Each portion of fruit or vegetable consumed halves the risk of oral cancer

Medline was used to find relevant papers; reference lists of retrieved publications were also searched.

Studies were included if they met all of the following criteria: 1) they contained original data from case-control or cohort studies; 2) the primary outcome was clearly defined as cancers of the mouth, pharynx and hypopharynx (as defined by codes 141, 143-146,148 and 149 of the ninth revision of the International Classification of Diseases or other classifications that included these sites); 3) the exposure of interest was measured as servings (per day, week or month) of fruit, vegetables or both (other exposure measurements, such as mass per day, were excluded unless data were provided to transform information to servings per day); 4) they provided relative risk (RR) estimates and their 95% confidence intervals (CI), or sufficient data to calculate these parameters; 5) were published in the English language; and 6) were published before September 2005. If a study appeared in more than one article, data from the most recent publication were used for the statistical analysis. Studies restricted to oral cancer in subjects aged under 45 years were excluded.

Study quality was assessed and data were extracted independently by two investigators, differences being resolved by discussion. All studies were stratified by fruit or vegetable intake to evaluate any dose-response relations, and some of the studies were used to perform multivariate analyses to adjust for several confounders. Separate meta-analyses were conducted for fruit and vegetable consumption. Potential sources of heterogeneity between the studies were examined using the DerSimonian and Laird method. Sensitivity analyses and a multivariate metaregression analysis were performed to examine observed heterogeneity.

A total of 71 potentially relevant studies were identified: 16 were included in the meta-analysis. Seven studies had been carried out in Europe, five in the Americas and four in East Asia. Three case-control studies consisted solely of men and one study consisted solely of women. The pooled data allowed 65 802 and 57 993 subjects, respectively, to be included in analysis of fruit and vegetable consumption. The combined adjusted odds ratio (OR) estimates based on 16 studies showed that each portion of fruit consumed per day had a statistically significant effect, reducing the risk of oral cancer by 49% (OR, 0.51; 95% CI, 0.40-0.65). A similar effect was seen for vegetable consumption, with a significant reduction in the risk of oral cancer of 50% (OR, 0.50; 95% CI, 0.38-0.65). Homogeneity testing found a statistically significant heterogeneity for fruit consumption and vegetable consumption studies. This was examined using sensitivity analysis which did not substantially modify the main findings of the meta-analysis.

The consumption of fruit and vegetables was found to be associated with a reduced risk of oral cancer. Prospective studies are needed to confirm this result.