This study attempted to look at this issue:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dop
t=Abstract&list_uids=16267372&query_hl=1&itool=pubmed_docsum


Biol Res Nurs. 2005 Oct;7(2):106-17.
 
Differences between exclusive breastfeeders, formula-feeders, and
controls: a study of stress, mood, and endocrine variables.

Groer MW.

Research and Evaluation, University of Tennessee College of Nursing,
Knoxville, TN 37996-4180, USA. [log in to unmask]

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.


Esther G

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