Friday, May 09, 2008

Breastfeeding research redux

A few weeks ago, I blogged about a recently-published article about some research on the long-term effects of breastfeeding. Just to remind you, the study was comparing 2 groups: a group of hospitals that supported breastfeeding in their new moms, and a group of hospitals that just did their regular support with their new moms. The researchers followed these moms and kids for 6-1/2 years. That article found that there were "no consistent and significant differences in behavioral strengths or difficulties in children (who were breastfed more, and breastfeeding more) did not lead to any detectable reductions in emotional difficulties, hyperactivity, or conduct or peer problems or to improvement in pro-social behavior..... We found no evidence that the breastfeeding promotion intervention affected the mother's relationship with her partner or with her child nor her satisfaction with motherhood in general." So - I thought that was the end of that. The study didn't find any great benefits to breastfeeding. End of story.

But NO.

The Boston Globe had another article about the benefits of breastfeeding this week, and referred to this same larger study (the PROBIT study), so of course I had to look into it. This article had a provocative headline: Study touts benefits of breast-feeding: Researchers link the practice to higher child IQ! Turns out another journal article was recently published, this time in the Archives of General Psychiatry (here's the link).

So it turns out that the researchers decided to analyze this part of the results separately (just to drive me crazy). They were looking at differences in IQ between the 2 groups (the breastfeeding supported group and the "unsupported" group - sorry, couldn't resist!). For this part of the study, they used the WAIS, which is an IQ test for kids, and also teacher evaluations of the kids' academic performance in reading, writing, math, etc. Remember, these kids are only 6.5, so I'm not sure exactly what constitutes "academic performance" in this age group, but anyway, that's what they were looking at.

So the results sound very sexy. "Our results," report the researchers, "strongly suggest that prolonged and exclusive breastfeeding improves cognitive development as measured by IQ and teachers' academic ratings at age 6.5 years." Wow.

But there's a caveat. Basically, the pediatricians administering the IQ tests had a lot of "variation" in their results, which leads to "wide confidence intervals" around the observed IQ differences. This means that the different pediatricians were administering the test differently, and some of the differences in IQ could just be due to chance, and NOT due to the differences in breastfeeding. Hmm.

The authors had other caveats, too, such as the fact that the pediatricians administering the IQ tests were not blinded (i.e. they knew which group the kids were in, which could lead to bias - slightly enhancing the scores of the kids who they knew were breastfed, for example). NONE of these critiques of the research (made by the researchers themselves!) made it into the sexy headlines. Also, the researchers weren't sure what it was about breastfeeding that might make kids smarter: was it something in the breast milk itself, or was it the social interaction between mom and baby during breastfeeding?

So we are back to where we started. This wonderful study hasn't really answered the questions about breastfeeding benefits at all.

I feel like the results of this study should be: more breastfeeding might lead to greater intelligence in kids, but we aren't sure. But that isn't a very sexy headline.

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