Association between fruit and vegetable consumption and oral cancer: a meta-analysis of observational studies1,2

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Abstract
Background: Oral cancer ranks as the seventh most common form of cancer worldwide. Recent reports have examined the effect of fruit and vegetable intake on the risk of oral cancer, but results are controversial. Objective: A meta-analysis was performed to arrive at quantitative conclusions about the contribution of fruit and vegetable intakes to the occurrence of oral cancer. Design: A comprehensive, systematic bibliographic search of medical literature published up to September 2005 was conducted to identify relevant studies. Separate meta-analyses were conducted for fruit and vegetable consumption. The effect of portion or daily intake of fruit or vegetables on the risk of oral cancer was calculated. A multivariate meta-regression analysis was performed to explore heterogeneity. This multivariate meta-regression analysis examined the effect of quality score, the type of cancers included, citrus fruit and green vegetable consumption, and the time interval for dietary recall of the studies on the role of fruit or vegetable consumption in the risk of oral cancer. The presence of publication bias was assessed with a funnel plot for asymmetry. Results: Sixteen studies (15 case-control studies and 1 cohort study) met the inclusion criteria and were included in the meta-analysis. The combined adjusted odds ratio (OR) estimates showed that each portion of fruit consumed per day significantly reduced the risk of oral cancer by 49% (OR: 0.51; 95% CI: 0.40, 0.65). For vegetable consumption, the meta-analysis showed a significant reduction in the overall risk of oral cancer of 50% (OR: 0.50; 95% CI: 0.38, 0.65). The multivariate meta-regression showed that the lower risk of oral cancer associated with fruit consumption was significantly influenced by the type of fruit consumed and by the time interval of dietary recall. Conclusion: The consumption of fruit and vegetables is associated with a reduced risk of oral cancer.