Breast-feeding for a longer time improves a child's understanding of language at age 3, and their scores on intelligence tests at age 7, according to a new study.
The study, which looked at the practice of breast-feeding in more detail and accounted for more potentially confoundingfactors that previous work, shows that breast-feeding indeed benefits children's cognitive development, the researchers said.
"In summary, our results support a causal relationship of breast-feeding in infancy with [comprehension of] language at age 3 and with verbal and nonverbal IQ at school age," the researchers wrote in their study published today (July 29) in the journal JAMA Pediatrics. The findings support recommendations for feeding babies only breast milk until they are 6 months old, and continuing breast-feeding through at least age 1.
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"This is a confirming study — it shows things that have been alluded to. It had a large number of participants and was well-controlled," said Dr. Ruth Lawrence, professor of gynecology and pediatrics at the University of Rochester Medical Center in New York, who was not involved with the study. [11 Facts Every Parent Should Know About Their Baby's Brain]
Researchers led by Dr. Mandy Belfort, of Boston Children’s Hospital, looked at about 1,300 participants in a study called Project Viva, a long-term study of the factors related to pregnancy and childbirth.
While other studies have compared breast-fed children with those who are fed infant formula, many studies have lumped all children who were "ever breast-fed" together into one group, putting together children who may have been breast-fed for only a short time with those breast-fed a great deal longer.
In the new study, the researchers looked at whether mothers had exclusively breast-fed their babies, or whether the child also consumed formula. They also collected data on the age of weaning.
For every additional month that children were breast-fed, their scores at age 3 on a picture vocabulary test increased, the researchers found. The link held even when researchers accounted for other factors known to influence children's scores, such as their mothers' IQs, and the amount of stimulation and emotional support the children received at home.
Children's scores on other tests at age 3, which measured fine motor skills, visual spatial abilities and drawing skills, showed no link with longer breast-feeding, the researchers said.
At age 7, children's scores on tests of verbal and nonverbal intelligence also showed an increase with each month longer that the child was breast-fed. However, scores on tests of drawing abilities and visual memories also showed no link with breast-feeding.
The results show that a family's economic status and a mother's educational level do not deflect the influence of breast-feeding, Lawrence said. The more disadvantaged children in the study also showed an impact of being breast-fed.
The researchers also looked at the extent to which a mother's fish intake during breast-feeding might the children's test scores, but found no link.
Follow Karen Rowan @karenjrowan. Follow LiveScience @livescience, Facebook &Google+. Originally published on LiveScience .
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