‘Got Milk?’ Not an Idle Query
Breast Milk Is ‘Liquid Gold’ for Infants, Hinde Says
Mother’s milk does so much more than just feed a baby. Along with fats, proteins, vitamins and minerals, it also supplies hormones, stem cells and immune factors that help protect babies from disease-causing organisms, explained Dr. Katie Hinde at a Wednesday Afternoon Lecture recently in Masur Auditorium.
“Because of these myriad functions, breast milk is considered liquid gold and breastfeeding is a gold standard that’s advanced by many national and international bodies that guide public health and medical decision-making,” said Hinde, an associate professor at Arizona State University’s School of Human Evaluation and Social Change.
Mother’s milk may prevent, treat or cure many of the world’s infant health problems such as obesity and diarrhea, the leading cause of child mortality, she said.
Most of what’s known about breast milk comes from research on dairy cattle, mammary gland dysfunction, the development of breast milk substitutes like formulas and from evolutionary biology. Until recently, there has been relatively little research on what’s actually in breast milk.
In her lab, Hinde studies the milk rhesus monkey mothers make for their babies. “The ‘biological recipe’ of milk for sons and daughters can differ,” she observed. Mothers who gave birth to a daughter produced more milk than mothers who gave birth to a son—a finding subsequently replicated in cows. The milk produced for daughters contained more calcium. The milk produced for sons is richer in fat and protein.
“This doesn’t mean that one milk is biased or better,” she said. Rather, the “skeletal development of primate females is faster than the skeletal development of males. These sex-differentiated developmental trajectories are seen in rhesus monkeys, chimpanzees and humans.” In other words, daughters need more minerals, sooner, because they grow faster.
Milk can also influence a baby’s temperament. Hinde’s research indicates that mothers who produced milk with higher levels of cortisol had babies that gained weight faster, were more nervous and less confident. A daughter’s temperament was also correlated with the mother’s social rank, Hinde added.
“This makes us suspect that milk cortisol is programming a ‘cheaper infant’ that is more nervous and less confident. And this may be leading to behavioral inhibition and lower activity budgets,” she said.
The presence of cortisol was best predicted by how many times the mother gave birth. The fewer offspring a mother had, the higher the concentration of cortisol. After each infant, the ability of the mammary gland to produce more milk improves.
“Young mothers—and not just because of their size—are handicapped by their mammary glands’ ability to synthesize milk.” Hinde said they are “producing less milk for their young—fewer calories due to lower volume.”
Within the last year, she noted, there have been several studies of human breast milk. These have identified what she described as exceptional features in human milk.
One study, led by researchers from the University of California, Davis, identified more than 1,500 proteins in human milk. Hinde said these proteins help digestion, foster immune development and aid in processing macro nutrients. Some of the proteins may also be involved in neurodevelopment of infants.
Another study found breast milk may protect infants from HIV. Each year, 240,000 children are infected with HIV. Half will contract it through breastfeeding. However, 85 percent of nursing mothers don’t pass the virus along to their children. Researchers showed infection rates are lower in human milk compared to cow and rhesus milk. Hinde said it’s unclear why. Further research is ongoing.
Mother’s milk feeds not only the infant, but also its microbiome. There are hundreds of different oligosaccharides—complex sugars—found in mother’s milk. They are the third most common component in breast milk after lactose and fat. Hinde said the sugars promote the growth of beneficial bacteria in the digestive tract and inhibit the colonization of harmful bacteria.
Hinde hopes these findings could one day lead to “precision milk” for vulnerable infants—such as in neonatal intensive care units—who do not have access to their own mother’s milk. Improved targeting of personalized milk has the potential to provide added value compared to the standardized formula and donor milk options currently available.