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."
