Assessment of the efficacious dose of arachidonic and docosahexaenoic acids in preterm infant formulas: fatty acid composition of erythrocyte membrane lipids.

The nutritional requirements of preterm infants for the long chain polyunsaturated essential fatty acids, arachidonic acid (AA) and docosahexaenoic acid (DHA), have not been clearly defined. The present study evaluated preterm infants of less than 2.3 kg birth weight fed a commercial formula (Preemie SMA) devoid of AA and DHA and compared this control group with similar infant groups fed one of three formulas containing a range of 0.32 to 1.1% AA and 0.24 to 0.76% DHA. An analogous group of infants fed their mothers' breast milk and a breast milk fortifier (when indicated) was also studied. Erythrocyte membrane phospholipids were isolated from blood samples collected at 12 d of age and after a further 4 wk of feeding. Infants fed the formula without AA and DHA showed a reduction in AA level in erythrocyte phosphatidylcholine, and a reduced level of DHA in phosphatidylethanolamine in comparison with infants fed breast milk or infant formula containing AA and DHA. Supplementing infant formula with increasing levels of AA and DHA produced a clear dose response in the levels of AA and DHA found in erythrocyte membrane phospholipids. From comparison of membrane phospholipid fatty acid composition it appears that a formula level of 0.32-1.1% AA and 0.24-0.76% DHA provides sufficient levels of these fatty acids to achieve a similar fatty acid composition to that of infants fed human milk for most of the lipid fractions examined.