Science You Can Use: Does breastfeeding really cause peanut and tree nut allergies?

A recent Australian study about breastfeeding and peanut and tree nut allergies has caused a big stir in the last week, and for good reason.  The authors’ head-turning conclusion:  exclusive breastfeeding may cause peanut and tree nut allergies in children.

There’s no dispute that peanut and tree nut allergies are on the rise, and parents and providers the world over are looking for the cause or causes.   So, could this study be the answer?

In this study the authors surveyed over 15,000 parents of Australian kindergartners about their infant feeding practices and any allergies to peanuts and tree nuts.  They concluded:

The likelihood of developing a nut allergy was 1.5 times higher in children who were solely breast fed in the first six months of life, than in children who were exposed to other foods and fluids. Protection against nut allergy was found in children who were fed food and fluids other than breast milk.

One author commented:  “Our results contribute to the argument that breast feeding alone does not appear to be protective against nut allergy in children – it may, in fact, be causative of allergy.”

This, on its face, is a very interesting finding.  But there are a few problems with the study’s methodology, and one big problem with the authors recommendations, to consider.

With regard to methodology, there is the problem of poor recall on the part of the study participants who were asked to remember what they did five years prior, and there is the association/causation conflation – both common problems in breastfeeding research.

But the bigger problem with this study is that we don’t know if the children who had these food allergies had a family history of them, or if they had allergic symptoms in infancy prior to the end of exclusive breastfeeding.

Professor Katie Allen, pediatric gastroenterologist and food allergy researcher at the Australian Murdoch Children’s Research Institute, noted in an interview for the Australian public broadcasting corporation that:

“Families with an increased risk of allergies tend to breastfeed longer, and their children more likely to have allergies because of family history.”

So it is true that it looks like mothers who breastfeed for longer are more likely to have [children with] allergies, but it’s the fact that they are more likely to have allergies that makes them breastfeed for longer,” she says.

And if the children had early symptoms of allergy (again, we don’t know), it may be that their mothers opted to breastfeed exclusively longer in an attempt to reduce the allergic response, making it appear as though exclusive breastfeeding caused the allergies.

These issues are vexing enough, but a larger problem rests with one of the authors’ conclusions:  pregnant and nursing moms shouldn’t eat peanuts and tree nuts because doing so could increase the risk of allergies.

Based on the data collected for this study, it doesn’t appear that one could draw any conclusions about mothers’ intake of these foods and its bearing on allergies.

The authors didn’t collect data on what mothers ate (and it would have been difficult to do accurately – do you remember what you ate five years ago?).  So we don’t know if the mothers whose children developed allergies ate peanuts or tree nuts in pregnancy or breastfeeding, or not.  And because we don’t know this, we don’t know if it has any bearing on the outcome.  What if the mothers of kids who developed allergies abstained from peanut and tree nuts, and this caused the response?  What if it’s the other way around?  Did the allergies develop because of or in spite of maternal consumption?  We can’t say one way or the other from the data.

Indeed, Allen notes:  “We think exposure to small amounts [of allergens] helps to train the immune system and is safe and may even protect against allergy. However, we need some more formal evidence for us to be sure of it,” she says.

So, if you’re concerned about your baby developing a peanut or tree nut allergy, what do you make of this latest research?  If you feel puzzled, you’re not alone.

The American Academy of Pediatrics 2012 revised breastfeeding policy reflects the confusing and contradictory nature of the evidence on this topic:

There is a protective effect of exclusive breastfeeding for 3 to 4 months in reducing the incidence of clinical asthma, atopic dermatitis, and eczema by 27% in a low-risk population and up to 42% in infants with positive family history.  There are conflicting studies that examine the timing of adding complementary foods after 4 months and the risk of allergy, including food allergies, atopic dermatitis, and asthma, in either the allergy-prone or nonatopic individual…One problem in analyzing this research is the low prevalence of exclusive breastfeeding at 6 months in the study populations. Thus, research outcomes in studies that examine the development of atopy and the timing of introducing solid foods in partially breastfed infants may not be applicable to exclusively breastfed infants.

Professor Allen’s conclusion?  “Parents can be reassured that what they eat during pregnancy and lactation, at this point in time, appears to have no effect whatsoever on their allergic risk.”

We’ll let you take it from there!

Does your child have a peanut or tree nut allergy?  What do you make of this study and the authors’ recommendations?

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4 Comments | Last revised on 07/19/2012

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