PDF《and Iron》

18 mo of age in preterm infants fed formula with 0.4% ? linolenic acid (18:3n-6), 0.3% ARA and 0.17% DHA from egg lipids, which included cho- lesterol (26). These ?ndings suggest different sources of ARA and DHA can differ in their effects on preterm infant growth and development. Several studies concur that dietary DHA increases the early development of visual acuity in preterm infants (23,27). An advantage in tests of mental and language development has also been reported in small preterm infants ?1,250g birth- weight fed formula with DHA and ARA (23). The improved visual and neural development in the latter studies show that 1.2% energy as LNA present in the unsupplemented formula does not meet the n-3 fatty acid requirements of preterm infants. Essential fatty acid requirements. One approach to address the nutrient needs of preterm infants is to match the plasma nutrient levels of the fetus. However, fetal plasma is charac- terized by low VLDL and LDL, low LA and high ARA and DHA (8). Human milk, infant formula, or IV lipids are pro- vided to attain growth rates approaching that of the third trimester fetus, and triglyceride-rich lipoproteins high LA emerge as a major plasma lipid transport particle. Feeding with triglycerides high in LA as a major energy source make it unlikely that plasma ARA and DHA levels similar to the third trimester fetus can be achieved in parenterally or enterally fed infants. Figure 1. Risk periods for alterations in essential fatty acid (blue box) and iron (red boxes) metabolism during early human brain development. Brain development chart adapted from reference 2. 100R GEORGIEFF AND INNIS Alternatively, an estimate of needs can be derived from estimates of fatty acid accretion in fetal tissue. Autopsy tissue analyses have estimated an accretion of

552 mg/d n-6 fatty acids and

67 mg/d n-3 fatty acids during the last trimester of gestation (28). Most of the n-3 fatty acids accumulated is DHA, while fetal liver and adipose tissue contain about 2-fold more ARA than LA (29). Fetal brain accretion has been estimated as 5.8 mg n-6 and 3.1 mg n-3 fatty acids/d, representing about 1.1% and 4.65% total body accretion. It is not known if the fetal brain is protected during limited DHA availability;

how- ever, prenatal n-3 fatty acid deprivation does result in a large de?cit in fetal brain DHA in animals (30). Estimation of the essential fatty acid intakes of preterm infants fed at

120 mL/kg with human milk or formula, or given IV lipid (Table 1) shows the marked overabundance of LA and LNA compared with the estimated fetal ac........