While many the medical benefits of breastfeeding such as improved immune function have been clearly established, its effect on child behavior and cognition has somewhat more difficult to determine. This has been due to a variety of reasons. Because randomization is not possible for breastfeeding studies, researchers have had to rely on naturalistic study designs. Since mothers who breastfeed are, on average, more highly educated and tend to have higher income levels than mothers who don’t breastfeed, it can be challenging to tease out the
independent effect of breastfeeding from these other variables. In addition, there remains much that is not known about any possible mechanisms that underlie this link. To address some of these issues, a new study by Luby and colleagues was recently published in the Journal of the American Academy of Child and Adolescent Psychiatry.
The data from the study come from the Preschool Depression Study that has followed a sample of children for 11 years since around age 3. Admittedly, this study was not designed to look at breastfeeding and the authors had to piece together the necessary components with what they already had. As would be expected, the study oversampled children with emotional-behavioral problems, and a total of 63% of the subjects had experienced significant depression or anxiety at the last follow-up (and this was one of the variables controlled for in the analyses). Between the ages of 9 and 14, a total of 148 of these subjects underwent a structural MRI scan. General linear models and process mediation models were used to test the hypothesis that breastfeeding was associated with significantly higher IQ, after controlling for important factors such as caregiver level of education. They also tested the hypothesis that any association was mediated through the association between breastfeeding and brain grey matter volume. Breastfeeding was scored as a dichotomous yes or no variable. IQ was assessed through two different tests when children were between the ages of 8 and 15.
The authors found that, after statistically controlling for some potential confounds, breastfed infants had both significantly higher IQs as well as increased volumes of whole grey matter and subcortical and cortical grey matter. In terms of raw numbers, the mean IQ for breastfed infants was 109 versus 99 in the nonbreastfed infants. However, after accounting for caregiver education levels, breastfeeding added a more modest 3% of the variance to the model. Their mediation analyses demonstrated that the increase in IQ was mediated through an increase in subcortical grey matter.
The authors concluded that their data support the link between breastfeeding and increased IQ and, going further, they suggested that the mechanism of this association might involve an increase in subcortical grey matter. In the Discussion section, the authors go into some hypotheses regarding how all this might work, including direct effects of the breastmilk long-chain polyunsaturated fatty acids on neurodevelopment combined with positive effects that stem from the close physical contact and stimulation that occurs during breastfeeding. The authors urge greater efforts to encourage breastfeeding as a public health priority.
Luby J, et al. Breastfeeding and Childhood IQ: The Mediating Role of Gray Matter Volume. JAACAP 2016: epub ahead of print.