Increased breast-feeding during the first months of life appears to raise a child's verbal IQ, according to a study of nearly 14,000 children that was released Monday.
The study in Archives of General Psychiatry found that 6-year-olds whose mothers were part of a program that encouraged them to breast-feed had verbal IQs that were an average of 7.5 points higher than those of children in a control group.
The researchers said that their findings suggested that the longer an infant is exclusively fed breast milk, the greater the IQ improvement.
The results echo smaller previous studies that found children and adults who were breast-fed tended to have higher IQs than whose who were not.
Lead author Dr. Michael Kramer, a professor of pediatrics at McGill University in Montreal, said the IQ improvements were modest and might not be noticeable on an individual basis. But he added that the increase could have a significant effect on society.
"We're not talking about making a child who has trouble in school and is dropping out into a genius," he said. "But if we can increase IQ by 3 to 4 points in the whole population, we can have fewer children at the low end and more Einsteins at the high end."
The latest study tracked breast-fed infants born between June 1996 and December 1997 in Belarus. Half of the infants and mothers were assigned to an experimental program designed to promote breast-feeding, while the remaining infants and mothers received regular pediatric and follow-up medical care.
The breast-feeding program included increased counseling and instruction when women visited doctors or clinics.
At the end of three months, 72% of infants in the experimental group were still breast-feeding to some degree, compared with 60% in the group that did not receive breast-feeding support.
The researchers believe that what drove the results was the substantially higher number of infants who were exclusively breast-fed in the experimental group: 43% compared with 6% of infants in the control group.
All children in the study were interviewed and examined between 2002 and 2005, when they were an average of 6 1/2 years old. The children's academic performance also was evaluated by their teachers.
Besides the improvement in their verbal IQ scores, children in the experimental group scored an average of 4.9 points higher on tests that specifically measured vocabulary.
Compared with children in the control group, children in the experimental group had overall IQ scores 5.9 points higher than those of children in the control group and better academic assessments from their teachers, but the improvements were not deemed statistically significant.
Kramer said that more research was needed to determine whether the benefits were related to a component of breast milk or to the physical and social interaction between mother and child that is inherent in breast-feeding.
The World Health Organization and the American Academy of Pediatrics recommend that infants receive only breast milk during the first six months of life. Children who are breast-fed are believed to have health advantages, including fewer gastrointestinal problems.
Last week, the national Centers for Disease Control and Prevention reported that breast-feeding in the U.S. was at an all-time high, with 77% of new mothers saying they breast-fed their children compared with 60% in 1993-1994.