Nutrients, neurotransmitters and infant behavior.

In recent years, short-term effects of the composition of each meal on the synthesis of brain neurotransmitters have been studied. This paper reviews studies of the influence of dietary precursors such as tryptophan and other competing amino acids on serotonin synthesis and metabolism and emphasizes the important influence of insulin. The paper then focuses on assessment of newborn state behavior, since evidence in adult humans has suggested a relationship between sleep behavior and brain serotonin levels. Several studies are then summarized. First, a study of healthy full-term newborns examining the relationship between diet and sleep behavior showed that infants fed tryptophan entered active and quiet sleep sooner than infants fed valine and low carbohydrate. Other studies designed to examine the influence of hyperinsulinemia on this system are then described. An observational study of newborns of diabetic mothers during the first weeks of life showed that they were quieter babies, with difficulties in visual orientation and motor performance. Plasma amino acid ratios studied during a glucagon-stimulation test in an infant with hyperinsulinemia showed a marked increase in parallel with changes in insulin levels. The results suggest that infant sleep behavior can be a sensitive dependent variable in studies of behavioral effects of diet and suggests that variations in serotonin levels may play a modulating role.