Journal Article

Green tea, black tea and colorectal cancer risk: a meta-analysis of epidemiologic studies

Can-Lan Sun, Jian-Min Yuan, Woon-Puay Koh and Mimi C. Yu

in Carcinogenesis

Volume 27, issue 7, pages 1301-1309
Published in print July 2006 | ISSN: 0143-3334
Published online April 2006 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgl024
Green tea, black tea and colorectal cancer risk: a meta-analysis of epidemiologic studies

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Experimental studies have supported tea as a chemopreventive agent for colorectal cancer. No quantitative summary of the epidemiologic evidence on tea and colorectal cancer risk has ever been performed. The current meta-analysis included 25 papers conducted in 11 countries across three continents (North America, Asia and Europe). Summary odds ratios (ORs) for highest versus non/lowest tea consumption levels were calculated based on fixed and random effects models. The meta-regression and stratified methods were used to examine heterogeneity across studies. For green tea, the combined results from eight studies indicated a reduced risk of colorectal cancer with intake [summary OR = 0.82, 95% confidence interval (CI) = 0.69–0.98]. The protective effect is mainly found among the three case–control studies of colon cancer (summary OR = 0.74, 95% CI = 0.60–0.93). Results from studies of rectal cancer irrespective of study design (case–control versus cohort) (summary OR = 0.99, 95% CI = 0.71–1.37) and cohort studies of colon cancer (summary OR = 0.99, 95% CI = 0.79–1.24) were compatible with the null hypothesis. For black tea, the summary OR derived from 20 studies was 0.99 (95% CI = 0.87–1.13). There is wide divergence in results across the 20 individual studies; formal tests for homogeneity across studies revealed statistically significant differences in findings across all studies (P < 0.001), amongst the 7 cohort studies (P = 0.002), and amongst the 13 case–control studies (P < 0.001). Despite the strong evidence from in vitro and non-human in vivo studies in support of green and black tea as potential chemopreventive agents against colorectal cancer, available epidemiologic data are insufficient to conclude that either tea type may protect against colorectal cancer in humans.

Keywords: CI, confidence interval; HCC, hospital-based case–control study; OR, odds ratio; PCC, population-based case–control study; RR, relative risk

Journal Article.  6200 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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