Maternal lifestyle and nutrient intakes during pregnancy and exclusive breastfeeding in relation to risk factors for breast cancer: The Japan Environment and Children's Study.

Breastfeeding has many benefits for infant growth and maternal health, such as reducing breast cancer risk. However, data on maternal factors influencing breastfeeding are insufficient. To clarify the associations between maternal lifestyle and diet during pregnancy and exclusive breastfeeding (EBF), we conducted a prospective study of pregnant women within the framework of the Japan Environment and Children's Study (a nationwide birth cohort study). Of 97,413 pregnant women recruited between January 2011 and March 2014, 27,775 with a singleton first live birth whose dietary data during pregnancy and lactation data were complete were eligible. Using logistic regression, we evaluated the associations between lifestyle factors including smoking and prepregnancy body mass index and intake of nutrients (macronutrients, isoflavones, and dietary fiber), some of which are known risk factors of breast cancer, and EBF for one month postpartum (initiation of EBF). To investigate the associations of these factors with EBF for 6 months (continuation of EBF), 9582 women who had successfully completed one-month EBF were further followed up. Smoking and prepregnancy obesity were inversely associated with the initiation and continuation of EBF. Intakes of protein, fat, isoflavone, and dietary fiber were positively associated (p trend = 0.0001 for dietary fiber), and carbohydrate intake was inversely associated with the initiation of EBF. Dietary fiber intake was also associated with the continuation of EBF (p trend = 0.048). These findings indicate that maternal lifestyles during pregnancy affect lactation performance. Lifestyle adjustments during pregnancy may have favorable effects on maternal and children's health through successful breastfeeding.