Does breastfeeding improve the intelligence of babies?

The Pediatric Insider

© 2013 Roy Benaroch, MD

A new study published in JAMA Pediatrics shows that breastfeeding is good for your baby’s IQ—or does it? USA Today thinks so, with their headline “More evidence that breast-feeding may boost babies’ IQs”. Reuters is less direct: “Breastfeeding tied to kids’ intelligence”.  An editorialist for JAMA put the findings this way: “Breastfeeding an infant for the first year of life would be expected to increase his or her IQ by about 4 points.”

Sounds good to me. But is that really the conclusion that the study ought to have reached?

I know I’m treading on thin ice here. Pediatricians are supposed to be all rah-rah about nursing, and failing to be 100% supportive of any new finding that lends further support for nursing may be tantamount to apostasy. Hopefully I’ve got the cred to get away with this—my blog has always been supportive of breastfeeding, and I’m one of the few pediatricians I know of in my area that has been trained to treat tongue-tie, specifically to help women be successful in nursing.

So what does the study show? The details are behind a paywall, so you’ll have to take my word for it. It is a very dense and complex study, with a lot of tables and a whole lot of discussion of how scores are adjusted and covariates controlled. Basically, researches studied a cohort of about 1000 babies in Massachusetts born in 1999-2002. At six months of life, their moms filled out questionnaires regarding breastfeeding (along with their own diets, health information, and a whole lot of other things.) At 3 and 7 years, the children and moms underwent multiple tests of intelligence—not, technically, IQ tests, but tests that are thought to be good surrogates for IQ at younger ages. Then, looking backwards, the authors looked for correlations between those scores and how long the babies had been nursed. Depending on the “model” presented (there were 4 sets of data), the intelligence measures were controlled for age, sex, gestational age, birth weight, race, maternal age, smoking, parity, language, income, household income, marital status, and parents’ educational level. Not all data was available for all babies, which is understandable, so some of the information was “imputed.”

At age 3, two tests that were felt to reflect intelligence were administered, one of which was broken into 3 parts—so 4 tests were reported. At age 7, 3 tests were given, one of which was broken in to 2 subtests. So, net, 8 tests of intelligence were given to these children (remember that number.)

The results, as presented in Table 5, show that at age 3, 1 of the 4 tests showed improved scores among babies who had breastfed at 6 months (compared to babies who had never breastfed or had weaned or had mixed feedings.) At age 7, 1 of the 4 tests showed improvement compared to never breastfed or weaned babies, but not mixed-fed babies; another 1 showed improvement among weaned, but not never-breastfed or mixed-fed babies. Let’s mix those two together and say that a consistent improvement was correlated with nursing in 1 of 4 tests at age 7. Net: 2 of the 8 tests given to these children showed a difference for babies who had nursed at least some; 6 of the 8 showed no difference at all.

The authors in their conclusion, the JAMA editorialist, and the news outlets are saying that this study is very supportive of the association with increased IQ. They could have chosen any of these headlines:

  1. Tests show improved intelligence in breastfed babies.
  2. Some tests show improved intelligence in breastfed babies.
  3. Most tests do not show improved intelligence in breastfed babies.

I think #3 is most intellectually honest. Sure, 2 of the 8 tests were positive; but 6 of 8 were not. In the aggregate, this study may provide some support for increased intelligence among breastfed children – none of the tests showed decreased intelligence – but the support isn’t strong, and it isn’t even consistent among the tests.

But that kind of nuanced message is boring. And it doesn’t fit the current narrative or what we expect of these studies, and it doesn’t fit into the message that pediatricians want to give women. We want more babies breast fed. I want more babies breast fed. But presenting this study as a slam dunk, that breastfeeding will improve your child’s IQ, is dishonest. In the long run, I think overstating our hand may end up undermining breastfeeding success. It will certainly add to the guilt of women who don’t breastfeed.

And don’t even get me started on the “correlation doesn’t equal causation” thing. JAMA editorialist and USA Today headline writer: you can’t conclude from a study like this that breastfeeding caused the increased markers of IQ seen in 2 out of 8 tests.

I have to admit: I’ve been known to tell women that nursing isn’t your only job, and it really isn’t your only important job, and it certainly isn’t your most important job. There’s far more to being a good mom than how you feed your kiddos. Moms are under tremendous pressure to nurse, and to deliver “naturally”, and to have the correct BPA-free sippy cups and the baby monitor that uses the correct frequency and the 100% certified organic fair trade avocados and the … well, the list seems to grow and grow, and it seems to be getting more and more competitive. Parenting, and nursing in particular, is not a contest. I don’t think this current study gives any further bonus points to the “winners”, and that’s OK with me.

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12 Comments on “Does breastfeeding improve the intelligence of babies?”

  1. Rachel Says:

    Thank you for an intelligent and rational explanation of this study.

    I have to ask though – why do you care if more babies are breastfed?

    It seems that though the benefits to breastfeeding are real, they are actually quite small and probably not worth all the hype that is currently surrounding it. Formula is a perfectly acceptable substitute and I have not seen any significant evidence to the contrary despite what seems to be almost desperation on the part of the media and breast-feeding advocates/scientists to prove otherwise.

    (Obviously, these comments pertain to the developed world where families have access to clean water.)

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  2. Dr. Roy Says:

    Rachel, there are some significant, though modest, benefits to breastfeeding over bottle feeding. The most robust evidence is about immune benefits. For example, a breastfed baby gets about 1/2 an ear infection fewer a year. From the point of view of an individual mom making a decision about her individual baby, 1/2 an ear infection isn’t a strong benefit– but from a public health point of view, if ALL babies were breastfed in the USA, that would work about to about a 1/2 to one million fewer ear infections a year. (I’m mixing old and new data here, so that may not be the best estimate, but it is a large number no matter how you slice it.) Nursing also seems to prevent diarrhea/vomiting illnesses as well as ordinary upper respiratory infections. Again, not by a big number for each child, but in the aggregate increased breastfeeding would have a significant and positive public health impact, especially when you consider that preventing these infections in babies would secondarily prevent them in parents, school teachers, and the rest of us.

    There are other at least putative benefits of breastfeeding. My impression is also that many (certainly not all!) women enjoy nursing and look at it as a positive experience for them and their babies. There’s pretty good evidence that breastfed babies have fewer allergic disorders, too, and may have less risk of obesity later on. Again, I agree with you that these benefits numerically aren’t huge, but they are important. I try to represent them realistically when discussing these issues w/ families.

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  3. Josh Says:

    I agree with most of what you’ve said; however, you seem to take issue with the fact that only 2 of the 8 tests show increased intelligence. I don’t think that anyone would predict a full 8 out of 8 tests showing improve intelligence as each test measures a different part of the construct referred to as intelligence. The fact that 2 out of the 8 tests show improvement while 0 out of 8 tests show a decrease with breastfeeding seems consistent with the notion of the association of increased intelligence with breastfeeding. The effects are small and probably clinically negligible, but present.

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  4. Personally nursing has helped me lose pregnancy weight and I like it. I don’t think women should be shamed into it, but support for those who choose to would be nice. I think nursing moms should have some decent places in public to nurse reasonably comfortably and discretely and shouldn’t get the stink eye from passers by. Saw this on buzzfeed today and definitely good satire. http://www.babble.com/baby/formula-fed-baby-enters-medical-school-satire/

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  5. Dr. Roy Says:

    Couldn’t agree more– and great link!

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  6. Chellanne Says:

    If we correctly take the breastfed baby as the ‘biological norm’ and the formula fed baby as the experimental subject. The correct 3 possible headlines from this study would be:

    1. Tests show reduced intelligence in formula-fed babies.
    2. Some tests show reduced intelligence in formula-fed babies.
    3. Most tests do not show reduced intelligence in formula-fed babies.

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  7. Rachel Says:

    I wonder – do you wish that more babies were kept out of daycare?

    Surely reducing the number of babies that attend daycare would reduce illnesses in both babies and the general population much more significantly than breastfeeding. If reducing illness is the primary reason behind the huge breastfeeding advocacy movement that permeates our medical and public health establishments, then why is a factor that must be so much more important in preventing illness completely ignored? Why don’t we have signs on the entrances to daycare centers stating “home care is best” and why don’t we have public health campaigns encouraging women to stay home and take care of their babies themselves. Why is there no WHO code banning advertising for day cares? Isn’t the baby staying home with mom or other relatives the “biological norm”?

    I’m assuming that we don’t have public health campaigns encouraging families to keep babies out of day care because it would be ridiculous: a lot of moms can’t afford to keep their babies home with them and frankly, a lot of moms would go crazy having to staying home with their babies all day every day. Even though these babies who go to daycare may get more colds and GI infections (and maybe even lose an IQ points or two since they are not getting as much one on one attention as they would be at home?) , they turn out just fine anyways. If it would be ridiculous and offensive to have a “home is best” campaign, why is it not ridiculous and offensive to have a “breast is best” campaign.

    Of course, lots of women enjoy breastfeeding but that does not seem like a valid reason for anyone to “want more babies breastfed”. Breastfeeding should be a choice that is supported and encouraged if the individual mother wants to do it but, in my opinion, it is not anyone else’s business – anyone else including moms who judge other moms on the Internet or at baby massage classes, public health departments, the City of New York, the AAP, my local hospital, and intelligent and thoughtful pediatrician bloggers.

    (I hope this is not too argumentative – I love your blog and find it refreshing and insightful. Breastfeeding advocacy is just a topic that I’ve been trying to puzzle out since my kids were babies and I was unable to breastfeed them. Oh, and for the record they’ve never had an ear infection, have iron stomachs and have only thrown up once or twice in their combined 10 years on the planet, and have neither asthma, allergies or eczema. I may be biased, but they also don’t seem to be missing any IQ points…).

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  8. Rachel Says:

    Emily – I LOVE the Babble article. Thanks for sharing.

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  9. Dr. Roy Says:

    Rachel, the health impact of day care is complex and far from one-sided. Infections can be delayed, but probably not prevented; and there is some evidence that earlier exposures to “germy” environments can prevent allergic disease. The effect on neurocognitive development is complicated, too– there’s evidence that early formal learning experiences can improve school readiness in socially disadvantaged neighborhoods. Then, of course, there’s the economic effects, and the family dynamic, and the effect on mom’s (usually mom’s, rarely dad’s) career trajectory.

    Pediatricians like myself have a dual role. We have our patients in the exam rooms, who we treat as individuals. In that setting I try to be gently supportive of nursing, while looking out for times when it is not going well to offer appropriate support and advice. I certainly don’t belittle or harangue.

    At the same time, like all pediatricians, I have a public health interest, which I try to support by public education here on the blog. I do support public health and workplace efforts to make it easier for women to breast feed, because the advantages outweigh the disadvantages. At the same time I hope I’m not contributing to an atmosphere that makes life more difficult for women who don’t breast feed. It’s a difficult balance.

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  10. Misty Says:

    My kids are all formula fed from birth and are smart, bright and healthy. Not smart are the women who breastfeed their babies until they can ask for it, now THAT’S the real problem!!
    Regarding the 3 points replacing the words, that’s disgraceful. When will you bf nazis get a life and focus on your own children rather than trying to put everyone else down?!?

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  11. Linda Says:

    That’s great your kids are smart, bright and healthy and I agree people shouldn’t be shamed into feeding one way or another. But saying people shouldn’t shame you, right after you put down mom’s who extend breastfeeding (which is their right and a perfectly fine choice) is a little contradictory and makes you look like the “Nazi”.

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  12. Erin Says:

    Rachel’s point is good, I think. Daycare may not be the perfect example, but surely there are lots of worthy public health positions that don’t get nearly the guilt-laden attention that breastfeeding gets. Given the obesity epidemic, it seems like discouraging video games would do a lot more for public health than would discouraging baby formula. But ain’t no doctor or nurse or poster or stranger lurking in the video game aisle badgering individual parents, “If you loved your child, you wouldn’t give them a video game.” There is no warning label on video games reminding parents that outdoor play is best for development and health. There aren’t whole communities and support groups designed to keep parents from providing video games and support other types of play. And video games aren’t EVER necessary for a child the way baby formula is often necessary. Video games may not be the best example either, but again, putting such a disproportionate public health burden on the shoulders of sleep-deprived and hormonal new moms seems ridiculous when there are so many bigger threats to public health.

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