Healthcare professionals know the many benefits of human milk to infant health. Especially fascinating is how human milk varies based on the timing of childbirth. It continues to change over the duration of breastfeeding to meet the needs of the growing infant and offer a defense against illness.
Infants born preterm are particularly vulnerable to multiple morbidities as a result of their fragile health and developmental state. Human milk fits the term “liquid gold” in neonatal intensive care due to its ability to impact the occurrence of many of these morbidities, including late-onset sepsis, necrotizing enterocolitis (NEC), and retinopathy of prematurity (ROP). It is one of the first defense mechanisms we can use to ward off devastating disease and illness in these immunocompromised, at-risk infants.
What makes preterm human milk so special for these infants who are born too early? How does a mother’s early birth experience and her own biology impact her breast milk composition? There are many answers to those questions. Today we are focusing on a few specific ways the human body helps to compensate for an early birth, and minimize the increased health risks that come with it, through the advantages of human milk.
Preterm human milk versus term human milk
Higher levels of distinct bioactive molecules
Bioactive molecules protect against infection and inflammation, and help immune maturation and organ development, among other things. Preterm human milk has higher levels of these bioactive molecules, including lactoferrin. Lactoferrin is a protein which aids in digestion and improves the assimilation of macronutrients and micronutrients in human milk. Due to this ability, it is being investigated as a unique therapeutic agent to improve outcomes.
Overall protein content is significantly higher
Preterm infants are born without the benefit of term intrauterine growth time. The increased level of protein in mother’s milk helps them to achieve this growth. Also tied to protein intake during the neonatal period are brain growth and later life cognitive function, which makes this increase in protein a vital natural function of human milk tailored to the preterm infant.
Despite the protein increase in mother’s milk, preterm infants still require careful mixtures and administration of additional amounts of protein, amino acids, calories, minerals and trace elements through both intravenous and enteral feeding methods. Additional research is required to fully understand optimal amounts to improve growth, development and functional capacity.
Protein levels do decrease in human milk over the first 4 to 6 weeks of life in both preterm and term human milk. These distinct differences appear in the proteins at differing stages of lactation. If mother’s own milk is not available and donor milk is, it has been recommended that the donor milk be matched to the developmental stage of the infant if at all possible. Yet matching to infant developmental stage may be very difficult, and NICUs should not be discouraged in their human donor milk efforts. In the event of donor milk use, it is safe to say that using human donor milk is better than not using human milk at all (based on many study findings).
Higher levels of epidermal growth factor (EGF)
EGF is found in amniotic fluid and human milk, with preterm human milk showing higher levels of EGF than term human milk. Why is this important? EGF is a critical factor in decreasing risk of necrotizing enterocolitis (NEC). EGF is needed for the maturation and healing of intestinal mucosa, which is where NEC occurs and where preterm infants are vulnerable. Once in the intestine, it influences an increase in:
- DNA synthesis
- Cell division
- Absorption of water and glucose
- Protein synthesis
As a major carbohydrate in human milk, lactose increases in human milk over time with dramatic increases shown in preterm milk. Lactose is a disaccharide and is a crucial energy source. Low birth weight infants actually absorb greater than 90% of lactose in human milk. Though some volume is not absorbed, it does not go to waste: Callen et al note that “unabsorbed lactose from human milk feeding creates a softer stool consistency, improves absorption of minerals, and increases beneficial intestinal flora.”
Next up are the oligosaccharides (HMOs). These act as prebiotics and decoys (bind to pathogens). HMOs have been shown to be beneficial in preventing bacterial attachment and assist with preventing NEC.
Finally, there are the glycosaminoglycans (GAG). These amazing decoys tempt pathogens to bind to them instead of the enterocyte, resulting in an antimicrobial effect. Preterm milk has been shown to have more GAG than term milk, which makes sense when considering the limited development of preterm infants.
These 4 ways that preterm human milk differs from term human milk barely touch the surface of this fascinating topic. What it comes down to, however, is the amazing ability of a mother’s body to anticipate the needs of its newborn, whether term or preterm. Science has shown us the diversity and many functions of human milk as a resource to heal, prevent illness, and to encourage healthy growth, even down to the timing of birth.
Looking for more to read on this subject?
Read The Human Milk Dynamic Duo: Bacteria and Sugar
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Hay, WW., Thureen, P. (2010, August). Protein for preterm infants: how much is needed? How much is enough? How much is too much? Pediatrics and Neonatology 51(4): 198-207. doi: doi: 10.1016/S1875-9572(10)60039-3
Ballard, O., Morrow. A.L. (2013, February). Human milk composition: Nutrients and bioactive factors. Pediatric Clinics of North America 60(1): 49-74. doi: 10.1016/j.pcl.2012.10.002
Callen, J., Pinelli, J. (2005) A review of literature examining the benefits, challenges, incidence and duration, and barriers to breastfeeding term infants. Advances in Neonatal Care, 5(2): 72-88.
Underwood, M.A. (2013, February). Human milk for the preterm infant. Pediatric Clinics of North America, 60(1):189-207. Doi 10.1016/j.pcl.2012.09.008
Lönnerdal, B. (2003) Nutritional and physiologic significance of human milk proteins. American Society for Clinical Nutrition. Retrieved 24 May 2016 from http://ajcn.nutrition.org/content/77/6/1537S.full