Researchers from New Zealand and Canada assessed the long-term outcomes of asthma and atopy related to breastfeeding.
Breastfeeding is widely advocated to reduce risk of atopy and asthma, but the evidence for such an effect is conflicting.
The study cohort consisted of 1037 children born in Dunedin, New Zealand, between 1972 and 1973, and residing in the local area at age 3 years.
The children were assessed every 2 to 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.
| Breastfed children have more allergies.
Of the 1037 eligible children, 504 (49%) were breastfed for 4 weeks or longer, while 533 (51%) were not.
The research team found that more children who were breastfed were atopic at all ages (from 13 to 21 years) to cats, house dust mites, and grass pollen, than those who were not breastfed.
In addition, more children who were breastfed reported current asthma at each assessment between age 9 and 26 years than those who were not.
Breastfeeding effects were not affected by parental history of hayfever or asthma.
The researchers conducted a multifactor analysis, controlling for socioeconomic status, parental smoking, birth order, and use of sheepskin bedding in infancy.
This found odds ratios of 1·94 for the presence of any allergy at age 13 years, 2·40 for current asthma at 9 years, and 1·83 for current asthma at 9 to 26 years.
Professor Malcolm Sears' team concluded, "Breastfeeding does not protect children against atopy and asthma, and may even increase the risk".