Breastfeeding and the incidence of endometrial cancer: A meta-analysis

Several epidemiological studies have investigated the association between breastfeeding and endometrial cancer (EC). However, the results of the studies are controversial. Thus, we conduct this meta-analysis to explore the association between breastfeeding and EC and to evaluate the possible does-response relationship between duration of breastfeeding and EC. PubMed, Web of Science, Chinese National Knowledge Infrastructure, China biology medical literature database, Wan fang databases and Database of Chinese Scientific and Technical Periodicals were searched for eligible observational studies up to 11 July 2015. Random effects model was used to calculate the pooled relative risks (RRs) and restricted cubic spline model was adopted for the does-response analysis. Fifteen articles with 623570 participants were identified. The RRs of these studies suggested that breastfeeding was associated with the reduced risk of EC (high versus low/no: RR = 0.74; 95% confidence interval (CI), 0.58–0.95). In subgroup analyses, a significant association of breastfeeding with EC risk was found in Asia (RR = 0.57, 95% CI 0.37–0.87), and an inverse association of breastfeeding with EC risk was found in cohort studies (RR = 0.62, 95% CI 0.41–0.94). The results were also significant after adjusted for hormone use (RR = 0.63, 95% CI 0.41–0.97) and body mass index (RR=0.65, 95% CI 0.44–0.96). A linear relationship was found of breastfeeding with EC (p for nonlinearity = 0.93), and it indicated that EC risk decreased by 1.2% for one month increment of breastfeeding. This meta-analysis indicates that long term breastfeeding might be associated with decreased risk of EC.