NEW YORK - Breast-fed kids are smarter, according to a Harvard University study that found the longer babies are nursed, the greater their intelligence.
The research, which followed more than 1,000 women and their babies, found that each additional month a child was breast-fed resulted in better language skills at 3 years old and intelligence at age 7, compared with babies not breast-fed. The findings were published Monday in JAMA Pediatrics.
The study is one of the largest to look at the role of breast-feeding on a child's intelligence, the authors said. It also underscores the need to support mothers in the workplace and in public to enable them to breast-feed their babies during the first year of life, said Dimitri Christakis, who wrote an accompanying editorial in the journal.
"With this we can close the book and decide there is a link between child breast-feeding and intelligence," said Christakis, a professor of pediatrics at Seattle Children's Research Institute, a pediatric medical research center, in a July 26 telephone interview. "The fact that breast-feeding really promotes cognition in our children is something we should all care about. It takes a village to breast-feed a child. We should take the actions necessary not to just initiate breast-feeding but to sustain it."
Still, breast-feeding is not the only contributing factor to intelligence, said Mandy Belfort, the lead study author and a neonatologist at Boston Children's Hospital and an assistant professor of pediatrics at Harvard Medical School.
"It's important to point out that breast-feeding is just one factor that influences a child's intelligence," Belfort said in a July 26 interview. "Our results shouldn't make parents feel bad for the choice they have made."
The American Academy of Pediatrics suggests exclusive breast-feeding for six months after birth before adding food, and that mothers continue to nurse until the child is at least 1 year old.
In the U.S., about 77 percent of women whose babies were born in 2009 started breast-feeding when their child was born. That number dropped to 47 percent at 6 months of age and 26 percent at 12 months, according to the U.S. Centers for Disease Control and Prevention.
It's not known how breast milk benefits intelligence, Belfort said. It may be nutrients in the milk help the developing brain or the way mom and baby interact during breast-feeding, she said. More studies are needed.
"I hope our findings provide a scientific basis for women to make choices about not only whether to breast-feed or not, but for how long to continue breast-feeding," she said.
Belfort said parents also should speak to their babies, including newborns, and expose them to a lot of language to help promote language development.
Researchers in the study followed more than 1,000 pregnant women and their babies until the children were age 7. After controlling for maternal intelligence, they found that IQ scores for 7-year-olds increased by about one-third of a point for every month of breastfeeding. That means a 7-year-old child who was breast-fed as a baby for 12 months would score four points higher on intelligence tests than a child who was never breast-fed, Belfort said.
The findings also hinted that children's intelligence benefited when their moms ate more fish while breastfeeding than those who ate less fish, but the results weren't statistically significant, Belfort said.