The PROBIT study is a large randomised controlled study aimed at reducing childhood gastrointestinal infection by promoting breast feeding. Secondary outcomes included atopic eczema and asthma.1 However, the recent paper was written as if the study's main aim was to test the association between prolonged and exclusive breast feeding and asthma and allergy.2 When no statistical difference was found, the authors erroneously concluded that breast feeding has no effect on these outcomes.
This conclusion cannot be drawn from this study design and cannot be extended to different populations. The post hoc analysis, with grouped breastfeeding classes, is more suited to the aim of the paper, but it has methodological and interpretative limitations, such as confounding.
The intervention promoted exclusive and prolonged breast feeding in women who wished to breast feed. This approach can test only whether the duration of breast feeding or exclusion of allergens in the first months of life reduces risk of asthma and allergy in the children of mothers who wish to breast feed. It cannot investigate differences in asthma and allergy rates resulting from a mother's decision to breast feed, or the effect of colostrum or immediate skin to skin contact after birth.
The results cannot readily be extrapolated to populations with higher rates of asthma and allergy. The prevalence of allergy was low—family (parental and sibling) history of atopy was <5% compared with >80% (excluding siblings) in New Zealand.3
The wide confidence intervals suggest that all important confounding and predictor variables may not have been included in the multivariate model. Major concerns exist about the quality of the skin prick test—the only objective measure of atopy used.
Breast feeding may not protect against asthma and allergy, but this study cannot prove this hypothesis. Rather, it shows that in a Belarusian population, promotion of breast feeding in women who wish to breast feed does not alter the risk of asthma and allergy at 6.5 years.
Competing interests: None declared.
References
- 1.Kramer MS, Chalmers B, Hodnett ED, Sevkovskaya Z, Dzikovich I, Shapiro S, et al. Promotion of breastfeeding intervention trial (PROBIT): a randomized trial in the Republic of Belarus. JAMA 2001;285:413-20. [DOI] [PubMed] [Google Scholar]
- 2.Kramer MS, Matush L, Vanilovich I, Platt R, Bogdanovich N, Sevkovskaya Z, et al; the Promotion of Breastfeeding Intervention Trial (PROBIT) Study Group. Effect of prolonged and exclusive breast feeding on risk of allergy and asthma: cluster randomised trial. BMJ 2007;335:815-8. (20 October.) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Sears MR, Greene JM, Willan AR, Wiecek EM, Taylor DR, Flannery EM, et al. A longitudinal, population-based, cohort study of childhood asthma followed to adulthood. N Engl J Med 2003;349:1414-22. [DOI] [PubMed] [Google Scholar]