Exposure to breast milk in infancy and risk of breast cancer
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Early life exposures, such as being breastfed in infancy, may influence the risk of breast cancer in adulthood. We evaluated the risk of breast cancer in relation to ever having been breastfed in infancy among 9,442 women who participated in a population-based, case–control study. Cases were identified through cancer registries in three states (Massachusetts, New Hampshire, and Wisconsin); controls were identified through statewide drivers’ license lists or medicare lists. Data on known and suspected risk factors were obtained through telephone interview. We used unconditional logistic regression to assess the relation of breast cancer with ever having been breastfed and with breastfeeding duration (available for only 19% of breastfed women) in premenopausal women (1,986 cases and 1,760 controls) and postmenopausal women (2,600 cases and 2,493 controls). We found no evidence that ever having been breastfed in infancy was associated with breast cancer risk in either premenopausal women (odds ratio [OR] = 0.96; 95% confidence interval [CI] = 0.83–1.10) or postmenopausal women (OR = 0.98; 95% CI = 0.87–1.10). The association did not differ according to breast cancer stage, mother’s history of breast cancer, or any other reproductive factor assessed. Likewise, we found no association between breastfeeding duration and risk of breast cancer. Our results did not support the hypothesis that exposure to breast milk in infancy influences the risk of adult breast cancer.
KeywordsBreast cancer Breastfeeding Menopausal status Risk factors
The authors are grateful to Drs. Henry Anderson, Patrick L. Remington, Meir J. Stampfer, Walter C. Willett, John A. Baron, and E. Robert Greenberg, Laura Stephenson and the staff of the Wisconsin Cancer Reporting System, Susan T. Gershman and the staff of the Massachusetts Tumor Registry, Marguerite Stevens and the staff of the New Hampshire Cancer Registry, and Linda Haskins, Heidi Judge, Laura Mignone, and Shafika Abrahams-Gessel along with the study interviewers and programmers in all three states for assistance with data collection. We are especially grateful to the study participants, whose generosity made this research possible.
This study was supported by National Cancer Institute grants R01 CA47147, R01 CA47305, and R01 CA69664.
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