Reproductive factors in relation to risk of brain tumors in women: an updated meta-analysis of 27 independent studies

Previous studies on the association between reproductive factors and brain tumor risk in women have provided inconclusive findings. Thus, an updated meta-analysis was performed to obtain more precise risk estimates for brain tumor regarding several common reproductive factors. A comprehensive literature search for relevant publications in the PubMed and Embase databases was carried out from their inception up to June 20, 2014. Pooled relative risks (RRs) with corresponding 95 % confidence intervals (CIs) were calculated. There were 27 independent studies with a total of 12,129 cases and 1,433,915 controls included into the present meta-analysis. We found that an elevated risk of brain tumors (RR = 1.17, 95 % CI 1.06-1.29, P = 0.002), particularly glioma (RR = 1.33, 95 % CI 1.15-1.54, P < 0.001), was related to older age at menarche. Interestingly, stratified analysis by type of brain tumors showed that the longer duration of breast feeding was associated with the risk of meningioma negatively but glioma positively (for meningioma: RR = 0.76, 95 % CI 0.64-0.91, P = 0.002; for glioma: RR = 1.70, 95 % CI 1.14-2.55, P = 0.010). No significant association was observed when estimating the roles of other reproductive factors including parity, age at first birth, menopausal status, and age at menopause in brain tumorigenesis. Our study suggests that older age at menarche is a risk factor of brain tumors and glioma in particular. Additionally, more studies are warranted to further elucidate roles and mechanisms of common reproductive factors in the risk of brain tumors.