This summary table contains detailed information about research studies. Summary tables are a useful way to look at the science behind many breast cancer guidelines and recommendations. However, to get the most out of the tables, it’s important to understand some key concepts. Learn how to read a research table.
Introduction: Breastfeeding lowers the risk of breast cancer. Findings from large pooled and meta-analyses that combined data from many studies have shown women who breastfeed have a lower risk of breast cancer compared to those who don't breastfeed [1-4].
Two meta-analyses have found breastfeeding reduced the risk of both hormone receptor-positive (estrogen receptor-positive and/or progesterone receptor-positive) and hormone receptor-negative (estrogen receptor-negative and/or progesterone receptor-negative) breast cancers [4-5].
Learn more about breastfeeding and breast cancer risk.
Learn about the strengths and weaknesses of different types of studies.
See how this risk factor compares with other risk factors for breast cancer.
Study selection criteria: Large pooled and meta-analyses.
Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
(number of participants)
Relative Risk of Breast Cancer in Women who Breastfed Compared to Women who Did Not
RR (95% CI)
Pooled and meta-analyses
Nelson et al. 
Bernier et al. 
* For 1 year of breastfeeding
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