Folate Intake and the Risk of Breast Cancer: A Dose-Response Meta-Analysis of Prospective Studies

Background: Previous observational studies regarding the existence of an association between folate intake and the risk of breast cancer have been inconsistent. This study aimed to summarize the evidence regarding this relationship using a dose-response meta-analytic approach. Methodology and Principal Findings: We performed electronic searches of the PubMed, EmBase, and Cochrane Library databases to identify studies published through June 2013. Only prospective observational studies that reported breast cancer effect estimates with 95% confidence intervals (CIs) for more than 2 folate intake categories were included. We excluded traditional case-control studies because of possible bias from various confounding factors. Overall, we included 14 prospective studies that reported data on 677,858 individuals. Folate intake had little effect on the breast cancer risk (relative risk (RR) for highest versus lowest category = 0.97; 95% CI, 0.90-1.05; P = 0.451). Dose-response meta-analysis also suggested that a 100 mg/day increase in folate intake had no significant effect on the risk of breast cancer (RR = 0.99; 95% CI, 0.98-1.01; P = 0.361). Furthermore, we used restricted cubic splines to evaluate the nonlinear relationship between folate intake and the risk of breast cancer, and discovered a potential J-shaped correlation between folate intake and breast cancer risk (P = 0.007) and revealed that a daily folate intake of 200-320 mg was associated with a lower breast cancer risk; however, the breast cancer risk increased significantly with a daily folate intake >400 mg. Conclusion/Significance: Our study revealed that folate intake had little or no effect on the risk of breast cancer; moreover, a dose-response meta-analysis suggested a J-shaped association between folate intake and breast cancer.