A mother's immune status depends on her feeding strategy

Researchers at the University of California, Santa Barbara, have found that mothers' immune status in postpartum changes depending on how they feed their baby. Certain inflammatory proteins — substances released as part of the immune response — peak at different times of day depending on whether mothers breastfeed, pump milk, or formula feed, according to a paper published in the journal Scientific Reports.

"This is a great study; there are so many unanswered questions about maternal health in the postpartum period," said Amy Boddy, a biologist and evolutionary theorist in the UCSB Department of Anthropology and senior author of the paper. It's a rare, in-depth look at immunity from a mother's perspective in the postpartum period, which she hopes will serve as a starting point for future research.

In fact, she said, most of the research on the effects of breastfeeding focuses on the infant, with numerous findings about the benefits of breastfeeding for a child's immunity and development. In the long term, mothers who breastfed also have a lower risk of developing certain types of cancer and diabetes.

But what about women in the first months and years after childbirth? To investigate this, Boddy, lead author and co-principal investigator Carmen Hove and team followed 96 women in the Seattle area who had given birth over the previous six months and collected their saliva twice within 24 hours: once before bed and again in the morning. After waking up.

Since the COVID-19 pandemic had just begun and everyone was in quarantine, the researchers found themselves in an unexpectedly ideal experimental situation, where the mothers' environment was strictly monitored for infections that could skew immunity scores.

"It was kind of the perfect natural experiment because we were studying the function of the immune system, and the reports were that no one was sick," Boddy said. The goal was to track the cyclical levels of five types of proteins (designated CRP, IL-1β, IL-6, IL-8 and TNF-α) that indicate inflammation, a marker of the immune response.

"Breastfeeding has previously been shown to trigger a complex inflammatory response," Boddy explained. "Inflammation is not always bad—the breasts are rebuilding, functioning and doing things in the body."

The diurnal patterns of these proteins mean that, generally speaking, their concentrations tend to be higher in the morning and lower in the evening. What the researchers were interested in was identifying unusual levels in the normal fluctuations of these proteins and how they corresponded to the infant feeding strategies of new mothers.

For several proteins, there were no measurable differences in levels in the morning and evening, regardless of whether mothers expressed milk or breastfed. However, for C-reactive protein (CRP), the researchers found that levels peaked in the evening in women who were actively breastfeeding, reversing the normal diurnal trend.

"We expected that low lactation rates would be associated with a relatively high morning CRP peak and vice versa," Hove said. "What we ultimately found was that among mothers who reported heavy lactation, whether breastfeeding or pumping, CRP was higher at night." Further research is needed to determine the precise effects of this unique pattern in breastfeeding mothers.

"We don't know exactly what's going on," Boddy said. "Maybe incomplete emptying of the breasts leads to inflammation." Or perhaps this inflammation is a response to healing after pregnancy. Perhaps incomplete evacuation is a change in behavior due to stress. Perhaps the stress is a result of interrupted sleep associated with 24/7 breastfeeding schedules.

"We don't have a cause-and-effect relationship, it's just an association," she said. "This study shows that there is a unique immune profile and we need to study this further."

This study reveals the true complexity of postpartum breastfeeding. Breastfeeding is part of an ongoing physiological dialogue between mother and newborn that benefits the baby, Boddy said.

"In evolutionary biology, there is a concept of maternal-fetal conflict. The idea is that when there are two bodies in the same maternal unit, the baby always wants a little more than the mother can provide," she explained. This study dives into the gray area of postpartum health from a mother's perspective, especially in the areas of breastfeeding and immunity.

Indeed, despite the ideal promoted by institutions such as the World Health Organization that "breastfeeding is best," the researchers found that even among their sample of educated, relatively affluent women, there was a combination of feeding strategies that underscored the complexities of exclusive feeding breasts.

"There's been a lot of pushback, mostly from breastfeeding mothers, about time constraints. Our society doesn't make it easy for us to breastfeed and maintain lactation," said Boddy, who breastfed both of her children and found it "difficult to achieve breastfeeding goals." feeding."

Additionally, there are no clear recommendations on when to stop breastfeeding. When do the physiological and other benefits to the mother of this ongoing dialogue begin to decline? Can this information provide insight into other trends, such as maternal mortality?

Researchers hope to study this topic in more depth and on a more individual level to identify additional patterns in postpartum health and breastfeeding, such as the influence of different hormones involved in lactation.

"I think this study has opened up more questions than it has answered. We'd like to follow some of these same women throughout their postpartum experience," Boddy said. "It's always been difficult to find the best way to feed our children, and breastfeeding is so demanding."