Breast-feeding has been linked--often effusively--to more smarts. In fact, a stack of medical studies in recent years has led many parents to believe that breast-feeding is a must if they want their children to do well in school.
Such conclusions may have been a bit hasty. The latest study on the effects of breast-feeding suggests that many of the earlier studies don't make the grade when it comes to good scientific research.
A paper in the June issue of Pediatrics analyzed 40 studies on the link between breast-feeding and cognitive development, 68% of which concluded that breast-feeding promotes intelligence. The studies showed, among other things, that breast-fed babies score higher on cognitive tests, get better grades in school and have higher IQs as adults than babies who were bottle-fed. Some found that intelligence increases for each additional month that a baby is breast-fed.
But researchers from Yale University and the University of Chicago say their analysis shows that most of the studies had serious flaws. Only two, in fact, met all the authors' criteria for quality research; one of those found a "significant" effect of breast-feeding on intelligence; the other found no correlation.
"The studies have not been very good--and there have been a lot of them," says Dr. Anjali Jain, who co-wrote the analysis. One major problem with the studies, she says, is they often didn't take into account the importance of factors besides breast milk. Some of those factors may be responsible for the intelligence gains. "Breast-feeding itself takes a fair amount of motivation," she says. "Just being a motivated parent is important. But a bottle-fed child could also be [cognitively] stimulated by a motivated mother."
Another flaw with much of the research was that it failed to accurately measure how much breast-feeding took place, such as by recording the amount of time spent breast-feeding or whether the baby also received formula, Jain says.
However, other experts say the evidence for a connection between breast-feeding and intelligence is still persuasive.
Good breast-feeding studies are difficult to do because researchers "can't tell one mother to breast-feed and another she cannot" for purposes of their study, says Dr. Ruth Lawrence, a breast-feeding expert at the University of Rochester School of Medicine. But that doesn't mean health experts should disregard a preponderance of evidence showing a link, she says.
"There is a lot of data on breast-feeding and intelligence," Lawrence notes. The new analysis could be flawed, too, suggests Kim Cavaliero, a spokeswoman for La Leche League International, a Schaumburg, Ill., organization that promotes breast-feeding and supports the claims of enhanced intelligence.
"The [researchers] of the study in Pediatrics are interpreting data," says Cavaliero. "Who is really to say that their interpretation is correct?"
Until there is more convincing data, however, Jain, an associate at the University of Chicago, argues that breast-feeding shouldn't be promoted via the intelligence hook.
"There is a back-to-breast-feeding movement, which I'm very much in favor of. But I think we feel the need, as a society, to ... try to link it to something" instead of trusting our intuition that breast-feeding is generally a good thing, says Jain, herself a breast-feeding mom.
Research on breast-feeding suggests it can not only spur cognitive development but can also help protect children from some infectious diseases and reduce the risks of disorders such as diabetes and obesity later in life. By breast-feeding, women may lower their premenopausal risk of breast and ovarian cancer, according to the U.S. Department of Health and Human Services.
But the touting of specific benefits can lead to enormous guilt in women who can't breast-feed, leading them to fear that their children will not be as smart as they could have been or that they will have more ear infections than their breast-fed playmates.
The breast-feeding and intelligence link "has been used often to make women who have a lot of trouble breast-feeding feel horrible," says Jain. "For working women, it's incredibly hard to maintain breast-feeding."
About 64% of American women breast-feed their infants to some extent. However, by the baby's sixth month, only 29% of mothers are breast-feeding, according to federal government figures. Lawrence agrees that people should consider breast-feeding based on its overall benefit.
"I think people get hung up on the idea that breast-feeding makes a child smart," says Lawrence, a member of the American Academy of Pediatrics' Task Force on Breastfeeding. "It doesn't make a child smart. It facilitates the brain's development so children can reach their full potential."
But, Lawrence says, there is legitimate interest surrounding research on breast-feeding and brain development.
"The brain is going to double in size during the first year of life," she says. "Why not give it the best nourishment possible?"