Follow up tests on the children at 6 years showed the breastfed group averaged about six points higher in IQ.
However, the pediatricians performing the IQ tests knew ahead of time which children were breastfed, a potential source of bias.
When a subset of kids was tested independently, the difference in IQ was just three points in favor of the breastfed children.
Doctors say this improved mental function, on top of boosting immunity and reducing allergy risk, is just one more good reason to breastfeed.
But skeptics still question whether the IQ difference is real, or even whether it matters much.
Evaluations from the children's teachers showed both groups performed slightly above grade level in reading, writing and arithmetic, no matter how they were fed as infants.
