Abstract
Breast-feeding is usually considered helpful in reducing the incidence of allergy and asthma by delaying introduction of food allergens. Previous studies, often with short follow up, have yielded conflicting evidence of benefits of breast-feeding. We used a New Zealand birth cohort to determine whether breast-feeding conferred protection against development of atopy and asthma later in childhood. These 1037 subjects have been reviewed for evidence of asthma on multiple occasions to age 21 years. Skin testing to 11 common allergens was performed at age 13 years and 21 years. Those breast-fed for less than 4 weeks (n=70) had outcomes similar to those not breast-fed at all (n=463) and so were included in the non-breast-fed group (total n = 533) to compare with the 504 subjects breast-fed for at least 4 weeks. Those breast-fed for 4 weeks or more were significantly more likely at age 13 to have a positive skin test to cat (18.0% vs 8.4%, p<0.001), house dust mite (35.5% vs 24.2%, p<0.001) or any tested allergen (52.7% vs 37.8%, p<0.001). Children who were breast-fed were also more likely to have been diagnosed with asthma by age 9 years (11.8% vs 6.5%, p=0.008). The effect of breast-feeding on atopy was still apparent at age 21 when there was a greater prevalence of positive skin test to cat (31.6% vs 22.6%, p=0.003), house dust mite (60.3% vs 50.7%, p=0.004) and any tested allergen (69.3% vs 60.2%, p=0.005) in the breast-fed group. The increased risk of sensitization at age 13 associated with breast-feeding was seen both in those with and without a family history of atopic disease (either mother or father reporting asthma or hay fever), in first born and non-first born children, and in male and female children. At age 21, the increased risk of atopy associated with breast-feeding was most evident and significant in male subjects. The relative risks (R.R.) of allergy and asthma associated with breast-feeding were adjusted in multivariate analysis for family history, pet ownership in early childhood, socioeconomic status and birth order. Breast-feeding for at least 4 weeks increased the R.R. for current asthma at age 9 to 2.40 (95% C.I. 1.36, 4.26, p<0.005), mite sensitivity to 1.70 (1.21, 2.38, p<0.005) and sensitivity to any allergen to 1.94 (1.43, 2.64, p<0.005). The R.R. for cat allergy associated with breast-feeding was dependent on family history (FH), being 5.27 (2.22, 12.52, p<0.005) in those with a negative FH, and 1.68 (0.91, 3.10) in those with a positive FH. We conclude that, in this birth cohort of New Zealand children, breast-feeding significantly increased the likelihood of developing sensitization to common allergens throughout childhood, and more than doubled the risk of developing physician-diagnosed asthma in childhood.