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Breast-feeding moms more aggressive, study says

bear, woman, anger, stock
bear, woman, anger, stock Wikimedia Commons/istockphoto

(CBS) Girl power? Maybe it should be grrrrl power, at least when it comes to mothers who breast-feed their babies. Nursing moms protect their babies twice as aggressively as their bottle-feeding counterparts, according to a provocative new study.

"Breast-feeding mothers aren't going to go out and get into bar fights, but if someone is threatening them or their infant, our research suggests they may be more likely to defend themselves in an aggressive manner," study author Dr. Jennifer Hahn-Holbrook, a UCLA psychologist, said in a written statement.

What explains a phenomenon that some are calling the "mama bear" effect? The study suggests that the act of nursing blunts women's physiological reaction to perceived threats, tamping down fear and giving them extra courage to defend themselves and their babies.

For the study - published in the September issue of Psychological Science - researchers recruited three groups of women: 18 nursing mothers, 17 moms who used formula to feed their infants, and 20 non-mothers. As her baby was taken care of nearby, each woman was pitted against an overtly rude research assistant in a series of computerized time-reaction contests - and encouraged to celebrate each victory by pushing a button to deliver a sound blast.

What happened? The blasts delivered by the breast-feeding moms were twice as loud and as long as those given by non-mothers and nearly twice as loud as long as those given by bottle-feeding moms. The researchers viewed the bigger blasts as a sign of aggression.

And measurements of the moms' blood pressure showed that breast-feeders had pressures significantly lower than those of bottle-feeders or non-mothers. Lower blood pressure suggests reduced anxiety.

The so-called "lactation aggression" phenomenon has been identified in rats, mice, lions, deer, sheep, and other non-human mammals, Dr. Hahn-Holbrook said. But she said she believed hers was the first study to demonstrate the phenomenon in humans.

If breast-feeding helps moms protect newborns from danger, it's just one of many benefits of breast-feeding. In a call to action to support breast-feeding issued in January, the U.S. surgeon general said breast-feeding protects babies from diarrhea, pneumonia, and other infections as well as sudden infant death syndrome (SIDS) and subsequent obesity. In addition, moms who breast-feed are less likely to develop breast and ovarian cancer.

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