The Who, What, Where, When and Sometimes, Why.

Breastfeeding and breast cancer risk

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.

Study

Study Population
(number of participants)

Relative Risk of Breast Cancer in Women who Breastfed Compared to Women who Did Not
RR (95% CI)

Before Menopause

After Menopause

Pooled and meta-analyses

Nelson et al. [1]

14 studies

0.87 (0.77-0.98)

 

Bernier et al. [2]

9 studies

0.76 (0.66-0.87)

0.83 (0.68-1.01)

CGHFBC [3]

147,275

0.94 (0.91-0.97)*

* For 1 year of breastfeeding

References

  1. Nelson HD, Zakher B, Cantor A, et al. Risk factors for breast cancer for women aged 40 to 49 years: a systematic review and meta-analysis. Ann Intern Med. 156:635-648, 2012.
  2. Bernier MO, Plu-Bureau G, Bossard N, et al. Breast feeding and risk of breast cancer: a meta-analysis of published studies. Hum Reprod Update. 6(4):374-386, 2000.
  3. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and breast feeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50,302 women with breast cancer and 96,973 women without the disease. Lancet 20:187-195, 2002.
  4. Lambertini M, Santoro L, Del Mastro L, et al. Reproductive behaviors and risk of developing breast cancer according to tumor subtype: A systematic review and meta-analysis of epidemiological studies. Cancer Treat Rev. 49:65-76, 2016.  
  5. Ma H, Bernstein L, Pike MC, Ursin G. Reproductive factors and breast cancer risk according to joint estrogen and progesterone receptor status: a meta-analysis of epidemiological studies. Breast Cancer Res. 19;8(4):R43, 2006. 

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