Women will have increased risk of breast cancer for many years after pregnancy and the protection from the disease will start only after 30 years after their last child.

‘Breast cancer risk was higher in women who were older at first birth, had more births and had a history of breast cancer in the family.’

According to senior author Dale Sandler, Ph.D., head of the Epidemiology Branch at the National Institute of Environmental Health Sciences (NIEHS), part of NIH, a few prior studies reported an increase in breast cancer risk after childbirth. However, most of what researchers knew about breast cancer risk factors came from studies of women who have gone through menopause. Since breast cancer is relatively uncommon in younger women, it is more difficult to study. 




Researchers combined data from approximately 890,000 women from 15 long-term studies across three continents, to understand the relationship between recent childbirth and breast cancer risk in women age 55 and younger.
"We were surprised to find that an increase in breast cancer risk lasted for an average of 24 years before childbirth became protective," said Sandler. "Before this study, most researchers believed that any increase in risk lasted less than 10 years."
The scientists also found that the association between recent childbirth and breast cancer risk was stronger for women who were older at first birth, had more births, or had a family history of breast cancer. Breastfeeding did not appear to have any protective effect, even though it is generally thought to reduce breast cancer risk. Many of these additional factors were not addressed in earlier studies, underscoring the statistical power of this larger project.
Sandler and first author Hazel Nichols, Ph.D., of the University of North Carolina Lineberger Comprehensive Cancer Center, started the study when Nichols was a research fellow at NIEHS. Nichols explained that childbirth is an example of a risk factor that is different for younger women than older women.
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Nichols and Sandler both stressed the importance of keeping these findings in perspective. Breast cancer is uncommon in young women. An increase in the relative risk of breast cancer in women under age 55 translates to a very small number of additional cases of breast cancer per year.
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Source-Eurekalert