Carcinogenesis Advance Access published online on April 25, 2006
Carcinogenesis, doi:10.1093/carcin/bgl024
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1 University of Minnesota Cancer Center, Minneapolis, Minnesota 55455, USA
* To whom correspondence should be addressed. Experimental studies have supported tea as a chemopreventive agent for colorectal cancer. No quantitative summary (i.e., meta-analysis) has been conducted on this issue, separated by tea types. The current meta-analysis included 21 papers published up to January 2005, which examined the association in 10 countries and provided data on consumption of green and/or black tea and colorectal cancer risk. Summary odds ratios (ORs) for highest vs. non- or lowest tea consumption levels were calculated based on fixed and random effects models. Heterogeneity between studies was examined via the Q statistics. For green tea, the combined results from the six studies indicated a reduced risk of colorectal cancer with intake [summary OR=0.79, 95% confidence interval (CI) = 0.64-0.97]. The protective effect is mainly supported by the four case-control studies (summary OR=0.74, 95% CI=0.63-0.86). Results from the two cohort studies are compatible with the null hypothesis (summary OR=1.02, 95% CI=0.80-1.31). For black tea, the summary OR derived from 17 studies was 1.00 (95% CI=0.88-1.14). However, there is wide divergence in results across the individual studies; formal tests for homogeneity across studies revealed statistically significant difference across all 17 studies, across the six cohort studies, and across the 11 case-control studies. 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
Can-Lan Sun, E-mail: canlans{at}umn.edu
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