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.