The Atlantic magazine just published an article written by Hanna Rosin questioning the general perception that research strongly supports that breast-feeding is better than formula.

This is actually a pretty well researched journalistic piece about cognitive development and breastfeeding that raises a number political and scientific issues regarding breast-feeding.

In certain overachieving circles, breast-feeding is no longer a choice—it’s a no-exceptions requirement, the ultimate badge of responsible parenting. Yet the actual health benefits of breast-feeding are surprisingly thin, far thinner than most popular literature indicates. Is breast-feeding right for every family? Or is it this generation’s vacuum cleaner—an instrument of misery that mostly just keeps women down

Although the author seems to overstate the “weaknesses” of the literature on the benefits of breast-feeding, she touches on a very important issue: The difference between statistical vs. clinical significance. That is, even when a statistical difference is found, such difference may be clinically inconsequential. This is due to what “statistically difference” actually means (which varies depending on the statistical procedure used). When two groups are “statistically different” in one measure (let’s say for example ‘IQ scores’), this may only mean that the difference observed between the groups is very unlikely to be due to chance. It does not necessarily mean that the differences between the groups are “big,” –if by “big” we mean that the differences are actually noticeable or even predictive of any other factor (happiness, success, school performance, etc, etc). So many times we find statistically significant differences between groups that are actually not clinically meaningful.

Let’s take the breast feeding and IQ example. In 1999 Anderson and colleagues (Anderson et al. 1999. Breast-feeding and cognitive development: a meta-analysis. American Journal of Clinical Nutrition, Vol. 70, No. 4, 525-535) conducted a meta-analysis of 20 studies that examined the effects of breast-feeding on intellectual functioning. They found that among the studies that properly controlled for confounding variables (variables that could explain the group differences), kids who were breast-fed had higher cognitive scores than kids who were formula-fed, and this effect was stronger for low-birth-weight infants. However the effects were very mild, in that breast-feeding resulted in an average of 3 additional IQ-equivalent points. Given the nature (not so precise) of our IQ and cognitive scales, 3 points is well within the normal variation in IQ scores that we would expect from the same person from one day to another. Although, there are other statistical issues involved (the expected normal variation is actually mostly due to error, while error accounts for only a small part of the differences between the groups), the main issue is that while the 3 point difference was “statistically significant”, such 3 point difference may or may not be clinically meaningful. However, Anderson’s meta-analysis also showed that among low-birth-weight babies, the improvement was 5 points, and at this 5-point level we may begin to see some large clinically meaningful differences (in school performance, achievement, etc). This is also in line with a recent article on the effects of breast-feeding on very-low-birth-weight babies, which I will be reviewing soon.

Lastly, I am not in any way making an argument against breast-feeding. Cognitive performance is just one of a multitude of factors that have been found to benefit from best-feeding. The data are very consistent showing benefits in multiple domains. Hanna Rosin is correct in that the research is not conclusive, but such inconsistencies are inherent to most medical and psychological research. Yet, Hanna Rosin raised a very interesting issue regarding how we evaluate scientific findings.

James W Anderson, Bryan M Johnstone, & Daniel T Remley (1999). Breast-feeding and cognitive development: a meta-analysis American Journal of Clinical Nutrition,, 70 (4), 525-535 DOI:;=tf_ipsecsha

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5 Responses to The case against breast-feeding: How many IQ points does breast-feeing really buy you?

  1. marag says:

    It never occurred to me to breastfeed my kids because it would make them smarter. In fact, I hadn’t even read any research on that subject. I thought the strongest research was showing *health* benefits, like fewer allergies, colds, etc.

    Also, breastfeeding is significantly *less* work than bottlefeeding. I can’t believe that any woman who’s tried both would think bottles are less work. Ugh.

  2. Thanks Marag of your comments. You are correct that the bulk of research on breast-feeding is related to health effects, and specifically immune functioning. I selected IQ simply to discuss the statistical vs. clinical significance issue. I’m just much more familiar with the IQ literature as I’m a psychologist :-) .

    Thanks for visiting! Nestor.

  3. Melodie says:

    Thank you for not making an argument against breastfeeding just because Rosin pointed out some flaws in the scientific literature regarding things like IQ. Her article was a very dangerous one that many people are going to start thinking is all true just because she did do good journalistic research. But she left out so many things and there are so many things to say. I am glad as a professional, you can say “such inconsistencies are inherent to most medical and psychological research,” which is true, but does not mean breastfeeding is no still the best for mom and baby. Thanks for this.

  4. Andrea says:

    What I see as the biggest flaw in almost all discussions & research dealing with breastfeeding is the idea the breastfeeding some how has benefits. How can the standard, normal offer a benefit? There needs to be a paradigm shift. Breastfeeding doesn't increase IQ, not getting breastmilk decreases IQ-clinically meaningful or not.

  5. anat says:

    i thought it was a poor obnoxious article by a bitter guilty breastfeeding to quit mom. truth is breastfeeding is preferable but NOT necessary. it may be more medically indicated in at risk kids and that cant be ignored. and she also raises a point about the bonding aspect which cant be achieved at the same level from a bottle but that mortifies her because who wants to be stuck without bottles. the article shouldve been called “I cant breastfeed all the time and thats ok!”

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