Purpose: Ecologic, migrant, and secular trend studies suggest an association between the Western diet and the risk of breast cancer. We examined data from the Nurses Health Study II to evaluate the association between major dietary patterns and the risk of breast cancer among pre-menopausal women.
Methods: We derived "Western" and "prudent" dietary patterns from the responses of 90,638 premenopausal women, aged 26 to 46 years at baseline in 1991, who completed validated food frequency questionnaires in 1991 and 1995. These patterns were then evaluated for their associations with risk of breast cancer.
Results: During 8 years of follow-up, we documented 710 cases of invasive breast cancer. The multivariate RR (95% CI) comparing highest to lowest quintiles of cumulative average score were 0.90 (0.68-1.18, p-value, test for trend = 0.54) for the prudent dietary pattern and 0.97 (0.71-1.33, p-value, test for trend = 0.97) for the Western dietary pattern.
Conclusions: Our findings suggest that there is no overall association between dietary patterns and risk of breast cancer. However, we found an inverse association between the prudent dietary pattern and breast cancer risk among ever smokers, but the test for interaction was not significant. We suggest that this finding merits further evaluation.