First randomized trial finds breastfeeding doesn’t lower asthma, allergy risk
Reported September 11, 2007
TORONTO (CP) – The first ever randomized trial to look at the much debated question of whether breastfeeding protects an infant from developing asthma and allergies found that children who were breastfed as babies were not at a lower risk of developing these conditions.
In fact, children whose mothers were in the group urged to continue to breastfeed their children exclusively were more likely to test positive later for five common allergies – dust mites, cat dander, birch and grass pollens and fungi.
But the lead author cautioned against concluding that breastfeeding might actually raise the risk a child will develop asthma or allergies.
Dr. Michael Kramer said that because of problems that occurred in the execution of this study, people should be careful about what they read into that part of it.
“My colleagues and I are very comfortable inferring that there’s no protective effect,” said Kramer, a pediatrician and epidemiologist at Montreal Children’s Hospital and scientific director of the Canadian Institutes of Health Research’s Institute of Human Development and Child and Youth Health.
“Whether there’s really an increased risk or not is in the eyes of the beholder. … I would reserve judgment and I would hope readers would as well.”
And he stressed women should not see this study as evidence they should not breastfeed.
“There are not many good reasons not to breastfeed…. There are lots of good reasons to breastfeed, and some of them are very solid. So I think somebody would be crazy not to breastfeed because of this.”
The study, based on nearly 14,000 pairs of mothers and babies in Belarus, was published online Wednesday by the British Medical Journal.
For years debate has raged over whether something about breastfeeding protects against allergies and asthma. The idea is rooted in evidence that breast milk has immune modulating properties that protect infants from infection. But whether the same holds true for auto-immune diseases like allergies is not yet clear.
But others argue there might be a causal link between the resurgence of breastfeeding in the past decade or so and the similarly timed explosive increase in the rates of asthma and allergies in developed countries.
Results of studies looking at the issue have been mixed. One thing they had in common, though, is that most were what are called observational studies, which simply look at outcomes that occur without scientific intervention.
The evidence derived from these kinds of studies isn’t considered as compelling as when scientists randomly assign people to receive – or not – a drug or an intervention. In this case, the intervention was enrolment in a program that encouraged new mothers to breastfeed longer.
This study randomly selected hospitals to either offer the program or not, and followed up on the children when they were about six and a half years old. Mothers were asked questions about whether their child suffered from asthma, wheezing or hay fever symptoms or had itchy rashes or eczema. The children were also skin tested against the common allergens.
But an unexpected problem occurred in the large and expensive trial. Six of the 31 hospitals and clinics had “exceedingly” high rates of positive results for the allergy skin tests, leading the researchers to conclude something was amiss.
Kramer admitted the turn of events was heartbreaking, given how long the study had taken to mount and run, and the fact that it’s unlikely another such randomized study would be conducted.
(This type of study would be impossible to conduct in North America, because hospital obstetrics units are designed to actively encourage breastfeeding. In Belarus in the mid 1990s, when this study started, those programs were not the norm.)
When skin test data from all 31 sites were analyzed, there were no statistically significant differences between the two groups of children. When the six sites with the wonky results were excluded, the children whose mothers were urged to breastfeed longer were between 1.5 and 3.5 per cent more likely to have positive allergy skin tests.
The authors suggested the study underscores the importance of exploring other explanations for the increasing prevalence of allergies and asthma.
“I don’t think we should blame the increase in breastfeeding for the increase in allergy. I think it almost certainly has another explanation,” Kramer said.
“This is not going to be the last word on the subject. It may be the last randomized trial but I don’t think we understand enough about what causes these very complex diseases.”