The protective breast

Research highlights novel protective mechanisms and lactation biomarkers

Breast milk contains nutrients and bioactive factors that are essential for babies’ health. Proteins, such as growth hormones, enzymes and immunoglobulins, control a baby’s nutrient assimilation, growth and immunity. Carbohydrates, such as lactose, provide energy. Fatty acids, such as arachidonic acid and docosahexaenoic acid, stimulate brain and eye development. Vitamins, minerals and bioactive factors, like stem cells, immune cells, and oligosaccharides, also regulate growth and immunity in the infant.

But breast milk is more than simply food: It protects babies from infections and confers long-term physical and intellectual benefits. If mothers breast-feed for six months or longer, the babies maximize those benefits. Although approximately 77 percent of women breast-feed right after delivery, only 17 percent continue to breast-feed exclusively until six months. One study estimates that if 90 percent of women breast-fed for six months, it could save the U.S. $13 billion dollars in medical costs over the span of people’s lives. To promote breast-feeding initiatives in the U.S., the United States Breastfeeding Committee has declared August National Breastfeeding Awareness Month.

Recent research highlights the novel mechanisms by which breast milk protects infant health. For example, human milk oligosaccharides have no nutritional value for the breast-fed infant. They are actually food sources for beneficial gut bacteria. The gut bacteria digest the oligosaccharides using glycosidase enzymes to produce energy-rich monosaccharides. Fucosylated oligosaccharides in the milk resemble the surface receptors of intestinal cells. These oligosaccharides act as decoys for E. coli and norovirus and prevent them from infecting the intestines.

Immediately after a woman delivers a baby, milk synthesis and secretion follows with a surge in two hormones, prolactin and oxytocin. For some women, medical issues, like hormonal imbalances, cause low milk supply, which is a common reason for discontinuing breastfeeding early.

So some researchers are seeking biomarkers that signify lactation issues in pregnant women. Shannon Kelleher and colleagues at the Penn State College of Medicine report that zinc transporter protein 2, which transports zinc into milk in the mammary gland, is crucial for proper lactation. Kelleher's team found that the loss of ZnT2 impaired mammary gland development by reducing prolactin-induced activation of p-stat5 signaling, which controls mammary-epithelial cell proliferation and differentiation. Lactating mice without ZnT2 produced 30 percent less milk. Additionally, the milk had lower levels of fat and lactose.

Indumathi Sridharan Indumathi Sridharan earned her bachelor’s degree in bioinformatics in India. She holds a Ph.D. in molecular biochemistry from Illinois Institute of Technology, Chicago. She did her postdoctoral work in bionanotechnology at Northwestern University.