Does the Mediterranean dietary pattern or the Healthy Diet Index influence the risk of breast cancer in a large British cohort of women?

Background/objective: To assess the risk of developing breast cancer associated with consumption of two common dietary patterns: a Mediterranean dietary pattern and a dietary pattern, which conforms to the World Health Organization Healthy Diet Index (WHO HDI).
Subjects/methods: Dietary data from a 217-item food frequency questionnaire were used to generate two dietary patterns according to pre-defined criteria in women from the UK Women's Cohort Study. Survival analysis using Cox regression was used to estimate hazards ratios for risk of breast cancer adjusted for known confounders.
Results: This analysis included 828 incident cases of breast cancer in 33,731 women with a mean follow-up of 9 years. There were no statistically significant associations between either the Mediterranean dietary pattern or the WHO HDI and risk of breast cancer. In premenopausal women, there was a nonsignificant trend suggesting that increasing compliance with the Mediterranean diet was associated with lower risk of breast cancer. Maximal adherence to the Mediterranean diet was associated with hazards ratio=0.65 (95% confidence interval: 0.42-1.02, P trend=0.09) compared with minimal adherence. In postmenopausal women, no clear trends were observed.
Conclusions: In this study, no strong association between the risk of breast cancer and the consumption of either a Mediterranean-type diet or one characterized by adherence to the WHO HDI was observed. In premenopausal, but not postmenopausal women, there was a nonsignificant inverse association with increasing adherence to the Mediterranean diet pattern.