Breast Milk and Premature Babies

One of the most fascinating aspects of human breast milk is that the milk literally changes during the course of a nursing relationship. The earliest secretions from the breast — called colostrum — are high in antibodies and protein. Transitional milk comes in a few days post-delivery, and milk changes once again at around two weeks post-delivery. The changes in breast milk occur to meet the changing needs — and changing maturity — of the human infant.

A new study published in the medical journal Pediatrics reports on yet another phase of milk that occurs in the case of a premature delivery (Gabrielli et al). It appears that lactating mothers of premature infants (average age studied was just shy of 28 weeks gestational age) produce milk that is much lower in lactose than the milk produced by mothers of full-term infant.

Lactose is a small sugar molecule made up of two smaller sugar units, called glucose and galactose. To digest lactose, the human intestine uses an enzyme called lactase, which breaks lactose into its separate glucose and galactose components; these are then absorbed into the bloodstream and can be taken up by the cells for energy. While some adults are lactose intolerant, a condition that results from insufficient production of the lactase enzyme, this condition is very, very rare in babies. Premature infants, however, generally don’t digest lactose to the same extent as full-term newborns (see, for instance, MacLean et al, Chiles et al), largely because of reduced lactase activity until the ninth month of gestation (see, for instance, Antonowicz et al, Aurrichio et al, Dahlqvist et al). This reported finding — that breast milk for preemies is especially low in a sugar they find hard to digest — is simply another neat example of human milk conforming to the needs of the human infant, regardless of the circumstances.

Another interesting finding of the study dealt with some pretty technical genetic issues. Stated simply, there are larger sugars than lactose (collectively called oligosaccharides) in human milk, and there are quite a large variety of these larger sugars. While all women produce most of the oligosaccharides, production of some of them requires enzymes that not everyone has. Two different genes (they go by the technical names Le and Se, but we’ll call them Gene 1 and Gene 2 for simplicity’s sake) are involved; women with Gene 1 can make Enzyme 1, and women with Gene 2 can make Enzyme 2. As a result, there are four different types of milk resulting from four different possible gene/enzyme combinations. According to the study, about 70% of women have both genes and produce both enzymes. These women produce the largest number and greatest variety of oligosaccharides. About 20% of the population lacks Gene 1 and therefore lacks Enzyme 1, but has Enzyme 2. About 9% of the population has Gene 1/Enzyme 1, but lacks Gene 2/Enzyme 2. These two groups of women produce fewer total oligosaccharides and a smaller variety of oligosaccharides than women with both genes/enzymes. About 1% of the population lacks both genes, and therefore both enzymes. These women consequently produce the smallest total number and smallest variety of oligosaccharides.

Because oligosaccharides aren’t digested, generally speaking, they don’t contribute to the caloric content or nutritional value of breast milk (Coppa et al). Instead, they pass through the gut and act as soluble fiber, which helps to promote regularity of bowel movements and keep bowel movements soft. They also appear to help prevent pathogenic bacteria from adhering to the gut wall, which helps prevent infection, and they seem to promote the growth of healthy gut bacteria (Bode). Finally, because they pass into the bloodstream to some extent in undigested form (Rudloff et al), it’s hypothesized that they could play a role in immune system function, or act as precursors for a variety of important molecules including some involved in brain function. The milk from mothers of preterm infants appears to be especially high in oligosaccharides, according to the Gabrielli study, which the authors hypothesize is particularly important for these smallest babies. On the basis of their findings, the authors emphasize the importance of human breast milk, ideally from the mother and as opposed to formula, as a source of nutrition for preterm babies.  The authors further note that the differences between women in terms of oligosaccharide production, and the importance of a wide variety of oligosaccharides in milk, justifies the mixing of milk from donors rather than the use of single-donor milk should a baby require breast milk supplementation.


If you’re interested in donating milk, the Human Milk Banking Association of North America needs donations.


Which of human milk’s various properties interests you most?


Antonowicz et al. Development and distribution of lysosomal enzymes and disaccharidases in human fetal intestine. Gastroenterology. 1974 Jul;67(1):51-8.

Aurrichio et al. Intestinal glycosidase activities in the human embryo, fetus, and newborn. Pediatrics. 1965 Jun;35:944-54.

Bode, L. Human milk oligosaccharides: prebiotics and beyond. Nutr Rev. 2009 Nov;67 Suppl 2:S183-91.

Chiles et al. Lactose utilization in the newborn; role of colonic flora. Pediatr Res. 1979; 13:365.

Coppa et al. Characterization of oligo- saccharides in milk and feces of breast-fed infants by high-performance anion- exchange chromatography. Adv Exp Med Biol. 2001;501:307-14.

Dahlqvist et al. Development of the intestinal disaccharidase and alkaline phosphatase activities in the human foetus. Clin Sci. 1966 Jun;30(3):517-28.

Gabrielli et al. Preterm milk oligosaccharides during the first month of lactation. Pediatrics. 2011 Dec;128(6):e1520-31. Epub 2011 Nov 28.

MacLean et al. Lactose malabsorption by premature infants: magnitude and clinical significance. J Pediatr. 1980 Sep;97(3):383-8.

Rudloff et al. Urinary excretion of lactose and oligosaccharides in preterm infants fed human milk or infant formula. Acta Paediatr. 1996 May;85(5):598-603.


4 Comments (+add yours?)

  1. Megyn @Minimalist Mommi
    Dec 07, 2011 @ 20:15:33

    Gosh, science+boobs=boy’s dream 😉

    But seriously, this is pretty amazing stuff! I often “blame” my mom for my bad immune system as I was formula fed. Out of our family of 4 (The Hubs, two wild boys, & I), I was the only formula fed one and just so happen to be the one who gets sick most frequently. If only breast milk would work for me now!


  2. Ashley @ C is for Cockerham
    Dec 07, 2011 @ 23:18:08

    Very interesting. I had no idea about the sugars. I wonder what kind of milk I make?


  3. Katy Crookston
    Dec 08, 2011 @ 16:20:59

    The human body is an amazing instrument. It’s also interesting that there is not a milk bank in the Phoenix area considering that this is such a large city.


  4. Alice Callahan (@scienceofmom)
    Dec 09, 2011 @ 04:51:29

    This is a super-cool study and a great explanation of it! Thanks for the article!


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