title: Breastfeeding Mode and Risk of Breast Cancer: A Dose-Response Meta-Analysis.
abstract: BACKGROUND
  Breastfeeding reduces women's risk of breast cancer. Since exclusive breastfeeding has a stronger hormonal effect, it could theoretically result in a greater reduction in breast cancer risk than any breastfeeding mode. No meta-analysis has examined breast cancer risk by breastfeeding mode. Research aim: The authors conducted a meta-analysis for breast cancer risk in parous women who breastfed exclusively or in any mode versus parous women who formula fed their infants, and they estimated the summary dose-response association by the accumulated duration of any breastfeeding mode.
  
  
  METHODS
  A systematic review of studies published between 2005 and 2015 analyzing breastfeeding and breast cancer risk in women was conducted in PubMed and EBSCOhost. A meta-analysis ( n = 65 studies) with fixed effects (or random effects, if heterogeneity existed) was carried out stratified by breastfeeding mode and menopausal and parity status. A summary dose-response association was estimated using the generalized least-squares method.
  
  
  RESULTS
  The summary relative risk (SRR) for breast cancer in parous women who breastfed exclusively was 0.72, 95% confidence interval (CI) [0.58, 0.90], versus parous women who had never breastfed. For parous women who breastfed in any mode, the SRR was lower in both premenopausal women (0.86, 95% CI [0.80, 0.93]) and postmenopausal women (0.89, 95% CI [0.83, 0.95]). There was no heterogeneity or publication bias. There is weak evidence of a difference between exclusive and any breastfeeding mode ( p = .08). The summary dose-response curve was nonlinear ( p < .001).
  
  
  CONCLUSIONS
  Exclusive breastfeeding among parous women reduces the risk of breast cancer compared with parous women who do not breastfeed exclusively.
authors.affiliation: 1 Center for Research on Health and Nutrition, National Institute of Public Health, Cuernavaca, Morelos, Mexico.
authors.forename: Mishel
authors.initials: M
authors.lastname: Unar-Munguía
authors.affiliation: 2 Center for Research on Population Health, National Institute of Public Health, Cuernavaca, Morelos, Mexico.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Torres-Mejía
authors.affiliation: 3 Center for Health Systems Research, National Institute of Public Health, Cuernavaca, Morelos, Mexico.
authors.forename: M Arantxa
authors.initials: MA
authors.lastname: Colchero
authors.affiliation: 4 Health Department, Iberoamerican University, Mexico City, Mexico.
authors.forename: Teresita
authors.initials: T
authors.lastname: González de Cosío
mesh_terms: D000328:Adult; D001942:Breast Feeding / Q000009:adverse effects* / Q000706:statistics & numerical data; D001943:Breast Neoplasms / Q000453:epidemiology / Q000209:etiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D011247:Pregnancy; D012307:Risk Factors
keywords: breast cancer; breastfeeding; breastfeeding duration; dose–response; exclusive breastfeeding; meta-analysis