Case–control study of green tea consumption and the risk of endometrial endometrioid adenocarcinoma

Green Tea in Reproductive Cancers: Could Treatment Be as Simple?

Green tea originates from the tea plant Camellia sinensis and is one of the most widely consumed beverages worldwide. Green tea polyphenols, commonly known as catechins, are the major bioactive ingredients and account for green tea's unique health benefits. Epigallocatechin-3-gallate (EGCG), is the most potent catechin derivative and has been widely studied for its pro- and anti-oxidative effects. This review summarizes the chemical and chemopreventive properties of green tea in the context of female reproductive cancers. A comprehensive search of PubMed and Google Scholar up to December 2022 was conducted. All original and review articles related to green tea or EGCG, and gynecological cancers published in English were included. The findings of several in vitro, in vivo, and epidemiological studies examining the effect of green tea on reproductive cancers, including ovarian, cervical, endometrial, and vulvar cancers, are presented. Studies have shown that this compound targets specific receptors and intracellular signaling pathways involved in cancer pathogenesis. The potential benefits of using green tea in the treatment of reproductive cancers, alone or in conjunction with chemotherapeutic agents, are examined, shedding light on new therapeutic strategies for the management of female reproductive cancers.

Antioxidative, Anti-Inflammatory, Anti-Obesogenic, and Antidiabetic Properties of Tea Polyphenols-The Positive Impact of Regular Tea Consumption as an Element of Prophylaxis and Pharmacotherapy Support in Endometrial Cancer

Endometrial cancer (EC) is second only to cervical carcinoma among the most commonly diagnosed malignant tumours of the female reproductive system. The available literature provides evidence for the involvement of 32 genes in the hereditary incidence of EC. The physiological markers of EC and coexisting diet-dependent maladies include antioxidative system disorders but also progressing inflammation; hence, the main forms of prophylaxis and pharmacotherapy ought to include a diet rich in substances aiding the organism’s response to this type of disorder, with a particular focus on ones suitable for lifelong consumption. Tea polyphenols satisfy those requirements due to their proven antioxidative, anti-inflammatory, anti-obesogenic, and antidiabetic properties. Practitioners ought to consider promoting tea consumption among individuals genetically predisposed for EC, particularly given its low cost, accessibility, confirmed health benefits, and above all, suitability for long-term consumption regardless of the patient’s age. The aim of this paper is to analyse the potential usability of tea as an element of prophylaxis and pharmacotherapy support in EC patients. The analysis is based on information available from worldwide literature published in the last 15 years.

A Narrative Review of the Role of Diet and Lifestyle Factors in the Development and Prevention of Endometrial Cancer

Simple Summary

The incidence and prevalence of endometrial cancer is increasing globally. The main factors involved in this increase have been the way women live today and what they eat and drink. In fact, the obesity pandemic that is sweeping across the planet is considered to be the main contributory feature. This review aims to introduce to a new audience, those that are not experts in the field, what is known about the different types of endometrial cancer and the mechanisms for their induction and protection. We also seek to summarise the existing knowledge on dietary and lifestyle factors that prevent endometrial development in susceptible populations and identify the main problem in this arena; the paucity of research studies and clinical trials that investigate the interaction(s) between diet, lifestyle and endometrial cancer risk whilst highlighting those areas of promise that should be further investigated.

Abstract

Endometrial cancer is the most common cancer affecting the reproductive organs of women living in higher-income countries. Apart from hormonal influences and genetic predisposition, obesity and metabolic syndrome are increasingly recognised as major factors in endometrial cancer risk, due to changes in lifestyle and diet, whereby high glycaemic index and lipid deposition are prevalent. This is especially true in countries where micronutrients, such as vitamins and minerals are exchanged for high calorific diets and a sedentary lifestyle. In this review, we will survey the currently known lifestyle factors, dietary requirements and hormonal changes that increase an individual’s risk for endometrial cancer and discuss their relevance for clinical management. We also examine the evidence that everyday factors and clinical interventions have on reducing that risk, such that informed healthy choices can be made. In this narrative review, we thus summarise the dietary and lifestyle factors that promote and prevent the incidence of endometrial cancer.

Green tea (Camellia sinensis) for the prevention of cancer

BACKGROUND

This review is an update of a previously published review in the Cochrane Database of Systematic Reviews (2009, Issue 3).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, and drinking habits vary cross-culturally. C sinensis contains polyphenols, one subgroup being catechins. Catechins are powerful antioxidants, and laboratory studies have suggested that these compounds may inhibit cancer cell proliferation. Some experimental and nonexperimental epidemiological studies have suggested that green tea may have cancer-preventative effects.

OBJECTIVES

To assess possible associations between green tea consumption and the risk of cancer incidence and mortality as primary outcomes, and safety data and quality of life as secondary outcomes.

SEARCH METHODS

We searched eligible studies up to January 2019 in CENTRAL, MEDLINE, Embase, ClinicalTrials.gov, and reference lists of previous reviews and included studies.

SELECTION CRITERIA

We included all epidemiological studies, experimental (i.e. randomised controlled trials (RCTs)) and nonexperimental (non-randomised studies, i.e. observational studies with both cohort and case-control design) that investigated the association of green tea consumption with cancer risk or quality of life, or both.

DATA COLLECTION AND ANALYSIS

Two or more review authors independently applied the study criteria, extracted data and assessed methodological quality of studies. We summarised the results according to diagnosis of cancer type.

MAIN RESULTS

In this review update, we included in total 142 completed studies (11 experimental and 131 nonexperimental) and two ongoing studies. This is an additional 10 experimental and 85 nonexperimental studies from those included in the previous version of the review. Eleven experimental studies allocated a total of 1795 participants to either green tea extract or placebo, all demonstrating an overall high methodological quality based on 'Risk of bias' assessment. For incident prostate cancer, the summary risk ratio (RR) in the green tea-supplemented participants was 0.50 (95% confidence interval (CI) 0.18 to 1.36), based on three studies and involving 201 participants (low-certainty evidence). The summary RR for gynaecological cancer was 1.50 (95% CI 0.41 to 5.48; 2 studies, 1157 participants; low-certainty evidence). No evidence of effect of non-melanoma skin cancer emerged (summary RR 1.00, 95% CI 0.06 to 15.92; 1 study, 1075 participants; low-certainty evidence). In addition, adverse effects of green tea extract intake were reported, including gastrointestinal disorders, elevation of liver enzymes, and, more rarely, insomnia, raised blood pressure and skin/subcutaneous reactions. Consumption of green tea extracts induced a slight improvement in quality of life, compared with placebo, based on three experimental studies. In nonexperimental studies, we included over 1,100,000 participants from 46 cohort studies and 85 case-control studies, which were on average of intermediate to high methodological quality based on Newcastle-Ottawa Scale 'Risk of bias' assessment. When comparing the highest intake of green tea with the lowest, we found a lower overall cancer incidence (summary RR 0.83, 95% CI 0.65 to 1.07), based on three studies, involving 52,479 participants (low-certainty evidence). Conversely, we found no association between green tea consumption and cancer-related mortality (summary RR 0.99, 95% CI 0.91 to 1.07), based on eight studies and 504,366 participants (low-certainty evidence). For most of the site-specific cancers we observed a decreased RR in the highest category of green tea consumption compared with the lowest one. After stratifying the analysis according to study design, we found strongly conflicting results for some cancer sites: oesophageal, prostate and urinary tract cancer, and leukaemia showed an increased RR in cohort studies and a decreased RR or no difference in case-control studies.

AUTHORS' CONCLUSIONS

Overall, findings from experimental and nonexperimental epidemiological studies yielded inconsistent results, thus providing limited evidence for the beneficial effect of green tea consumption on the overall risk of cancer or on specific cancer sites. Some evidence of a beneficial effect of green tea at some cancer sites emerged from the RCTs and from case-control studies, but their methodological limitations, such as the low number and size of the studies, and the inconsistencies with the results of cohort studies, limit the interpretability of the RR estimates. The studies also indicated the occurrence of several side effects associated with high intakes of green tea. In addition, the majority of included studies were carried out in Asian populations characterised by a high intake of green tea, thus limiting the generalisability of the findings to other populations. Well conducted and adequately powered RCTs would be needed to draw conclusions on the possible beneficial effects of green tea consumption on cancer risk.

A Review of Integrative Medicine in Gynaecological Oncology

In recent years complementary and alternative medicine (CAM) has increasingly been the focus of international research. Numerous subsidised trials (7903) and systematic reviews (651) have been published, and the evidence is starting to be integrated into treatment guidelines. However, due to insufficient evidence and/or insufficient good quality evidence, this has mostly not translated to practice recommendations in reviews by the Cochrane collaboration gynaecology group. There is nevertheless a not insignificant number of CAM providers and users. The percentage of oncology patients who use CAM varies between 5 and 90 %. Doctors have been identified as the main providers of CAM. Half of gynaecologists offer CAM because of personal conviction or on suggestion from colleagues. This must be viewed in a critical light, since CAM is mostly practiced without appropriate training, often without sufficient evidence for a given method - and where evidence exists, practice guidelines are lacking - and lack of safety or efficacy testing. The combination of patient demand and lucrativeness for doctors/alternative medicine practitioners, both based on supposed effectiveness CAM, often leads to its indiscriminate use with uncertain outcomes and significant cost for patients. On the other hand there is published, positive level I evidence for a number of CAM treatment forms. The aim of this article is therefore to review the available evidence for CAM in gynaecological oncology practice. The continued need for research is highlighted, as is the need to integrate practices supported by good evidence into conventional gynaecological oncology.

Green tea, black tea consumption and risk of endometrial cancer: a systematic review and meta-analysis

BACKGROUND

Several studies have assessed the association between green and black tea consumption and the risk of endometrial cancer (EC) and have yielded inconsistent results.

OBJECTIVE

The purpose of this meta-analysis is to systematically analyze the effect of green tea and black tea on EC risk.

METHODS

PubMed, Embase, Cochrane Library and China Biological Medicine Database were searched through February 2, 2015 to identify studies that met pre-stated inclusion criteria. Overall relative risk (RR) was estimated based on the highest and lowest levels of green/black tea consumption. Dose-response relationships were evaluated with the data from categories of green/black tea intake in each study.

RESULTS

For green tea, the summary RR indicated that the highest green tea consumption was associated with a reduced risk of EC (RR 0.78, 95 % CI 0.66-0.92). Furthermore, an increase in green tea consumption of one cup per day was associated with an 11 % decreased risk of developing EC. (RR 0.89, 95 % CI 0.84-0.94). For black tea, no statistically significant association was observed in the meta-analysis (highest versus non/lowest, RR 0.99, 95 % CI 0.79-1.23; increment of one cup/day, RR 0.99, 95 % CI 0.94-1.03). The power of the estimate of green tea and black tea with risk of EC was 84.33 and 5.07 %, respectively. The quality of evidence for the association between green and black tea with EC risk was moderate and very low, respectively.

CONCLUSIONS

The results from this meta-analysis indicate that green tea, but not black tea, may be related to a reduction of EC risk. Large population-based randomized controlled trials and large prospective cohort studies are required to obtain a definitive conclusion and determine the mechanisms underlying this association.

Evaluation of cost versus antioxidant determinants in green tea dietary supplements

OBJECTIVE

To investigate the association between cost and (a) chemical constituents and (b) antioxidant activity as quality determinants of select green tea supplements available in the United States.

DESIGN/SETTING

Laboratory analysis of green tea using HPLC and antioxidant assay methods.

MAIN OUTCOME MEASURES

Correlation between selected quality parameters and daily cost based on the serving size as stated in the label. Quality was defined in terms of (a) catechin levels (validated high-performance liquid chromatography method), (b) total phenolic content (Folin-Ciocalteu method), and (c) antioxidant activity (total antioxidant capacity and diphenylpicryl hydrazyl free-radical scavenging).

RESULTS

A wide range of variation in marker levels and antioxidant activity was observed in the evaluated products. Catechin levels correlated well with the total phenolic content in each product while antioxidant activities were not as consistent when correlated with catechin/polyphenol levels. There was also a low correlation between product cost and quality.

CONCLUSION

Our results indicate that product cost does not always reflect quality, at least within the selected range of products. Thus, for a pharmacist to be able to recommend quality green tea dietary supplements, factors other than cost should be considered.

Tea Consumption and Endometrial Cancer Risk: Meta-Analysis of Prospective Cohort Studies

Several lines of evidence suggest that tea consumption may reduce the risk of endometrial cancer due to antioxidant properties of tea, but the results of prospective data to date are inconsistent. We thus conducted a meta-analysis of prospective cohort studies to examine the relationship between tea consumption and endometrial cancer risk, using a random-effects model. We identified 5 eligible cohort studies, which included 231,870 female participants and 1831 cases for endometrial cancer. The pooled relative risk (RR) for the highest (median 2 cups/day) vs. no/lowest category of tea consumption on endometrial cancer risk was 0.95 [95% confidence interval (CI): 0.80-1.12] with no significant heterogeneity (P for heterogeneity = 0.68, I(2) = 0.0%). By country of origin, the pooled RR of 3 studies conducted in the United States was 1.00 (95% CI: 0.83-1.21), in which black tea was consumed by most people. Because of limited data on Asian population, the association of green tea on endometrial cancer was not calculated separately. There was no indication of publication bias (Begg's P = 0.46; Egger's P = 0.43). Our findings from prospective data do not support a role of tea consumption in endometrial carcinogenesis. More prospective cohort studies with green tea consumption should be conducted.

Tea and coffee and risk of endometrial cancer: cohort study and meta-analysis

BACKGROUND

Previous reports, mostly from retrospective studies, suggested possible protective effects of both tea and coffee against endometrial cancer, but recent reports from prospective studies generally showed weaker or null associations.

OBJECTIVES

We investigated endometrial cancer risk in relation to tea and coffee consumption in a large prospective study and did a meta-analysis of published results.

DESIGN

Daily consumption of tea and coffee was recorded in 560,356 participants (without a hysterectomy) in the UK Million Women Study of whom 4067 women developed endometrial cancer during 5.2 million person-years of follow up (average: 9.3 y per woman).

RESULTS

With the use of Cox proportional hazards regression, we showed no significant association between endometrial cancer risk and consumption of either tea (multivariate adjusted RR per cup daily: 1.00; 95% CI: 0.98, 1.02) or coffee (RR per cup daily: 0.98; 95% CI: 0.96, 1.01). Our meta-analyses showed no significant association between endometrial cancer risk and tea consumption and a weak association for coffee consumption in prospective studies, but there may have been selective publication of only part of the evidence.

CONCLUSIONS

There is little or no association between tea consumption and endometrial cancer risk. If there is any association with coffee consumption, it appears to be weak.

Endometrial cancer in relation to coffee, tea, and caffeine consumption: a prospective cohort study among middle-aged women in Sweden

This study aimed to add to prospective data on the possible inverse association between coffee consumption and endometrial cancer risk, already supported by several case-control studies. Coffee and tea consumption and possible confounding factors were assessed among 42,270 women aged 30-49 years at enrollment in 1991-1992 in the Swedish Women's Lifestyle and Health cohort study, with complete follow-up through 2009. We calculated caffeine intake per day; Cox proportional hazard models were used to estimate multivariable relative risks (mRR) for endometrial cancer with 95% confidence intervals (CIs). One hundred forty-four endometrial cancers were diagnosed during follow-up. Women with and without endometrial cancer had a similar mean daily coffee consumption (549 vs. 547 g), tea consumption (104 vs. 115 g), and caffeine intake (405 vs. 406 mg). Compared to those consuming <2 cups of coffee per day, women consuming >3 cups had a mRR of 1.56 (95% CI: 0.94-2.59; P for trend = 0.17). Compared with the lowest tertile of caffeine intake, the highest tertile had a mRR of 1.32 (95% CI: 0.87-1.99; P for trend = 0.27). Our study provides no convincing evidence of an association between coffee consumption, tea consumption, or caffeine intake and endometrial cancer risk among middle-aged women.

Food intake and the risk of endometrial endometrioid adenocarcinoma in Japanese women

The present study examined the association between food intake and endometrial cancer restricted to endometrial endometrioid adenocarcinoma (EEA) using a case-control study in Japanese women. One hundred sixty-one cases and 380 controls who completed a questionnaire regarding demographic, lifestyle, and food frequency questionnaire were analyzed. Odds ratio (OR) between selected food intakes and EEA were calculated by logistic regression analysis. After adjustment putative confounding factors, the higher intakes of vegetables [odds ratio (OR) = 0.47, 95% confidence interval (CI) = 0.26-0.83], peanuts (OR = 0.48, CI = 0.27-0.86), fish (OR = 0.52, CI = 0.29-0.93), boiled egg (OR = 0.24, CI = 0.33-0.92), instant noodles (OR = 1.94, CI = 1.12-3.34), instant food items (OR = 2.21, CI = 1.31-3.74), and deep-fried foods (OR = 2.87, CI = 1.58-5.21) were associated with a risk for EEA. The inverse association with a risk of EEA was also seen in higher intakes (g/1000 kcal) for vegetables (0.45, CI = 0.25-0.81) and fish (0.53, CI = 0.30-0.94) as compare to lower intake. Higher intake of vegetables, peanuts, fish, and boiled egg was associated with a reduced risk for EEA, whereas instant noodles, instant food items, and deep-fried foods was associated with an increased risk for EAA as compared to lower levels of intake.

Meta-analysis of green tea drinking and the prevalence of gynecological tumors in women

We performed a meta-analysis of the correlation between drinking green tea and the risk of female ovarian tumors. Related literature (2000-2010) was retrieved from PubMed, EMbase, CBMdisc, CNKI, and Wanfang databases. The relationship between the prevalence of ovarian cancer and drinking tea in cohort studies was explored. RevMan5.1.0 software was used for the meta-analysis. A total of 6 case control studies and cohort studies were included. A total of 9113 participants, 3842 cases, and 5271 control cases were included in our analysis. Our analysis indicates that drinking green tea can significantly decrease the risk of ovarian cancer (odds ratio = 0.81; 95% confidence interval = 0.73-0.89; P < .0001). Further research is needed to explore the relationship between drinking green tea and the risk of ovarian tumor in different groups of people and with different tea types and dosages.

A prospective cohort study of coffee consumption and risk of endometrial cancer over a 26-year follow-up

BACKGROUND

Coffee has been reported to lower levels of estrogen and insulin, two hormones implicated in endometrial carcinogenesis, but prospective data on the relation between coffee consumption and risk of endometrial cancer are limited.

METHODS

We prospectively assessed coffee consumption in relation to endometrial cancer risk in the Nurses' Health Study (NHS) with 67,470 female participants aged 34 to 59 in 1980. Cumulative average coffee intake was calculated with all available questionnaires to assess long-term effects. Cox regression models were used to calculate incidence rate ratios (RR), controlling for other risk factors.

RESULTS

Fewer than 4 cups of coffee per day were not associated with endometrial cancer risk. However, women who consumed 4 or more cups of coffee had 25% lower risk of endometrial cancer than those who consumed less than 1 cup per day (multivariable RR = 0.75; 95% CI = 0.57-0.97; P(trend) = 0.02). We found the similar association with caffeinated coffee consumption (RR for ≥4 vs. <1 cup/d = 0.70; 95% CI = 0.51-0.95). For decaffeinated coffee consumption, a suggestive inverse association was found among women who consumed 2 or more cups per day versus <1 cup/mo. Tea consumption was not associated with endometrial cancer risk.

CONCLUSIONS

These prospective data suggest that four or more cups of coffee per day are associated with a lower risk of endometrial cancer.

IMPACT

Drinking of coffee, given its widespread consumption, might be an additional strategy to reduce endometrial cancer risk. However, addition of substantial sugar and cream to coffee could offset any potential benefits.

Green and black tea in relation to gynecologic cancers

SCOPE

Observational studies have evaluated the relationship between green tea intake and cancers of the ovary and endometrium, but we are not aware of the published studies on green tea intake and risk of human papillomavirus (HPV)-related cancers of the cervix, vagina, or vulva.

METHODS AND RESULTS

A critical review of the published literature on tea intake and risk of ovarian and endometrial cancers was conducted. In meta-analyses, we report inverse associations for green tea intake and risk of ovarian cancer (odds ratio [OR]=0.66; 95% confidence interval [CI]: 0.54, 0.80), and for green tea and risk of endometrial cancer (OR=0.78, 95% CI: 0.62, 0.98). There was no association for black tea and ovarian cancer risk (OR=0.94, 95% CI: 0.87, 1.02) and a positive association with endometrial cancer risk (OR=1.20, 95% CI: 1.05, 1.38). We summarized the experimental evidence supporting the antiviral and immunomodulatory activities of green tea catechins, and results from randomized clinical trials that demonstrated green tea catechin efficacy on treatment of cervical lesions and external genital warts.

CONCLUSION

Observational data support a protective role of green tea on risk of ovarian and endometrial cancers. Observational data are needed to evaluate whether green tea reduces risk of human papillomavirus-related cancers.

Green tea, phytic acid, and inositol in combination reduced the incidence of azoxymethane-induced colon tumors in Fisher 344 male rats

Experimental as well as epidemiologic studies in human populations provide evidence that consumption of phytochemicals reduces the incidence of degenerative diseases. Green tea (GT) catechins are known for their antioxidative potential. Phytic acid (PA) also acts as a natural antioxidant and may have numerous health benefits. This experiment was designed to investigate the inhibitory effects of combinations of 1% and 2% GT, PA, and inositol (I) in reducing the incidence of azoxymethane-induced colon tumors in Fisher 344 male rats. After an acclimatization period of 1 week, nine groups of rats (15 rats per group) were initially assigned to consume AIN 93 G diet and later AIN 93 M diet after 20 weeks of age. Treatments were given in drinking water. All rats received azoxymethane injections (16 mg/kg of body weight) subcutaneously at 7 and 8 weeks of age. Rats were killed at 45 weeks of age by CO(2) euthanasia. Tumor incidence (93.76%) and the number of tumors per tumor-bearing rat ratio (2.25) were significantly (P<.05) higher in the control group compared with treatment groups. Glutathione S-transferase activity was significantly (P<.05) higher in rats fed combinations of 2% GT+PA+I and GT+PA (33.25 ± 1.23 and 29.83 ± 1.10 μmol/mL, respectively) compared with other groups. These findings suggest that the synergistic effect of the 2% level of GT, PA, and I may reduce the incidence of colon tumors and therefore have potential as a chemopreventive agent.

Coffee and tea consumption and endometrial cancer risk in a population-based study in New Jersey

We evaluated the role of tea and coffee and substances added (sugar/honey, creamers, and milk) on endometrial cancer risk in a population-based case-control study in six counties in New Jersey, including 417 cases and 395 controls. Multivariate odds ratios (OR) and 95% confidence intervals (CI) were computed using unconditional logistic regression. There was a moderate inverse association with coffee consumption, with an adjusted OR of 0.65 (95% CI: 0.36-1.17) for women who reported more than two cups/day of coffee compared to none. Tea consumption appeared to increase risk (OR: 1.93; 95% CI: 1.08-3.45), but after including the variables sugar/honey and cream/milk added to tea in the model, the risk estimate was attenuated and no longer statistically significant (OR: 1.77; 95% CI: 0.96-3.28 for those consuming more than one cup/day of tea compared to nonusers). There was a suggestion of a decreased risk associated with green tea, but the confidence interval included one (adjusted OR for one or more cups/week vs. none: 0.75; 95% CI: 0.48-1.18). We found an association with adding sugar/honey to tea, with those adding two or more teaspoons/cup having an OR of 2.66 (95% CI: 1.42-4.98; p for trend <0.01) after adjusting for relevant confounders. For sugar/honey added to coffee the corresponding OR was 1.43 (95% CI: 0.81-2.55). Our results indicate that sugars and milk/cream added to coffee and tea should be considered in future studies evaluating coffee and tea and endometrial cancer risk.

Tea consumption and risk of endometrial cancer: a metaanalysis

OBJECTIVE

The objective of the study was to assess the association between tea consumption and endometrial cancer.

STUDY DESIGN

Studies were identified by searching PubMed and EMBASE databases and screening the references of retrieved articles. The summary relative risk (RR) with 95% confidence interval (CI) was calculated.

RESULTS

The combined RR for ever drinkers vs non/lowest drinkers was 0.85 (95% CI, 0.77-0.94). Compared with non/lowest drinkers, the summary RR was 0.88 (95% CI, 0.78-0.98) for low to moderate drinkers and 0.75 (95% CI, 0.64-0.88) for high drinkers. An increase in tea intake of 2 cups/day was associated with a 25% decreased risk of endometrial cancer. In subgroup analyses, tea consumption was significantly associated with reduced endometrial cancer risk in Asian studies and studies using interviewing techniques. Furthermore, the protective effect of green tea on endometrial cancer seemed more evident than that of black tea.

CONCLUSION

Findings from this metaanalysis suggest that tea consumption may reduce the risk of endometrial cancer. Because of the limited number of studies, further prospective studies are needed to explore the protective effect of tea on endometrial cancer.

Green tea consumption and the risk of liver cancer in Japan: the Ohsaki Cohort study

OBJECTIVES

To investigate the association between green tea consumption and liver cancer incidence.

METHODS

We prospectively followed 41,761 Japanese adults aged 40-79 years, without a history of cancer at the baseline or any missing data for green tea consumption frequency. Cox proportional hazards models were used to calculate hazard ratios (HR) with 95% confidence intervals (CI), adjusted for age, alcohol drinking, smoking, the consumption of coffee, vegetables, dairy products, fruit, fish, and soybean.

RESULTS

Over 9 years of follow-up, among 325,947 accrued person-years, the total incidence of liver cancer was 247 cases. We found that green tea consumption was inversely associated with the incidence of liver cancer. In men, the multivariate-adjusted HRs (95% CIs) for liver cancer incidence with different green tea consumption categories were 1.00 (reference) for <1 cup/day, 0.83 (0.53-1.30) for 1-2 cups/day, 1.11 (0.73-1.68) for 3-4 cups/day, and 0.63 (0.41-0.98) for >/=5 cups/day (p for trend = 0.11). The corresponding data among women were 1.00 (reference), 0.68 (0.35-1.31), 0.79 (0.44-1.44), 0.50 (0.27-0.90) (p for trend = 0.04).

CONCLUSIONS

Green tea consumption is associated with a reduced risk of liver cancer incidence.

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.