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?

4 thoughts on “Science You Can Use: Does breastfeeding really cause peanut and tree nut allergies?

  1. Thanks for this, Tanya. As a mom to a nursing toddler with severe food allergies, this whole thing just makes me angry and frustrated and confused.

    I have read some materials suggesting that perhaps the development of food allergies can be tied to moms avoiding peanuts and nuts during pregnancy and breastfeeding… because in cultures where moms eat lots of peanuts and give bits of boiled peanut to babies, peanut allergy is rare. But really—–who knows? Those also may be environments that aren’t as over-sanitized or full of toxic chemicals. The studies all seem to contradict each other. And there are so many factors——another recent study showed that exposure to triclosan (anti-bacterial found in numerous U.S. hand soaps and cleaning products) is strongly associated with food allergy development.

    My 2-year-old (still nursing!) has eczema and severe life-threatening allergies aplenty——to tree nuts, eggs, sesame, mustard seed, and cow’s milk. And I did exclusively breastfeed until a bit past 6 months. However, I did NOT restrict my diet at all with allergies in mind while breastfeeding or pregnant—I avoided raw fish and raw milk/cheese, but not peanuts, nuts, eggs, etc.

    The doctors first suspected she had cow’s milk and/or soy allergy when she was colicky as a newborn, so I eliminated them from my diet and it seemed to help… So of COURSE I didn’t even consider formula of any kind to be an option whatsoever and despite serious challenges with breastfeeding and pumping (repeated bouts of thrush, oversupply, vasospasms) I have kept at it (though I quit pumping at a year).


  2. The whole business of allergies and diets is a confusing one. I have noticed an increase in allergy sensitivity in children born to vegetarian mothers. My daughter was cow milk intolerant from birth but at 7 months when I stopped nursing we tried her little by little on cow’s milk and over 6 months she became non allergic to organic cows’ milk. She has eaten nuts, fish and all sorts of things that my hubby is allergic to since she was 4-6 months and has no reactions to these. I believe part is genetic and part diet and what you are able to get your child to eat as early as possible. I am not a vegetarian , I add!


  3. I definitely don’t think that exclusively breastfeeding could possibly increase risk of allergy. Children in developing and poorer countries have much lower rates of allergy than in developed countries. And many of these people traditionally breastfeed babies for longer periods of time.

    However I do think that the doctor’s point about maternal diet may be valid. I don’t think it is a good idea to eat raw nuts during pregnancy and lactation. During my first pregnancy, my husband convinced me to eat raw walnuts everyday against my better judgement, and my son developed tree nut allergy symptoms before 3 years. In most older cultures, nuts are usually cooked or roasted before they are eaten. This could be a factor.

    In Indian communities with a traditional vegetarian diet, allergies are very uncommon. I don’t think vegetarianism has any effect on this as another poster mentioned.


  4. in many countries children are breast fed into toddlerhood and there are no allergies, say for example my own country, India, till my previous generation, Ive heard of school going children being breast fed, but none of them – I repeat none of them had any kind of allergy. As a mother of son with allergies I do know that US, Australia, UK & Ireland are top countries for allergies – not sure if it is the weather, the food (chemical ridden) or what, but there is something in these countries which is not in the other countries. So in these countries, irrespective of whether the children are breast fed or not, the incidence of allergies will be higher. I had both my children in Ireland, when I found out about my son’s allergies, I went to India for my second pregnancy and spent my first and second trimester there. My son who was breast fed for 20 months had allergies and my daughter who was breast fed for 4.5 years doesn’t have allergies!


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