(CN) — Shedding new light on old research about how young pregnancy can reduce a woman’s risk of breast cancer, the National Institutes of Health reported Friday that such benefits do not appear to kick in for several decades.
While prior research was done on women who had already gone through menopause, the NIH study involved data from more than 88,000 women under 55 across three continents.
NIH, which conducted the new study with members of International Premenopausal Breast Cancer Collaborative Group, noted that the research trends stem in large part from the fact that breast cancer is much less common in younger women, making it more difficult to study.
The new focus finds support for the link between childbirth and lower risk for developing breast cancer, but says this protection may not start until at least 30 years after the last child is born.
In fact, the findings of the study shows that breast cancer risk can increase in the years immediately after childbirth, with the risk being strongest at five years after childbirth.
"We were surprised to find that an increase in breast cancer risk lasted for an average of 24 years before childbirth became protective," said Dale Sandler, senior author of the study and head of the Epidemiology Branch at the National Institute of Environmental Health Sciences. "Before this study, most researchers believed that any increase in risk lasted less than 10 years."
Researchers found no apparent link between breastfeeding and lower risk of breast cancer, but they did see a stronger breast cancer risk for woman who have a child at an older age, had more births or a history of breast cancer in the family.
Hazel Nichols, with the University of North Carolina Lineberger Comprehensive Cancer Center, emphasized that childbirth is an example of a risk factor that is different for younger women than it is for older women.
"This difference is important because it suggests that we may need to develop tools for predicting breast cancer risk that are specific to young women," Nichols said in a statement. "Doing so would help women talk to their health care providers about when they should start mammography screening."
The number of breast cancer cases in woman under 55 will remain small, even with these new findings of possible risk.
Sandler and Nichols co-led the study with researchers at the Institute of Cancer, London.