Do breastfed babies become brainier kids? Some studies say yes, but new research shows no direct link between breastfeeding and intelligence later in life.

In the largest study ever to address the issue, researchers found a positive impact for breastfeeding on intelligence only when other potential contributors -- such as the mother’s IQ and the parents’ educational and economic status -- were not taken into consideration.

When these variables were considered, breastfeeding was found to have little impact on a child’s IQ.

The study included 5,475 children and mothers in the U.S. who participated in an ongoing youth development survey. The findings were published today in BMJ Online First.

The researchers also identified 332 sibling pairs in which one child was breastfed and the other was not. No significant difference in intelligence was found among the breastfed and nonbreastfed siblings.

“The mother’s IQ was by far the most important variable, accounting for 70 percent to 75 percent of the difference [between children who were and were not breastfed]", researcher Geoff Der, MCS, tells WebMD.

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78-Year-Old Question

The first study linking breastfeeding to greater intelligence later in life appeared almost 80 years ago. But the research since that time has been mixed.

“Although the majority of studies concluded that breastfeeding promotes intelligence, the evidence from higher quality studies is less persuasive,” researcher Anjali Jain, MD, and colleagues wrote in 2002 in the journal Pediatrics.

When Der and colleagues combined their own results with those from other studies that also considered maternal intelligence, they again found little evidence of a link between breastfeeding and intelligence.

“We took three different approaches to examining this question within this one paper, and the results converged quite nicely,” Der says.

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Breastfeeding Still Best

Der and colleagues from the British research group Medical Research Council expressed surprise that maternal intelligence has been overlooked in so many studies examining the impact of breastfeeding on intelligence. Even many recent studies have failed to consider maternal IQ.

They add that the latest findings should not be interpreted as meaning that new moms now have less reason to breastfeed.

“Even if it does not enhance intelligence, breastfeeding remains an unequalled way of providing ideal food for the healthy growth and development of infants,” they write.

Breastfeeding has been shown to lower an infant’s risk of infections and even sudden infant death syndrome (SIDS), and it is believed to help protect against allergies, diabetes, and obesity later in life.

“We would never suggest that any woman should choose not to breastfeed on the basis of our findings,” Der says. “Clearly, there are many good reasons to breastfeed.”

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By Salynn Boyles, reviewed by Louise Chang, MD

SOURCES: Der, G. BMJ Online First, Oct. 4, 2006. Geoff Der, MSC, statistician, Medical Research Council, U.K. Jain, A. Pediatrics, June 6, 2002; vol 109: pp 1044-1053. WebMD Feature: “Making the Breastfeeding Decision.”