Presented at the Neonatal Society 2003 Autumn Meeting.
Mayes C1, Burdge GC2, Bingham A1, Murphy JL2, Tubman RJ3, Wootton SA2 (introduced by Prof. M Thoresen)
1 Dept of Child Health, Queen’s University of Belfast, Northern Ireland
2 Institute of Human Nutrition, University of Southampton, UK
3 Neonatal Intensive Care Unit, Royal Maternity Hospital, Belfast, Northern Ireland
Aims: Docosahexaenoic acid (DHA) is an integral part of cell membranes and is important for the development and function of the central nervous system. Preterm infants can convert a-linolenic acid (ALNA) to DHA (1) in an attempt to meet an estimated DHA requirement of 35 mg/kg/day (2). Supplementation of preterm formulas with DHA is recommended leading to developmental advantages (3). For the first time the overall handling of ALNA by the preterm infant has been studied in terms of absorption, ß-oxidation and conversion to DHA. The contribution of ALNA conversion to DHA requirements is estimated. Queens University of Belfast granted ethical permission.
Methods: Preterm babies on the same low birth weight formula were given 20mg/kg of [U-¹³C] ALNA emulsified with a formula feed. ¹³C content of stool measured using CF-IRMS was used to measure absorption. Excretion of ¹³CO2 on breath over 24 hours was used to estimate partitioning of [U-¹³C] ALNA towards beta-oxidation. 1ml blood samples were taken at 0, 6, 24, 72 and 168 h; plasma lipids extracted and labelled n-3 fatty acid concentrations were measured by GCC-IRMS.
Results: 20 pre-term babies [median (range) corrected gestation 33 (30-37) weeks, study weight 1.69 (1.03-2.08) kg] were recruited. Median (range) excretion in stool was 7.0 (2-26.2) % which was a negatively correlation with gestation (r= -0.57, p=0.008). Median excretion on breath as ¹³CO2 was 12.8 (7.6-19.0) %. All babies synthesised labelled DHA, mean (SD) cumulative DHA was 0.31 (0.21) µmol/L. We estimate from the ratio of cumulative ALNA to DHA that a 1.6 kg baby will synthesise 5 mg of DHA/day from the ALNA available in a preterm formula. 42 mg of preformed DHA should be ingested per day by a 1.6 kg infant (with 34 mg remaining if DHA undergoes similar absorption and oxidation as ALNA). In total approximately 39 mg of DHA may be available per day representing a shortfall of 17 mg/day below estimated requirements of 35 mg/kg/day (56 mg).
Conclusions: The preterm infant’s ability to meet DHA requirements may be limited by malabsorption, use of ALNA for beta-oxidation and limited conversion of ALNA to DHA. DHA supplementation of preterm formulas is essential to meet the shortfall between ALNA conversion and DHA requirement. The estimate suggests that present formula supplementation may be insufficient to meet DHA requirements of 35 mg/kg.
References
1. Carnielli VP Pediatr Res 1996; 40: 169-174.
2. Clandinin MT et al. Early Hum.Dev. 1981;5:355-66.
3. Simmer K. The Cochrane Library, Issue 3, 2002. Oxford: Update software.