BREAST-FEEDING AND BREAST-CANCER RISK

A population-based case-control study of breast cancer with a focus on premenopausal women under 45 years of age, conducted in three geograp hic regions of the United States, enabled the evaluation of risk in re lation to varying breastfeeding practices. Among premenopausal parous women (1,211 cases, 1,120 random-digit-dialing controls), a history of breastfeeding for two or more weeks was associated with a relative ri sk (RR) of 0.87 (95 percent confidence interval [CI] = 0.7-1.0), This relationship was not altered substantially by removing from the refere nce group women who had problems with breastfeeding in the first two w eeks, including those with insufficient milk production. Risk was not related substantially to number of children breastfed or length of bre astfeeding, although a relatively low risk was observed among those br eastfeeding for the longest duration examined (RR = 0.67, CI = 0.4-1.1 for an average period per child of 72 or more weeks), Women who began to breastfeed at a young age (< 22 years) experienced the greatest re duction in risk, but other timing parameters (e.g., interval since fir st or last breastfeeding) were not predictive of risk Risks were not m odified substantially by age or menopause status, although the number of menopausal subjects examined was limited Use of medications to stop breast milk was unrelated to risk (RR = 1.04), The results of this st udy do not support the notion that breastfeeding substantially reduces breast cancer risk; however, this may reflect the fact that most of o ur study subjects breastfed only for limited periods of time (average breastfeeding per child of 30 weeks), Further studies are needed to cl arify the relationship of breastfeeding to breast cancer risk, and to determine possible etiologic mechanisms underlying any observed associ ations.