May 5, 2008 -- Breastfeeding may make your kid more intelligent, according to the latest study on the subject.
Exclusive, long-term breastfeeding improves a child's verbal intelligence and other intelligence measures, says researcher Michael S. Kramer, MD, professor of pediatrics, epidemiology and biostatistics at the McGill University Faculty of Medicine in Montreal.
The study was published in the May edition of Archives of General Psychiatry.
Children who were breastfed longer scored higher on average at age 6 1/2 years in verbal intelligence, nonverbal intelligence, and overall intelligence, Kramer finds. Teachers rated them higher in reading and writing than children who weren't breastfed as long or as exclusively.
"Prolonged and exclusive breastfeeding makes kids smarter," Kramer tells WebMD. "I would say as a target for mothers, if they could exclusively breastfeed for three months and continue to breastfeed for some degree for one year, that would be good."
Breastfeeding exclusively [with no formula supplements] for six months would be even better, Kramer says. But he concedes that is difficult for many women, especially if they return to work.
Breastfeeding and IQ: Studying the Data
A host of studies have looked at breastfeeding and IQ. "Most of the studies have found an association between breastfeeding and higher IQ," Kramer tells WebMD. But most have been what scientists call observational studies, with children whose mothers chose to breastfeed compared with those children whose mothers chose not to.
Kramer and others say these studies may be affected by differences in the way moms who breastfeed interact with their children and those who don't.
Kramer and his colleagues looked at almost 14,000 children in Belarus who visited 31 hospitals and clinics there. The participants are part of the large-scale study known as the Promotion of Breastfeeding Intervention Trial (PROBIT). The researchers assigned half to an intervention that encouraged them to breastfeed exclusively long term or to another group that got the usual maternity care and child care.
This approach is considered more feasible and ethical than assigning mothers to breastfeed or bottle-feed.
"Those who got the breastfeeding intervention breastfed longer and more exclusively," Kramer says. The number of mothers still breastfeeding exclusively at three months was seven times higher in the intervention group of mothers -- 43% compared to 6% of those who didn't get the intervention.
Breastfeeding and IQ: Test Results
When the kids reached age 6 1/2, the children's pediatricians gave them intelligence tests. If they were in school, teachers evaluated their academic performance in reading, writing, math, and other subjects.
The strongest effect, Kramer says, was improvement in verbal IQ. On average, those in the intervention group scored 7.5 points higher on tests measuring verbal intelligence, such as vocabulary, which was statistically significant (meaning not due to chance). They scored 2.9 points higher on those tests measuring nonverbal intelligence and 5.9 points higher on tests measuring overall intelligence.
Kramer says the nonverbal and overall IQ test score differences were not statistically significant -- but just barely. He says the more important point is that he found an overall trend to improvement in the measures in the long-term or exclusively breastfed children.
Teachers rated the breastfed intervention group's reading and math better than the control group children.
"I think it's a modest effect," Kramer says. The IQ advantage for the long-term breastfed children, he says, is similar to what has been found in research for first borns vs. younger siblings.
"It's not the difference between a genius and a mentally retarded child," he says.
Breastfeeding and IQ: Breast Milk or Social Interaction?
Whether the boost in IQ is due to the breast milk itself -- such as healthy fatty acids or other substances -- or the physical and social interaction that is part and parcel of breastfeeding is unknown, Kramer and others say.
"A mother who breastfeeds is likely to spend more time with her child," he says, as well as read to them later and do other activities. "The amount of time, the closeness, the way she interacts with the kids, undoubtedly differs between breastfeeding and non-breastfeeding mothers."
The bulk of studies on the topic, he adds, have shown a positive link. One notable exception: a study published in 2006 in the British Medical Journal concluded that breastfeeding has "little or no effect on intelligence in children." The study involved more than 5,400 children.
Kramer says his study is sounder because of a more rigorous methodology.
Breastfeeding and IQ: Second Opinion
Not surprisingly, a spokesman for La Leche League International, which promotes breastfeeding, calls the new study findings "significant and valid." Not every paper or research study has found an association, says Lawrence M. Gartner, MD, a spokesman for the league and professor emeritus from the University of Chicago.
"But the huge majority of them do show a positive effect -- improvement in IQ and school performance."
"I think there is more and more evidence that points this way," says Dennis Woo, MD, chairman of the department of pediatrics at Santa Monica UCLA & Orthopaedic Hospital, who reviewed the study for WebMD. However, he wonders if cultural influences may play a role since the study was conducted in Eastern Europe, and if the same results would hold for U.S. breastfeeding mothers. Woo also works as a consultant for formula companies.
"We can't generalize [the findings] to all populations necessarily," agrees Jennifer Shu, MD, an Atlanta pediatrician and author of Heading Home with Your Newborn, published by the American Academy of Pediatrics. "But there is no downside [to breastfeeding]."
A slightly different interpretation of the findings is proposed by Ruth A. Lawrence, MD, chairwoman of the academy's section on breastfeeding and a neonatologist at the University of Rochester School of Medicine in New York. "What the study says to me is, breastfeeding does not make your child smarter, it allows your child to reach full potential. If you have a child with chromosomal abnormalities and Down syndrome, for instance, and breastfeed, you are not going to make that child a genius. You are going to allow that child to reach his full potential."
The American Academy of Pediatrics recommends exclusive breastfeeding for the first six months, suggesting mothers can continue as long as it is mutually acceptable.
According to the CDC, 73.8% of U.S. mothers who gave birth in 2004 ever breastfed. Of those, 41.5% still breastfed at six months, but just 11.3% exclusively through six months. The data is in the Breastfeeding Report Card, issued in 2007.