Carcinogenesis Advance Access first published online on April 25, 2006
This version published online on May 2, 2006
Carcinogenesis, doi:10.1093/carcin/bgl024
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1 The Cancer Center, University of Minnesota, Minneapolis, MN 55455, USA
* To whom correspondence should be addressed. 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 vs. 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 vs. 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.
Received July 6, 2005
Revised February 13, 2006
Accepted March 22, 2006
REVIEW
Green tea, black tea and colorectal cancer risk: a meta-analysis of epidemiologic studies
Can-Lan Sun 1,
Jian-Min Yuan 1 *,
Woon-Puay Koh 2,
and
Mimi C. Yu 1
2 Department of Community, Occupational and Family Medicine, National University of Singapore, Singapore 117597
Jian-Min Yuan, E-mail: jyuan{at}umn.edu
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