Serum Leptin Does Not Predict Body Fat Mass in the Very Low Birthweight Infant 1546

Abstract

Leptin is a hormone produced by adipocytes that regulates body weight and has been found to correlate with the percentage of body fat in children and adults. In addition, leptin is also produced by the placenta and a positive correlation between cord blood leptin levels and birthweight suggests a role for leptin as a fetal growth factor. In the premature infant several studies have demonstrated a higher accretion of body fat when compared to fetuses of the same post-conceptual age and accurate measures of body fat might be useful in guiding nutritional decisions in this population. In this initial study we therefore set out to examine leptin levels in the very low birthweight infant and correlate with other measures of body fat including skinfold measurements and dual energy x-ray absorptiometry (DEXA). Four infants with a mean birthweight of 890 grams and gestational age of 27.7 weeks were studied. Infants were greater than 1 week of age and initiating feeds at enrollment and underwent weekly anthropometric measurements in addition to serum leptin levels until discharge or back transport. All infants manifested adequate weight gain and linear growth as well as increases in skinfold thickness suggesting deposition of subcutaneous fat. In addition, one infant underwent DEXA evaluation revealing 7.3% body fat at one month of age which increased to 9.3% at seven weeks of age. However, no serum leptin was detected in this infant at the time of the DEXA measurements. Suprisingly only one of the four infants had detectable serum leptin with a mean level of.19 ng/ml utilizing an ultrasensitive RIA. We conclude that serum leptin as it is currently measured is not useful to predict body fat mass in the very low birthweight infant. We further speculate that the lack of detectable leptin may be important in altering the extrauterine accretion of body fat in the prematurely born infant.