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Stress Hormone Levels in Women Reduced During Lactation
Women who breast-feed their infants produce lower levels of
stress response hormones than do women who bottle-feed, according
to research conducted by the National Institute of Mental Health
(NIMH). The study is the first to explore the effects of
lactation on hormonal stress responses in humans.
The NIMH researchers, led by Margaret Altemus, M.D.,
theorize that lactation-induced suppression of stress responses
serves several purposes for both mother and baby. First, it may
help to conserve energy needed for production of breast milk.
Second, it may minimize the psychological stress associated with
the demands of infant care, thus enhancing milk release. Third,
it may improve immune function during the postpartum period.
During any stressful situation, the brain's neuroendocrine,
or hormonal, systems are activated. In the hypothalamus, the
brain's "control center" for the neuroendocrine system, various
stress response hormones are released--including vasopressin and
corticotropin-releasing hormone, or CRH. CRH and vasopressin
have arousing effects in the brain and also travel to the
pituitary gland, where they trigger the release of
adrenocorticotropic hormone, or ACTH. ACTH, in turn, stimulates
the adrenal glands to produce cortisol, which mobilizes energy
for the body's response to stress.
Studies of rats have shown that lactation suppresses a
variety of physiological responses to stress, including the
release of several stress hormones. To determine whether the
same changes take place in humans, Altemus and her colleagues
studied twenty postpartum women--10 who were lactating and 10 who
were not. Women in the study were between 7 and 18 weeks
postpartum, and between 24 and 36 years of age.
The researchers used treadmill exercise--the same type of
"stress test" given to cardiac patients--to elicit the hormonal
stress response. Each woman performed treadmill exercise for 20
minutes, and blood hormone levels were taken before, during, and
after the exercise was completed.
Before the treadmill test, levels of ACTH, cortisol, and
vasopressin were similar in both the lactating and non-lactating
groups. In response to the stress of exercise, all participants
showed an increase in hormone levels; however, the increase was
significantly less among women who were breast-feeding their
babies compared to those who were bottle-feeding. Lactating
women had lower levels of ACTH and cortisol and showed a trend
toward a lower vasopressin response than did non-lactating women.
While the exact mechanisms responsible for the reduction of
stress hormone responses during lactation remain to be
determined, the findings could help to shed light on the
biological underpinnings of stress and anxiety disorders.
According to Altemus, increased levels of the stress
hormones vasopressin and CRH have been associated with obsessive-
compulsive disorder (OCD), a type of anxiety disorder, in humans.
Both hormones also promote fearful behaviors when administered to
"Preliminary research has also shown that lactation appears
to reduce the symptoms of anxiety disorders," said Altemus.
"However, more work needs to be done to help us pinpoint which
elements of lactation physiology are responsible for producing
this anti-stress effect."
The study, "Suppression of Hypothalmic-Pituitary-Adrenal
Axis Responses to Stress in Lactating Women," is published in the
October issue of the Journal of Clinical Endocrinology and
Metabolism. Other authors of the report are Patricia Deuster,
Ph.D., Elise Galliven, C. Sue Carter, Ph.D., and Philip
W. Gold, M.D.
Information provided by the NIMH.