Olive oil and risk of breast cancer: a systematic review and dose-response meta-analysis of observational studies.

Olive oil consumption has been suggested to be inversely associated with breast cancer risk, likely due to its high monounsaturated fatty acid and polyphenol content. The purpose of this meta-analysis was to assess the association between olive oil and breast cancer risk, including assessing the potential for a dose-response association. We performed a systematic search of PubMed, Web of Science, CINAHL, and Cochrane Central Register of Controlled Trials (CENTRAL) through June 2020, identifying 10 observational studies (two prospective studies and 8 case-control studies) for inclusion in the present meta-analysis. We estimated summary odds ratios (OR) and 95% confidence intervals (CI) for the highest versus lowest olive oil intake category across studies using random effect models, and assessed the dose-response relationship between olive oil and breast cancer risk using restricted cubic splines. The summary OR comparing women with the highest intake to those with the lowest category of olive oil intake was 0.48 (95% CI = 0.09-2.70) in prospective studies and 0.76 (95% CI=0.54-1.06) in case-control studies, with evidence of substantial study heterogeneity (prospective: I2 = 89%, case-control: I2 = 82%). There was no significant dose-response relationship for olive oil and breast cancer risk; the OR for a 14 g/day increment was 0.93 (95% CI=0.83 - 1.04). There may be a potential inverse association between olive oil intake and breast cancer; however, since the estimates are non-significant and the certainty level is very low, additional prospective studies with better assessment of olive oil intake are needed.