Some previous work suggests that exclusive breast-feeding protects against atopic disease and asthma, but other studies fail to support this conclusion. The best way of demonstrating protection against childhood asthma is to follow up a large cohort of children prospectively from birth, assessing both exposures and outcomes. Such a study recently was conducted in Western Australia in a cohort established in 1989-1992, in which 2187 children were followed up to age 6 years. An association between the duration of exclusive breast-feeding and the risk of atopy or asthma at age 6 was sought by logistic regression analysis, controlling for a number of confounding factors, such as gender, gestational age, early child care, and smoking in the household.
Introducing milk other than breast milk before age 4 months significantly increased the risk of asthma and atopy-related outcomes. The odds ratio for physician-diagnosed asthma was 1.25; for three or more episodes of wheezing since age 12 months, 1.41; and for wheezing in the past year, 1.31. The age at first wheezing and age when asthma was diagnosed both were less when nonbreast milk was introduced within the first 4 months of life. The odds ratios also were increased for sleep disorder secondary to wheezing in the past year (1.42) and a positive skin prick test reaction to at least one common aeroallergen (1.30). These findings suggest that maintaining exclusive breast-feeding until at least age 4 months may protect against asthma or atopy developing later in childhood.
Br Med J 1999;319:815-819