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Breastfeeding Appears To Be Protective Against Asthma in Young Children


  • Does breastfeeding versus formula feeding help prevent asthma in young children?

Clinical Bottom Lines

  1. Breastfeeding until at least 9 months appears to have a protective effect against asthma in children 12-24 months.
  2. The odds ratio of having asthma in children 12-24 months is 2.39 if breastfed less than 9 months compared with breastfeeding beyond 9 months of age.
  3. The effect of breastfeeding appears to be stronger with longer duration, with statistical significance seen for breastfeeding beyond 9 months of age.

Summary of Key Evidence

  1. Data were obtained from Canadian National Longitudinal Survey of Children and Youth which uses a survey of 2184 mothers of children 12-24 months from a "complex clustered sampling scheme representative of Canadian childhood population."1
  2. Confounders associated with asthma and breastfeeding were adjusted for in the multiple regression analysis (prenatal maternal smoking, prematurity, LBW, low maternal education).
  3. There appears to be a dose-response effect with statistical significance >9 mo (the longer the breastfeeding the better the prevention against asthma):

Odds ratios (99% CI) for asthma in breastfeeding:
<2mo: 1.11 (0.68-1.83)
<6mo: 1.62 (0.86-3.08)
<9mo: 2.39 (0.95-6.03)
Note: No difference for any of these (OR of 1 lies within these confidence intervals).

Additional Comments

  • This study is consistent with a recent systematic review which showed protective effects with an odds ratio of 0.7 overall in breastfed babies and 0.52 in breastfed babies of atopic families.2
  • The protective effect of breastfeeding may be due to a decrease in allergic sensitization and modulation of the infant's immune system by secretion of immunologic factors in breastmilk.
  • It would be interesting to see if there was still a decrease in incidence of asthma in children older than 2 years old. It would also be interesting to know if exclusive breastfeeding vs. early introduction of solids would change the results.


  1. Dell S, Tell T. Breastfeeding and asthma in young children. Archives of Pediatrics and Adolescent Medicine 2001; 155:1261-1265.
  2. Gdalevich M, Mimouni D, Mimouni M. Breast-feeding and the risk of bronchial asthma in childhood: a systematic review with meta-analysis of prospective studies. Journal of Pediatrics 2001; 139:261-6.

CAT Author: Amy Doil MD

CAT Appraisers: Katherine Layton MD

Date appraised: February 18, 2002

Last updated October 15, 2002
Department of Pediatrics and Communicable Diseases
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