Determinants of infant feeding method in relation to risk factors for breast cancer

Background. Breastfeeding is considered to be an important factor for mater nal and children's health. However, the epidemiological findings related to the effect of breastfeeding on women's health, especially with respect to breast cancer development, are inconsistent. Determinants of infant feeding method may contribute to the inconsistency. Methods. A total of 24,769 women aged 40-64 in Miyagi Prefecture, Japan, re sponded to a self-administered questionnaire survey in 1990. Using the data obtained from 22,085 parous women, we calculated odds ratios (ORs) for the choice of "breastfeeding only" during reproductive period. Results. Late age at menarche (greater than or equal to 16 years, OR = 1.57 ) and high body mass index (BMI) at 20 years of age (greater than or equal to 24, OR = 1.31) were associated with the choice of breastfeeding only. La te age at birth of first child (greater than or equal to 28 years, OR = 0.2 9), history of breast cancer in mother (OR = 0.68), and high educational le vel (more than a high school education, OR = 0.53) reduced the possibility of choosing breastfeeding only. Conclusion. The results indicate that the choice of infant feeding method i s associated with several breast cancer risk factors. Based on this finding , we should construct appropriate breast cancer risk models for parous wome n and investigate the changes in the effects of breastfeeding and other bre ast cancer risk. factors among these risk models. Especially in a risk mode l controlling for breastfeeding, the effects of other breast cancer risk fa ctors should be reevaluated. Through comparisons among different risk model s, we may find the best-fitted risk model and identify the true effect of b reastfeeding. (C) 2000 American Health Foundation and Academic Press.