Oral Oncology xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Oral Oncology journal homepage: www.elsevier.com/locate/oraloncology
Association of tea consumption and the risk of oral cancer: A meta-analysis Wanchun Wang a,⇑, Yu’e Yang b, Wenyi Zhang a, Wenlong Wu c a
Department of Periodontology and Oral Mucosal Diseases, Qingdao Stomatological Hospital, Qingdao, China Department of Pediatric Dentistry, Qingdao Stomatological Hospital, Qingdao, China c Department of Epidemiology and Health Statistics, Medical College of Qingdao University, Qingdao, China b
a r t i c l e
i n f o
Article history: Received 23 September 2013 Received in revised form 16 November 2013 Accepted 15 December 2013 Available online xxxx Keywords: Tea consumption Oral cancer Meta-analysis
s u m m a r y Objectives: Epidemiological studies evaluating the association of tea consumption and the risk of oral cancer risk have produced inconsistent results. Thus, we conducted a meta-analysis to assess the relationship between tea consumption and oral cancer risk. Methods: Pertinent studies were identified by a search in PubMed, Web of Knowledge and Wan Fang Med Online. The fixed or random effect model was used based on heterogeneity test. Publication bias was estimated using Egger’s regression asymmetry test. Results: Finally, 14 articles with 19 studies comprising 4675 oral cancer cases were included in this meta-analysis. The relative risk (95% confidence interval) of oral cancer for the highest versus the lowest category of tea consumption was 0.853 (0.779–0.934), and the association was significant between oral cancer risk and green tea consumption [0.798 (0.673–0.947)] but not in the black tea consumption [0.953 (0.792–1.146)]. The associations were also significant in Asian and Caucasian. Conclusions: Our analysis indicated that tea consumption may have a protective effect on oral cancer, especially in green tea consumption. Ó 2013 Elsevier Ltd. All rights reserved.
Introduction Oral cavity cancer, comprising cancer of tongue, buccal mucosa, upper or lower gingival, floor of mouth and hard palate, represents the eighth most frequent cancer worldwide [1]. In China, it was reported that the incidence rate and mortality rate of oral cavity cancer were 3.29 per 100,000 and 1.49 per 100,000 in 2008 [2]. Oral cancer is a serious problem in many parts of the world [3], mainly due to its low survival rate [4] and poor life quality [5,6], especially for advanced oral cancer cases. Thus, primary prevention is important. Many studies have shown that oral cancer is associated with genetic factors [7–9]. Furthermore, many environmental factors such as tobacco smoking [10], alcohol drinking [11], fruit and vegetables [12] can also affect the incidence of oral cancer. Tea, which is derived from the leaves of the plant Camellia sinensis, is one of the most popular beverages consumed worldwide, and generally the most consumed are black tea and green tea. Evidence from laboratory studies strongly showed the inhibition of tumorigenesis by tea and its constituents [13,14]. Up to date, a number of epidemiologic studies have been published
to explore the relationship between tea consumption and oral cancer risk. However, the results are not consistent. Therefore, we conducted a meta-analysis to (1) first assess the oral cancer risk for the highest vs. lowest categories of tea consumption; (2) assess the heterogeneity among studies and publication bias. Methods Search strategy We performed a literature search up to June 2013 using the databases of PubMed, Web of Knowledge and Wan Fang Med Online. The following search terms were used: ‘tea’ and ‘oral cancer’ without restrictions. Moreover, we reviewed the reference lists from retrieved articles to search for further relevant studies. Two investigators searched articles and reviewed of all retrieved studies independently. Disagreements between the two investigators were resolved by consensus with a third reviewer. Inclusion criteria
⇑ Corresponding author. Address: Department of Periodontology and Oral Mucosal Diseases, Qingdao Stomatological Hospital, Dexian Road, Qingdao, China. Tel./fax: +86 53282821902. E-mail address: [email protected] (W. Wang).
All relevant studies reporting the association of tea and oral cancer risk were considered for inclusion. The inclusion criteria were as follows: (1) case-control or cohort study assessing the
1368-8375/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.oraloncology.2013.12.014
Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
2
W. Wang et al. / Oral Oncology xxx (2014) xxx–xxx
association between tea consumption and oral cancer risk; (2) the exposure of interest was green tea, black tea or total tea consumption; (3) the outcome of interest was oral cancer; (4) results including relative risk (RR) or OR and its 95% CIs, or providing us with sufficient information to calculate them and (5) the abstracts were included if they provide the RR (95% CI) of oral cancer associated with tea consumption. Accordingly, the following exclusion criteria were also used: (1) reviews and (2) repeated or overlapped publications. Data extraction The following data were collected from all studies independently by two investigators: the design type (case-control study or cohort study), the first author’s last name, publication year, location where the study was performed, sample size and number of cases, variables adjusted for in the analysis, RR estimates (we presented all results with RR for simplicity) with corresponding 95% CI for the highest versus lowest categories of tea and oral cancer, respectively. For studies that reported results from various covariate analyses, we abstracted the estimates based on the model that included the most potential confounders. If there was disagreement between the two investigators about eligibility of the data, it was resolved by consensus with a third reviewer. Statistical analysis The pooled measure was calculated as the inverse varianceweighted mean of the natural logarithm of multivariate adjusted RR with 95% CI for the highest vs. lowest levels to assess the association of tea consumption and oral cancer risk. The Q test and I2 of Higgins and Thompson [15] were used to assess heterogeneity among included studies. I2 describes the proportion of total variation attributable to between-study heterogeneity as opposed to random error or chance. In the presence of substantial heterogeneity (I2 > 50%) [16], the DerSimonian and Laird random-effect model was adopted as the pooling method; otherwise, the fixed-effect model was used as the pooling method. Publication bias was estimated using Begg0 funnel plot [17] and Egger0 s regression asymmetry test [18]. A study of influence analysis [19] was conducted to describe how robust the pooled estimator is to removal of individual studies. An individual study is suspected of excessive influence if the point estimate of its omitted analysis lies outside the 95% CI of the combined analysis. All the statistical analyses were performed with STATA version 10.0 (Stata Corporation, College Station, TX, USA). Two-tailed P 6 0.05 was accepted as statistically significant. Results Characteristics of studies The search strategy identified 343 articles from PubMed, 595 articles from the Web of Knowledge and 24 articles from Wan Fang Med Online. 30 articles were reviewed in full after reviewing the title/abstract. One article reported the upper aerodigestive tract cancer with tea consumption and one article reported the coffee and tea consumption with the risk of oral cancer. 12 articles were review. Two articles that did not report the risk estimate were also excluded. Finally, 14 articles [20–33] were included in this meta-analysis. Fig. 1 presents the flow chart for exclusion/inclusion process. For tea consumption and oral cancer, data from 14 articles with 19 studies (4 prospective studies and 15 case-control studies) were used including 4675 oral cancer cases. 6 studies were carried out in China, 4 in United States, 3 in Brazil, 2 in Italy, 2 in Japan, 1 in
Figure 1. The flow chart for exclusion/inclusion process.
France and 1 in Denmark. Inverse association of tea consumption with risk of oral cancer was reported in 4 studies. Five studies were carried out to assess the association between green tea and oral cancer. The detailed characteristics of the relevant studies are shown in Table 1. Quantitative synthesis Highest tea consumption level versus lowest level was significantly associated with the risk of oral cancer [summary RR = 0.853, 95% CI = 0.779–0.934, I2 = 23.8%] (Fig. 2). Five studies with 1313 cases were carried out for green tea and three studies with 1127 cases were carried out for black tea to assess the risk of oral cancer. Significant association was found between oral cancer and green tea (RR = 0.798, 95% CI = 0.673–0.947, I2 = 0.0%) (Fig. 3), but not in black tea (RR = 0.953, 95% CI = 0.792–1.146, I2 = 0.0%). The associations were significant between tea consumption and oral cancer in Asian (RR = 0.866, 95% CI = 0.764–0.982, I2 = 0.0%) and Caucasian (RR = 0.822, 95% CI = 0.717–0.943, I2 = 36.2%). For the study design, significant associations were also found in prospective studies (RR = 0.796, 95% CI = 0.651–0.974, I2 = 0.0%) and case-control studies (RR = 0.868, 95% CI = 0.785–0.960, I2 = 31.7%), respectively. The main results are summarized in Table 2. Influence analysis and publication bias Influence analysis showed that no individual study had excessive influence on the association of tea consumption and oral
Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
W. Wang et al. / Oral Oncology xxx (2014) xxx–xxx
3
Table 1 Characteristics of studies on tea consumption and oral cancer risk. First author, year
Country
Study design
Cases, age
Tea type
RR (95%CI) for highest versus lowest category
Adjustment for covariates
Radoi et al. (2013) [20]
France
Casecontrol
593, 1 cup/d, >1cup/wk, T polymorphism in the interleukin-8 gene and oral cancer risk: a metaanalysis. Gene 2013;522:168–76. [8] Wang W, Zhao Y, Yang J, Lin B, Gu H, Cao X, et al. Cyclin D1 polymorphism and oral cancer: a meta-analysis. Mol Biol Rep 2013;40:87–95. [9] Li W, Chen J, Liu C. Glutathione S-transferase P1 Ile105Val polymorphism and oral cancer risk: a meta-analysis. Int J Med Sci 2013;10:392–8. [10] IARC Monographs programme on the evaluation of the carcinogenic risk of chemicals to humans. Preamble. IARC Monogr Eval Carcinog Risk Chem Hum 1986; 39:13–32. [11] Ferreira Antunes JL, Toporcov TN, Biazevic MG, Boing AF, Scully C, Petti S. Joint and independent effects of alcohol drinking and tobacco smoking on oral cancer: a large case-control study. PLoS ONE 2013;8:e68132. [12] Chainani-Wu N, Epstein J, Touger-Decker R. Diet and prevention of oral cancer: strategies for clinical practice. J Am Dent Assoc 2011;142:166–9. [13] Yang CS, Wang H, Li GX, Yang Z, Guan F, Jin H. Cancer prevention by tea: Evidence from laboratory studies. Pharmacol Res 2011;64:113–22. [14] Lambert JD, Elias RJ. The antioxidant and pro-oxidant activities of green tea polyphenols: a role in cancer prevention. Arch Biochem Biophys 2010;501:65–72. [15] Higgins JP, Thompson SG. Quantifying heterogeneity in a meta-analysis. Stat Med 2002;21:1539–58. [16] Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. BMJ 2003;327:557–60. [17] Begg CB, Mazumdar M. Operating characteristics of a rank correlation test for publication bias. Biometrics 1994;50:1088–101. [18] Egger M. Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997;315:629–34. [19] Tobias A. Assessing the in fluence of a single study in the meta-analysis estimate. Stata Tech Bull 1999;47:15–7. [20] Radoi L, Paget-Bailly S, Menvielle G, Cyr D, Schmaus A, Carton M, et al. Tea and coffee consumption and risk of oral cavity cancer: results of a large population-based case-control study, the ICARE study. Cancer Epidemiol 2013;37:284–9. [21] Fu JY, Gao J, Zhang ZY, Zheng JW, Luo JF, Zhong LP, et al. Tea consumption and the risk of oral cancer incidence: A case-control study from China. Oral Oncol 2013;49:918–22. [22] Hildebrand JS, Patel AV, McCullough ML, Gaudet MM, Chen AY, Hayes RB, et al. Coffee, tea, and fatal oral/pharyngeal cancer in a large prospective US cohort. Am J Epidemiol 2013;177:50–8. [23] Ren JS, Freedman ND, Kamangar F, Dawsey SM, Hollenbeck AR, Schatzkin A, et al. Tea, coffee, carbonated soft drinks and upper gastrointestinal tract cancer risk in a large United States prospective cohort study. Eur J Cancer 2010;46:1873–81. [24] Ide R, Fujino Y, Hoshiyama Y, Mizoue T, Kubo T, Pham TM, et al. A prospective study of green tea consumption and oral cancer incidence in Japan. Ann Epidemiol 2007;17:821–6. [25] Toporcov TN, Antunes JL, Tavares MR. Fat food habitual intake and risk of oral cancer. Oral Oncol 2004;40:925–31.
Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
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[26] Tavani A, Bertuzzi M, Talamini R, Gallus S, Parpinel M, Franceschi S, et al. Coffee and tea intake and risk of oral, pharyngeal and esophageal cancer. Oral Oncol 2003;39:695–700. [27] Takezaki T, Hirose K, Inoue M, Hamajima N, Kuroishi T, Nakamura S, et al. Tobacco, alcohol and dietary factors associated with the risk of oral cancer among Japanese. Jpn J Cancer Res 1996;87:555–62. [28] Bundgaard T, Wildt J, Frydenberg M, Elbrond O, Nielsen JE. Case-control study of squamous cell cancer of the oral cavity in Denmark. Cancer Causes Control 1995;6:57–67. [29] Zheng T, Boyle P, Willett WC, Hu H, Dan J, Evstifeeva TV, et al. A case-control study of oral cancer in Beijing, People’s Republic of China. Associations with nutrient intakes, foods and food groups. Eur J Cancer B Oral Oncol 1993;29B:45–55. [30] Pintos J, Franco EL, Oliveira BV, Kowalski LP, Curado MP, Dewar R. Mate, coffee, and tea consumption and risk of cancers of the upper aerodigestive tract in southern Brazil. Epidemiology 1994;5:583–90. [31] Mashberg A, Boffetta P, Winkelman R, Garfinkel L. Tobacco smoking, alcohol drinking, and cancer of the oral cavity and oropharynx among U.S. veterans. Cancer 1993;72:1369–75. [32] Franceschi S, Barra S, La Vecchia C, Bidoli E, Negri E, Talamini R. Risk factors for cancer of the tongue and the mouth. A case-control study from northern Italy. Cancer 1992;70:2227–33. [33] Franco EL, Kowalski LP, Oliveira BV, Curado MP, Pereira RN, Silva ME, et al. Risk factors for oral cancer in Brazil: a case-control study. Int J Cancer 1989;43:992–1000. [34] Qin J, Xie LP, Zheng XY, Wang YB, Bai Y, Shen HF, et al. 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;354:852–7. [35] Adhami VM, Ahmad N, Mukhtar H. Molecular targets for green tea in prostate cancer prevention. J Nutr 2003;133:2417S–24S. [36] Sartippour MR, Heber D, Ma J, Lu Q, Go VL, Nguyen M. Green tea and its catechins inhibit breast cancer xenografts. Nutr Cancer 2001;40:149–56. [37] Wang Y, Yu X, Wu Y, Zhang D. Coffee and tea consumption and risk of lung cancer: a dose-response analysis of observational studies. Lung cancer 2012;78:169–70.
[38] Qin J, Xie B, Mao Q, Kong D, Lin Y, Zheng X. Tea consumption and risk of bladder cancer: a meta-analysis. World J Surg Oncol 2012;10:172. [39] Wang X, Lin YW, Wang S, Wu J, Mao QQ, Zheng XY, et al. A meta-analysis of tea consumption and the risk of bladder cancer. Urol Int 2013;90:10–6. [40] Wu S, Li F, Huang X, Hua Q, Huang T, Liu Z, et al. The association of tea consumption with bladder cancer risk: a meta-analysis. Asia Pac J Clin Nutr 2013;22:128–37. [41] Zheng P, Zheng HM, Deng XM, Zhang YD. Green tea consumption and risk of esophageal cancer: a meta-analysis of epidemiologic studies. BMC Gastroenterol 2012;12:165. [42] Sang LX, Chang B, Li XH, Jiang M. Green tea consumption and risk of esophageal cancer: a meta-analysis of published epidemiological studies. Nutr Cancer 2013;65:802–12. [43] Wu Y, Zhang D, Kang S. Black tea, green tea and risk of breast cancer: an update. Springerplus 2013;2:240. [44] Khafif A, Schantz SP, al-Rawi M, Edelstein D, Sacks PG. Green tea regulates cell cycle progression in oral leukoplakia. Head Neck 1998;20:528–34. [45] Hsu SD, Singh BB, Lewis JB, Borke JL, Dickinson DP, Drake L, et al. Chemoprevention of oral cancer by green tea. Gen Dent 2002;50:140–6. [46] Babich H, Krupka ME, Nissim HA, Zuckerbraun HL. Differential in vitro cytotoxicity of (-)-epicatechin gallate (ECG) to cancer and normal cells from the human oral cavity. Toxicol In Vitro 2005;19:231–42. [47] Lee MJ, Lambert JD, Prabhu S, Meng X, Lu H, Maliakal P, et al. Delivery of tea polyphenols to the oral cavity by green tea leaves and black tea extract. Cancer Epidemiol Biomarkers Prev 2004;13:132–7. [48] Otake S, Makimura M, Kuroki T, Nishihara Y, Hirasawa M. Anticaries effects of polyphenolic compounds from Japanese green tea. Caries Res 1991;25:438–43. [49] Makimura M, Hirasawa M, Kobayashi K, Indo J, Sakanaka S, Taguchi T, et al. Inhibitory effect of tea catechins on collagenase activity. J Periodontol 1993;64:630–6. [50] Sakanaka S, Aizawa M, Kim M, Yamamoto T. Inhibitory effects of green tea polyphenols on growth and cellular adherence of an oral bacterium Porphyromonas gingivalis. Biosci Biotechnol Biochem 1996;60:745–9.
Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
Contents lists available at ScienceDirect
Oral Oncology journal homepage: www.elsevier.com/locate/oraloncology
Association of tea consumption and the risk of oral cancer: A meta-analysis Wanchun Wang a,⇑, Yu’e Yang b, Wenyi Zhang a, Wenlong Wu c a
Department of Periodontology and Oral Mucosal Diseases, Qingdao Stomatological Hospital, Qingdao, China Department of Pediatric Dentistry, Qingdao Stomatological Hospital, Qingdao, China c Department of Epidemiology and Health Statistics, Medical College of Qingdao University, Qingdao, China b
a r t i c l e
i n f o
Article history: Received 23 September 2013 Received in revised form 16 November 2013 Accepted 15 December 2013 Available online xxxx Keywords: Tea consumption Oral cancer Meta-analysis
s u m m a r y Objectives: Epidemiological studies evaluating the association of tea consumption and the risk of oral cancer risk have produced inconsistent results. Thus, we conducted a meta-analysis to assess the relationship between tea consumption and oral cancer risk. Methods: Pertinent studies were identified by a search in PubMed, Web of Knowledge and Wan Fang Med Online. The fixed or random effect model was used based on heterogeneity test. Publication bias was estimated using Egger’s regression asymmetry test. Results: Finally, 14 articles with 19 studies comprising 4675 oral cancer cases were included in this meta-analysis. The relative risk (95% confidence interval) of oral cancer for the highest versus the lowest category of tea consumption was 0.853 (0.779–0.934), and the association was significant between oral cancer risk and green tea consumption [0.798 (0.673–0.947)] but not in the black tea consumption [0.953 (0.792–1.146)]. The associations were also significant in Asian and Caucasian. Conclusions: Our analysis indicated that tea consumption may have a protective effect on oral cancer, especially in green tea consumption. Ó 2013 Elsevier Ltd. All rights reserved.
Introduction Oral cavity cancer, comprising cancer of tongue, buccal mucosa, upper or lower gingival, floor of mouth and hard palate, represents the eighth most frequent cancer worldwide [1]. In China, it was reported that the incidence rate and mortality rate of oral cavity cancer were 3.29 per 100,000 and 1.49 per 100,000 in 2008 [2]. Oral cancer is a serious problem in many parts of the world [3], mainly due to its low survival rate [4] and poor life quality [5,6], especially for advanced oral cancer cases. Thus, primary prevention is important. Many studies have shown that oral cancer is associated with genetic factors [7–9]. Furthermore, many environmental factors such as tobacco smoking [10], alcohol drinking [11], fruit and vegetables [12] can also affect the incidence of oral cancer. Tea, which is derived from the leaves of the plant Camellia sinensis, is one of the most popular beverages consumed worldwide, and generally the most consumed are black tea and green tea. Evidence from laboratory studies strongly showed the inhibition of tumorigenesis by tea and its constituents [13,14]. Up to date, a number of epidemiologic studies have been published
to explore the relationship between tea consumption and oral cancer risk. However, the results are not consistent. Therefore, we conducted a meta-analysis to (1) first assess the oral cancer risk for the highest vs. lowest categories of tea consumption; (2) assess the heterogeneity among studies and publication bias. Methods Search strategy We performed a literature search up to June 2013 using the databases of PubMed, Web of Knowledge and Wan Fang Med Online. The following search terms were used: ‘tea’ and ‘oral cancer’ without restrictions. Moreover, we reviewed the reference lists from retrieved articles to search for further relevant studies. Two investigators searched articles and reviewed of all retrieved studies independently. Disagreements between the two investigators were resolved by consensus with a third reviewer. Inclusion criteria
⇑ Corresponding author. Address: Department of Periodontology and Oral Mucosal Diseases, Qingdao Stomatological Hospital, Dexian Road, Qingdao, China. Tel./fax: +86 53282821902. E-mail address: [email protected] (W. Wang).
All relevant studies reporting the association of tea and oral cancer risk were considered for inclusion. The inclusion criteria were as follows: (1) case-control or cohort study assessing the
1368-8375/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.oraloncology.2013.12.014
Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
2
W. Wang et al. / Oral Oncology xxx (2014) xxx–xxx
association between tea consumption and oral cancer risk; (2) the exposure of interest was green tea, black tea or total tea consumption; (3) the outcome of interest was oral cancer; (4) results including relative risk (RR) or OR and its 95% CIs, or providing us with sufficient information to calculate them and (5) the abstracts were included if they provide the RR (95% CI) of oral cancer associated with tea consumption. Accordingly, the following exclusion criteria were also used: (1) reviews and (2) repeated or overlapped publications. Data extraction The following data were collected from all studies independently by two investigators: the design type (case-control study or cohort study), the first author’s last name, publication year, location where the study was performed, sample size and number of cases, variables adjusted for in the analysis, RR estimates (we presented all results with RR for simplicity) with corresponding 95% CI for the highest versus lowest categories of tea and oral cancer, respectively. For studies that reported results from various covariate analyses, we abstracted the estimates based on the model that included the most potential confounders. If there was disagreement between the two investigators about eligibility of the data, it was resolved by consensus with a third reviewer. Statistical analysis The pooled measure was calculated as the inverse varianceweighted mean of the natural logarithm of multivariate adjusted RR with 95% CI for the highest vs. lowest levels to assess the association of tea consumption and oral cancer risk. The Q test and I2 of Higgins and Thompson [15] were used to assess heterogeneity among included studies. I2 describes the proportion of total variation attributable to between-study heterogeneity as opposed to random error or chance. In the presence of substantial heterogeneity (I2 > 50%) [16], the DerSimonian and Laird random-effect model was adopted as the pooling method; otherwise, the fixed-effect model was used as the pooling method. Publication bias was estimated using Begg0 funnel plot [17] and Egger0 s regression asymmetry test [18]. A study of influence analysis [19] was conducted to describe how robust the pooled estimator is to removal of individual studies. An individual study is suspected of excessive influence if the point estimate of its omitted analysis lies outside the 95% CI of the combined analysis. All the statistical analyses were performed with STATA version 10.0 (Stata Corporation, College Station, TX, USA). Two-tailed P 6 0.05 was accepted as statistically significant. Results Characteristics of studies The search strategy identified 343 articles from PubMed, 595 articles from the Web of Knowledge and 24 articles from Wan Fang Med Online. 30 articles were reviewed in full after reviewing the title/abstract. One article reported the upper aerodigestive tract cancer with tea consumption and one article reported the coffee and tea consumption with the risk of oral cancer. 12 articles were review. Two articles that did not report the risk estimate were also excluded. Finally, 14 articles [20–33] were included in this meta-analysis. Fig. 1 presents the flow chart for exclusion/inclusion process. For tea consumption and oral cancer, data from 14 articles with 19 studies (4 prospective studies and 15 case-control studies) were used including 4675 oral cancer cases. 6 studies were carried out in China, 4 in United States, 3 in Brazil, 2 in Italy, 2 in Japan, 1 in
Figure 1. The flow chart for exclusion/inclusion process.
France and 1 in Denmark. Inverse association of tea consumption with risk of oral cancer was reported in 4 studies. Five studies were carried out to assess the association between green tea and oral cancer. The detailed characteristics of the relevant studies are shown in Table 1. Quantitative synthesis Highest tea consumption level versus lowest level was significantly associated with the risk of oral cancer [summary RR = 0.853, 95% CI = 0.779–0.934, I2 = 23.8%] (Fig. 2). Five studies with 1313 cases were carried out for green tea and three studies with 1127 cases were carried out for black tea to assess the risk of oral cancer. Significant association was found between oral cancer and green tea (RR = 0.798, 95% CI = 0.673–0.947, I2 = 0.0%) (Fig. 3), but not in black tea (RR = 0.953, 95% CI = 0.792–1.146, I2 = 0.0%). The associations were significant between tea consumption and oral cancer in Asian (RR = 0.866, 95% CI = 0.764–0.982, I2 = 0.0%) and Caucasian (RR = 0.822, 95% CI = 0.717–0.943, I2 = 36.2%). For the study design, significant associations were also found in prospective studies (RR = 0.796, 95% CI = 0.651–0.974, I2 = 0.0%) and case-control studies (RR = 0.868, 95% CI = 0.785–0.960, I2 = 31.7%), respectively. The main results are summarized in Table 2. Influence analysis and publication bias Influence analysis showed that no individual study had excessive influence on the association of tea consumption and oral
Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
W. Wang et al. / Oral Oncology xxx (2014) xxx–xxx
3
Table 1 Characteristics of studies on tea consumption and oral cancer risk. First author, year
Country
Study design
Cases, age
Tea type
RR (95%CI) for highest versus lowest category
Adjustment for covariates
Radoi et al. (2013) [20]
France
Casecontrol
593, 1 cup/d, >1cup/wk, T polymorphism in the interleukin-8 gene and oral cancer risk: a metaanalysis. Gene 2013;522:168–76. [8] Wang W, Zhao Y, Yang J, Lin B, Gu H, Cao X, et al. Cyclin D1 polymorphism and oral cancer: a meta-analysis. Mol Biol Rep 2013;40:87–95. [9] Li W, Chen J, Liu C. Glutathione S-transferase P1 Ile105Val polymorphism and oral cancer risk: a meta-analysis. Int J Med Sci 2013;10:392–8. [10] IARC Monographs programme on the evaluation of the carcinogenic risk of chemicals to humans. Preamble. IARC Monogr Eval Carcinog Risk Chem Hum 1986; 39:13–32. [11] Ferreira Antunes JL, Toporcov TN, Biazevic MG, Boing AF, Scully C, Petti S. Joint and independent effects of alcohol drinking and tobacco smoking on oral cancer: a large case-control study. PLoS ONE 2013;8:e68132. [12] Chainani-Wu N, Epstein J, Touger-Decker R. Diet and prevention of oral cancer: strategies for clinical practice. J Am Dent Assoc 2011;142:166–9. [13] Yang CS, Wang H, Li GX, Yang Z, Guan F, Jin H. Cancer prevention by tea: Evidence from laboratory studies. Pharmacol Res 2011;64:113–22. [14] Lambert JD, Elias RJ. The antioxidant and pro-oxidant activities of green tea polyphenols: a role in cancer prevention. Arch Biochem Biophys 2010;501:65–72. [15] Higgins JP, Thompson SG. Quantifying heterogeneity in a meta-analysis. Stat Med 2002;21:1539–58. [16] Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. BMJ 2003;327:557–60. [17] Begg CB, Mazumdar M. Operating characteristics of a rank correlation test for publication bias. Biometrics 1994;50:1088–101. [18] Egger M. Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997;315:629–34. [19] Tobias A. Assessing the in fluence of a single study in the meta-analysis estimate. Stata Tech Bull 1999;47:15–7. [20] Radoi L, Paget-Bailly S, Menvielle G, Cyr D, Schmaus A, Carton M, et al. Tea and coffee consumption and risk of oral cavity cancer: results of a large population-based case-control study, the ICARE study. Cancer Epidemiol 2013;37:284–9. [21] Fu JY, Gao J, Zhang ZY, Zheng JW, Luo JF, Zhong LP, et al. Tea consumption and the risk of oral cancer incidence: A case-control study from China. Oral Oncol 2013;49:918–22. [22] Hildebrand JS, Patel AV, McCullough ML, Gaudet MM, Chen AY, Hayes RB, et al. Coffee, tea, and fatal oral/pharyngeal cancer in a large prospective US cohort. Am J Epidemiol 2013;177:50–8. [23] Ren JS, Freedman ND, Kamangar F, Dawsey SM, Hollenbeck AR, Schatzkin A, et al. Tea, coffee, carbonated soft drinks and upper gastrointestinal tract cancer risk in a large United States prospective cohort study. Eur J Cancer 2010;46:1873–81. [24] Ide R, Fujino Y, Hoshiyama Y, Mizoue T, Kubo T, Pham TM, et al. A prospective study of green tea consumption and oral cancer incidence in Japan. Ann Epidemiol 2007;17:821–6. [25] Toporcov TN, Antunes JL, Tavares MR. Fat food habitual intake and risk of oral cancer. Oral Oncol 2004;40:925–31.
Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
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Please cite this article in press as: Wang W et al. Association of tea consumption and the risk of oral cancer: A meta-analysis. Oral Oncol (2014), http:// dx.doi.org/10.1016/j.oraloncology.2013.12.014
