Breastfeeding does not protect against asthma and allergic diseases

A longitudinal study in this week’s issue of THE LANCET provides compelling evidence that breastfeeding does not protect against asthma and atopy in childhood and early adulthood—authors of the study suggest that breastfeeding may actually increase the risk of these diseases.

Breastfeeding is widely advocated to reduce the risk of atopy and asthma, but the evidence for this effect is conflicting. Malcolm Sears and colleagues from McMaster University, Canada, and the University of Otago, New Zealand, assessed the long-term outcomes of asthma and atopy related to breastfeeding in a New Zealand population.

Around 1000 children from Dunedin, New Zealand, who were born between 1972 and early 1973 were studied. They were assessed for respiratory function and asthma symptoms every 2-5 years up to age 26 years. Tests for allergies by the skin prick test were done at ages 13 and 21. Half the children studied had been breastfed.

More children who were breastfed were allergic between the ages of 13 to 21 years to cats, house-dust mites, and grass pollen. More children who were breastfed were asthmatic between the ages of 9 to 26 years. Breastfeeding effects were not affected by parental history of hayfever or asthma. When possible confounding factors such as socioeconomic status, parental smoking, birth order, and use of sheepskin bedding in infancy were taken into account, children breastfed for more than four weeks were around twice as likely to have allergic disease or asthma in later childhood than children who were not breastfed.

Malcolm Sears comments: “Breastfeeding could be promoted for many reasons, including optimum nutrition and reduction of risk of infant infections. However, the role of breastfeeding in protection of children against atopy and asthma cannot be supported on the basis of the present balance of evidence.”

In an accompanying Commentary (p 887), Peter Sly from the Telethon Institute for Child Health Research, and Patrick Holt from the Centre for Child Health Research, Perth, Australia, state that the differing research findings in this field create a confusing picture for scientists and patients alike; however they conclude: “Although there are many valid reasons for encouraging breastfeeding during the first 4-6 months of life, based on the current evidence the prevention of asthma and allergies is not one of them.”