Consumption of olive oil and risk of breast cancer in U.S. women: results from the Nurses' Health Studies.

BACKGROUND: Olive oil consumption may reduce breast cancer risk, but it is unclear whether olive oil is beneficial for breast cancer prevention in populations outside of Mediterranean regions, namely in the U.S., where the average consumption of olive oil is low compared with Mediterranean populations. We examined whether olive oil intake was associated with breast cancer risk in two prospective cohorts of U.S. women.

METHODS: We used multivariable-adjusted time-varying Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence interval (CI) for breast cancer among 71,330 (Nurses' Health Study, 1990-2016) and 93,295 women (Nurses' Health Study II, 1991-2017) who were free of cancer at baseline. Diet was assessed by a validated semi-quantitative food frequency questionnaire every 4 years.

RESULTS: During 3,744,068 person-years of follow-up, 9,638 women developed invasive breast cancer. The multivariable-adjusted HR (95% CI) for breast cancer among women who had the highest consumption of olive oil (>1/2 tablespoon/d or >7 g/d) compared with those who never or rarely consumed olive oil, was 1.01 (0.93, 1.09). Higher olive oil consumption was not associated with any subtype of breast cancer.

CONCLUSION: We did not observe an association between higher olive oil intake and breast cancer risk in two large prospective cohorts of U.S. women, whose average olive oil consumption was low. Prospective studies are needed to confirm these findings and to further investigate whether different varieties of olive oil (e.g., virgin and extra virgin olive oil) may play a role in breast cancer risk.