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The Breast and the BrightestDoes nursing really affect your kid's IQ?

By Emily Bazelon
Posted Thursday, Nov. 8, 2007, at 5:47 PM ET
Illustration by Robert Neubecker. Click image to expand.

In my corner of the world, breast-feeding is not really optional. Among the women with whom I talk about babies and kids, I can't think of anyone I know in my approximate age bracket who didn't try. My friends who quit at three months seemed like rebels. And when I cut off my sons, after more than a year each, I felt a little heartless because I know so many kids who zealously nursed into toddlerhood.

Nursing is cozy and nurturing, not to mention remarkably efficient—never again will I provide for my children's needs so gracefully (OK, that's not the right word for the pumping part of it). But it can also get a little fanatical. Mothers who adopt children are left out. And when breast-feeding doesn't come easily—an unusual but real occurrence—women sometimes go to great and uncomfortable lengths involving all manner of awkward contraptions. They do this because they think that they'll be depriving their babies if they give up as nursing failures. Breast-feeding is supposed to protect against childhood cancer, obesity, allergies, infections, and global warming (I made up only the last one). Some of the claims, like a lower rate of infant respiratory infections, seem to hold up; others, like reduced odds of adult obesity, probably don't.

Now there's new evidence about the gold ring of breast-feeding benefits—extra IQ points. It's a finding with a twist. The researchers report that breast-fed babies get an average IQ advantage of 6.8 points—a nice step up—but only if they carry a certain genetic variant. If you've got the gene and your mother nurses you, she is making you smarter. If you don't have the gene, the nursing is for naught, IQ-wise. What are we to make of this?

Practically speaking, probably nothing. A series of caveats apply. This is only one study, and there are lots of other reasons to breastfeed (or not to). Plus, 90 percent of the population has the genetic variant that conveys the IQ boost, so the odds are in the suckler's favor. But as food for thought, this study has all kinds of goodies. It's a pretty riveting example of a dynamic that scientists call "G × E," for genes times environment—the notion that it's not nature or nurture that exclusively makes people who they are, but nature interacting with nurture. G × E starts cropping up a lot, once you look for it, and the concept makes sense intuitively. Why wouldn't the meshing of our genes and our experiences have its own influence? But G × E doesn't really resolve the hard questions about the haves and have-nots that the nature-nurture debate spawns. It merely reframes them—and opens the door to predict-the-future-of-your-kid information, via genetic testing, that for many parents is equal parts tantalizing and scary.

The new breast-feeding-IQ study was conducted by the lab of Avshalom Caspi and Terrie Moffitt, smart and careful scientists whom I've written about before. Caspi and Moffitt looked at two large groups of kids, one of more than 1,000 from New Zealand and the other of about 2,200 from England. They asked mothers about whether they'd breast-fed via questionnaire, when the kids were 3 and 2 years old (not the best method for data-collection, but at least the kids were still young). In New Zealand, 57 percent of the kids were breast-fed; in England, 48 percent. Then the authors looked at a gene called FADS2. It plays a role in regulating the production of some special fatty acids present in breast milk, which may help spark cognitive development (though there is controversy about this, Slate contributor Sydney Spiesel tells me). There are three variants of this gene. Two of them include an allele (the "C allele") that conveys a significant IQ boost—but only in conjunction with breast-feeding. In other words, if you have the gene but your mother doesn't nurse you, you're a bit dumber than you otherwise would be. If you don't have the lucky allele, you don't get the IQ boost however much mother's milk you imbibe.

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Emily Bazelon is a Slate senior editor.
Illustration by Robert Neubecker.
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Remarks from the Fray Editor:

As with anything touching on the benefits of breast feeding, Emily Bazelon's article has brought out articulate champions from both sides of the breast-feeding wars. Jheurf relates a harrowing tale of watching his infant's health take a second seat to the cause of promoting breast feeding among new mothers. On the other side of the debate, Sarvis compares the preference for formula feeding to a "voluntary colostomy" movement. Other excellent posts are excerpted below. –G.A.

Remarks from the Fray:

It's not that I think mothers who can't breastfeed are not as good as mothers who can. It's that I think mothers who don't but could ought to at least take the trouble to educate themselves about it, and to give their children at least a few weeks of the one meal you don't have to prepare in a busy day.

I wonder how much of women's reluctance to breastfeed when they are able has to do with the actual difficulty involved, and how much has to do with fear. Fear of saggy boobs leading to sexual rejection, fear of being castigated for displaying boobs, fear of being the sole supplier of meals for another human being, especially at 4 am, fear of bodily fluids, fear of being overwhelmed, fear of being a mammal, fear of men's fear about women's bodies and power, fear of the general public's fear of boobs.

As long as someone's out there lying to women and saying that breast milk is no better than formula, so they can make a few more bucks, it's a lot easier to let your fears overcome every other consideration.

--Isonomist

(To reply, click here.)

I have never met a new mother that didn't have some type of difficulty early on. It is the rare mother and newborn combo that results in flawless breastfeeding right from the start. Yes, it's "natural" but so is walking and you have to struggle to learn how to do that as well. We do mothers a great disservice by telling them that the need to breastfeed, it's so important, etc but not providing support once they give birth.

It's little comments like these that make me wonder - is the author betraying a bias, showing that she really does think that all of the moms that cite difficulty as the reason that they don't breastfeed are full of it? Or am I being defensive and hypersensitive? Why, when it comes to our children are we so invested in what others think?

--gracep117

(To reply, click here.)

It was precisely studies of this kind that purported to show that hormone replacement therapy for post-menopausal women saved lives. Doctors were reassured that every conceivable confounding factor had been taken into account and "controlled for", with the final result being that hormone replacement was a great thing. Women who got hormone replacement in these studies DID live longer and get fewer diseases.

But when more rigorous studies were done, it turned out to be completely wrong. Hormone replacement therapy didn't save lives - it killed! The reason women who took it lived longer in those earlier studies was because they were DIFFERENT than the women who didn't in many other ways that had nothing to do with hormone replacement therapy, despite all the researchers' assurances that everything had been "controlled for".

As a result, a generation of women was exposed to needless risk based on faulty science, and thousands probably died. In my opinion, it is one of the great shames of modern medicine. It was exactly the same kind of study design that led to that tragic result, so think twice before believing stuff like this.

--mnemon

(To reply, click here.)

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