Adherence to Mediterranean diet and the risk of breast cancer: a meta-analysis

Background: For a long period of time, the Mediterranean diet (MD) has been regarded by many as a very healthy and balanced daily diet that may be related to the incidences of many types of cancer. However, the association between an MD and breast cancer risk remains inconsistent even though many studies about the topic have been conducted. Hence, we performed a meta-analysis to evaluate the relationship between an MD and breast cancer risk. Methods: We searched PubMed, Medline, and EMBASF, for relevant articles published earlier than May 2017. "Mediterranean diet" combined with "breast cancer" and "breast carcinoma" were used as search terms. The combined relative risk (RR) and corresponding 95% confidence interval (CI) were used to evaluate the association between an MD and breast cancer risk. Results: A total of 18 articles were included in our meta-analysis; the studies spanned 11 years, ranging from 2006 to May 2017. Ten cohort and 8 case-control studies were included. Seven studies analyzed breast cancer incidence separately in premenopausal and postmenopausal women, whereas 6 studies were performed only in postmenopausal women, for a total of 13 analyses in postmenopausal women and 7 analyses among premenopausal women. Our meta-analysis revealed a significant and inverse association of the MI) and breast cancer risk (RR: 0.92, 95% CI: 0.86, 0.99). Stratification analysis by study design and menopause status revealed a significant inverse association between the MD and breast cancer risk in casecontrol studies (RR: 0.85, 95% CI: 0.73, 0.99) and postmenopausal women (RR: 0.91, 95% CI: 0.85, 0.97) but not in cohort studies and premenopausal women. Conclusions: Our meta-analysis revealed that an MD is significantly associated with a reduction of breast cancer risk in women, especially postmenopausal women. The MD can be suggested to women, especially postmenopausal women, as a healthy diet to reduce breast cancer risk.