Abstract
Newborn's attraction to the breast milk odors is one of the fundamental behavioral responses that human newborns share with other mammalian species, but little is known about the effects of the breast milk odors on stress response. In the present study, we examined whether breast milk odors affect the stress responses to a capillary puncture on the heel (heelsticks) during routine blood draws to screen for phenylketonuria in 5 days-old infants. Forty eight healthy infants were randomly assigned to the following four groups, 1) control group which was exposed to saline as a sham odor, 2) mother's milk group which was exposed to their own mother's milk odor, 3) other mother's milk group which was exposed to other mother's milk odor and 4) formula milk group which was exposed to formula milk odor. To assess the infant distress, their facial expression (grimacing) and crying were recorded by video camera and their body movements were recorded by actigraph. This study was approved by the ethics committee of Nagasaki University. As we expected, infants showed significantly more distress after heelsticks in all groups. However, stress responses to the heelsticks were significantly attenuated by their own mother's milk odor, but neither by other mother's milk nor formula milk odors. These results suggest that the mother's milk odor has not only an attractive effect but also a calming effect on their own infant. [J Physiol Sci. 2006;56 Suppl:S178]
