Olive oil intake and breast cancer risk: An updated systematic review and meta-analysis

Abstract

Abstract: Introduction: Breast cancer is the most common malignancy and the main cause of cancer-related deaths among women in worldwide. Dietary fat intake may be associated with an increased risk of breast cancer. But evidence has shown that the effect of vegetable oils such as olive oil is not certain. Various epidemiological studies have shown that olive oil compounds have a protective role in reducing the risk of breast cancer, especially in countries bordering the Mediterranean Sea. Our aim in this study was to extend our knowledge of the revised association of olive oil intake and breast cancer risk in retrospective epidemiologic and prospective cohort studies by updating a systematic review and meta-analysis, with more emphasis on recently published studies. Methods: To find the most relevant original articles, a systematic search was conducted in PubMed, Scopus, Web of Science, Cochrane, and Google scholar using MeSH (Medical subject heading) and non-MeSH keywords until August 1, 2023. The Newcastle-Ottawa scale was used to evaluate the quality of included studies. Data were extracted from 18 case-control studies, 7 cohort studies, and 2 cross-sectional studies. Relative risk was estimated with odds ratio using random-effect or fixed-effect models. Heterogeneity between studies was evaluated by I2 index (I-squared) and Forest plot diagram. Meta-regression was also used for regression analysis to determine the potential source of heterogeneity among studies. Funnel plot and Egger's test were used to evaluate publication bias. Sensitivity analysis was conducted to evaluate the effects of each study on the pooled effect size. Data analysis was performed using STATA 14 statistical software. Results: The pooled OR of olive oil intake in retrospective epidemiological studies including case-control studies 0.78 (0.65-0.95) with evidence of significance of heterogeneity (I2 =80.1%) and cross-sectional studies 0.74 (0.59-0.93) with no significance of heterogeneity (I2 < 0.01). Also, the pooled OR of olive oil intake in prospective cohort studies 0.99 (0.96-1.03) with no significance of heterogeneity (I2 < 0.01). Due to high heterogeneity in case-control studies, meta-regression analysis was performed, and the results showed a decrease in I2 to 60%, which still has high heterogeneity according to the determined cut-off. The results of Funnel plot and Egger's test in case-control studies (P = 0.122) and prospective cohort studies (P = 0.343) indicate the absence of evidence of publication bias. Conclusion: In this meta-analysis study, adherence to olive oil intake reduces the risk of breast cancer in retrospective epidemiological studies including case-control studies and cross-sectional studies, which is statistically significant. In prospective cohort studies, no significant difference in breast cancer risk was observed among individuals with high olive oil intake vs low olive oil intake. Although this relationship was not significant. Since there were certain limitations in some of the studies included in this systematic review and meta-analysis, further research is necessary to confirm our findings. Keywords: Olive oil; breast cancer; prospective cohort; cross-sectional; case-control; systematic review; meta-analysis.