Exclusive Breastfeeding Not All That? The Magical (Limited) Powers of Breast Milk

Did you catch the recent U.K. study questioning whether women should exclusively breastfeed for six months? Before anyone gets too excited, the authors still recommend breastfeeding for at least a year or until the child spits out the boob. The authors still recommend exclusive breastfeeding but suggest 4 months might be better than 6 months. Moreover, they offer further proof of the much-hyped powers of breast milk on the developing immune system, specifically the prevention of food allergies.

Take a look at the study's findings published online at Pediatrics:

RESULTS: Infants who were diagnosed with food allergy by the time they were 2 years of age were introduced to solids earlier (≤16 weeks of age) and were less likely to be receiving breast milk when cow’s milk protein was first introduced into their diet.

Let's break it down:

Kids with allergies got solid food (e.g. rice, carrots) earlier on average. 

Kids with allergies also were less likely to be breastfeeding at the time they first got cow's milk protein (e.g. formula, yogurt, an added ingredient, etc.).

The authors describe this time period when babies are still breastfeeding and first sampling other substances as an "overlap." They theorize this"overlap" period allows breast milk to use its magical powers to pump up the youngsters' immune systems and thus protect them against food allergies: 

"My theory was that if food allergens -- those things that infants actually become allergic to -- aren't there at the same time as the breast milk, the breast milk can't educate the immune system," [lead researcher Kate Grimshaw, Ph.D., a research fellow and allergy specialist at the University of Southamptons] said. WebMD
Let's ignore the anthropomorphism and the image of breast milk lecturing cytokines and such. In order to work its magic, breast milk must mingle with other food/formula (here, mostly cow's milk protein). Without the bovine assistances, in whatever form, breast milk isn't all that.  It doesn't reduce allergy risks on its own. 

Here's where it gets more interesting...

Dr. Grimshaw and colleagues report these super powers don't kick in until about 4 months but we'll get to that in a minute.

Just so we're clear about the supreme potency of breast milk, kids with allergies didn't get any less breast milk than those wheezing, itching, and the like. There were no significant differences in breastfeeding between the allergy and control groups. How long mothers breastfed did not appear to effect whether their children developed allergies. Nor did duration of exclusive breastfeeding appear to matter. 

Let me re-state. Breastfeeding, exclusively or not, did not appear to reduce allergies.  

What does this mean in terms of the current 6-months exclusive breastfeeding stance? The authors speculate the recommendation has acted to limit the overlap period and thus potentially increase the incidence of allergies. 

Mind you, they don't recommend mothers introduce foods prior to 4 months owing to the fact allergic kids got solids earlier than the others. Not even for the breast milk babies. Especially not the formula babies. 

But let's take a closer look at that 4 months part again because it's not quite that neat and simple. Go figure. Some curious bits are skipped over or completely absent in the media. Although the allergic kids on average were introduced to solid foods earlier, the control kids got them the earliest. Both groups look much the same in terms of eating until 3 months (13 weeks) and I'm pretty sure that here we're talking real food too (i.e. not including formula) but I'm not 100% certain considering the authors seem to interchange terms within the paper*.  In any case, nobody was eating much. Between 12 and 16 weeks (3 to 4 months), 15% of allergic kids compared to 9% of control kids were eating food. 

The figure in the journal article illustrates the eating patterns of the two groups. 

Figure 3: Timing of introduction of solids to food-allergic and control groups (credit: AAP)

Before 12 to 13 weeks, the controls (the greens) were more likely to receive solids than the allergic kids (blue). After then more allergic kids eating solids until after 6 months when everybody's eating.

What is so magical about 4 months? 

At that point the differences between the two groups appear to be at their greatest. The researchers noted this when looking at the data then tested whether kids who had solids before then were more likely to develop allergies (actually they report it as complementary food, even use it in the title of the paper but don't define it, likely food but not formula) and as we discussed, the answer turned out to be yes. The authors concluded introducing food before 17 weeks appears "to promote allergic disease" but waiting until after 17 weeks, "seems to promote tolerance."

It's not immediately obvious what this means in terms of the overlap effect. It is not obvious if the overap effect operates before this point although the researchers report "(t)his finding implies that the mechanism, which acts post17 weeks of age, is a nonallergen-specific tolerogenic immunologic mechanism..." In other words, they think the protective effects of breast milk operate only after this time period. 

It's a bit complicated and gerry-rigged, the post-17 week mechanism. Why? It involves combining the age-at-first-solids results and the overlap results into a cohesive theory. The first results addressed only solid food, the second, cow's milk protein (formula, yogurt, etc.). The overlap results don't specifically offer up 17 weeks as the starting point. The authors reasoned that because the age results suggest 17 weeks is a critical time period for allergy development (and solid food introduction) before this time the breast milk can't override the effects of possible antigens (i.e. food). After that point, they suggest breast milk helps prevent allergies. 

What does this mean in terms of practical advice?

No worries, the researchers attempted to sum it up, especially for mothers who dare to not breastfeed: 

Women who are not breastfeeding are encouraged to introduce solids after 17 weeks of age, Dr. Grimshaw says. Science Daily

“Don’t introduce solids until 17 weeks,” said the lead author, Kate E. C. Grimshaw, a nutritionist at the University of Southampton, “and if you can wait longer, that’s fine, too. At whatever age you begin solid foods, you should continue breast-feeding as well. And for those who cannot breast-feed, the advice not to introduce solid foods until 17 weeks is still applicable.” New York Times

Note the "cannot breastfeed." As opposed to "not breastfeeding" or "using formula." Is it any surprise in the journal article the authors refer to breastfed babies getting their first taste of formula or food as "losing exclusivity." 

By the way, the overlap effect showed up only with cow's protein. Let me re-state that too. The super powers of breast milk only showed up when kids got cow's milk and in this study that meant formula. So the advice to keep breastfeeding while introducing solids to prevent allergies is not supported by this study. The advice should be to keep breastfeeding while introducing and feeding formula and/or other foods with cow's milk protein. Moreover, allergic kids weren't introduced to cow's milk in any form** earlier than other kids, suggesting supplementing breast milk during breastfeeding doesn't raise risk of allergies. 

True, the study was constrained by the fact not many kids still breastfeeding got much food. Most "lost their exclusivity" by drinking whey-based formula. So although the researchers tested for an overlap effect between breast milk and "any food", the results weren't significant perhaps because not many babies got food while still breast feeding. Perhaps further researcher will find that evidence. At this point, however, there is no evidence that breastfeeding while introducing solids prevents allergies. That's not this study. That's merely supposition right now.

Also the researchers couldn't test how this overlap might apply to the development of specific food allergies because, again, few breastfed babies were eating foods. Nor could they investigate a potential overlap effect between common allergens (peanuts, fish) and breast milk because these foods are commonly introduced after weaning.

Read the study. It's free for now and very knotty. Lots of great detail. 

*Some terms are defined in the paper but it's not always clear what the authors mean or the analyses use at all times. The confusing terms include cow's milk protein, solid food, semi-solid food, milk "in any form, " "milk as an ingredient" and complementary food (the last 3 undefined). 

**I think this means cow's milk protein in formula or other sources. Cow's milk "as an ingredient" however, did turn up significant differences between the two groups. Allergic kids receive milk in "as an ingredient" at an earlier age. I don't think this includes formula . Anyhow, it's an important point and might have to email the authors. 

UPDATE: Somehow a draft version was posted earlier. Mea culpa. 

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