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Association between breast feeding and asthma in 6 year old children: findings of a prospective birth cohort study

BMJ 1999; 319 doi: (Published 25 September 1999) Cite this as: BMJ 1999;319:815
  1. W H Oddy, senior research officer (Wendyo{at},
  2. P G Holt, National Health and Medical Research Council senior principal research fellowa,
  3. P D Sly, National Health and Medical Research Council principal research fellowa,
  4. A W Read, senior research officera,
  5. L I Landau, professorb,
  6. F J Stanley, professorc,
  7. G E Kendall, study coordinatorc,
  8. P R Burton, headd
  1. a TVW Telethon Institute for Child Health Research, PO Box 855, West Perth, Western Australia, Australia 6872
  2. b Faculty of Medicine and Dentistry, University of Western Australia, Nedlands, Western Australia, Australia 6009
  3. c TVW Telethon Institute for Child Health Research
  4. d Division of Biostatistics and Genetic Epidemiology, Department of Paediatrics, University of Western Australia, Princess Margaret Hospital for Children, Subiaco, Western Australia 6008, Australia
  1. Correspondence to: W H Oddy
  • Accepted 13 July 1999


Objectives: To investigate the association between the duration of exclusive breast feeding and the development of asthma related outcomes in children at age 6 years.

Design: Prospective cohort study.

Setting: Western Australia.

Subjects: 2187 children ascertained through antenatal clinics at the major tertiary obstetric hospital in Perth and followed to age 6 years.

Main outcome measures: Unconditional logistic regression to model the association between duration of exclusive breast feeding and outcomes related to asthma or atopy at 6 years of age, allowing for several important confounders: sex, gestational age, smoking in the household, and early childcare.

Results: After adjustment for confounders, the introduction of milk other than breast milk before 4 months of age was a significant risk factor for all asthma and atopy related outcomes in children aged 6 years: asthma diagnosed by a doctor (odds ratio 1.25, 95% confidence interval 1.02 to 1.52); wheeze three or more times since 1 year of age (1.41, 1.14 to 1.76); wheeze in the past year (1.31, 1.05 to 1.64); sleep disturbance due to wheeze within the past year (1.42, 1.07 to 1.89); age when doctor diagnosed asthma (hazard ratio 1.22, 1.03 to 1.43); age at first wheeze (1.36, 1.17 to 1.59); and positive skin prick test reaction to at least one common aeroallergen (1.30, 1.04 to 1.61).

Conclusion: A significant reduction in the risk of childhood asthma at age 6 years occurs if exclusive breast feeding is continued for at least the 4 months after birth. These findings are important for our understanding of the cause of childhood asthma and suggest that public health interventions to optimise breast feeding may help to reduce the community burden of childhood asthma and its associated traits.

Key messages

  • Asthma is the leading cause of admission to hospital in Australian children and its prevalence is increasing

  • Whether breast feeding protects against asthma or atopy, or both, is controversial

  • Asthma is a complex disease, and the relative risks between breast feeding and asthma or atopy are unlikely to be large; this suggests the need for investigation in a large prospective birth cohort with timely assessment of atopic outcomes and all relevant exposures

  • Exclusive breast feeding for at least 4 months is associated with a significant reduction in the risk of asthma and atopy at age 6 years and with a significant delay in the age at onset of wheezing and asthma being diagnosed by a doctor

  • Public health interventions to promote an increased duration of exclusive breast feeding may help to reduce the morbidity and prevalence of childhood asthma and atop


  • Funding WHO was supported by a research award from the Western Australian Health Promotion Foundation. The Western Australian pregnancy cohort study is funded by project and programme grants from the National Health and Medical Research Council of Australia, and GlaxoWellcome.

  • Competing interests None declared.

  • Accepted 13 July 1999
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