33 Dietary proteins and IGF I levels in preterm infants 2 weight z-score from birth to term was associated with a higher blood pressure in adulthood. However, this association did not remain significant after adjusting for gestational age at birth (32). Nonetheless a recent review by Lapillonne and Griffin on the effect of postnatal growth on metabolic and cardiovascular outcomes in preterm born adults concluded that, in contrast to growth during late infancy and childhood, growth up to 1 year was not associated with adult blood pressure, glucose tolerance or lipid profile (33). However, the studies described in the review were heterogenic and did not all take a possible confounding effect of nutrition and small versus appropriate for gestational age into account. Therefore the concern of a possible negative impact of initial growth restriction and subsequent catch-up growth expressed through several studies cannot yet be disregarded. Currently there is no full understanding of which infants will and which ones will not completely ‘catch-up’. As in children following adoption onemight hypothesize that infants with the lowest IGF I level in the early post term period are the ones who will show catch up growth. However to our knowledge as of yet there is no evidence supporting this hypothesis in preterm infants. This hypothesis regarding catch-up growth might depend on the plasticity of the neuroendocrine axes and target organs. In certain infants intrauterine or early-life insults may completely program the neuroendocrine axes and target organs. However if there is some plasticity left, alteration of the growth rate may occur. This might further depend on environmental factors, e.g. lack of comorbidities and sufficient nourishment, in combination with the genetic make-up of the infant. Remarkably, in term infants several studies did not find a correlation between IGF I and subsequent weight gain, while they did find a positive correlation with subsequent length gain. Thus higher IGF I levels were associated with a subsequent lower BMI (24, 34). This might imply that high IGF I levels protect against adiposity. Growth restricted and preterm infants would then be at increased risk of developing obesity, because of their presumably low IGF I levels. Indeed, in small for gestational age very low birth weight infants IGF I levels up to 3 months corrected age have been positively associated with lean mass at 2 years (35). Moreover preterms were found to have increased fat mass and decreased lean mass in childhood (9). However a recent meta-analysis could not confirm that this trend persists into adulthood (36). Yet it remains to be clarified whether IGF I is primarily associated with change in height or is equally related to change in weight. Surely IGF I is involved in bone accretion, but it is also implied in adipogenesis (37, 38). Indeed Stigson et al. found that higher IGF I levels at a postmenstrual age of 30 to 32 weeks were associated with increased bone mass (9). Also, a trend of higher IGF I levels was found in preterm infants who increased in bone strength compared to preterm infants with a decrease in bone strength measured by bone speed of sound (39). In line with these findings preterm infants born small for gestational age had decreased bone accretion at 6 months corrected age. In addition 20 year olds who were born
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