Milk-induced hypoalgesia in human newborns

Objective. To determine whether milk and its components reduce crying in newborns during and after blood collection for phenylketonuria evaluation. Methodology. Seventy-two normal newborns ingested 2 mL of milk (Similac), Ross Special Formula, fat, protein, lactose, sucrose, or water for the 2 minutes preceding blood collection via heel lance. Crying duration during and for the 3 minutes after the procedure was determined by scorers who were blind to the ingestive substance. Results. Sucrose and Similac each reduced crying during the blood collection procedure. Sucrose, fat, protein, and Ross Special Formula were effective during the 3-minute recovery period. Neither water nor lactose were effective during or after blood collection. Conclusion. Milk and some of its components are antinociceptive in human newborns. Based on previous studies, reduced crying during and after painful stimulation may be mediated through endogenous opioids. These findings are of potential clinical significance: natural protective mechanisms, normally engaged during suckling, may safely and noninvasively be activated to reduce newborn crying to painful stimulation.