Although there is some evidence suggesting that olive oil could reduce breast cancer (BC) risk, the epidemiological data are still relatively limited, not entirely consistent and mainly based on case-control studies. Therefore, we prospectively assessed the association between olive oil and BC risk in postmenopausal women from the Mediterranean cohorts within the European Prospective Investigation into Cancer and Nutrition. The analysis included 62,284 postmenopausal women recruited from Spain, Italy and Greece who had complete dietary data (collected from validated country-specific dietary questionnaires). The risk of BC (overall and by hormone receptor subtypes) was assessed using hazards ratios (HRs) obtained from Cox proportional hazards regression, while adjusting for known BC risk factors. After a mean follow-up of 9 years, 1,256 women were diagnosed with a primary incident invasive BC. The multivariate HRs for BC risk by olive oil intake (highest vs. lowest tertile of g/day/2,000 kcal) were 1.07 (95% CI = 0.91-1.25) in the adjusted model, 1.06 (95% CI = 0.91-1.24) in the model additionally adjusted for reproductive-related factors and 1.10 (95% CI = 0.92-1.31) for the model additionally adjusted for dietary factors. There was no association between olive oil and risk of estrogen or progesterone receptor-positive tumors, but a suggestion of a negative association with estrogens and progesterone receptor-negative tumors. The results from our prospective study showed that olive oil consumption during adult life was not associated with the risk of BC. However, larger prospective studies are still needed to explore possible differences related to hormone receptor status.
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