The association between fat mass and the risk of breast cancer: A systematic review and meta-analysis

Background & aims: Several cohort and case control studies examined the association between fat mass (FM) and the risk of breast cancer; however, findings are conflicting. The purpose of the present study was to systematically review this association and conducted a meta-analysis, if possible. Method: A systematic search of PubMed/Medline, Scopus, Web of Science and Embase databases was conducted for cohort and case control studies, between January 2000 and 31 March 2018 with no language limitations. Multivariate adjusted relative risk (RR) estimates with 95% confidence intervals (CI) for each category of FM were pooled to examine the association. Results: Finally, 12 papers were considered for quantitative synthesis. The pooled RR for the highest vs. the lowest FM (%) of cohort studies was 1.44 (95% CI: 1.33, 1.56; I-2: 63.3%, p = 0.008). The overall effect size for adjusted case control studies showed no significant association (1.49, 95% CI: 0.77, 2.90; I-2: 93.2%; p = 0.001). After stratification by menopause, it was revealed that the association between FM and the risk of breast cancer in post menopausal women (2.29, 95% CI: 1.12, 4.68; I-2: 92%, p = 0.0001) was significant, while there was no significant association in pre-menopausal women (0.68, 95% CI: 0.18, 2.58; I-2: 81.3%; p = 0.02). Conclusion: Cohort studies showed that higher FM is positively associated with the risk for breast cancer. However, only case control studies on post-menopausal women showed a positive link. Due to limited studies and high heterogeneity, findings should be interpreted with caution. More cohort studies are needed to clarify this association. (C) 2018 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.