Variety in Fruit and Vegetable Consumption and the Risk of Lung Cancer in the European Prospective Investigation Into Cancer and Nutrition
Buchner FL, Bueno-de-Mesquita HB, Ros MM, et al
Cancer Epidemiol Biomarkers Prev. 2010;19:2278-2286
Study Summary
The European Prospective Investigation Into Cancer and Nutrition Study, a multinational study of the relationship between diet and malignancies, prospectively followed the diets of 452,187 participants for whom "complete [dietary] information" was available. During the mean follow-up period of 8.7 years, 1613 participants were diagnosed with lung cancer. A Diet Diversity Score (DDS) was used to quantify the variety of fruit and vegetable consumption of each participant, and the associations between DDS and lung cancer were calculated, making adjustments for smoking and other relevant variables where possible. Participants who were diagnosed with a cancer within 2 years of enrollment were excluded from the results. The DDS instrument scores fruits and vegetables separately and places them into a number of subgroups within each of 2 major categories (eg, root vegetables would be scored as a subgroup separate from leaf vegetables).
The results show that the risk for lung cancer decreased with increasing variety in fruit and vegetable consumption. The hazard ratio for the quartile of participants with the greatest DDS was 0.77 (95% confidence interval, 0.64-0.94) compared with the quartile that had the lowest dietary diversity (P = .02). Intermediate DDS results were associated with intermediate reductions in lung cancers. The inverse association between dietary diversity and incidence of lung cancers was limited to current smokers, and there was a lower risk for squamous cell carcinomas but not other lung cancers. Data on known potential confounding factors, particularly consumption of meat and alcohol, as well as physical activity and education levels, were available but did not affect the outcome.
Viewpoint
Several earlier studies have suggested a role for fruits and vegetables in reducing the incidence of malignancies, as summarized in the World Cancer Research Fund report of 2007. However, those studies did not evaluate the role of the diversity of fruit and vegetable consumption in the development of cancer. Plants contain a wide range of bioactive agents, not one of which is solely responsible for cancer reduction, hence the need to investigate the role of diversity in the intake of fruits and vegetables and the utility of the DDS instrument.
A weakness of the study by Buchner and associates pertains to reliance on dietary recall, with the difficulties of ascertaining portion sizes, and so forth. The assumption that the quantity of plant products a person eats correlates with the diversity of those plant products is a reasonable, if uncertain, one. However, the amount of fruits and vegetables consumed by an individual is likely to be less important (with respect to cancer prevention) and subject to more recall bias than the diversity of vegetables consumed. A person might more easily remember eating eggplant or okra than how much of it he or she ate.
Other weaknesses were related to some of the regional differences, such as the range of fruits and vegetables available for consumption among the participating countries and other experimental details. The probable impact of these differences, however, was considered minor.
The strengths of this study are its prospective design, the immense size of the cohort, the length of the observation period, the very large amounts and quality of data that were obtained, and the geographic and ethnic heterogeneity of the participants. These factors add to the credibility of the study and widen the applicability of the study's findings.
The conclusion of this study seems clear: consumption of a wide variety of fruits and vegetables is associated with an overall reduction in lung cancer rates of about 23%. However, the reduction was limited to current smokers and was almost entirely a consequence of fewer squamous cell lung cancers. The reasons for the latter remain to be investigated by future research. Despite this important and encouraging finding, it should not be overlooked that smoking cessation is still by far the most effective way to avoid lung and several other cancers.
Abstract