The study, conducted by researchers at the Retina Foundation of the Southwest in Dallas, Texas, appears in the March Developmental Medicine and Child Neurology. The article is available on the journal's website at http://www.cup.cam.ac.uk/journals/dmc/birch.pdf. The study is one of several planned to determine if the substances are safe and effective and should be added to infant formulas in the U.S.
The substances, docosahexaenoic acid (DHA) and arachidonic acid (AA), are fatty acids present in human breast milk and, prior to birth, are supplied through the placenta to the developing fetus. Both DHA and AA are believed to play a role in the development of the nervous system. Although not used in infant formulas in the U.S., both substances are routinely added to infant formula throughout Europe and Asia.
"This study is an important step in the comprehensive array of studies needed to determine whether these substances should be added to infant formula," said Duane Alexander, M.D., Director of the NICHD.
In planning their study, the researchers sought to overcome the limitations of previous studies, which produced ambiguous results, explained the principal investigator, Eileen Birch, Ph.D. Some showed a positive effect on intelligence, others showed no effect, while another showed that DHA decreased vocabulary scores. Dr. Birch explained that some of the earlier studies showing no effect apparently did not use a sufficient amount of DHA to influence intelligence scores. In addition, the results of a large, multicenter study are difficult to interpret, because this large study used an earlier version of the Bayley Scales of Infant Development (BSID). The BSID is a standardized test used to gauge small children's development. This earlier version of the test had less emphasis on cognitive tasks than the newer version.
The study tested the intelligence scores of 56 18-month-old children. The children were divided randomly into three groups. One group had received formula containing only DHA, while another received formula containing DHA and AA. The control group received a commercial infant formula that did not contain either substance. All three groups of children were enrolled in the study within five days of their birth and received one of the three formula types for 17 weeks.
The children's overall intelligence and motor skills were tested using the Bayley Scales of Infant Development, 2nd edition (BSIDII), which has greater emphasis on cognitive tasks than did the earlier version. No differences were seen among the three groups on the Psychomotor Development Index, which measures motor skills, such as walking, jumping, and drawing. However, the children differed significantly on the Mental Development Index (MDI) of the BSIDII. This index measures small children's memory, their ability to solve simple problems, and their language capabilities.
The children in the control group received an average MDI score of 98-slightly below the national average for U.S. children of 100. The DHA group received an average score of 102.4, and the DHA plus AA group received an average score of 105.
Dr. Birch noted that the current study was a followup to an earlier study of the children's visual acuity. In this test-visual evoked potential acuity (VEP)-the infants' ability to see fine detail was measured at 6, 17, 26, and 52 weeks of age. In this earlier study, the children's VEP scores differed significantly, with the DHA/AA group receiving the best visual acuity.
In the future, Dr. Birch and her coworkers are planning a study of three times the number of children as in the current study, to determine if the same gains hold true. Also, the researchers plan additional studies to assess the metabolic effects of the two substances, by trying to determine if the additional DHA and AA cause any alterations in the ability of blood to flow and clot, antioxidant defense mechanisms, or total cholesterol and triglyceride levels. They will also test the children in the current study in four years, to see if their gains in intelligence scores persist into early childhood.