Duration of breast-feeding and the incidence of type 2 diabetes mellitus in the Shanghai Women’s Health Study

AIMS/HYPOTHESIS: The aim of this study was to examine the association between lifetime breast-feeding and the incidence of type 2 diabetes mellitus in a large population-based cohort study of middle-aged women. METHODS: This was a prospective study of 62,095 middle-aged parous women in Shanghai, China, who had no prior history of type 2 diabetes mellitus, cancer or cardiovascular disease at study recruitment. Breast-feeding history, dietary intake, physical activity and anthropometric measurements were assessed by in-person interviews. The Cox regression model was employed to evaluate the association between breast-feeding and the risk of type 2 diabetes mellitus. RESULTS: After 4.6 years of follow-up, 1,561 women were diagnosed with type 2 diabetes mellitus. Women who had breastfed their children tended to have a lower risk of diabetes mellitus than those who had never breastfed [relative risk (RR) = 0.88; 95% CI, 0.76–1.02; p = 0.08]. Increasing duration of breast-feeding was associated with a reduced risk of type 2 diabetes mellitus. The fully adjusted RRs for lifetime breast-feeding duration were 1.00, 0.88, 0.89, 0.88, 0.75 and 0.68 (p trend = 0.01) for 0, >0 to 0.99, >0.99 to 1.99, >1.99 to 2.99, >2.99 to 3.99 and ≥4 years in analyses adjusted for age, daily energy intake, BMI, WHR, smoking, alcohol intake, physical activity, occupation, income level, education level, number of live births and presence of hypertension at baseline. CONCLUSIONS/INTERPRETATION: Breast-feeding may protect parous women from developing type 2 diabetes mellitus later in life.