Does breastfeeding decrease the risk of breast cancer?

Breastfeeding and Breast Cancer Risk Reduction

Breastfeeding significantly reduces the risk of breast cancer, with longer duration of breastfeeding providing greater protection. This protective effect is well-established across multiple guidelines and research studies.

Evidence for Breast Cancer Risk Reduction

• The American Academy of Pediatrics confirms that breastfeeding decreases maternal breast cancer rates 1
• Mothers who breastfeed experience a lower risk of breast cancer, along with reduced risks of type 2 diabetes, ovarian cancer, and hypertension 1
• The protective effect appears to follow a dose-response relationship:
  • Breastfeeding for 12 months or longer provides the maximum protection 2
  • Each 12 months of breastfeeding decreases breast cancer risk by 4.3% 3
  • This protection is in addition to the 7.0% risk reduction per birth 3

Mechanism of Protection

The protective effect of breastfeeding against breast cancer is attributed to several mechanisms:

• Hormonal changes during lactation that reduce lifetime estrogen exposure
• Differentiation of breast tissue during milk production
• Reduced number of ovulatory cycles during lactation periods
• Shedding of breast tissue during lactation that may contain cells with potential DNA damage

Population Impact

The impact of breastfeeding on breast cancer rates is substantial:

• The Collaborative Group on Hormonal Factors in Breast Cancer found that if women in developed countries breastfed as long as women in developing countries, breast cancer incidence would be reduced by more than half 3
• Breastfeeding could account for almost two-thirds of this estimated reduction 3

Specific Breast Cancer Subtypes

• Breastfeeding is associated with reduced risk of triple-negative breast cancer (TNBC) 1
• Women with TNBC had a shorter duration of breastfeeding per child compared to women with non-TNBC 1
• Exclusive breastfeeding appears to provide greater protection than any breastfeeding mode, with a summary relative risk of 0.72 (95% CI 0.58-0.90) 4

Recommendations for Breast Cancer Risk Reduction

• The European Society for Medical Oncology (ESMO) recommends breastfeeding as part of risk reduction strategies for individuals at increased risk of breast cancer 1
• Physical exercise, avoiding obesity, and breastfeeding are recommended for breast cancer risk reduction 1
• For BRCA1 mutation carriers, breastfeeding is particularly associated with reduced breast cancer risk 1

Duration Considerations

• Longer duration of breastfeeding provides greater protection against breast cancer 3
• Breastfeeding for 12 months or longer cumulatively offers maximum protection 2
• The American Academy of Pediatrics supports continued breastfeeding for 2 years or beyond as mutually desired 1

Additional Health Benefits

Beyond breast cancer risk reduction, breastfeeding provides other maternal health benefits:

• Reduced risk of ovarian cancer (30% reduction) 1
• Reduced risk of type 2 diabetes (32% reduction) 1
• More rapid return of uterine tone postpartum 1

Clinical Application

When counseling women about breast cancer risk reduction:

1. Discuss breastfeeding as an important modifiable risk factor for breast cancer
2. Emphasize that longer duration provides greater protection
3. Encourage breastfeeding for at least 12 months cumulatively across all children when possible
4. Provide appropriate support resources to help women achieve their breastfeeding goals
5. Reassure women that any amount of breastfeeding provides some benefit compared to no breastfeeding

The evidence clearly demonstrates that breastfeeding is an effective, natural strategy for reducing breast cancer risk, with benefits that extend to both mother and child.