Researchers assessed infants’ cortisol following a routine (but often distressing) bath at 5 weeks of age to determine whether sleeping arrangements affect how infants manage stress. Infants who co-slept, spending at least half the night in the same room with their moms (most were not in the same bed), had lower cortisol after bathing than did infants who slept in their own rooms. Other variables (e.g., breastfeeding, maternal responsiveness) did not account for the results.
Tollenaar, M. S., Beijers, R., Jansen, J., Riksen-Walraven, J. M. A., & de Weerth, C. (2012). Solitary sleeping in young infants is associated with heightened cortisol reactivity to a bathing session but not to a vaccination. Psychoneuroendocrinology, 37, 167-177.
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