Despite a series of often conflicting studies, breastfeeding has been advocated for the prevention of asthma with the majority of the evidence showing a protective association. It remains unclear how the association between breastfeeding and asthma develops as children get older and whether this association is influenced by maternal or paternal allergy.
A longitudinal study in Holland (1) was carried out to assess the association between breastfeeding and asthma in children from 1 to 8 years of age (n=3115), taking into consideration maternal and paternal allergy. Data on breastfeeding and asthma was collected by yearly questionnaires. 83.1 per cent (n = 2588) of the children were breastfed with 34.7 per cent (n = 1081) being breastfed for >16 weeks. At 8 years, the asthma risk was significantly lower in children breastfed for >16 weeks compared with those who were not breastfed. Unfortunately, no data was available on exclusive breastfeeding, however the authors argue that using exclusive breastfeeding instead of any breastfeeding would probably strengthen the associations shown in the study. The results showed an association with reduced risk of asthma irrespective of parental allergy status.
In a commentary about this study (2) in the same edition of the journal, Oddy makes suggestions about why this protective effect of breastfeeding against asthma is plausible. She suggests for example, that there may be interactions with asthma and overweight. It is also likely that by providing an immediate line of defence against infectious agents, breastmilk is able to help compensate directly for the immaturity of the newborn immune system to resist infection at the time when it is most vulnerable. Protection may also be through many of the other factors in milk, including bioactive enzymes, hormones, growth factors, cytokines and immunological agents, which augment and stimulate the development of the immature host defence. Early milk has an abundance of cytokines at a time when neonatal organ systems are immature, suggesting that these bioactive components of milk may be important in neonatal development. In addition studies in animals as well as humans have demonstrated that airborne allergens transferred to the offspring via the breastmilk could induce antigen-specific tolerance in the offspring resulting in protection against allergic airway disease.
1. Scholtens S., Wijga AH., Kerkhof M. et al (2009) Breast feeding, parental allergy and asthma in children followed for 8 years. The PIAMA birth cohort study Thorax;64:604-609; doi:10.1136/thx.2007.094938
2. Oddy W. (2009)Breast feeding and childhood asthma. Thorax 2009;64:558-559; doi:10.1136/thx.2008.105130
