A birth cohort of 4,089 infants was followed prospectively in Stockholm, Sweden. Information about various exposures was obtained by parental questionnaires when the infants were 2 months old, and about allergic symptoms and feeding at 1 and 2 years of age. Duration of exclusive and partial breastfeeding was assessed separately. Children exclusively breastfed for four months or more exhibited less asthma, less atopic dermatitis and less suspected allergic rhinitis by 2 years of age.

There was a significant risk reduction for asthma related to partial breast feeding for six months or more. Five possible allergic disorders — asthma, suspected allergic rhinitis, atopic dermatitis, food allergy related symptoms, and suspected allergic respiratory symptoms after exposure to pets or pollen — were studied. Exclusive breastfeeding prevented children from having multiple allergic disease during the first two years of life. The authors concluded that exclusive breastfeeding seems to have a preventive effect on the early development of allergic disease, including multiple allergic disease, up to 2 years of age.

Kull I et al (2002). Breast feeding and allergic diseases in infants--a prospective birth cohort study. Arch Dis Child 87: 478-481.