Olive oil consumption has been suggested to be inversely associated with
breast cancer risk, probably due to its high MUFA 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 through June 2020, identifying ten observational studies (two prospective studies and eight case-control studies) for meta-analysis. We estimated summary OR and 95 % CI for the highest v. 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/d 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.