Lactation and breast cancer risk.

BACKGROUND Data from the Carolina Breast Cancer Study, a population-based, case-control study of breast cancer in African-American and white women residents of North Carolina, were evaluated to determine whether specific aspects of lactation are associated with a reduction in the risk of breast cancer. METHODS Analyses included 751 parous cases and 742 parous controls frequency-matched on age and race. Information on lactation, reproductive history, lifestyle characteristics and family history were obtained through a personal interview. RESULTS When women who breastfed were compared to those who never breastfed, odds ratios and 95% confidence intervals of 0.8 (0.5-1.1) and 0.7 (0.5-0.9) were found for women 20-49 years and 50-74 years, respectively. Similar inverse associations were observed for each of three categories of lifetime duration (1-3, 4-12, 13+ months). The inverse associations persisted and did not vary when number of children breastfed, ages at first and last lactation and lactational amenorrhoea were examined. CONCLUSIONS Our findings suggest that any lactation, regardless of duration or timing, is associated with a slight reduction in the risk of breast cancer among younger and older parous women.