Menstrual and reproductive factors and type 2 diabetes risk: The Japan Public Health Center‐based Prospective Study

AIMS/INTRODUCTION: Menstrual and reproductive factors, including age at menarche, parity and breast‐feeding, have been linked to type 2 diabetes risk. We prospectively investigated the association between these factors and type 2 diabetes risk in a large Japanese cohort. MATERIALS AND METHODS: Participants were 37,511 women aged 45–75 years who participated in the baseline (1990–1993), second (1995–1998) and third surveys (2000–2003) of the Japan Public Health Center‐based Prospective Study, and who had no history of diabetes at the second survey. Menstrual and reproductive history was ascertained using questionnaires at the baseline and second surveys. Odds ratios of self‐reported, physician‐diagnosed type 2 diabetes over the 5‐year period from the second survey were estimated using logistic regression. RESULTS: At the third survey, 513 new cases of type 2 diabetes were self‐reported. The odds ratios of type 2 diabetes tended to increase with the number of parity, after adjustment for covariates other than body mass index (P for trend = 0.029). The multivariable‐adjusted odds ratios of type 2 diabetes for women with three or more births was 1.56 (95% confidence interval 0.96–2.53) compared with those who were nulliparous. The association between parity and type 2 diabetes risk was attenuated after additional adjustment for body mass index (P for trend = 0.12). No factors other than parity were significantly associated with type 2 diabetes risk. CONCLUSIONS: Higher parity might be associated with an increased risk of type 2 diabetes among Japanese women, partly through increasing bodyweight.