Effect of light on diurnal variation of blood amino acids in neonates.

Normal newborns show a diurnal variation of blood amino acid concentration, with lower values at 04.00 h and higher at 12.00 h. Three groups of infants, each consisting of 10 normal, full-term neonates, remained under different lighting conditions for 24 h and blood amino acids were determined at 04.00 and 12.00 h. Group A remained under continuous light, group B had the eyes covered, and group C was exposed to intermittent light, with the lights dimmed between 22.00 and 04.00 h. Group A showed a reversal of blood amino acid periodicity with a mean decrease of total amino acid concentration by 17.7% at 12.00 h (p less than 0.025). In group B there was no statistically significant difference between 04.00 and 12.00 h values. Group C showed the usual amino acid periodicity with a mean increase of total amino acid concentration by 36.1% at 12.00 h (p less than 0.005). The differences observed between groups A and C were statistically highly significant (p less than 0.0005). These data indicate that lighting conditions may affect the diurnal variation of blood amino acids and this should be considered for infants who remain under continuous light for prolonged periods in neonatal units.