Review for 10.1186/s12876-023-02928-8 (2023)

Title: Association between tea consumption and colorectal cancer: a systematic review and
meta-analysis of a population-based study
Version: 1 Date: 29 Jun 2023
Reviewer's report:
Limited search scope: The meta-analysis only included articles published in English until May
2022, which might exclude relevant studies published in other languages or after the specified
time frame. This could introduce bias and affect the comprehensiveness of the analysis. please
update the date of your search as well.
Heterogeneity of included studies: The high heterogeneity (I2=99.5%) observed in the analysis
raises concerns about the consistency of the results. The causes of such heterogeneity should
have been thoroughly explored and discussed.
Inconsistent findings: While the overall analysis suggests no significant association between
tea consumption and colorectal cancer (CRC) risk, the subgroup analysis reveals contradictory
results across different geographic regions and tea types. The lack of a clear explanation for
these discrepancies weakens the reliability of the conclusions.
Quality assessment and risk of bias: The Newcastle-Ottawa Scale was used to assess study
quality, but the specific criteria for high and low quality were not clearly defined. The potential
risk of bias in the included studies should have been discussed in more detail.
Inclusion of different study designs: The meta-analysis included various study designs, including
case-control studies, cohort studies, and a randomized controlled trial. Combining data from
different study designs can introduce additional heterogeneity and potentially impact the validity
of the results.
Limited data extraction: The information extracted from the included studies seems limited to
basic characteristics such as sample size, tea types, and cancer sites. More detailed data, such
as specific tea consumption levels or duration, could have provided further insights into the
association between tea consumption and CRC risk.
Lack of dose-response analysis: The meta-analysis did not include a comprehensive dose-
response analysis to explore the potential relationship between different levels of tea
consumption and CRC risk. This analysis could have provided valuable information on the dose-
dependent effect of tea consumption.
Possible publication bias: While Egger's test suggested no significant publication bias, it is
important to consider that negative or non-significant results might be less likely to be published,
leading to potential publication bias. This limitation should be acknowledged and discussed.
Insufficient consideration of confounding factors: The analysis did not adequately address the
potential confounding factors, such as lifestyle, dietary habits, and genetic predispositions,
which could influence the association between tea consumption and CRC risk. The impact of
these factors on the results should have been explored and discussed.
Lack of discussion on limitations: The limitations of the meta-analysis, including the potential
impact of unmeasured confounders, the inability to establish causality, and the generalizability
of the findings, were not extensively discussed. Providing a comprehensive discussion of the
limitations would have enhanced the interpretation of the results.