Relationship between green tea drinking and the risk of colorectal cancer; a systematic review and meta-analysis

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Abstract
Introduction: Green tea drinking is one of the traditional methods to prevent colorectal cancer (CRC). The present study proposes a systematic review and meta-analysis approach to investigate the relationship between green tea drinking and CRC risk. Materials and Methods: The literature survey has been carried out using the previously published studies in the Google Scholar search engine and various electronic databases, including Scopus, Cochrane, Web of Science, Embase, and PubMed. The review process has continued until July 13, 2021. Besides, the Q test and I2 index were employed to evaluate the heterogeneity of the studies. STATA 14 software has been conducted to analyze the gathered dataset. It is essential to note that the significance level for statistical tests was set to 5% (P value < 0.05). Results: The results of 18 studies accomplished on 44,992 patients aged 19-80 years have been used to compute the relative risk of green tea consumption in CRC (OR [odds ratio] = 0.99; 95% CI: 0.83-1.18), colon (OR=0.97; 95% CI: 0.85-1.10), and rectum (OR=1; 95% CI: 0.86-1.16). Although green tea consumption was a protective factor in Asia and the United States, it was considered a risk factor in Australia. The general population studies classified green tea as a risk factor for CRC, while hospital studies considered this product as a protective factor. Conclusion: The findings showed that green tea had the most significant effect on reducing the colon cancer risk, while it had the minimum influence on CRC. Additionally, it did not affect rectal cancer. It is essential to note that these relationships were not statistically significant. Registration: The current protocol was also registered on PROSPERO (#CRD42021276257, https://www.crd.york. ac.uk/prospero/display_record.php?ID=CRD42021276257).

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