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A recent study published in the September 11 British Medical Journal online found that prolonged and exclusive breastfeeding provided no protective effect against the risk of asthma and allergy. The study, titled “Effect of prolonged and exclusive breast feeding on risk of allergy and asthma: cluster randomized trial,” was performed by McGill University's Dr. Michael Kramer and funded by the Canadian Institutes of Health Research (CIHR). According to Dr. Kramer, this study “is the largest randomized trial ever done in the area of human lactation.”
The study examined 13,889 children who had been selected at birth from 31 Belarussian maternity hospitals in the randomized Promotion of the Breastfeeding Intervention Trial (PROBIT). During the PROBIT trial, researchers recruited moms in maternity hospitals and clinics in Belarus who expressed a desire to start breastfeeding prior to birth. The women were then randomly divided into two groups. The intervention group was encouraged to breastfeed as long and as exclusively as possible, while the control group got no such support. Women in the intervention group breastfed significantly longer than women in the control group (the number of women who exclusively breastfed at three months was seven times higher in the intervention group).
The follow-up took place from December 2002 to April 2005, when the children were six and a half years old. Asthma and allergies were assessed via the international study of asthma and allergies in childhood (ISAAC) questionnaire as well as a skin prick test of five common allergens (house dust mite, cat, birch pollen, mixed northern grasses, and alternaria). The study found that the percentage of children who had allergies was approximately the same in both groups and there was no significant difference in the percentage of children with asthma. Additionally, there were “highly significant increases” in positive skin prick tests for all allergens tested among those who were exclusively breastfeed for three or more months as compared to those exclusively breastfeeding for less than three months.
One limitation of this study is that the prevalence of allergic symptoms were lower among PROBIT children than usually seen in the US and Canada. However, in 2002, another study, conducted among 1,037 New Zealand infants, found that babies who had been breastfed for more than four weeks had almost double the risk of contracting asthma and allergies in their childhood compared with counterparts who had been fed on infant formula. According to Dr. Kramer, “In New Zealand, allergy and asthma are even more common than they are in Canada. This suggests that there is nothing unusual about the PROBIT setting that would explain our results." Therefore, the authors conclude that “public health measures to increase the initiation, duration, and exclusivity of breast feeding seem unlikely to have a major impact on reducing the incidence of atopic diseases.”
Posted September 2007
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