Long-term relation between breastfeeding and development of atopy and asthma 
in children and young adults: a longitudinal study 

Malcolm R Sears, Justina M Greene, Andrew R Willan, D Robin Taylor, Erin M 
Flannery, Jan O Cowan, G Peter Herbison, Richie Poulton 

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Departments of Medicine (Prof M R Sears FRACP, J M Greene) and Clinical 
Epidemiology and Biostatistics (A R Willan PhD), McMaster University, 
Hamilton, Ontario, Canada; Departments of Medicine (D R Taylor MRCP, E M 
Flannery, J O Cowan) and Preventive and Social Medicine (G P Herbison MSc, R 
Poulton PhD), Dunedin School of Medicine, University of Otago, Dunedin, New 
Zealand

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Correspondence to: Prof Malcolm R Sears, Firestone Institute for Respiratory 
Health, St Joseph's Healthcare and McMaster University, 50 Charlton Avenue, 
Hamilton, Ontario L8N 4A6, Canada (e-mail:[log in to unmask])

Summary 


Background Breastfeeding is widely advocated to reduce risk of atopy and 
asthma, but the evidence for such an effect is conflicting. We aimed to 
assess long-term outcomes of asthma and atopy related to breastfeeding in a 
New Zealand birth cohort. 


Methods Our cohort consisted of 1037 of 1139 children born in Dunedin, New 
Zealand, between April, 1972, and March, 1973, and residing in Otago province 
at age 3 years. Children were assessed every 2-5 years from ages 9 to 26 
years with respiratory questionnaires, pulmonary function, bronchial 
challenge, and allergy skin tests. History of breastfeeding had been 
independently recorded in early childhood. 


Findings 504 (49%) of 1037 eligible children were breastfed (4 weeks or 
longer) and 533 (51%) were not. More children who were breastfed were atopic 
at all ages from 13 to 21 years to cats (p=0·0001), house dust mites 
(p=0·0010), and grass pollen (p<0·0001) than those who were not. More 
children who were breastfed reported current asthma at each assessment 
between age 9 (p=0·0008) and 26 years (p=0·0008) than those who were not. 
Breastfeeding effects were not affected by parental history of hayfever or 
asthma. Multifactor analysis controlling for socioeconomic status, parental 
smoking, birth order, and use of sheepskin bedding in infancy, showed odds 
ratios of 1·94 (95% CI 1·42-2·65, p<0·0001) for any allergen positive at age 
13 years, 2·40 (1·36-4·26, p=0·0003) for current asthma at 9 years, and 1·83 
(1·35-2·47, p<0·0001) for current asthma at 9-26 years by repeated-measures 
analysis. 


Interpretation Breastfeeding does not protect children against atopy and 
asthma and may even increase the risk. 


Lancet 2002; 360: 901-07 

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