Open Access

Tea consumption and risk of bladder cancer: a meta-analysis

World Journal of Surgical Oncology201210:172

https://doi.org/10.1186/1477-7819-10-172

Received: 17 March 2012

Accepted: 13 August 2012

Published: 25 August 2012

Abstract

Background

Tea consumption has been reported to be associated with an decreased risk of several types of cancers. However, the results based on epidemiological studies on the association of tea consumption with bladder cancer were inconsistent. This meta-analysis was undertaken to evaluate the relationship between tea consumption and bladder cancer risk.

Methods

Eligible studies were retrieved via both computer searches and review of references. The summary relative risk (RR) with 95% confidence interval (CI) was calculated.

Results

Twenty three studies met the inclusion criteria of the meta-analysis. No association with bladder cancer was observed in either overall tea consumption group (OR =0.94, 95% CI 0.85-1.04) or subgroups stratified by sex, study design, geographical region or tea types.

Conclusions

Our findings did not support that tea consumption was related to the decreased risk of bladder cancer.

Keywords

Green teaBlack teaBladder neoplasmsMeta-analysis

Background

In the United States, an estimated 70,530 new cases of bladder cancer will be diagnosed and approximately 14,680 deaths were attributed to bladder cancer in 2010 [1]. Bladder cancer is the most expensive cancer to survey and treat because of the need for frequent interval cystourethroscopy, urine cytology and radiological evaluations [2]. Therefore, more and more attention has been given to chemoprevention. Cancer chemoprevention is defined as the use of natural, synthetic, or biologic chemical agents to reverse, suppress, or prevent carcinogenic progression to invasive cancer. Bladder cancer has a protracted course of progression and may be ideal for chemoprevention strategies [3].

Tea, derived from the plant Camellia sinensis, is one of the most common beverages consumed worldwide, especially in China. Multiple lines of evidence support a protective effect of tea on various cancers [4]. The emperor of China, ShenNung, is credited with first describing the therapeutic effects of tea in 2737 BC [5]. Studies conducted on cell-culture systems and animal models show that tea or the active ingredient in tea, polyphenols, could afford protection against a variety of cancer types [4]. However, the results based on epidemiological studies on the association of tea consumption with bladder cancer were inconsistent. A meta-analysis conducted in 2001 suggested the consumption of tea seems not to be related to an increased risk of urinary tract cancer [6].

The purpose of the present study was to update and quantitatively assess the association between tea consumption and the risk of bladder cancer by summarizing the results of published cohort and case-control studies. We also sought to address the unresolved issue of whether this relationship differs across the tea type.

Results

In total, we identified 35 papers examining the risk of bladder cancer with tea consumption published between 1966 and December 2011, and these were reviewed by 2 authors. We found no relevant non-English language papers in this field. Six studies were excluded because of insufficient information to compute its relative risk (RR) and 95% confidence interval (CI) [79], or a summary odds ratio (OR) adjusted for at least age, sex and smoking [1012]. Six studies were excluded because they were found to be subsets of other studies or have overlapping data and were excluded [1318]. Thus, 23 studies [1941] were included in the meta-analysis on the association of tea consumption with bladder cancer risk. There were six cohorts [26, 29, 31, 33, 38, 40] and seventeen case–control studies; nine of these were population-based [1921, 23, 27, 30, 34, 37, 41] and eight were hospital-based case-control studies [22, 24, 25, 28, 32, 35, 36, 39]. Of the twenty-three studies, seventeen were conducted in Western countries [17, 2027, 29, 30, 3234, 36, 37, 40, 41], and six were conducted in Asia [19, 28, 31, 35, 38, 39]. Only eight articles reported association between consumption of specific tea types (green or black tea) and the risk of bladder cancer [19, 23, 25, 26, 31, 35, 38, 39]. Information on tea consumption was obtained by interview, self-administered questionnaire or both techniques.

Table 1 presents the basic characteristics of each study included in our meta-analysis. Of the seventeen case-control studies, most studies found no significant association between tea consumption and bladder cancer, whereas four studies reported significantly increased risks [20, 28, 36, 41], and three found inverse associations [19, 30, 35]. Of the six cohort studies, five reported no significant association between tea consumption and bladder cancer [26, 29, 31, 38, 40], whereas one found significantly decreased risk [33].
Table 1

Study characteristics of published cohort and case-control studies on tea consumption and bladder cancer

Authors and year

Study design

Country

Study period

Cases/ subjects

Anatomical site of urinary tract

Tea type

Variables of adjustment

Tea drinking assessment

Ros et al. [40]

Cohort

European countries

1992-2000

513/233,236

Urinary tract

Tea

Age, sex, smoking status

Questionnaire

Hemelt et al. [39]

HCC

China

2005-2008

419/384 (green tea)

Bladder

Green tea

Age, sex, smoking status, smoking frequency, and smoking duration adjusted odds ratios

Questionnaire

408/385 (black tea)

Black tea

Kurahashi et al. [38]

Cohort

Japan

1990-2005

164/49,566 (men)

Bladder

Green tea

Age, area, smoking status, alcohol and coffee consumption

Questionnaire

42/54,874 (women)

Jiang et al. [37]

PCC

US

1987-1999

1,586/1,586

Bladder

Tea

Age, sex, race, level of education, use of NSAIDs, carotenoid intake, number of years as hairdresser/barber, cigarette smoking status, duration of smoking, and intensity of smoking.

Questionnaire

Stefani et al. [36]

HCC

Uruguay

1996-2000

255/501

Bladder

Tea

Age, sex, residence, urban/rural status, education, family history of bladder cancer among first-degree relatives, body mass index, occupation, smoking status, years since quitting, number of cigarettes smoked per day, maté drinking, soft drink intake, milk intake, and, coffee drinking

Both

Wakai et al. [35]

HCC

Japan

1994-2000

124/744

Urinary tract

Green tea

Age, sex, cumulative consumption of cigarettes, year of first visit

Questionnaire

Black tea

Woolcott et al. [34]

PCC

Canada

1992-1994

927/2118

Bladder

Tea

Age, sex, education level, current smoking, cumulative smoking, and intake of energy, calcium, fibre and beer

Questionnaire

Zeegers et al. [33]

Cohort

Netherland

1986-1992

569/3,123

Bladder

Tea

Age, sex, number of cigarettes/day, years of cigarette smoking, and coffee consumption

Questionnaire

Geoffery-Perez et al. [32]

HCC

France

1984-1987

765/765

Bladder

Tea

Age, sex smoking, residence, center

Interview

Bianch et al. [30]

PCC

USA

1986-1989

1,452/2,434

Bladder

Tea

Age, sex, education, smoking status, family history of bladder cancer, high risk occupation, total beverage consumption, years of chlorinated surface water, vegetable and coffee consumption

Questionnaire

Nagano et al. [31]

Cohort

Japan

1979-1981

114/3,8540

Bladder

Green tea

Age, gender, radiation dose, smoking status, education level, body-mass index, and calendar time

Questionnaire

Black tea

Lu et al. [28]

HCC

Taiwan

1996-1997

40/160

Bladder

Tea

age, sex, date of admission, family history, ethnicity, and smoking status.

Questionnaire

Michaud et al. [29]

Cohort

US

1986-1996

252/47,909

Bladder

Tea

Geographic region, age, pack-years of smoking, current smoking status, energy intake, intake of fruits and vegetables, and intake of all other beverages.

Questionnaire

Bruemmer et al. [27]

PCC

US

1987-1990

262/405

Bladder

Tea

Age, sex, smoking, county

Interview

Chyou et al. [26]

Cohort

US

1965-1968

96/7,995

Urinary tract

Green tea

Age, smoking

Both

Black tea

Kunze et al. [25]

HCC

Germany

1977-1985

675/675

Urinary tract

Black tea

Age, sex, smoking

Interview

D’Avanzo et al. [24]

HCC

Italy

1985-1990

555/855

Bladder

Tea

Age, sex, education, smoking habits, alcohol drinking and exposure to occupational risk

Interview

Nomura et al. [23]

PCC

US

1977-1986

261/522

Urinary tract

Black tea

Age, sex, pack-years of cigarette smoking

Interview

Clavel et al. [22]

HCC

France

1984-1987

690/690

Bladder

Tea

Age, sex, smoking

Interview

Slattery et al. [18]

PCC

US

1977-1982

419/889

Bladder

Tea

Age, sex, smoking status, diabetes and bladder infection

Interview

Risch et al. [21]

PCC

Canada

1979-1982

876/1,668

Bladder

Tea

Age, sex, residence, and lifetime cigarette consumption.

Interview

Jensen et al. [20]

PCC

Denmark

1979-1981

371/771

Bladder

Tea

Age, sex, smoking status,

Interview

Ohno et al. [19]

PCC

Japan

1976-1978

293/589

Urinary tract

Black tea

Age, smoking

Interview

PCC: population-based case-control study, HCC: hospital-based case-control study, NSAIDs: non-steroidal anti-inflammatory drugs, Both: questionnaire and interview.

Figure 1 plots the pooled risk estimates for overall tea consumption by study design. When all these studies were analyzed together, no association was observed for tea consumption with bladder cancer (OR 0.94, 95% CI 0.85, 1.04) and the summary ORs were similar across study design and source of the controls in case-control studies. No statistically significant heterogeneity was observed when all the studies were analyzed together. However, we noted some heterogeneity in the population-based case-control studies (I2 58.2%, P = 0.014). After excluding one study by Slattery et al. [41], which reported the highest point estimates, the P-value for heterogeneity in the subgroup was no longer statistically significant (I2 15.2%, P 0.311), and the summary OR was not significantly changed (OR 0.94, 95% CI 0.83, 1.05). There was no indication of publication bias from the Begg funnel plot (Figure 2).
Figure 1

A forest plot showing risk estimates from case-control and cohort studies estimating the association between tea consumption and risk for bladder cancer.

Figure 2

Funnel plot of tea consumption and bladder cancer risk.

The results of subgroup analyzes by sex (men and women), geographical region (US/Canada, Europe, Uruguay and Asia) and tea type (green tea and black tea) are shown in Table 2. The OR estimates from subgroup analysis varied little, showing tea consumption was not associated with the likelihood of bladder cancer when separately analyzed by sex, geographical regions or tea type. In the subgroup analysis by tea type (Figure 3), we noted that green tea or black tea consumption was not associated with bladder cancer risk (OR 0.97, 95% CI 0.73, 1.21; OR 0.79, 95% CI 0.59, 0.99). There was weak heterogeneity among studies for black tea. We performed a sensitivity analysis, which removed one study at a time. This analysis confirmed the stability of the results for black tea. No indication of publication bias was observed from either with the Egger or Begg test in any subgroup.
Table 2

Summary of pooled odds ratios (ORs)for bladder cancer by sex, geographical region, and tea type

Subgroup

Number of studies

Pooled OR

Q-test for heterogeneity

Egger test

Begg test

(95% CI)

P-value (I2score)

P-value

P-value

All studies

23

0.94 (0.85, 1.04)

0.103 (28.3%)

0.518

0.267

Sex

Men

10

1.03 (0.91, 1.14)

0.534 (0.0%)

0.446

0.348

Women

9

0.85 (0.69, 1.01)

0.461 (0.0%)

0.638

0.348

Geographical region

Asia

6

0.85 (0.69, 1.00)

0.784 (0.0%)

0.360

0.348

Europe

7

0.92 (0.77, 1.08)

0.841 (0.0%)

0.789

0.881

Uruguay

1

4.10 (0.00, 8.20)

-

-

-

US/Canada

9

1.02 (0.83, 1.21)

0.008 (61.2%)

0.723

0.835

Tea type

Green tea

5

0.97 (0.73, 1.21)

0.793 (0.0%)

0.377

0.221

Black tea

7

0.79 (0.59, 0.79)

0.176 (33.1%)

0.381

0.764

Figure 3

Forest plots showing the risk estimates from each study and the pooled risk estimates for green tea and black tea.

Discussion

There has been considerable interest in the possible impact of tea consumption on bladder cancer risk due to the modifiable nature of tea consumption. In this meta-analysis of epidemiological studies of the association between tea and risk of bladder cancer including six cohorts and seventeen case-control studies, we found that tea consumption was not associated with reduced risk of bladder cancer.

A previous meta-analysis by Zeegers et al. [6] found no association between tea consumption and bladder cancer risk. The authors reported that the consumption of tea seems not to be related to an increased risk of urinary tract cancer. Our finding is consistent with their results. However, our study included 11 studies published after 2000 that were not included in the previous meta-analysis. We pooled the OR estimates by sex (men and women), tea type (green tea and black tea), geographical region (US/Canada, Europe, Uruguay and Asia), and study design (cohort or case-control studies).

Studies conducted on cell-culture systems and animal models as well as human epidemiological studies show that tea could afford protection against a variety of cancer types. Several laboratory studies have tried to investigate the link between tea and bladder cancer. Most of tea research on bladder cancer to date has focused on the effect and mechanism of green tea. It is generally agreed that many of the chemoprevention effects of green tea are mediated by polyphenols. The major catechins in green tea are epigallocatechin-3-gallate (EGCG), epicatechin-3-gallate, epigallocatechin, and epicatechin. EGCG accounts for 50% to 80% of catechin in green tea. Our previous study indicates that EGCG induces apoptosis in human bladder cancer T24 cells [42]. Kemberling et al. found that green tea (15% of which are polyphenols) have shown efficacy against rat bladder cancer induced by N-(4-hydroxybutyl)-N-bytyl-nitrosame (OH-BBN) [5]. The non-significant findings regarding the effects of tea consumption on bladder cancer in our meta-analyses contradict the results of previous experimental studies on this topic using in vitro bladder cancer cell lines and in vivo animal models. The difference between the results from experimental studies and our meta-analyses is likely to be due to the lower quantities of human tea consumption compared to the doses used in experimental studies and the fact that bioavailability is an important factor for consideration.

As a meta-analysis of previously published observational studies, our study has several limitations that need to be taken into account when considering its contributions. First, our meta-analysis only included published articles. Unpublished studies were not searched for our analysis. Second, we did not include studies with insufficient information to estimate an adjusted OR, which could bring publication bias even though no significant evidence of publication bias was observed in the Egger or the Begg tests. Third, our meta-analysis is likely affected by some misclassification of tea consumption. Tea exposure is mostly assessed regarding the number of cups of tea consumed daily or weekly. However, cup size may vary considerably. Fourth, only eight studies performed analyses and reported the RR separately for black tea and green tea. All other studies referred simply to tea. Finally, studies included in our meta-analysis were mainly conducted in Europe, US, Canada, Uruguay, and Asia; therefore, we are not able to generalize our findings for all populations. Also, most studies just included bladder cancer without specifying the type. Transitional cell carcinoma is the most common type of cancer in these regions and we found no relevant papers on squamous cell carcinoma. So the results are mainly based on transitional cell carcinoma but not squamous cell carcinoma.

Conclusions

In conclusion, in this pooled analysis of six cohort and seventeen case-control studies, we did not find that tea consumption was associated with decreased risk of bladder cancer. Given the small number of cohort studies included in this meta-analysis, further research from large epidemiological studies is needed in this area.

Methods

Literature research

We searched and reviewed the MEDLINE database using PubMed, Web of Science and the Cochrane Library, using selected common key words related to tea consumption and bladder cancer risk in case-control and cohort studies. We also scanned bibliographies of relevant articles in order to identify additional studies. As the key words for the literature search, we selected tea for the exposure factors, and bladder cancer for the outcome factors. The articles evaluating the relationship of urinary tract cancer and tea consumption were also retrieved, because the overwhelming majority of tumors occurred in the bladder, and the renal pelvis and ureter are covered by the same urothelium. The term bladder cancer was used as a synonym for these neoplasms.

Each identified publication was reviewed and included in the analysis if all the following criteria were met: first, they had to be case-control or cohort studies; second, papers reported in English between 1966 and December 2011; last, the result of each study was expressed as relative risk (RR) or odds ratio (OR) together with its corresponding 95% confidence interval (95% CI) adjusted for age, sex and smoking at the least, or sufficient information allowing us to compute them.

Data extraction

Data from all articles were retrieved independently by JQ and QM while the methods and results sections were removed and coded to blind the assessors to this information. The following data were collected: the first author’s name, the year of publication, country of origin, the study design (cohort or case-control), number of participants (cases and cohort size, or cases and controls), anatomical site of the neoplasm, adjusted effects estimates, exposure assessment and adjusted covariates. Considering that bladder cancer is a rare disease, the RR was assumed to be approximately the same as the OR, and the OR was used as the study outcome. Adjusted ORs were extracted directly from the original reports. If studies reported sex-stratified age- and smoking-adjusted ORs, we calculated the overall age-, smoking- and sex-adjusted OR by combining these estimates using the method of Mantel and Haenszel [43].

Statistical analysis

We pooled data using the DerSimonian and Laird random effects models [44], which considers both within-study and between-study variation. Subgroup analyses were performed according to sex (male or female), study design (cohort or case-control studies), the study location (US/Canada, Europe, Uruguay or Asia) and tea types (green tea, black tea). We quantified the extent of heterogeneity using the Q-test [44] and the I2 score [45], and P < 0.05 was considered statistically significant. Publication bias was assessed using the tests of Egger [46] and Begg [47]. All statistical analyzes were performed using Stata Statistical Software, version 10.0.

Abbreviations

RR: 

relative risk

CI: 

confidence interval

OR: 

odds ratio

NSAID: 

non-steroidal anti-inflammatory drug

EGCG: 

epigallocatechin-3-gallate

OH-BBN: 

N-(4-hydroxybutyl)-N-bytyl-nitrosame.

Declarations

Acknowledgements

This study was supported by grants from the National Natural Science Foundation of China (Grant Number 30900552).

Authors’ Affiliations

(1)
Department of Urology, First Affiliated Hospital, Zhejiang University School of Medicine
(2)
Department of Urology, Tongde Hospital of Zhejiang Province

References

  1. Jemal A, Siegel R, Xu J, Ward E: Cancer statistics, 2010. CA Cancer J Clin. 2010, 60: 277-300. 10.3322/caac.20073.View ArticlePubMedGoogle Scholar
  2. Lattouf JB: Chemoprevention in bladder cancer: What's new?. Can UrolAssoc J. 2009, 3: S184-S187.Google Scholar
  3. Busby JE, Kamat AM: Chemoprevention for bladder cancer. J Urol. 2006, 176: 1914-1920. 10.1016/j.juro.2006.07.004.View ArticlePubMedGoogle Scholar
  4. Yang CS, Maliakal P, Meng X: Inhibition of carcinogenesis by tea. Annu Rev Pharmacol Toxicol. 2002, 42: 25-54. 10.1146/annurev.pharmtox.42.082101.154309.View ArticlePubMedGoogle Scholar
  5. Kemberling JK, Hampton JA, Keck RW, Gomez MA, Selman SH: Inhibition of bladder tumor growth by the green tea derivative epigallocatechin-3-gallate. J Urol. 2003, 170: 773-776. 10.1097/01.ju.0000081278.64511.96.View ArticlePubMedGoogle Scholar
  6. Zeegers MP, Tan FE, Goldbohm RA, van den Brandt PA: Are coffee and tea consumption associated with urinary tract cancer risk? A systematic review and meta-analysis. Int J Epidemiol. 2001, 30: 353-362. 10.1093/ije/30.2.353.View ArticlePubMedGoogle Scholar
  7. Morgan RW, Jain MG: Bladder cancer: smoking, beverages and artificial sweeteners. Can Med Assoc J. 1974, 111: 1067-1070.PubMed CentralPubMedGoogle Scholar
  8. Simon D, Yen S, Cole P: Coffee drinking and cancer of the lower urinary tract. J Natl Cancer Inst. 1975, 54: 587-591.PubMedGoogle Scholar
  9. Iscovich J, Castelletto R, Esteve J, Munoz N, Colanzi R, Coronel A, Deamezola I, Tassi V, Arslan A: Tobacco smoking, occupational exposure and bladder cancer in Argentina. Int J Cancer. 1987, 40: 734-740. 10.1002/ijc.2910400604.View ArticlePubMedGoogle Scholar
  10. Howe GR, Burch JD, Miller AB, Cook GM, Esteve J, Morrison B, Gordon P, Chambers LW, Fodor G, Winsor GM: Tobacco use, occupation, coffee, various nutrients, and bladder cancer. J Natl Cancer Inst. 1980, 64: 701-713.PubMedGoogle Scholar
  11. Pelucchi C, Negri E, Franceschi S, Talamini R, La Vecchia C: Alcohol drinking and bladder cancer. J Clin Epidemiol. 2002, 55: 637-641. 10.1016/S0895-4356(02)00397-9.View ArticlePubMedGoogle Scholar
  12. Demirel F, Cakan M, Yalcinkaya F, Topcuoglu M, Altug U: The association between personal habits and bladder cancer in Turkey. IntUrolNephrol. 2008, 40: 643-647.Google Scholar
  13. Heilbrun LK, Nomura A, Stemmermann GN: Black tea consumption and cancer risk: a prospective study. Br J Cancer. 1986, 54: 677-683. 10.1038/bjc.1986.226.PubMed CentralView ArticlePubMedGoogle Scholar
  14. De Stefani E, Boffetta P, Ronco AL, Deneo-Pellegrini H, Acosta G, Mendilaharsu M: Dietary patterns and risk of bladder cancer: a factor analysis in Uruguay. Cancer Causes Control. 2008, 19: 1243-1249. 10.1007/s10552-008-9195-9.View ArticlePubMedGoogle Scholar
  15. La Vecchia C, Negri E, Franceschi S, D'Avanzo B, Boyle P: Tea consumption and cancer risk. Nutr Cancer. 1992, 17: 27-31. 10.1080/01635589209514170.View ArticlePubMedGoogle Scholar
  16. Nagano J, Kono S, Preston DL, Mabuchi K: A prospective study of green tea consumption and cancer incidence, Hiroshima and Nagasaki (Japan). Cancer Causes Control. 2001, 12: 501-508. 10.1023/A:1011297326696.View ArticlePubMedGoogle Scholar
  17. Hartge P, Hoover R, West DW, Lyon JL: Coffee drinking and risk of bladder cancer. J Natl Cancer Inst. 1983, 70: 1021-1026.PubMedGoogle Scholar
  18. Slattery ML, Schumacher MC, West DW, Robison LM: Smoking and bladder cancer. The modifying effect of cigarettes on other factors. Cancer. 1988, 61: 402-408. 10.1002/1097-0142(19880115)61:2<402::AID-CNCR2820610233>3.0.CO;2-U.View ArticlePubMedGoogle Scholar
  19. Ohno Y, Aoki K, Obata K, Morrison AS: Case–control study of urinary bladder cancer in metropolitan Nagoya. Natl Cancer InstMonogr. 1985, 69: 229-234.Google Scholar
  20. Jensen OM, Wahrendorf J, Knudsen JB, Sorensen BL: The Copenhagen case–control study of bladder cancer. II. Effect of coffee and other beverages. Int J Cancer. 1986, 37: 651-657. 10.1002/ijc.2910370503.View ArticlePubMedGoogle Scholar
  21. Risch HA, Burch JD, Miller AB, Hill GB, Steele R, Howe GR: Dietary factors and the incidence of cancer of the urinary bladder. Am J Epidemiol. 1988, 127: 1179-1191.PubMedGoogle Scholar
  22. Clavel J, Cordier S: Coffee consumption and bladder cancer risk. Int J Cancer. 1991, 47: 207-212. 10.1002/ijc.2910470208.View ArticlePubMedGoogle Scholar
  23. Nomura AM, Kolonel LN, Hankin JH, Yoshizawa CN: Dietary factors in cancer of the lower urinary tract. Int J Cancer. 1991, 48: 199-205. 10.1002/ijc.2910480208.View ArticlePubMedGoogle Scholar
  24. D'Avanzo B, La Vecchia C, Franceschi S, Negri E, Talamini R, Buttino I: Coffee consumption and bladder cancer risk. Eur J Cancer. 1992, 28A: 1480-1484.View ArticlePubMedGoogle Scholar
  25. Kunze E, Chang-Claude J, Frentzel-Beyme R: Life style and occupational risk factors for bladder cancer in Germany. A case–control study. Cancer. 1992, 69: 1776-1790. 10.1002/1097-0142(19920401)69:7<1776::AID-CNCR2820690721>3.0.CO;2-P.View ArticlePubMedGoogle Scholar
  26. Chyou PH, Nomura AM, Stemmermann GN: A prospective study of diet, smoking, and lower urinary tract cancer. Ann Epidemiol. 1993, 3: 211-216. 10.1016/1047-2797(93)90021-U.View ArticlePubMedGoogle Scholar
  27. Bruemmer B, White E, Vaughan TL, Cheney CL: Fluid intake and the incidence of bladder cancer among middle-aged men and women in a three-county area of western Washington. Nutr Cancer. 1997, 29: 163-168. 10.1080/01635589709514619.View ArticlePubMedGoogle Scholar
  28. Lu CM, Lan SJ, Lee YH, Huang JK, Huang CH, Hsieh CC: Tea consumption: fluid intake and bladder cancer risk in Southern Taiwan. Urology. 1999, 54: 823-828. 10.1016/S0090-4295(99)00281-2.View ArticlePubMedGoogle Scholar
  29. Michaud DS, Spiegelman D, Clinton SK, Rimm EB, Curhan GC, Willett WC, Giovannucci EL: Fluid intake and the risk of bladder cancer in men. N Engl J Med. 1999, 340: 1390-1397. 10.1056/NEJM199905063401803.View ArticlePubMedGoogle Scholar
  30. Bianchi GD, Cerhan JR, Parker AS, Putnam SD, See WA, Lynch CF, Cantor KP: Tea consumption and risk of bladder and kidney cancers in a population-based case–control study. Am J Epidemiol. 2000, 151: 377-383. 10.1093/oxfordjournals.aje.a010217.View ArticlePubMedGoogle Scholar
  31. Nagano J, Kono S, Preston DL, Moriwaki H, Sharp GB, Koyama K, Mabuchi K: Bladder-cancer incidence in relation to vegetable and fruit consumption: a prospective study of atomic-bomb survivors. Int J Cancer. 2000, 86: 132-138. 10.1002/(SICI)1097-0215(20000401)86:1<132::AID-IJC21>3.0.CO;2-M.View ArticlePubMedGoogle Scholar
  32. Geoffroy-Perez B, Cordier S: Fluid consumption and the risk of bladder cancer: results of a multicenter case–control study. Int J Cancer. 2001, 93: 880-887. 10.1002/ijc.1411.View ArticlePubMedGoogle Scholar
  33. Zeegers MP, Dorant E, Goldbohm RA, van den Brandt PA: Are coffee, tea, and total fluid consumption associated with bladder cancer risk? Results from the Netherlands Cohort Study. Cancer Causes Control. 2001, 12: 231-238. 10.1023/A:1011245627593.View ArticlePubMedGoogle Scholar
  34. Woolcott CG, King WD, Marrett LD: Coffee and tea consumption and cancers of the bladder, colon and rectum. Eur J Cancer Prev. 2002, 11: 137-145. 10.1097/00008469-200204000-00005.View ArticlePubMedGoogle Scholar
  35. Wakai K, Hirose K, Takezaki T, Hamajima N, Ogura Y, Nakamura S, Hayashi N, Tajima K: Foods and beverages in relation to urothelial cancer: case–control study in Japan. Int J Urol. 2004, 11: 11-19. 10.1111/j.1442-2042.2004.00740.x.View ArticlePubMedGoogle Scholar
  36. De Stefani E, Boffetta P, Deneo-Pellegrini H, Correa P, Ronco AL, Brennan P, Ferro G, Acosta G, Mendilaharsu M: Non-alcoholic beverages and risk of bladder cancer in Uruguay. BMC Cancer. 2007, 7: 57-10.1186/1471-2407-7-57.PubMed CentralView ArticlePubMedGoogle Scholar
  37. Jiang X, Castelao JE, Groshen S, Cortessis VK, Shibata DK, Conti DV, Gago-Dominguez M: Water intake and bladder cancer risk in Los Angeles County. Int J Cancer. 2008, 123: 1649-1656. 10.1002/ijc.23711.View ArticlePubMedGoogle Scholar
  38. Kurahashi N, Inoue M, Iwasaki M, Sasazuki S, Tsugane S: Coffee, green tea, and caffeine consumption and subsequent risk of bladder cancer in relation to smoking status: a prospective study in Japan. Cancer Sci. 2009, 100: 294-291.View ArticlePubMedGoogle Scholar
  39. Hemelt M, Hu Z, Zhong Z, Xie LP, Wong YC, Tam PC, Cheng KK, Ye Z, Bi X, Lu Q: Fluid intake and the risk of bladder cancer: results from the South and East China case–control study on bladder cancer. Int J Cancer. 2010, 127: 638-645. 10.1002/ijc.25084.View ArticlePubMedGoogle Scholar
  40. Ros MM, Bas Bueno-de-Mesquita HB, Buchner FL, Aben KK, Kampman E, Egevad L, Overvad K, Tjonneland A, Roswall N, Clavel-Chapelon F: Fluid intake and the risk of urothelial cell carcinomas in the European Prospective Investigation into Cancer and Nutrition (EPIC). Int J Cancer. 2011, 128: 2695-2708. 10.1002/ijc.25592.View ArticlePubMedGoogle Scholar
  41. Slattery ML, West DW, Robison LM: Fluid intake and bladder cancer in Utah. Int J Cancer. 1988, 42: 17-22. 10.1002/ijc.2910420105.View ArticlePubMedGoogle Scholar
  42. Qin J, Xie LP, Zheng XY, Wang YB, Bai Y, Shen HF, Li LC, Dahiya R: A component of green tea, (−)-epigallocatechin-3-gallate, promotes apoptosis in T24 human bladder cancer cells via modulation of the PI3K/Akt pathway and Bcl-2 family proteins. Biochem Biophys Res Commun. 2007, 354: 852-857. 10.1016/j.bbrc.2007.01.003.View ArticlePubMedGoogle Scholar
  43. Mantel N, Haenszel W: Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst. 1959, 22: 719-748.PubMedGoogle Scholar
  44. DerSimonian R, Laird N: Meta-analysis in clinical trials. Control Clin Trials. 1986, 7: 177-188. 10.1016/0197-2456(86)90046-2.View ArticlePubMedGoogle Scholar
  45. Higgins JP, Thompson SG, Deeks JJ, Altman DG: Measuring inconsistency in meta-analyses. BMJ. 2003, 327: 557-560. 10.1136/bmj.327.7414.557.PubMed CentralView ArticlePubMedGoogle Scholar
  46. Egger M, Davey Smith G, Schneider M, Minder C: Bias in meta-analysis detected by a simple, graphical test. BMJ. 1997, 315: 629-634. 10.1136/bmj.315.7109.629.PubMed CentralView ArticlePubMedGoogle Scholar
  47. Begg CB, Mazumdar M: Operating characteristics of a rank correlation test for publication bias. Biometrics. 1994, 50: 1088-1101. 10.2307/2533446.View ArticlePubMedGoogle Scholar

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© Qin et al.; licensee BioMed Central Ltd. 2012

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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