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Kids who were breastfed longer have higher IQs, new study shows

Young children who were breastfed as infants scored higher on intelligence tests than formula-fed kids, and the longer and more exclusively they were breastfed, the greater the difference, say Harvard University researchers in a study published today in JAMA Pediatrics.

This study adds “to the body of literature of the association between duration of breastfeeding and cognition,” says NBC News diet and health editor Madelyn Fernstrom, Ph. D., CNS. But does breastfeeding make your child smarter? Fernstrom says this study shows an association, not cause and effect.

The researchers analyzed 1,312 expectant mothers enrolled between 1999 and 2002 in Project Viva, a study in eastern Massachusetts examining pregnancy and child health, and the children they delivered.

The researchers found that 7-year-olds whose moms had done any breastfeeding during the child’s first year - exclusively or in combination with formula - gained a little more than a third of a point in verbal IQ for each month of breastfeeding compared to children who were never breastfed. That means if the mom did any mix of breastfeeding for the entire 12 months, the gain would be 4.2 verbal IQ points.

The association between breastfeeding and intelligence was stronger when researchers broke out children whose moms exclusively breastfed during the first six months. Those 7-year-olds showed an increase of four-fifths of a point in verbal IQ each month over children who were never breastfed. That translates into a 4.8 point gain in verbal IQ if exclusively breastfed during their entire first six months of life.

The results were similar although smaller in magnitude for non-verbal IQ.

“I would take three or four IQ points any given day,” says pediatrician Michael Georgieff, director of the Center for Neurobehavioral Development at the University of Minnesota Medical School. Georgieff was not involved in the current study. “It’s a pretty significant shift, especially demographically across the world if everyone were to make that gain.” For context, the average IQ is 100, and about 67 percent of people have IQ scores somewhere between 85 and 115. 

Georgieff praised the study’s design. There is really good evidence that breastfeeding reduces ear infections, diarrhea and eczema in infants, he says, but “it’s really hard to do studies of cognition.” That’s because there are many variables associated with both a child’s tested intelligence and a mother’s choice to breastfeed.  

The Harvard study, unlike most past studies, controlled for these and other variables, including the mother’s intelligence, education level, and any postpartum depression; family income and home environment; and the child’s race, ethnicity, sex and birth weight.

“As a result, we felt we were able to get a reasonable estimate of what the relationship is between the length of breastfeeding and the IQ of the child at school age,” says Dr. Mandy Belfort, lead author and assistant professor of pediatrics at Harvard Medical School.

The study results show that “exclusive breastfeeding is becoming more and more important,” says physicist Sean Deoni, head of Brown University’s Advanced Baby Imaging Lab and lead author of a recent brain imaging study that linked exclusive breastfeeding to enhanced brain development in children. “And it’s not like you get an early advantage that falls away. Their study showed that the advantage seems to persist,” says Deoni.

Belfort says researchers don’t know for sure why breast milk may increase cognition. “All the nutrients we know that are important for infants are also in formula, but there may be others that we don’t know about yet that are responsible” for this small but significant effect.

For example, beneficial fatty acids found in breast milk have been routinely added to formula in the United States since about 2002. But a class of carbohydrates called oligosaccharides found in breast milk and thought to be beneficial to a baby’s health and brain development is not yet found in formula, says Georgieff.

In addition, it is difficult to make cow’s milk mimic human milk because “you just never get the entire matrix right - all the proteins and fats and all the live cells that are in there,” says Georgieff. “We are only starting to learn now what all those things are and how they work together.”

In the meantime, Belfort says the study’s findings support the current breastfeeding recommendations of the American Academy of Pediatrics: Babies should be exclusively breastfed for about the first 6 months of life, meaning no additional foods or fluids unless medically indicated. Babies should continue to breastfeed for a year and for as long as mother and baby desire, says the academy.

But while 70 percent of women in the United States start breastfeeding, by the six-month mark, only 35 percent are still breastfeeding, according to Dr. Dmitri Christakis, co-chair of the Excellence in Paediatrics Global Breastfeeding Initiative, in an editorial accompanying today’s research paper. Christakis calls for insurance coverage of postpartum home visits by public health nurses and of breast pumps. And he says workplaces need to provide spaces for mother’s to use those pumps.

“If data continue to mount that extended breast feeding is a major health plus for child development, it would be important to create an environment where women are both willing and able to continue to breastfeed,” says Fernstrom.