29 Dietary proteins and IGF I levels in preterm infants 2 Introduction Postnatal growth restriction is a major problem faced in the care for preterm infants. At 36 weeks postmenstrual age 91% of all preterm infants show postnatal growth restriction (weight < -1.3 SD) (1). At term age approximately 30% of infants are reported to still be growth restricted (2). As survival rates of preterm infants with an increasingly younger gestational age rise, we are subsequently confronted with the long term sequelae of pretermbirth. At 11 years of age 40% of children born before 26 weeks of gestation have been reported to have serious neurocognitive impairment andmoderate to severe impairment of neuromotor function, vision and hearing was reported in respectively 10%, 9% and 2% of cases (3). Preterm birth and postnatal growth restriction have both been associated with impaired neurodevelopmental outcome (4). However Franz and colleagues found that only a small percentage of the variability, roughly 3%, of the mental processing composite score was explained by growth (5). There might be a common factor leading to both poor growth and poor neurodevelopment, e.g. a poor nutritional status or major neonatal morbidities. Nonetheless several studies suggest that there might be independent pathways (5, 6). Either way these poor ourcomes warrant an intervention. Furthermore preterm infants are prone to develop risk factors for the onset of the metabolic syndrome. They are reported to have lower insulin sensitivity, increased blood pressure and increased fat mass in childhood and young adulthood (79). Nutritional interventions in these infants have been found to influence the development of risk factors for the metabolic syndrome (10). Hence neonatologists are challenged to compose and administer a diet which limits postnatal growth restriction; yet with caution to also limit the development of risk factors for the onset of the metabolic syndrome. Dietary factors, endocrine function and the simple immaturity of organ systems are entangled in the endeavour to optimize postnatal growth and metabolic programming. Dietary proteins are essential in enabling a growth rate similar to intrauterine growth (11). Nevertheless the balance between proteins and other nutrients are essential to understand how growth and body composition in preterm infants can be optimized. Insulin-like growth factors (IGF) are a key in the endocrine regulation of growth. Notably IGF I has an anabolic and mitogenic effect which is crucial for symmetric growth due to the presence of the IGF I receptor in multiple cell types and tissues. Moreover IGF I synthesis in multiple peripheral tissues causes it to function as an auto- and paracrine factor which does not merely influence growth, but also organ functioning. IGF I’s possible influence on neurodevelopmental outcome may be potentiated through its trophic effect or through altering the functioning of the central nervous system. In this review we aim to explore the possible pathways relating neonatal dietary proteinintakeandIGFI levels togrowth, bodycompositionandneurodevelopmental outcome in infancy, childhood and young adulthood.
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