Mothers faced with the decision of whether or not to breastfeed now have new evidence to consider: skipping formula in favor of breast milk could affect a child’s intelligence later in life.
In a new study published in JAMA Pediatrics, lead author Dr. Mandy Belfort, of the Boston Children’s Hospital, sought to examine the link between the breastfeeding and a child’s cognitive function as they develop.
Belfort and her colleagues gathered data from 1,312 mothers and children in the United States, tracking everything from the mother’s frequency of breastfeeding to other factors including the mother’s intelligence, the mother and father’s education levels, measures of the home environment, the mother’s employment and the type of childcare the baby received.
While the link between breastfeeding and cognition had been previously explored, many earlier studies did not control for these additional factors.
“Many previous studies have been criticized because any link you might observe between breastfeeding and childhood intelligence could be explained by those other factors,” Belfort told
Belfort then performed a series of tests measuring the children’s cognitive development after infancy.  At age 3, the children underwent the higher Peabody Picture Vocabulary Test, a measure of receptive language, or how well a child understands language.
“A child’s receptive language is highly correlated with general intelligence as measured by more typical IQ tests,” Belfort said.
After analyzing the data, researchers discovered that for each additional month that a child was breastfed, through a year, their language score was .2 points higher – a statistically significant finding.
Then, at age 7, the same children were assessed using the Kaufman Brief Intelligence Test, a measure of the child’s IQ. For this test, each additional month that a child was breastfed through a year was correlated with an increase in IQ score by a third of a point – another statistically significant discovery.

However, when children took the Wide Range Assessment of Memory and Learning, which specifically tests memory and learning capabilities, the difference between children who were breastfed and those who weren’t was not significant.
The study authors were also interested in exploring whether or not there was a link between a mother’s consumption of fish and the intelligence of children who were breastfed – though they did not find any significant effect there either.
“I would say that it is reassuring, it didn’t seem like eating fish is harmful, because of concerns about mercury in fish,” Belfort said.
Though researchers were able to distinguish a small but clear link between breastfeeding and cognitive development, they remain uncertain as to why breast milk appears to be superior to infant formula.
“Formula is designed to be as close to breast milk as possible…but it is definitely possible that there are nutrients or non-nutrient factors in breast milk not in formula that may benefit baby’s brain,” Belfort said
Overall, Belfort noted that the study’s findings support national recommendations urging women to breastfeed exclusively through age 6 months and to continue at least partial breastfeeding through 1 year of age.
However, many factors go into a woman’s decision to breastfeed including whether or not she produces enough milk, how quickly she needs to return to work and how friendly her workplace is to breastfeeding.
“There are certainly many factors people have to weigh into making that decision,” Belfort said. “The cognitive advantage is relatively small so people need to weigh many, many different factors in making this decision.”
Overall, Belfort emphasizes that women should do what is best for them and their child – and if a woman chooses not to breastfeed, there are many other things she can do to ensure her child develops normally.
“There are so many things people can do to optimize a baby’s development, this is but one,” Belfort said. “Turn off the TV, talk to your baby, read to your baby, play with your baby. Those are really important ways to stimulate baby’s development.”