Human breast milk has the most complex chemical composition of any mammal's milk. It contains more than 200 different types of sugar molecules; the milk from a cow or mouse only contains about 30 to 50 different sugars.
The importance of these molecules to infants' nutrition and development is just becoming clear. A new review of the scientific findings on breast milk reveals a wide range of benefits and the possibility that breast milk may be the ultimate personalized medicine.
Advances in gene sequencing technologies will make it easier for researchers to study the composition of human breast milk and its role in culturing helpful bacteria in babies' intestinal tracts.
Infants are born without any bacteria in their gut. Yet within weeks of birth, their digestive tract is colonized by billions of bacteria. This microbial diversity appears to offer infants a big advantage.
Breast milk also helps support the development of a baby’s immune system. This process is established early. Breast milk secreted in the first few days after birth, the colostrum, is rich in antibodies that provide protection against different disease-causing organisms.
During the first few weeks of life, anti-inflammatory molecules in breast milk, cytokines, contribute to the development of immunity on the mucosal membranes found in organs that link the newborn to the external environment, such as the lungs, intestines and urinary tract. This immunity is selective. It provides protection against infectious organisms, but allows the baby's body to tolerate the non-toxic environmental substances that come its way.
After about the first month, the composition of breast milk changes from primarily supporting immunity to supporting infant growth. Its fat content increases, and so do the levels of hormones that control satiety, fat storage, growth and blood sugar levels. At the same time, levels of maternal antibodies decrease by more than 90 percent. The diversity of sugar molecules also decreases.
Breast milk reduces infant mortality rates and the risk of gut and respiratory infections, but there is little scientific evidence suggesting longer-term benefits. Breast milk serves many important functions in newborns and infants, and children do thrive without it.
Advances in gene sequencing technologies will make it easier for researchers to study the composition of human breast milk. The authors believe the next few years will bring a better understanding of the hormones in human breast milk and the role of breast milk in culturing bacteria in a baby’s intestinal tract.
The article is published online in Trends in Biochemical Sciences.