interpretation and generalizability of the published observational findings. Several clinical trials with green tea derivatives are ongoing, and further research should help to clarify the clinical potential of EGCG for chemoprevention and/or chemotherapy applications.

Inhibition of mammary tumorigenesis in the C3(1)/SV40 mouse model by green tea

Previous studies show inhibitory effects of green tea in chemically induced mammary tumors or human tumor explants, but not in spontaneous tumor models that are more representative of human breast cancer. The C3(1)/SV40 mouse model is particularly suited for breast cancer prevention studies because it produces spontaneous ductal adenocarcinomas and a predictable time course for mammary tumorigenesis through a multistage progression similar to that occurring in humans. We therefore used this model to test the chemoprotective effects of green tea. Administration of 0.5% Polyphenon E (Poly E) (a standardized preparation of green tea extract) in drinking water delayed tumor onset and suppressed tumor growth by 40%, compared to tap water-fed animals, with no adverse side effects. Histological analysis of mammary glands showed that green tea slowed the progression of ductal lesions to advanced mammary intraepithelial neoplasias and suppressed tumor invasiveness. Green tea inhibited the proliferation of ductal epithelial cells and tumors and, overall, disrupted post-pubertal ductal growth. Immunohistochemical analyses also demonstrated that green tea inhibited angiogenesis through a decrease in both ductal epithelial and stromal VEGF expression and a decrease in intratumoral microvascular density. Our data strongly support the potential use of green tea as a breast cancer chemopreventive agent.

A strategy for controlling potential interactions between natural health products and chemotherapy: a review in pediatric oncology

The high prevalence of complementary and alternative medicine use including natural health products (NHPs) in the pediatric oncology population is well established. The potential for concurrent use of NHPs with conventional chemotherapy necessitates physician awareness regarding the potential risks and benefits that might come from this coadministration. Knowledge of interactions between NHPs and chemotherapy is poorly characterized; however, an understanding of potential mechanisms of interaction by researchers and clinicians is important. Concerns regarding the use of antioxidants during chemotherapy are controversial and evidence exists to support both adherents and detractors in this debate. Our review addresses issues regarding potential interactions between NHPs and chemotherapies used in pediatric oncology from a pharmacokinetic and pharmacodynamic perspective. Examples of combinations of NHP and chemotherapies are briefly presented in addition to a strategy to avoid (or induce) a possible interaction between a NHP and chemotherapy. In conclusion, more clinical research is needed to substantiate or preclude the use of NHPs in the treatment of cancer and especially in combination with chemotherapy.

Smoking, alcohol drinking, green tea consumption and the risk of esophageal cancer in Japanese men

BACKGROUND

Although smoking and alcohol drinking are established risk factors of esophageal cancer, their public health impact is unclear. Furthermore, the effect of green tea is controversial.

METHODS

The present study was based on a pooled analysis of two prospective cohort studies. A self-administered questionnaire about health habits was distributed to 9,008 men in Cohort 1 and 17,715 men in Cohort 2, aged 40 years or older, with no previous history of cancer. We identified 38 and 40 patient cases with esophageal cancer among the subjects in Cohort 1 (9.0 years of follow-up) and Cohort 2 (7.6 years of follow-up), respectively. Cox proportional hazards regression was used to estimate hazard ratios (HRs) of the risk of esophageal cancer incidence.

RESULTS

Cigarette smoking, alcohol drinking and green tea consumption were significantly associated with an increased risk of esophageal cancer. Compared with men who had never smoked, never drunk alcohol or green tea, the pooled multivariate HRs (95% confidence intervals) were 5.09 (1.80-14.40) (p for trend <0.0001), 2.73 (1.55-4.81) (p for trend=0.0002), or 1.67 (0.89-3.16) (P for trend=0.04) for men who were currently smoking ≥20 cigarettes/day, drinking alcohol daily, or drinking ≥5 cups green tea/day, respectively. The population attributable fractions of esophageal cancer incidence that was attributable to smoking, alcohol drinking and green tea consumption were 72.0%, 48.6%, and 22.1%, respectively.

CONCLUSIONS

Among the variables studied, smoking has the largest public health impact on esophageal cancer incidence in Japanese men, followed by alcohol drinking and green tea drinking.

Tea, hormone-related cancers and endogenous hormone levels

Tea is one of the most popular beverages consumed around the world, second only to water. There has been substantial interest in the potential role of tea in cancer prevention, particularly in respiratory and gastrointestinal tract cancers. Recent epidemiological data have linked tea intake to reduced risk of hormone-related cancers, including breast, ovarian and prostate cancers. Based on sparse data, there is suggestion that tea intake may influence circulating hormone levels, providing a plausible mechanism whereby tea intake may influence risk of hormone-related cancers. The major objectives of this paper are to review the epidemiological evidence on tea and risk of breast, ovarian, and prostate cancers as well as the human and non-human studies on tea and circulating hormone levels. We pay special attention to some of the limitations of the human studies and discuss future research needs.