(USATODAY.com) - There's strong evidence that breast-feeding during infancy provides babies with many health benefits, from decreasing gastrointestinal tract infections and middle ear infections to reducing the risk of obesity and diabetes for both mothers and babies.
Less conclusive is the suggestion that breast-feeding may offer infants intellectual benefits as well. But a new study, out Monday in the journalJAMA Pediatrics, offers new evidence on that association.
"It adds to the literature in support of the idea that breast-feeding does positively impact a child's intelligence," says lead author Mandy Belfort, a pediatrician at Boston Children's Hospital. "I don't think there's any one study that's going to be a complete slam dunk, but it's definitely evidence in support of that idea."
Based on data collected from 1,312 mothers and their babies, the study finds that infants who breast-fed for a longer duration through the first year of life scored higher on measures of language recognition at age 3 and on verbal and non-verbal IQ measures at age 7.
The study also found that mothers' consumption of fish while lactating did not produce a strong association with kids' later cognitive development. (Fish high in omega-3 fatty acids have been associated with brain development.)
"We found a little hint in that direction, but nothing definitive," says Belfort, who is also an assistant professor of pediatrics at Harvard Medical School. "And we certainly didn't find any evidence that eating fish while breast-feeding was harmful, which is important because there are some concerns about mercury in fish being toxic to the developing brain."
The researchers conducted assessment tests of both the mothers and infants to measure their cognition, and also determined breast-feeding behavior through detailed questions about the age at which solid foods and non-breast-milk liquids were introduced.
Compared with some other studies on the subject, this one does a better job of separating out confounding factors, such as maternal IQ, family income and education, that have been known to influence a child's IQ, says Gail Herrine, an obstetrics and gynecology physician at Temple University Health System in Philadelphia. She was not involved in the study.
"This article goes a little bit further in showing that more breast milk is better at increasing IQ levels," says Herrine, one of the conference chairs for the Academy of Breastfeeding Medicine international meeting this fall in Philadelphia.
Although nearly all national and international recommendations promote exclusive breast-feeding for the first 6 months of life and then breast milk along with solids through the first year, "we made no recommendations about what (mothers) should do or how long they should breast-feed," Belfort says. "We just observed how long and how much, and then looked at how that related to the child's later intelligence."
The analysis showed that age 7, breast-feeding an infant for the first year of life would be expected to increase his or her IQ by about four points.
At age 3, there was a somewhat weaker benefit, increasing performance by 2.5 points.
Further studies are needed to understand why these outcomes occur, says Belfort, adding that the findings "are not something a parent or teacher would discern in a child" but are more relevant from a public health standpoint.
Although there are women who are not able to breast-feed for health reasons or they choose not to, "it's important to realize that there are many things parents can do to optimize their child's development, and one of them is provide them breast milk," she adds.