Women with a family history of breast cancer face a lower risk of developing the disease pre-menopause if they have ever breastfed a child, says a new study.
The research has been reported in the August 10/24 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.
To reach the conclusion, Alison M. Stuebe, M.D., M.Sc., then of Brigham and Women's Hospital and Harvard Medical School, Boston, and now of the University of North Carolina at Chapel Hill, and colleagues used information from 60,075 women who had given birth and who participated in the Nurses' Health Study between 1997 and 2005. Each woman completed a detailed questionnaire on demographic characteristics, body measurements and lifestyle factors, with follow-up questionnaires every two years.
Breastfeeding history was assessed in detail on the 1997 questionnaire, and on each subsequent follow-up the women were asked to report whether they had been diagnosed with breast cancer.
Through the end of the study-June 2005-a total of 608 cases of premenopausal breast cancer were diagnosed, at an average age of 46.2 years. Women who had a first-degree relative with breast cancer had a lower risk of developing the disease if they had ever breastfed than if they had never breastfed. The association did not appear to change based on duration of breastfeeding, whether breastfeeding was exclusive or whether the woman experienced amenorrhea (absence of menstruation) as a result.
There was no association between breastfeeding and breast cancer among women without a family history.
Women who did not breastfeed but used medication to suppress breast milk production also appeared to have a lower risk of breast cancer than women who neither breastfed nor used lactation suppression. This association could be related to disordered involution, or a malfunction in the process by which mammary tissue returns to its pre-pregnant state caused by engorgement and inflammation, the authors note.
"Future studies of interactions among breastfeeding history, family history and genotypes associated with breast cancer risk will be needed to confirm these associations and explore underlying mechanisms," they write.
In the meantime, the observed risk reduction compared favorably to that experienced by high-risk women taking hormonal treatments such as tamoxifen, they continue.
"Moreover, breastfeeding is associated with multiple other health benefits for both mother and child. These data suggest that women with a family history of breast cancer should be strongly encouraged to breastfeed," they concluded.