The decisions whether to breast-feed and share a bed with the baby not only affect the welfare of the infant, but also the mother, a new study finds.
The women in the study with the best stress hormone patterns were the ones who breast-fed but refrained from sharing a bed with their baby, researchers found. The women who fared the worst were those who co-slept and didn't breast-feed.
The researchers were looking for the optimal daily rhythm in the women's stress hormone levels. An optimal rhythm is one in which levels of the stress hormone cortisol are high in the morning, to prepare a person for the day's events and stressors, and low in the evening, to allow for sleep.
Women who didn't breast-feed, or who shared a bed with their infant, had less-than-optimal daily rhythms.
The findings suggest that recommendations made by public health experts because they are good for infants — that they be breast-fed and that they sleep in their own bed — are good for mothers, too.
"The combination of those two things is also physiologically beneficial for mothers," said study researcher Clarissa Simon, of the Institute for Policy Research and School of Education and Social Policy at Northwestern University.
The study was presented this week at the American Public Health Association's annual meeting.
Previous studies have showed cortisol levels increase during pregnancy and drop immediately after childbirth, but few studies have looked at what happens in the later postpartum period.
In the new study, Simon and colleagues analyzed saliva samples from 195 women in a Chicago suburb six months after giving birth. Samples were collected when participants woke up, 30 minutes after waking, and at bedtime.
Mothers who breast-fed but did not co-sleep had the steepest declines in their cortisol levels from morning to evening — a pattern previously linked with good health. For example, studies have shown that people with this pattern are more likely to be in good cardiovascular health or to survive breast cancer, Simon said.
Mothers who did not breast-feed and did share a bed with their babies had less of a decline over the course of a day, Simon said.
Breast-feeding is a known stress reducer, Simon said. As for sharing a bed with an infant, it may lead to sleeping problems for the mother, which would be reflected in her stress hormone levels, she said.
Because the study was conducted in one suburb of Chicago, it's not clear whether the results apply to the general population, Simon said.
Pass it on: Mothers who breast-feed but do not share a bed with their baby have optimal stress hormone rhythms.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.