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.