Green tea consumption and lung cancer risk: the Ohsaki study

Tea intake and lung diseases: a Mendelian randomization study

Background

Existing studies on the relationship between tea intake and lung diseases have yielded inconsistent results, leading to an ongoing dispute on this issue. The impact of tea consumption on the respiratory system remained elucidating.

Materials and methods

We conducted a two-sample Mendelian randomization (MR) study to evaluate the associations between five distinct tea intake phenotypes and 15 different respiratory outcomes using open Genome-wide association study (GWAS) data. The inverse variance weighted (IVW) was used for preliminary screening and a variety of complementary methods were used as sensitivity analysis to validate the robustness of MR estimates. Pathway enrichment analysis was used to explore possible mechanisms.

Results

IVW found evidence for a causal effect of standard tea intake on an increased risk of lung squamous cell cancer (LSCC) (OR = 1.004; 95% CI = 1.001-1.007; P = 0.00299). No heterogeneity or pleiotropy was detected. After adjustment for potential mediators, including smoking, educational attainment, and time spent watching television, the association was still robust in multivariable MR. KEGG and GO enrichment predicted proliferation and activation of B lymphocytes may play a role in this causal relation. No causalities were observed when evaluating the effect of other kinds of tea intake on various pulmonary diseases.

Conclusion

Our MR estimates provide causal evidence of the independent effect of standard tea intake (black tea intake) on LSCC, which may be mediated by B lymphocytes. The results implied that the population preferring black tea intake should be wary of a higher risk of LSCC.

Anticarcinogenic potentials of tea catechins

Catechins are a cluster of polyphenolic bioactive components in green tea. Anticarcinogenic effects of tea catechins have been reported since the 1980s, but it has been controversial. The present paper reviews the advances in studies on the anticarcinogenic activities of tea and catechins, including epidemiological evidence and anticarcinogenic mechanism. Tea catechins showed antagonistic effects on many cancers, such as gynecological cancers, digestive tract cancers, incident glioma, liver and gallbladder cancers, lung cancer, etc. The mechanism underlying the anticarcinogenic effects of catechins involves in inhibiting the proliferation and growth of cancer cells, scavenging free radicals, suppressing metastasis of cancer cells, improving immunity, interacting with other anticancer drugs, and regulating signaling pathways. The inconsistent results and their causes are also discussed in this paper.

Associations of coffee and tea consumption with lung cancer risk

Associations of coffee and tea consumption with lung cancer risk have been inconsistent, and most lung cancer cases investigated were smokers. Included in this study were over 1.1 million participants from 17 prospective cohorts. Cox regression analyses were conducted to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Potential effect modifications by sex, smoking, race, cancer subtype and coffee type were assessed. After a median 8.6 years of follow-up, 20 280 incident lung cancer cases were identified. Compared with noncoffee and nontea consumption, HRs (95% CIs) associated with exclusive coffee drinkers (≥2 cups/d) among current, former and never smokers were 1.30 (1.15-1.47), 1.49 (1.27-1.74) and 1.35 (1.15-1.58), respectively. Corresponding HRs for exclusive tea drinkers (≥2 cups/d) were 1.16 (1.02-1.32), 1.10 (0.92-1.32) and 1.37 (1.17-1.61). In general, the coffee and tea associations did not differ significantly by sex, race or histologic subtype. Our findings suggest that higher consumption of coffee or tea is associated with increased lung cancer risk. However, these findings should not be assumed to be causal because of the likelihood of residual confounding by smoking, including passive smoking, and change of coffee and tea consumption after study enrolment.

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.

Evaluation of Anti-cancer and Pro-apoptotic Activities of Iranian Green Tea Extract Against A549,PC3, and MCF-7 Cancer Cell Lines

Introduction: Green tea contains active polyphenols including catechins. The goal of the current study was to evaluate anti-cancer effects of Iranian green tea extract (IGTE) on 3 human cancer cell lines including A549, PC3, and MCF-7. Methods: First, Camellia sinensis was obtained from Lahijan, a city in the north of Iran and then IGTE was prepared. Next, catechins of IGTE were determined using high-performance liquid chromatography (HPLC). Finally, the cell viability of different cancer cells was evaluated by treatment with IGTE at concentration between 100 and 1000 µg/mL for 72 hours using MTT assay. Cell death of treated cancer cells was assessed by DAPI staining and RT-PCR method. Results: Our results demonstrated the potential anti-tumor activity of IGTE on MCF-7 cells (IC50= 400 µM), A549 cells (IC50= 500 µM), and PC3 cells (IC50= 600 µM), respectively. Chromatin damages within the nucleus of the treated cancer cells were shown. In addition, we found that IGTE induced apoptosis by up-regulation of Bax (a pro-apoptotic protein) and down-regulation of Bcl2 (an anti-apoptotic protein). Conclusion: Herein, we showed that IGTE is a potent natural product with anti-tumor activity on breast, lung, and prostate cancer cells. The efficacy of current therapies against cancer is limited by a range of adverse effects, toxicity, and drug resistance; therefore, new therapeutic strategies and more effective agents, particularly with natural origin, are desired and green tea may be a potent candidate in the field of cancer therapy

Association of Lung Cancer and Tea-Drinking Habits of Different Subgroup Populations: Meta-Analysis of Case-Control Studies and Cohort Studies

BACKGROUND

We aimed to investigate the association between lung cancer and tea-drinking habits of different subgroup populations.

METHODS

Systematic search of the PubMed, Web of Science, China National Knowledge Infrastructure (CNKI) and Sinomed databases from database construction until January 2017 for English and Chinese language articles on association of lung cancer and tea drinking. Meta-analysis was used to calculate the combined odds ratio (OR) value and its 95% confidence interval (95% CI). The Newcastle-Ottawa scale was used to evaluate the quality of the studies and Q-test and I₂ was used for heterogeneity testing.

RESULTS

Forty two papers were included, 30 case-control studies included 14578 lung cancer patients and 180574 controls, 12 cohort studies included 543825 subjects, of which the outcome was 5085 with lung cancer. Tea drinkers were found to have a decreased OR of lung cancer compared with non-tea drinkers (OR 0. 80, 95% CI: 0. 73, 0. 87). Consumption of green, black or unspecified tea has a protective effect compared with not drinking tea at all. Increased intake of green tea to 7. 5 g per day can further reduce the OR of lung cancer (OR 0. 69, 95% CI: 0. 48-0. 98). Tea consumption had a protective effect against lung cancer in non-smokers, Further analysis found that drinking of one or more cups of tea a day has a protective effect on smokers (OR 0. 79, 95% CI: 0. 64-0. 96).

CONCLUSION

Tea drinking could be a protective factor in lung cancer.

The Cytoprotective Role of Antioxidants in Mammalian Cells Under Rapidly Varying UV Conditions During Stratospheric Balloon Campaign

The current age of dynamic development of the space industry brings the mankind closer to routine manned space flights and space tourism. This progress leads to a demand for intensive astrobiological research aimed at improving strategies of the pharmacological protection of the human cells against extreme conditions. Although routine research in space remains out of our reach, it is worth noticing that the unique severe environment of the Earth's stratosphere has been found to mimic subcosmic conditions, giving rise to the opportunity to use the stratospheric surface as a research model for the astrobiological studies. Our study included launching into the stratosphere a balloon containing mammalian normal and cancer cells treated with various compounds to examine whether these substances are capable of protecting the cells against stress caused by rapidly varying temperature, pressure, and radiation, especially UV. Owing to oxidative stress caused by irradiation and temperature shock, we used natural compounds which display antioxidant properties, namely, catechin isolated from green tea, honokiol derived from magnolia, curcumin from turmeric, and cinnamon extract. "After-flight" laboratory tests have shown the most active antioxidants as potential agents which can minimize harmful impact of extreme conditions on human cells.

In Search of Panacea-Review of Recent Studies Concerning Nature-Derived Anticancer Agents

Cancers are one of the leading causes of deaths affecting millions of people around the world, therefore they are currently a major public health problem. The treatment of cancer is based on surgical resection, radiotherapy, chemotherapy or immunotherapy, much of which is often insufficient and cause serious, burdensome and undesirable side effects. For many years, assorted secondary metabolites derived from plants have been used as antitumor agents. Recently, researchers have discovered a large number of new natural substances which can effectively interfere with cancer cells’ metabolism. The most famous groups of these compounds are topoisomerase and mitotic inhibitors. The aim of the latest research is to characterize natural compounds found in many common foods, especially by means of their abilities to regulate cell cycle, growth and differentiation, as well as epigenetic modulation. In this paper, we focus on a review of recent discoveries regarding nature-derived anticancer agents.

Tea consumption and the risk of biliary tract cancer: a systematic review and dose-response meta-analysis of observational studies

Recent studies have shown that tea consumption is associated with the reduced incidence of some types of cancer, possibly including biliary tract cancer. However, the epidemiological evidences for the association with risk of biliary tract cancer are contradictory. Thus, we performed meta-analysis of published observational studies to assess the association between tea consumption and risk of biliary tract cancer. Relevant studies were identified by searching PubMed, EMBASE, and ISI Web of Science published before October 2016. The Newcastle-Ottawa Scale was used to evaluate the quality of included studies, and publication bias was evaluated using funnel plots, and Begg's and Egger's tests. This meta-analysis includes eight studies comprising 18 independent reports. The incidence of biliary tract cancer reduced about 34% (significantly) for tea intake group in comparison with never intake group (summary odds ratio [OR] = 0.66; 95% confidence interval [CI] = 0.48-0.85). Additionally, an inverse relationship between tea intake and risk of biliary tract cancer was statistically significant in women (OR = 0.65; 95 % CI = 0.47-0.83), but not in men (OR = 0.86; 95% CI = 0.58-1.13). Dose- response analysis indicated that the risk of biliary tract cancer decreased by 4% with each additional cup of tea one day (relative risk [RR] = 0.96, 95% CI = 0.93-0.98, p = 0.001). In summary, tea intake is associated with decreased risk of biliary tract cancer, especially for women.

Green tea and anticancer perspectives: updates from last decade

Green tea is the most widely consumed beverage besides water and has attained significant attention owing to health benefits against array of maladies, e.g., obesity, diabetes mellitus, cardiovascular disorders, and cancer insurgence. The major bioactive molecules are epigallocatechin-3-gallate, epicatechin, epicatechin-3-gallate, epigallocatechin, etc. The anticarcinogenic and antimutagenic activities of green tea were highlighted some years ago. Several cohort studies and controlled randomized trials suggested the inverse association of green tea consumption and cancer prevalence. Cell culture and animal studies depicted the mechanisms of green tea to control cancer insurgence, i.e., induction of apoptosis to control cell growth arrest, altered expression of cell-cycle regulatory proteins, activation of killer caspases, and suppression of nuclear factor kappa-B activation. It acts as carcinoma blocker by modulating the signal transduction pathways involved in cell proliferation, transformation, inflammation, and metastasis. However, results generated from some research interventions conducted in different groups like smokers and nonsmokers, etc. contradicted with aforementioned anticancer perspectives. In this review paper, anticancer perspectives of green tea and its components have been described. Recent findings and literature have been surfed and arguments are presented to clarify the ambiguities regarding anticancer perspectives of green tea and its component especially against colon, skin, lung, prostate, and breast cancer. The heading of discussion and future trends is limelight of the manuscript. The compiled manuscript provides new avenues for researchers to be explored in relation to green tea and its bioactive components.

Tea and human health: biomedical functions of tea active components and current issues

Originating in China, tea and tea planting have spread throughout the world since the middle of the Tang dynasty. Now people from 160 countries in the world are accustomed to tea drinking. A brief history of tea's medicinal role in China and its spread to the world are introduced. The effectiveness of tea active components and tea drinking on major human diseases, including cancer, metabolic syndrome, cardiovascular disease, and neurodegenerative diseases, is discussed. Also presented are some related issues, such as the bioavailability of tea active components, the new formulations of tea polyphenols, and the safety for consumers of dietary supplements containing tea polyphenols.

Tea consumption and lung cancer risk: a meta-analysis of case-control and cohort studies

OBJECTIVE

Recent epidemiologic studies, especially cohort and case-control studies, have yielded inconsistent findings regarding the association between tea consumption and risk for lung cancer. The aim of this study was to assess a potential relationship between tea consumption and the incidence of lung cancer worldwide.

METHODS

A systematic literature search of PubMed, Web of Science, the Cochrane Library, Google Scholar, the Chinese Biomedical Database, and Wanfang Database was conducted from 1966 to January 2014 by two investigators. All cohort studies and case-control studies that evaluated the association of tea and lung cancer were included. Summary relative risks (RR) and the corresponding 95% confidence intervals (CIs) were calculated using a random-effects model. Quality assessments were performed using the Newcastle-Ottawa Scale. Heterogeneity was assessed using the Q and I(2) tests, and the source of heterogeneity was detected by meta-regression analysis. Publication bias was evaluated with Egger's regression symmetry test. Subgroup analyses and sensitivity analysis were performed.

RESULTS

Thirty-eight lung cancer studies (26 case-control studies and 12 cohort studies) with 59,041 cases and 396,664 controls were included. Overall tea consumption was significantly associated with decreased risk for lung cancer (RR, 0.78; 95% CI, 0.70-0.87). Subgroup analyses showed that tea consumption was associated with reduced risk for lung cancer in women (RR, 0.76; 95% CI, 0.62-0.93), case-control studies (RR 0.72; 95% CI 0.63-0.83), Western studies (RR, 0.85; 95% CI, 0.75-0.97), and studies in China and Japan (RR, 0.74; 95% CI, 0.62-0.88). Both green tea (RR, 0.75; 95% CI, 0.62-0.91) and black tea (RR, 0.82; 95% CI, 0.71-0.94) were significantly associated with reduced lung cancer risk. No significant association was found in men or in cohort studies.

CONCLUSION

Tea consumption may offer some protection against lung cancer.

Coffee consumption and the risk of prostate cancer: the Ohsaki Cohort Study

Background:

Epidemiological evidence regarding the effect of coffee on the incidence of prostate cancer is inconsistent. We aimed to investigate coffee consumption and the risk of prostate cancer risk in a general Japanese population.

Methods:

We conducted a prospective cohort study in Ohsaki city, Japan, where 18 853 men aged 40–79 years participated in a baseline survey. Coffee consumption was assessed via a validated self-administered questionnaire. During 11 years of follow-up (from January 1 1995 to December 31, 2005), 318 incident cases of prostate cancer were detected. The Cox proportional hazards regression model was used to calculate the hazard ratios (HRs) and 95% confidence interval (CIs).

Results:

There was a significant inverse association between coffee consumption and the incidence risk of prostate cancer. Compared with those who did not drink coffee, the multivariate adjusted HRs were 0.81 (95% CI: 0.61–1.07), 0.73 (95% CI: 0.53–1.00), and 0.63 (095% CI: 0.39–1.00) for those who drank coffee occasionally, 1–2 cups per day, and ⩾3 cups per day, respectively, with a P for trend of 0.02.

Conclusion:

This prospective finding from a Japanese population adds evidence that coffee intake is inversely associated with the incidence of prostate cancer.

Smoking, green tea consumption, genetic polymorphisms in the insulin-like growth factors and lung cancer risk

Insulin-like growth factors (IGFs) are mediators of growth hormones; they have an influence on cell proliferation and differentiation. In addition, IGF-binding protein (IGFBP)-3 could suppress the mitogenic action of IGFs. Interestingly, tea polyphenols could substantially reduce IGF1 and increase IGFBP3. In this study, we evaluated the effects of smoking, green tea consumption, as well as IGF1, IGF2, and IGFBP3 polymorphisms, on lung cancer risk. Questionnaires were administered to obtain the subjects' characteristics, including smoking habits and green tea consumption from 170 primary lung cancer cases and 340 healthy controls. Genotypes for IGF1, IGF2, and IGFBP3 were identified by polymerase chain reaction. Lung cancer cases had a higher proportion of smoking, green tea consumption of less than one cup per day, exposure to cooking fumes, and family history of lung cancer than controls. After adjusting the confounding effect, an elevated risk was observed in smokers who never drank green tea, as compared to smokers who drank green tea more than one cup per day (odds ratio (OR) = 13.16, 95% confidence interval (CI) = 2.96-58.51). Interaction between smoking and green tea consumption on lung cancer risk was also observed. Among green tea drinkers who drank more than one cup per day, IGF1 (CA)(19)/(CA)(19) and (CA)(19)/X genotypes carriers had a significantly reduced risk of lung cancer (OR = 0.06, 95% CI = 0.01-0.44) compared with IGF1 X/X carriers. Smoking-induced pulmonary carcinogenesis could be modulated by green tea consumption and their growth factor environment.

Associations between frequency of tea consumption and health and mortality: evidence from old Chinese

Tea consumption may be associated with reduced risk of morbidity and mortality; however, this association is not conclusive and has rarely been investigated among very old adults. The present study examines how self-reported frequency of tea consumption in daily life is associated with health and mortality among very old adults in China. The data are from a national longitudinal data set that included 32 606 individuals (13 429 men and 19 177 women) aged 65 years and older: 11 807 respondents aged 65 to 84 years and 20 799 respondents aged 85 years and older. A total of four measurements between 1998 and 2005 resulted in 51 668 observations. Hazard regressions showed that men who drink tea almost every day have a 10-20 % lower risk of death compared to their counterparts who seldom drink tea, after adjusting for numerous confounders including baseline health. This relationship was stronger in younger male elders aged 65 to 84 years than in the oldest-old men aged 85 years and older. However, frequency of tea consumption was not significantly associated with mortality in women. Our analyses further show that high frequency of tea consumption is significantly associated with reduced OR of disability in activities of daily living, cognitive impairment, self-rated poor health, cumulative health deficits and CVD in both young elders and the oldest-old, and in both men and women. These results suggest that the health benefit of drinking tea is universal. We conclude that frequent tea consumption probably helps one achieve healthy longevity and that men benefit more from such lifestyles.

Recent advances on tea polyphenols

Over the past decade many scientific and medical studies have focused on green tea for its long-purported health benefits. There is convincing evidence that tea is a cup of life. It has multiple preventive and therapeutic effects. This review thus focuses on the recent advances of tea polyphenols and their applications in the prevention and treatment of human cancers. Of the various polyphenols in tea, (-)-Epigallocatechin-3-gallate (EGCG) is the most abundant, and active compound studied in tea research. EGCG inhibits several molecular targets to inhibit cancer initiation and modulates several essential survival pathways to block cancer progression. Herein, we describe the various mechanisms of action of EGCG and also discuss previous and current ongoing clinical trials of EGCG and green tea polyphenols in different cancer types.

Recent advances on tea polyphenols

Over the past decade many scientific and medical studies have focused on green tea for its long-purported health benefits. There is convincing evidence that tea is a cup of life. It has multiple preventive and therapeutic effects. This review thus focuses on the recent advances of tea polyphenols and their applications in the prevention and treatment of human cancers. Of the various polyphenols in tea, (-)-Epigallocatechin-3-gallate (EGCG) is the most abundant, and active compound studied in tea research. EGCG inhibits several molecular targets to inhibit cancer initiation and modulates several essential survival pathways to block cancer progression. Herein, we describe the various mechanisms of action of EGCG and also discuss previous and current ongoing clinical trials of EGCG and green tea polyphenols in different cancer types.

Steep your genes in health: drink tea

Tea, one of the most commonly consumed beverages in the world, has many health benefits. Tea polyphenols support health by promoting antioxidant enzymes, promoting apoptosis, preventing angiogenesis, and modulating epigenetic change. Considerable basic science and epidemiologic evidence supports the regular consumption of this tasty, inexpensive beverage.

Green tea polyphenols as proteasome inhibitors: implication in chemoprevention

Next to water, tea is the most popular beverage in the world. The most abundant and active compound in green tea is (-)-epigallocatechin-3-gallate (EGCG), which is extensively studied for its cancer-preventive and anti-cancer activities as well as its cellular targets. One potential molecular target of EGCG is the proteasome. While molecular docking and structure-activity relationship (SAR) analysis suggests that the ester carbon of EGCG is important for mediating its proteasome-inhibitory activity, EGCG is very unstable under physiological conditions. Therefore, a series of analogs were synthesized aiming to improve stability and bioavailability of EGCG. Among them, peracetate-protected or the prodrug of EGCG was found to have increased bioavailability, stability, and proteasome-inhibitory activities against various human cancer cells and tumors compared to EGCG, suggesting its potential use for cancer prevention and treatment. Epidemiological studies have indicated that green tea consumption is associated with the reduced risk of cancers, especially associated with the reduced risk of late stage of cancers. This risk reduction may be attributed not only to proteasome inhibition, but also to numerous other intracellular molecules targeted by EGCG that are involved in cell cycle regulation, apoptosis, angiogenesis, and metastasis.

Green tea and prevention of esophageal and lung cancers

Green tea contains high concentrations of tea polyphenols that have shown inhibitory effects against the development, progress, and growth of carcinogen-induced tumors in animal models at different organ sites, including the esophagus and lung. Green tea polyphenols also have shown to suppress cell proliferation and induce apoptosis. Besides antioxidative property, green tea polyphenols have pro-oxidative activities under certain conditions and modulate phase II metabolic enzymes that can enhance the detoxification pathway of environmental toxicants and carcinogens. Although epidemiological studies have provided inconclusive results on the effect of green tea consumption against the development of esophageal and lung cancers in humans overall, the inverse association between green tea intake and risk of esophageal cancer risk is more consistently observed in studies with adequate control for potential confounders. Epidemiological studies also have demonstrated an inverse, albeit moderate, association between green tea consumption and lung cancer, especially in non-smokers. This article reviews data on the cancer-preventive activities of green tea extract and green tea polyphenols and possible mechanisms against the esophageal and lung carcinogenesis in experimental animals, and summarizes the current knowledge from epidemiological studies on the relationship between green tea consumption and esophageal and lung cancer risk in humans.

History of cholelithiasis and the risk of prostate cancer: the Ohsaki Cohort Study

An association between cholelithiasis and prostate cancer has been reported sporadically in previous case-control and experimental studies, suggesting that cholesterol may play a promotional role in prostate cancer development and progression. However, this relationship remains poorly understood, and population evidence based on a strict study design is needed. The authors examined the history of cholelithiasis and the development of prostate cancer in the Ohsaki cohort followed from 1995 to 2003, in which 230 new cases of prostate cancer were ascertained among 22,458 Japanese men. Baseline information, including history of cholelithiasis, was collected using a self-administered questionnaire. The Cox proportional hazards regression model was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). The results showed that patients with a history of cholelithiasis had a higher risk of prostate cancer with a multivariate adjusted HR of 1.72 (95% CI: 1.12-2.66), and especially for advanced prostate cancer, the corresponding value was 2.29 (95% CI: 1.21-4.35). The associations were robust after adjustment for different potential confounders. This population-based prospective cohort study indicates that a history of cholelithiasis is associated with an increased incidence of prostate cancer.

Association between green tea consumption and lung cancer risk

Green tea is a popular beverage and its health benefits are well known. However, inconsistent results have been reported in observational studies concerning the association between green tea consumption and the lung cancer risk. In this commentary, several methodological issues underlying the measurement of tea exposure are highlighted. The recommendations should be useful for designing and planning prospective cohort studies to ascertain the protective effect of green tea against lung cancer.

Green tea consumption and hematologic malignancies in Japan: the Ohsaki study

Several biologic studies have reported that green tea constituents have antitumor effects on hematologic malignancies. However, the effects in humans are uncertain. The authors used data from the Ohsaki National Health Insurance Cohort Study in Japan to evaluate the association between green tea consumption and the risk of hematologic malignancies. Study participants were 41,761 Japanese adults aged 40-79 years without a history of cancer at baseline who answered a food frequency questionnaire survey in 1994. During 9 years of follow-up beginning in 1995, the authors documented 157 hematologic malignancies, including 119 cases of lymphoid neoplasms and 36 cases of myeloid neoplasms. Hazard ratios were calculated by using the Cox proportional hazards regression model. Risk of hematologic malignancies was inversely associated with green tea consumption. The multivariate-adjusted hazard ratio of hematologic malignancies for 5 cups/day or more compared with less than 1 cup/day of green tea was 0.58 (95% confidence interval: 0.37, 0.89). The corresponding risk estimate was 0.52 (95% confidence interval: 0.31, 0.87) for lymphoid neoplasms and 0.76 (95% confidence interval: 0.32, 1.78) for myeloid neoplasms. This inverse association was consistent across sex and body mass index strata. In conclusion, green tea consumption was associated with a lower risk of hematologic malignancies.

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.

Regulation of cell growth through cell cycle arrest and apoptosis in HPV 16 positive human cervical cancer cells by tea polyphenols

Cervical cancer is the second most common malignant neoplasm in women, in terms of both incidence and mortality rates worldwide. The polyphenolic constituents of tea (Camellia sinensis) have gained considerable attention because of its anti-cancer properties against a variety of cancers. Here we studied the effects of green and black tea polyphenols (GTP and BTP), on cellular proliferation and cell death in the SiHa cells (human cervical cancer) expressing the human papilloma virus (HPV)-16. The result showed that both GTP and BTP inhibited proliferation of cells in dose and time dependent manner. Cell cycle analysis showed anti-proliferative effect of GTP which is associated with an increase in the G2/M phase and apoptotic effect of BTP in 24 h treated SiHa cells. Further, on increase of incubation time for 48 h, GTP caused induction of apoptosis up to 20% of SiHa cells. The role GTP and BTP in apoptosis was further confirmed by reduction in mitochondrial membrane potential and increased levels of membrane phosphatidylserine. Thus, our data suggests that tea polyphenols exhibit anti-cancer potential against cervical cancer by inhibition of cell growth and induction of apoptosis.

Green tea, black tea consumption and risk of lung cancer: a meta-analysis

Studies investigating the association of green tea and black tea consumption with lung cancer risk have reported inconsistent findings. To provide a quantitative assessment of this association, we conducted a meta-analysis on the topic. Studies were identified by a literature search in PubMed from 1966 to November 2008 and by searching the reference lists of relevant studies. Summary relative risk (RR) estimates and their corresponding 95% confidence intervals (CIs) were calculated based on random-effects model. Our meta-analysis included 22 studies provided data on consumption of green tea or black tea, or both related to lung cancer risk. For green tea, the summary RR indicated a borderline significant association between highest green tea consumption and reduced risk of lung cancer (RR=0.78, 95% CI=0.61-1.00). Furthermore, an increase in green tea consumption of two cups/day was associated with an 18% decreased risk of developing lung cancer (RR=0.82, 95% CI=0.71-0.96). For black tea, no statistically significant association was observe through the meta-analysis (highest versus non/lowest, RR=0.86, 95% CI=0.70-1.05; an increment of two cups/day, RR=0.82, 95% CI=0.65-1.03). In conclusion, our data suggest that high or an increase in consumption of green tea but not black tea may be related to the reduction of lung cancer risk.