Children breast-fed longer than six months scored a 3.8-point IQ margin over those who were bottle-fed, according to a seven-year study by researchers at Jagiellonian University Medical College in Poland.

Medical epidemiologist Wieslaw Jedrychowski and colleagues followed 468 babies born to nonsmoking mothers. The children were tested five times at regular intervals from infancy through preschool age. The data showed that cognitive abilities of preschoolers who were breast-fed scored significantly higher than bottle-fed infants, and IQ score was directly proportional to how long the infants had been breast-fed: IQs were 2.1 points higher in children who were breast-fed for three months; 2.6 points higher when babies were breast-fed for four to six months; 3.8 points higher in children breast-fed longer than six months. The results were published in the May 2011 issue of the European Journal of Pediatrics.

This research confirms observations reported 70 years ago by Carolyn Hoefer and Mattie Hardy in JAMA The Journal of the American Medical Association, as well as many subsequent studies. This body of research provides the scientific basis for the World Health Organization's recommendation that all infants should be exclusively breast-fed for the first six months of life. But what is the missing ingredient that undermines the cognitive development of bottle-fed babies?

Chemists searching for a specific compound in mother's milk have been overlooking the obvious difference between breast-feeding and bottle-feeding—something that could easily account for the difference in cognitive development, wrote Tonse Raju, a pediatrician and neonatalogist at the National Institute of Child Health and Human Development in the current issue of Breastfeeding Medicine, October 2011. (Raju was not involved in the Jedrychowski study.)

"Sometimes even the most obvious facts need to be reiterated," he wrote. "An infant suckling at his or her mother's breast is not simply receiving a meal, but is intensely engaged in a dynamic, bidirectional, biological dialogue." It is the physical and psychological bonding and interaction between infant and mother during breast-feeding that nurtures development of an infant's cognitive abilities.

Jedrychowski strongly agrees with Raju's statement, and adds: "I believe the IQ effect may in part be explained by this dynamic interaction between mother and child in the breast-feeding process."

Brain bulk and white matter in early life
During the first year of life, a baby's brain weight nearly doubles. Much of that increase comes from growth of white matter, the electrical insulation on nerve fibers that speeds transmission of electrical impulses at least 50 times faster than uninsulated fibers. New research provides insight into why formation of this insulation (myelination) takes place after birth—during childhood and adolescence. Early childhood experiences influence myelination and helps the developing brain adapt to its environment, rather than form along strict genetically determined lines.

Martin Teicher, a psychiatrist at Harvard Medical School and chief of the Laboratory of Developmental Psychopharmacology at McLean Hospital, says that his current research suggests that parental verbal affection is the most important factor affecting IQ early in life. And his previous research has showed that exposure to parental and peer verbal aggression is associated with alterations in white matter tracts. So it is not just brain bulk that increases in the first year of a baby's life; major developmental changes in visual, motor and voice-processing regions of the brain take place. These are the foundations for language acquisition, and all of them are influenced to a considerable extent by what a baby experiences.

Donna Ferriero, professor and chair of the Department of Pediatrics at University of California, San Francisco's Benioff Children's Hospital, agrees that experiences early in life can have a profound influence on children's cognitive development. "Certainly there is substantial preclinical and clinical literature arguing that early life stress negatively impacts brain development and future social and cognitive interactions," she says. "Conversely, there are data showing that environmental enrichment can reverse adverse effects of early brain injury."

Simply put, a bottle is a poor substitute for a breast when it comes to enriching a baby's brain. At such a critical time in an infant's development, the experience of suckling and engaging in a positive sensory exchange with the mother facilitates optimal nurturing of the growing brain.

Breast-feeding biochemistry
It is difficult to separate the nutritional and behavioral benefits of breast-feeding from epidemiologic data alone, Jedrychowski notes. There is a need for further experimental studies on mother–newborn interaction during breast-feeding.
Some of the links between that biochemistry and behavior are already worked out. "How a baby is fed versus what it is fed is an important factor that has been overlooked in many studies," Raju says. "Suckling at the breast results in changes in the mother's brain—increased blood flow and oxytocin release [a hormone promoting bonding between mother and infant], and probably in the baby's brain."

A study led by Terry Pivik at the Arkansas Children's Nutrition Center examining brain waves in infants and published last year in the journal Early Human Development supports Raju's conclusion. Electroencephalogram, or EEG, (brain-wave) activity was measured in infants who were either bottle-fed milk-based or soy-based formula or breast-fed to track neurodevelopment at three, six, nine and 12 months of age. The EEG changes reflect significant milestones in brain development, including increased myelination and synapse formation as well as development of connections between the left and right cerebral cortices. The research was motivated by contents in the formula and mother's milk, not the feeding method. The nutritionists were concerned that estrogenlike compounds in soy-based formula might have adverse effects on infant neuro-development, or that omega-3 polyunsaturated fatty acids, which are present in breast milk and absent from milk-based baby formula until recently, could explain why breast-feeding boosts a baby's cognitive development. The results were unexpected: Bottle-feeding, regardless of the formula used, accounted for the differences. Brain-wave development was similar in bottle-fed babies, regardless of whether milk-based or soy-based formula was used, but different in breast-fed infants "Mothers who must bottle-feed for work should use breast milk collected using a breast pump, but they should breast-feed at home at night," Raju advises.

Mothers who cannot breast-feed should not be alarmed; in fact if Raju's analysis is correct, they should be relieved. The missing ingredient may not be in the infant formula itself, but rather in the experience of an infant in a mother's arms feeding at her breast. This natural mode of feeding promotes the closest and most beneficial physical and emotional dialogue between mother and child, but recognizing the importance of this interaction, mothers and fathers of formula-fed infants can take care not to "overlook the obvious," and work to provide the ingredient that is missing in a baby bottle.