Gastroenterology

Gastroenterology

Volume 141, Issue 1, July 2011, Pages 106-118
Gastroenterology

Original Research
Clinical—Alimentary Tract
Nonlinear Reduction in Risk for Colorectal Cancer by Fruit and Vegetable Intake Based on Meta-analysis of Prospective Studies

https://doi.org/10.1053/j.gastro.2011.04.013Get rights and content

Background & Aims

The association between fruit and vegetable intake and colorectal cancer risk has been investigated by many studies but is controversial because of inconsistent results and weak observed associations. We summarized the evidence from cohort studies in categorical, linear, and nonlinear, dose–response meta-analyses.

Methods

We searched PubMed for studies of fruit and vegetable intake and colorectal cancer risk that were published until the end of May 2010. We included 19 prospective studies that reported relative risk estimates and 95% confidence intervals (CIs) of colorectal cancer-associated with fruit and vegetable intake. Random effects models were used to estimate summary relative risks.

Results

The summary relative risk for the highest vs the lowest intake was 0.92 (95% CI: 0.86–0.99) for fruit and vegetables combined, 0.90 (95% CI: 0.83–0.98) for fruit, and 0.91 (95% CI: 0.86–0.96) for vegetables (P for heterogeneity = .24, .05, and .54, respectively). The inverse associations appeared to be restricted to colon cancer. In linear dose–response analysis, only intake of vegetables was significantly associated with colorectal cancer risk (summary relative risk = 0.98; 95% CI: 0.97–0.99), per 100 g/d. However, significant inverse associations emerged in nonlinear models for fruits (Pnonlinearity < .001) and vegetables (Pnonlinearity = .001). The greatest risk reduction was observed when intake increased from very low levels of intake. There was generally little evidence of heterogeneity in the analyses and there was no evidence of small-study bias.

Conclusions

Based on meta-analysis of prospective studies, there is a weak but statistically significant nonlinear inverse association between fruit and vegetable intake and colorectal cancer risk.

Section snippets

Search Strategy

We updated the systematic literature review published in 200727 and searched the PubMed database up to May 2010 for cohort studies of fruit and vegetable intake and colorectal cancer risk. We followed a prespecified protocol, which includes details of the search terms used, for the review (http://www.dietandcancerreport.org/downloads/SLR_Manual.pdf). We also searched the reference lists of all the studies that were included in the analysis and the reference lists of the published systematic

Results

We identified 19 cohort studies (22 publications)5, 7, 8, 9, 10, 11, 13, 17, 18, 19, 20, 21, 22, 28, 29, 30, 31, 32, 33, 42, 43, 44 that were included in the analysis of the highest vs the lowest fruit and/or vegetable intake and colorectal cancer risk. Fifteen of these studies (18 publications)7, 8, 9, 10, 11, 13, 17, 18, 19, 21, 22, 28, 29, 31, 32, 33, 42, 43 were included in the dose–response analysis (Table 1, Figure 1). Five of the studies were from Europe, 10 from America, and 4 from Asia.

Discussion

In this meta-analysis, high vs low intake of fruit, vegetables and fruit and vegetables combined were associated with small but statistically significant reductions in colorectal cancer risk. In the linear dose–response analysis, a significant inverse association was observed only for vegetables. However, we found for the first time in a meta-analysis, to our knowledge, evidence of a nonlinear inverse association between fruits and for vegetables and colorectal cancer risk, with the greatest

Acknowledgments

We thank the systematic literature review team at the Wageningen University for their contributions to the colorectal cancer database. The systematic literature review team at Wageningen University conducted the search, data selection, and data extraction up to June 2006.

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    Conflicts of interest The authors disclose no conflicts.

    Funding This work was funded by the World Cancer Research Fund (grant number 2007/SP01) as part of the Continuous Update Project. The views expressed in this review are the opinions of the authors. They may not represent the views of the World Cancer Research Fund International/American Institute for Cancer Research and may differ from those in future updates of the evidence related to food, nutrition, physical activity and cancer risk. The sponsor of this study had no role in the decisions about the design and conduct of the study, collection, management, analysis or interpretation of the data or the preparation, review or approval of the manuscript.

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