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Does breastfeeding raise peanut allergy risk?

Splashed across the news today was a study from the Australian National University that reported a statistical link between breastfeeding and nut allergy, particularly peanut allergy. Exclusive breastfeeding for 6 months got an especially bad rap from the study authors, according to media reports. “Breast feeding… may, in fact, be causative of allergy”, the study authors have concluded.

So what’s going on?

At first I thought there might be something to it. After all, Australia’s own revised NHMRC guidelines are somewhat behind the times in their recommendations on when to introduce solids. The best, recent evidence from scientific studies suggests that there is a ‘critical period’ for introduction of many different types of solid foods. If the introduction of the food is delayed, it actually increases the risk of allergy. The timing of this ‘critical period’ for most of the foods studied appears to fall between 4-6 months. So breastfeeding exclusively for 6 months doesn’t leave a whole lot of time to introduce those foods. It would therefore seem likely that allergy risk may be higher in babies who are breastfed for 6 months.

I took the time to read the study, only to find that they appeared to have linked any breastfeeding at all with increasing a child’s risk of allergy.

The first problem I found with their published study was the authors’ claim in their introduction that:

“an increasing number of studies have implicated breast feeding as a cause of the increasing trend in nut allergy”.

Really? They made three citations to support this claim.

A single case report of an exclusively breastfed infant who had had an allergic reaction to peanuts.

  1. A study from 1986 on food allergy and maternal diet.
  2. A study from 1999 on exposure to peanuts in utero and during infancy.

I have a few brief points to make on those citations:

  1. A case report on a single infant is not a study that can be cited in support of a massive, population-wide increase in food allergies among children.
  2. 1986 was 26 years ago. If the authors have to reach that far back, they are probably having a hard time finding studies that support their case.
  3. Even 1999 was 13 years ago. See point 2. (And you feel old now, don’t you!)

It is hard to believe that the roughly 10-fold increase in specialist referrals for food allergy and fivefold increase in hospital referrals for food-related anaphylaxis that occurred in Australia over the last decade or so has been matched by comparable increases in the rate of breastfeeding or maternal consumption of peanut products. It’s implausible.

Speaking of implausible, here’s one more thing that jumped out at me that there was something off with the data in this study:

32% of parents reported breastfeeding exclusively for the first 6 months.

This is more than twice the actual rate of exclusive breastfeeding in Australia (around 14-15%), which suggests that participants misunderstood the question, or weren’t entirely truthful. The rate of exclusive breastfeeding in the ACT is higher, but nowhere near that much higher! This point should have been addressed by the authors but wasn’t.

They also give credence to the idea that part of the increased incidence in food allergies may be due to increased consumption of peanuts and peanut products by mothers and mothers-to-be, an idea I thought had been pretty well discarded by now.

Then I saw this quote from one of the study authors in the ABC’s report on their website:

“What we have uncovered is that from a biological point of view, there are risks for breastfeeding if women eat nuts during breastfeeding and probably during pregnancy,” he said.

“It is probably little fragments of nuts, proteins from nuts that mum had been eating. It is not the breast milk itself, it is the other very microscopic amounts of proteins and so on that you get from eating nuts.”

What he should have said was that from a statistical point of view, this study points to an increased risk of allergy among breastfed babies in Australia. And their (retrospective) study had nothing to do with studying proteins in breast milk.

The response from the Australian Breastfeeding Association reported in the ABC’s article bordered on incoherent and did nothing to highlight problems with the study’s findings. I really hope they can come up with something a bit better and actually have it reported.

I don’t think we will have to wait long for a proper analysis of this study. Until then we will have to put up with the media fear-mongering among new parents, with headlines implying that breastfeeding may increase the risk of potentially fatal peanut allergies. That’s a real shame.

Children’s Nutrition Research Centre

ChatBox Speech Pathology

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