NEW YORK -- Breastfed 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 breastfed resulted in better language skills at 3 years old and intelligence at age 7, compared with babies not breastfed. The findings were published last week in JAMA Pediatrics.
The study is one of the largest to look at the role of breastfeeding 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 breastfeed 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 breastfeeding 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 breastfeeding really promotes cognition in our children is something we should all care about. It takes a village to breastfeed a child. We should take the actions necessary not to just initiate breastfeeding but to sustain it."
Still, breastfeeding 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 breastfeeding 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 breastfeeding for six months after birth before adding food, and that mothers continue to nurse until their child is at least 1 year old.
In the U.S., about 77 percent of women whose babies were born in 2009 started breastfeeding 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 breastfeeding, she said. More studies are needed to better understand the relationship.
"I hope our findings provide a scientific basis for women to make choices about not only whether to breastfeed or not, but for how long to continue breastfeeding," 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 breastfed as a baby for 12 months would score four points higher on intelligence tests than a child who was never breastfed, Belfort said.
There was no association between breastfeeding and visual motor skills or visual memory, the authors said.
The findings also hinted that children's intelligence benefited when their moms ate more fish while breastfeeding then those who ate less fish, but the results weren't statistically significant, Belfort said.