Aug. 10 (HealthDay News) -- Women who breast-feed their babies even for short periods of time may lower their risk of developing premenopausal breast cancer if they have a family history of the disease.
"We saw a 59 percent lower risk of breast cancer among women with a family history who had ever breast-fed," stated Dr. Alison Stuebe, lead author of a study appearing in the Aug. 10/24 issue of the Archives of Internal Medicine. "It is surprising to see this really strong association with a pretty decreased risk."
Stuebe is an assistant professor of obstetrics and gynecology at the University of North Carolina at Chapel Hill School of Medicine, but she conducted the study while affiliated with Brigham and Women's Hospital/Harvard Medical School in Boston.
The risk reduction was seen in women who had breast-fed for as short a period as three months.
Numerous other benefits of breast-feeding have been found, not just for babies but for mothers as well.
A study released in April, for instance, found that women in their 60s who had breast-fed for more than 12 months over their lives were nearly 10 percent less likely to develop cardiovascular disease, and significantly less likely to develop heart disease risk factors, such as high blood pressure, diabetes and high cholesterol.
Previous research on the connection between breast cancer and breast-feeding has been limited, although other, less rigorous, studies have also suggested a decrease in risk.
This study looked at about 60,000 women who had given birth at least once and were participating in the Nurses' Health Study II.
The lowering in the risk of breast cancer was seen only in women who had breast-fed and who had a mother or sister who had had the malignancy. And it only applied to premenopausal breast cancer.
The lowering of risk was about the same as seen with hormonal treatments such as tamoxifen in women at high risk for a malignancy, the authors stated.
There was no reduced risk in women who did not have a family history of the disease. Nor was there any difference depending on how long the mother breast-fed or the intensity of breast-feeding (whether the baby was breast-fed exclusively or not).
The reduced risk did not seem to have any link with hormones, given that the risk did not differ with the amount of time a woman went without a period while breast-feeding.
The researchers postulated other hypotheses to explain the link.
"It may be something about the first couple of days postpartum if the woman doesn't breast-feed," Stuebe said. "The breast tissue has to shut down, and there's a lot of inflammation and discomfort. Perhaps on a molecular level there's going some kind of damage."
This theory is supported by the fact that women who used medication to stop lactating also had a lower risk.
"This data would suggest it's more of the effect of milk being taken out of the breast tissue after pregnancy that's beneficial," Stuebe said. "We know that just being pregnant reduces the risk of breast cancer compared with not having been pregnant. Getting milk out afterwards appears to be part of the phenomenon."
The real value of the study, added Dr. Richard Bleicher, co-director of the breast surgery fellowship at Fox Chase Cancer Center in Philadelphia, may be less in the clinical implications but in the fact that it helps point researchers towards avenues for understanding the mechanisms of breast cancer.
SOURCES: Alison M. Stuebe, M.D., assistant professor, obstetrics and gynecology, University of North Carolina at Chapel Hill School of Medicine; Richard J. Bleicher, M.D., co-director, breast surgery fellowship, Fox Chase Cancer Center, Philadelphia; Aug. 10/24, 2009, Archives of Internal Medicine