Objective: The relationship between gastric cancer and menstrual and reproductive history was investigated for 40,535 postmenopausal females from a large-scale prospective cohort in Japan (JACC: Japan Collaborative Cohort Study for Evaluation of Cancer Risk, sponsored by Monbusho). Methods: A Cox proportional hazard model was used to estimate risk with respect to menstrual and reproductive factors for gastric cancer mortality. The effects on risk of potential confounders such as lifestyle, dietary habits, and socioeconomic status were controlled for using a stepwise procedure. Results: During the study period (mean 8.2 years), 156 deaths due to gastric cancer were identified. Longer fertility tended to be inversely associated with risk of gastric cancer mortality, although the association was not significant. Late menopause had no obvious effect on gastric cancer risk. The risk ratio of delivery experience compared to no delivery was 0.62 (95% confidence interval 0.27-1.41), and this effect was consistent regardless of the number of deliveries. Early menarche was not associated with the risk of gastric cancer. The potential confounders were not seen to have distinct effects on the associations. Conclusions: Multiparity appears to confer a protective tendency on gastric cancer mortality
however, this result is inconsistent with previous reports. Further information needs to be accumulated from epidemiological studies in order to clarify the role of reproductive factors in gastric cancer.