Differences between exclusive breastfeeders, formula-feeders, and controls: a study of stress, mood, and endocrine variables.

The purpose of this study was to examine relationships among lactational status, naturalistic stress, mood, and levels of serum cortisol and prolactin and plasma adrenocorticotropic hormone (ACTH). Eighty-four exclusively breastfeeding, 99 exclusively formula-feeding, and 33 nonpostpartum healthy control women were studied. The postpartum mothers were studied cross-sectionally once between 4 and 6 weeks after the birth. Stress was measured using the Perceived Stress Scale, the Tennessee Postpartum Stress Scale, and the Inventory of Small Life Events. Mood was measured using the Profile of Mood States. Serum prolactin, plasma ACTH, and serum cortisol levels were measured by commercial ELISA (enzyme-linked immunosorbent assay) kits. Results indicate that breastfeeding mothers had more positive moods, reported more positive events, and perceived less stress than formula-feeders. Reports of stressful life events were generally equivalent in the two groups. Serum prolactin was inversely related to stress and mood in formula-feeders. When breast and formula-feeders were compared to controls, they had higher serum cortisol, lower stress, and lower anxiety. Breastfeeders had lower perceived stress than controls. Breastfeeders had lower depression and anger and more positive life events reported than formula-feeders. However, there were few correlations among stress, mood, and the hormones in postpartum mothers, and those only in formula-feeders, whereas strong relationships were found between serum ACTH and a number of stress and mood variables in controls. Postpartum mothers reported a range of stress and negative moods at 4 to 6 weeks, and in formula-feeders, serum prolactin was related to some of the stress and mood variables. Breastfeeding appears to be somewhat protective of negative moods and stress.