Breast-feeding has many known health benefits, but there's still debate about how it may influence kids' behavior and intelligence.
Now, a new study published in Pediatrics finds that children who are breast-fed for at least six months as babies have less hyperactive behavior by age 3 compared with kids who weren't breast-fed.
But the study also finds that breast-feeding doesn't necessarily lead to a cognitive boost.
Researchers studied 8,000 children in Ireland. At ages 3 and 5, the kids took standardized tests to measure cognitive abilities. Overall, the breast-fed kids scored a tad higher.
"But [the difference] wasn't big enough to show statistical significance," says study author Lisa-Christine Girard, a child-development researcher at University College Dublin.
In other words, the differences in scores were so small that researchers consider it a statistical wash. "We weren't able to find a direct causal link between breast-feeding and children's cognitive outcomes," Girard says.
"Our findings are not overly surprising," Girard told us. There are a multitude of factors that shape a kid's development – and intelligence.
Girard and her co-authors used a method to try to tease apart the effects of breast-feeding from all the factors that shape these outcomes.
She points out that mothers who choose to breast-feed tend to share a whole range of characteristics and habits.
"For example, mothers who breast-feed typically have higher levels of education," Girard says. And they tend to engage less in risky behaviors while they're pregnant, such as smoking. In addition, there are factors such as IQ, and varying home environments. "How many books are in the home, how much time is spent reading?" Girard and her colleagues wanted to consider all these kinds of differences.
Now, what's interesting is that before the researchers applied methodology designed to account for all these variables, breast-feeding was associated with better cognitive development outcomes almost across the board.
But when they accounted for all these socio-economic variables, the stand-alone effect of breast-feeding seemed to disappear.
The exception to this was the positive benefit of breast-feeding on hyperactive behavior. "The effect is small, but it's there," Girard explains. However, it's worth noting that the benefit of less hyper-active behavior was documented at age 3, but by age 5 it had faded away. The authors conclude that "the earlier observed benefit from breast-feeding may not be maintained once children enter school."
An editorial published alongside the study in Pediatrics points out that the topic of how breast-feeding may influence cognitive ability is controversial. The editorial points to four prior studies that found breast-feeding improved performance on IQ testing by 1.76 points, "suggesting a small but durable impact of breastfeeding on intelligence," Lydia Furman, a pediatrician with Case Western Reserve University's School of Medicine and the author of the editorial, wrote.
The new study is a sign that the debate continues. "This has been a debate for over 100 years, and we're working hard to understand the complete picture," Girard told us.
Of course, these findings don't alter the recommendations to breast-feed. There's overwhelming consensus that it's the optimal way to feed an infant. And the American Academy of Pediatrics recommends that, if possible, babies be breast-fed exclusively for about the first six months of life.
"There's a strong body of evidence to support that breast-feeding is one of the healthiest things we can do to support children's immune systems," Ellie Erickson, a pediatrician with Duke University, told us.
There are lots of benefits for babies — ranging from protection against infection to perhaps a lower risk of allergies. And for moms, breast-feeding lowers the risk of developing breast cancer later in life.
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