Wednesday, October 11, 2006

Does Breastfeeding Boost Children's Intelligence?

A recent study published in BMJ (Der et al 2006) asserts that maternal intelligence accounts for any IQ boost a breastfed baby may get, rather than the breastfeeding itself, as it was the more intelligent women who tended to breastfeed. You may have seen coverage of this study in news outlets, with headlines such as Link Between Breast-Feeding and Child's IQ Debunked (from the National Women's Health Information Center, no less). However, several "rapid responses" point out methodological problems that may influence the authors' conclusions. First among these is that the authors define breastfeeding status by whether the child was ever breastfed, without distinguishing, for example, between those who were breastfed once or for a year. Among US women (in recent studies - this paper's data is rather older), 70.3% ever breastfeed; the percentage is down to 38.5% by the time the child is 3 months old. There is a fairly dramatic dropping out of breastfeeding mothers, and the study's authors don't seem to account for this, viewing the issue as a "yes" or "no."

Among the comments:
"...it is not unreasonable to infer that this study misclassified a number of infants as 'breastfed' who would have been predominantly artificially fed. It is likely that many of these infants did not receive a clinically significant dose of breastmilk or breastfeeding. It is not surprising, then, that it found that “breastfeeding” did not significantly impact on the cognitive development of artificially fed infants."
"Presumably, the same could be "proven" statistically for drinking alcohol in pregnancy…that fetal alcohol effects aren't due to how much alcohol the mother drinks, but due to her intelligence. If overwhelming numbers of low-IQ women drink during pregnancy, the biological effects on the fetus of drinking alcohol might be said to be explained "more by intelligence" than by drinking alcohol."
"Most of the so-called breastfed children in this data set were likely partially breastfed for a time period measurable in weeks, not even months."

The conclusions the authors draw do seem questionable given their definitions of "breastfed." The main point I want to make, though, is that alarming, conclusive-sounding headlines on health topics may not always present the full or true picture of a study's findings or its limitations.

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MeSH Tags: Breast Feeding; Intelligence

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