The central nervous system of human infants has a uniquely high content of docosahexaenoic acid (DHA, 22:6¿-3), which is accreted during the brain growth spurt that occurs during the first year of life. Based on results from randomized controlled trials on visual acuity it is presently agreed that preterm infants have a conditional need for preformed DHA, but the data for term infants are inconclusive. The term infant studies are in general performed more recently and with higher levels of a-linolenic acid (LNA, 18:3¿-3) in the control formulas.
A meta-regression analysis of the data has shown that differences in the dose of ¿-3 poly-unsaturated fatty acid (PUFA) are an important factor in explaining the inconsistencies in the functional outcomes. Thus, the data on both term and preterm infants are in agreement with a classical dose-response relationship, but it is unknown at this stage whether dietary LNA could meet the ¿-3 PUFA requirements. Moreover, the potential long-term implications of the early improvements in visual function are not known. ¿-3 PUFA intake in the first year of life is also believed to affect infant cognitive development, although this question remains unresolved. Breast-feeding has been shown to confer a long-term advantage in cognitive performance of approximately 3 IQ-points relative to that in formula-fed subjects, but this difference could be due to confounding as well as specific components of human milk. The DHA-content of human milk depends on the maternal fish intake, which in many countries does not support optimal levels of DHA in the milk. Most maternal fish oil supplementation trials report no advantage to infant mental development during the first year of life, but many of these studies find positive associations between breast-milk DHA and neuro-developmental outcomes, mirroring the results of observational studies. Some of these studies indicate possible negative effects of ¿-3 LCPUFA, e.g. on language development, but the interpretation is complicated by lack of knowledge of the long-term predictive role of the employed early tests on cognitive development. Apart from direct mental effects, changes in the fatty acid composition of the central nervous system may also influence other types of behavior and body functions, such as the regulation of blood pressure. Early intake of ¿-3 PUFA has been shown to affect blood pressure later in life in both LCPUFA-supplemented formula-fed infants and ¿-3 PUFA deficient rats. This line of research is up-coming and we expect the next decade will provide us with new aspects of the effect of ¿-3 PUFA that need to be taken into consideration when making dietary recommendations for PUFAintake during growth.