Dietary patterns and the risk of female breast cancer among participants of the Canadian National Enhanced Cancer Surveillance System

OBJECTIVES: The role of diet in the etiology of breast cancer is not well understood despite extensive research. In the majority of this work, a single nutrient-based approach has been used which does not take into account combinations of food that are consumed. An alternative to the single nutrient approach is to identify patterns in the dietary intake information and relate these patterns to disease incidence. This investigation characterized dietary patterns among participants of a Canadian case-control study and related these dietary patterns to the incidence of breast cancer. METHODS: Dietary and other risk factor data from cases and controls of the Canadian National Enhanced Cancer Surveillance System were collected using self-administered questionnaires. Principal component factor analysis was used to classify individuals based on their dietary patterns. The relationship between these dietary patterns and breast cancer was evaluated using logistic regression. The derived odds ratios and their 95% confidence limits were adjusted for several factors, such as smoking, alcohol intake, environmental tobacco smoke exposure and obesity. RESULTS: In the 2,009 cases and 2,086 controls, three dietary patterns were identified: western, healthy and vitamin. The highest quartile of the "healthy" dietary pattern was related to a 22% decrease in breast cancer risk (95% CI: 0.61-1.00), relative to the lowest quartile. The fourth quartile of the "vitamin" dietary pattern was associated with a 14% decrease in breast cancer risk (95% CI: 0.70-1.04) relative to the first. No statistically significant associations between the "western" dietary pattern and breast cancer were found. These associations were neither confounded nor modified by menopausal status. CONCLUSION: Our analyses reveal that individual dietary items tend to cluster together in such a way that there are three distinct dietary patterns in this sample of Canadian women. Some of these patterns, in turn, were associated with the risk of breast cancer.