Association between body mass index and breast cancer risk: evidence based on a dose-response meta-analysis

Introduction: Breast cancer is the most common cancer in women worldwide. The association between body mass index (BMI) and breast cancer risk has been paid more attention in the past few years, but the findings are still controversial. To obtain a more reliable conclusion, we performed a dose-response meta-analysis on 12 prospective cohort studies comprising 22,728,674 participants. Methods: Linear and nonlinear trend analyses were conducted to explore the dose-response relationship between BMI and breast cancer risk. The summary relative risk (SRR) and 95% confidence intervals (CIs) were used to evaluate the cancer risk. Results: The overall results showed a weak positive association between a 5-unit increase in BMI and breast cancer risk, indicating that a 5 kg/m(2) increase in BMI corresponded to a 2% increase in breast cancer risk (SRR: 1.02, 95% CI: 1.01-1.04, p<0.001). Notably, further subgroup meta-analysis found that higher BMI could be a protective factor of breast cancer risk for premenopausal women (SRR: 0.98, 95% CI: 0.96-0.99, p<0.001). In addition, the dose-response result demonstrated that there was a linear association between BMI and breast cancer risk (P-nonlinearity = 0.754). Conclusion: In summary, this dose-response meta-analysis of prospective cohort studies showed that every 5 kg/m(2) increase in BMI corresponded to a 2% increase in breast cancer risk in women. However, higher BMI could be a protective factor in breast cancer risk for premenopausal women. Further studies are necessary to verify these findings and elucidate the pathogenic mechanisms.