Abstract: The Mediterranean diet has been related to a reduced risk of several common cancers but its role on breast cancer has not been quantified yet. We investigated the association between adherence to the Mediterranean diet and breast cancer risk by means of a hospital-based case-control study conducted in Italy and Switzerland. 3034 breast cancer cases and 3392 controls admitted to the same network of hospitals for acute, non-neoplastic and non-gynaecologic diseases were studied.
Adherence to the Mediterranean diet was quantitatively measured through a Mediterranean Diet Score (MDS), summarizing the major characteristics of the Mediterranean dietary pattern and ranging from 0 (lowest adherence) to 9 (highest adherence). We estimated the odds ratios (ORs) of breast cancer for the MDS using multiple logistic regression models, adjusting for several covariates. Compared to a MDS of 0–3, the ORs for breast cancer were 0.86 (95% confidence interval, CI, 0.76–0.98) for a MDS of 4–5 and 0.82 (95% CI, 0.71–0.95) for a MDS of 6–9 (p for trend = 0.008). The exclusion of the ethanol component from the MDS did not materially modify the ORs (e.g., OR = 0.81, 95% CI, 0.70–0.95, for MDS ≥ 6). Results were similar in pre- and post-menopausal women. Adherence to the Mediterranean diet was associated with a reduced breast cancer risk.