Full-term infants who are born small score an average of 11 points higher on IQ tests if they are exclusively breastfed for the first six months of life compared to those who are given formula or solids early on, according to findings published in the March Acta Paediatrica. The study was conducted by researchers at the National Institute of Child Health and Human Development (NICHD) and the Norwegian University of Science and Technology.

The study is consistent with earlier reports that full-term infants who were of normal size for their age scored 3 points higher on IQ tests at five years of age when breastfed exclusively for the first six months than did infants who either stopped breastfeeding before six months or had supplements such as formula or solids introduced into their diets.

The finding also discredits the widely held belief that supplementary feedings of formula and cereal, in addition to breast milk, will help these smaller infants reach normal size faster than they would on breast milk alone. Ten percent of all births in the United States are small for gestational age (SGA) or less than six pounds when born full term.

"This study provides strong evidence that exclusive breast feeding for the first six months benefits the cognitive development of both small and normal-size infants," said Duane Alexander, M.D., Director of the NICHD. "Also noteworthy is the observation that exclusive breast feeding does not compromise growth."

According to the study's principal investigator, Malla Rao, the researchers evaluated 220 full term SGA children and 299 full-term, appropriate for gestational age (AGA) children. The scientists conducted the study in Norway and Sweden, because mothers in those countries exclusively breast feed their infants for longer durations than women in the United States. The most recent United States statistics from the Third National Health and Nutrition Examination Survey indicate that while only 21 percent of infants are still being exclusively breastfed for 4 months, this percentage drops to 16 percent by six months of age.

The children were evaluated by study physicians at birth, at six weeks of age, and at three, six, nine, and 13 months of age. At each visit, the children's mothers were asked whether they had fed their children formula, milk, cereal, or other solids, and the age at which such foods were given. The researchers tested the children at 13 months by using the Bayley Scales of Infant Development, which measure children's motor skills and mental abilities. When the children were five years old, the researchers tested their intelligence with a Norwegian version of the Wechsler Preschool and Primary Scales of Intelligence. This test measures children's intellectual capacity, rating how well they perform on various verbal and nonverbal tasks.

By the time the infants were 24 weeks old, the researchers could find no evidence that supplements had increased the growth of either SGA or AGA infants. However, the researchers did find that, at five years of age, SGA children who were breastfed exclusively for the first 24 weeks of life scored approximately 11 points higher on the tests than did SGA children breastfed for 12 weeks.

"Exclusive breast feeding does not appear to hinder the growth of SGA infants," Mr. Rao said. "Our findings suggest that, whenever possible, exclusive breastfeeding for the first 24 weeks of life is the method of choice to enhance children's cognitive development."

The NICHD is part of the National Institutes of Health, the biomedical research arm of the Federal government. The Institute sponsors research on development before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. NICHD publications, as well as information about the Institute, are available from the NICHD website, http://www.nichd.nih.gov, or from the NICHD Information Resource Center, 1-800-370-2943; E-mail NICHDInformationResourceCenter@mail.nih.gov. News Release March 20, 2002.