Breastfeeding kids makes them smart, right? Guest post by Joel Schneider

The following is a guest blog post by Joel Schneider (Clinical psychologist, Illinois State University), a member of IQs Corner Virtual Community of Scholars project.

Breastfeeding kids makes them smart, right?

Well, maybe not!

A new paper by Der, Batty, and Deary (2006) suggests that although breast milk has many wonderful properties, IQ enhancement is not one of them. Here is a summary of the evidence:

• Like virtually every other study on the matter, this paper found in a large representative sample of U.S. mothers and their children that breast-fed children have higher IQ scores than children who were not breast-fed. The advantage is about 4.5 IQ points, which is substantial but not huge (a 4.5 point boost would move an average score to the 62^nd percentile).
• Unlike most other studies, this one also measured the IQ scores of the mothers. Once mothers’ IQ is controlled for statistically, the breast milk boost shrinks to only 1.3 IQ points.
• The researchers also found a subset of mothers in their sample who breastfed some of their children but not others. On average, the breast-fed siblings did not score significantly higher than their siblings who were not breast fed.
• A systematic review of other studies that also controlled for maternal IQ also found that breastfeeding had little effect on IQ.

This paper deals a strong blow to the theory that breastfeeding has long-term cognitive benefits beyond those that can be had from the responsible use of high-quality formula milk. It appears that the higher IQ of breast-fed children is not a result of the breast milk itself but is instead inherited directly from their high-IQ mothers.

It is possible that future research will refine our understanding of the cognitive benefits of breast milk. There is reason to believe that this paper is not final word on the matter. This study measured “IQ” with the Peabody Individual Achievement Test (PIAT), a test of math reasoning and reading comprehension. While it is true that this test correlates strongly with traditional IQ tests, traditional IQ typically measure a much broader array of abilities. It is possible that breast milk enhances abilities that were not measured by the PIAT. For example, perhaps breast milk enhances nonverbal reasoning, mental processing speed, or short-term memory. These kinds of abilities are less strongly influenced by the effects of schooling and the family environment and are more directly tied to the overall biological integrity of the brain.

The researchers strongly caution against overinterpreting the results of the study. It is not known how the results might have been different for preterm infants or for infants from developing nations. They agree with the World Health Organization’s statement that breast milk is “an unequalled way of providing ideal food for the healthy growth and development of infants.”

• Der, G., Batty, G.D., & Deary, I.J. (2006). Effect of breast feeding on intelligence in children: prospective study, sibling pairs analysis, and meta-analysis, British
  Medical Journal, doi:10.1136/bmj.38978.699583.55

Abstract

• Objective: To assess the importance of maternal intelligence, and the effect of controlling for it and other important confounders, in the link between breast feeding and children’s intelligence.
• Design: Examination of the effect of breast feeding on cognitive ability and the impact of a range of potential confounders, in particular maternal IQ, within a national database. Additional analyses compared pairs of siblings from the sample who were and were not breast fed. The results are considered in the context of other studies that have also controlled for parental intelligence via meta-analysis.
• Setting: 1979 US national longitudinal survey of youth.
• Subjects: Data on 5475 children, the offspring of 3161 mothers in the longitudinal survey.
• Main outcome measure: IQ in children measured by Peabody individual achievement test.
• Results: The mother’s IQ was more highly predictive of breastfeeding status than were her race, education, age, poverty status, smoking, the home environment, or the child’s birth weight or birth order. One standard deviation advantage in maternal IQ more than doubled the odds of breast feeding. Before adjustment, breast feeding was associated with an increase of around 4 points in mental ability. Adjustment for maternal intelligence accounted for most of this effect. When fully adjusted for a range of relevant confounders, the effect was small (0.52) and non-significant (95% confidence interval − 0.19 to 1.23). The results of the sibling comparisons and meta-analysis corroborated these findings.
• Conclusions: Breast feeding has little or no effect on intelligence in children. While breast feeding has many advantages for the child and mother, enhancement of the child’s intelligence is unlikely to be among them.

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