Background: A Mediterranean diet has a recognized beneficial effect on health and longevity, with a protective influence on several cancers. However, its association with breast cancer risk remains unclear.
Objective: We aimed to investigate whether adherence to a Mediterranean dietary pattern influences breast cancer risk.
Design: The Swedish Women's Lifestyle and Health cohort study includes 49,258 women aged 30 to 49 years at recruitment in 1991-1992. Consumption of foods and beverages was measured at enrollment using a food frequency questionnaire. A Mediterranean diet score was constructed based on the consumption of alcohol, vegetables, fruits, legumes, cereals, fish, the ratio of unsaturated to saturated fat, and dairy and meat products. Relative risks (RR) for breast cancer and specific tumor characteristics (invasiveness, histological type, estrogen/progesterone receptor status, malignancy grade and stage) associated with this score were estimated using Cox regression controlling for potential confounders.
Results: 1,278 incident breast cancers were diagnosed. Adherence to a Mediterranean dietary pattern was not statistically significantly associated with reduced risk of breast cancer overall, or with specific breast tumor characteristics. A RR (95% confidence interval) for breast cancer associated with a two-point increment in the Mediterranean diet score was 1.08 (1.00-1.15) in all women, and 1.10 (1.01-1.21) and 1.02 (0.91-1.15) in premenopausal and postmenopausal women, respectively. When alcohol was excluded from the Mediterranean diet score, results became not statistically significant.
Conclusions: Adherence to a Mediterranean dietary pattern did not decrease breast cancer risk in this cohort of relatively young women.