Lactation and breast cancer risk.

Breast cancer is a common disease with few practical preventive measures. The recent evidence that lactation, like other reproductive experiences, is associated with a modest reduction in breast cancer risk is therefore of great interest. Overall, the reduction in risk appears to be about 20% for ever breast feeding and is even greater for women with histories of prolonged lactation, or who initiate breast feeding at young ages. In many studies this risk reduction seems to be limited to premenopausal women. It appears unlikely that this inverse association is attributable either to higher risk among women who use lactation suppressants or who have difficulty either starting or continuing breast feeding. While a strong or consistent protective effect of lactation on breast cancer risk has not been observed in some large and well conducted studies, this likely reflects the limited breast feeding practices among modern women. If early, exclusive and extended breast feeding is necessary to achieve a breast cancer risk reduction, future studies among U.S. women may be unable to clarify this association.