Editors' ChoiceEarly Life Influences on Behavior

Got Milk?

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Science Translational Medicine  17 Mar 2010:
Vol. 2, Issue 23, pp. 23ec41
DOI: 10.1126/scitranslmed.3001043

Mother's milk and infant behavior—is there any connection? Sure, newborns were designed to breastfeed in order to survive. But can the calories and nutrients available from breast milk contribute to an infant's brain development and behavioral disposition? The "Barker hypothesis" postulates that adult disease is influenced by parental or environmental conditions during early development, and numerous studies have shown that metabolism, growth, immune function, and reproduction are influenced by "fetal programming." Most research on developmental programming has focused on the intrauterine environment and events that occur during fetal development, but what about the signals conveyed to the infant during lactation?

Now, research by Hinde and Capitanio suggests that the available milk energy (AME), the product of milk energy density (kcal/g) and milk yield (g), soon after birth may be a nutritional cue that calibrates an infant's behavior to environmental or maternal conditions. In their study of rhesus monkeys, the authors show that infants whose mothers produced greater AME during the early stages of infancy exhibited increased activity and greater confidence in stressful situations later in infancy. Furthermore, the two metrics used to assess the infants' behavior—activity (measured with objective behavioral observations) and confidence (gauged with subjective temperament ratings)—were correlated, suggesting that each was influenced by a single underlying trait.

Importantly, these findings are applicable to humans given the similarities between nonhuman primate and human physiology and are the first to suggest that natural differences in milk production between mothers can lead to variations in infant behavior and temperament.

K. Hinde, J. P. Capitanio, Lactational programming? Mother's milk energy predicts infant behavior and temperament in rhesus macaques (Macaca mulatta). Am. J. Primatol. 71, 1–8 (2010). [Full Text]

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