Diet and sleep patterns in newborn infants.

Sleep behavior is modulated by serotonergic neurons within the brain, and the synthesis and release of serotonin by such neurons is thought to be influenced by the availability of tryptophan, the amino acid precursor of serotonin. We investigated the effects on the sleep patterns of newborn infants of variations in diet designed to affect tryptophan availability. Twenty healthy newborns (two to three days of age) were randomly assigned to receive a feeding consisting either of tryptophan in 10 per cent glucose or valine in 5 per cent glucose (valine competes with tryptophan for entry into the brain). Sleep patterns during the three hours after this feeding were compared with those after a feeding of routine formula (Similac). The infants fed tryptophan entered active sleep 14.1 minutes sooner than they did after Similac, and entered quiet sleep 20 minutes sooner. Those fed valine entered active sleep 15.8 minutes later than they did after Similac, and entered quiet sleep 39 minutes later. The differences between the tryptophan and valine groups were significant (P less than 0.01 for active sleep and P less than 0.005 for quiet sleep). We conclude that variations in the composition of the diet may influence sleep behavior in newborns.