Indian Pediatr 2014;51: 966-967
Changes in Preterm Breast Milk Composition
with Advancing Infant Age
Somashekhar Nimbalkar and *Rohit Kumar Vasa
From Departments of Pediatrics, Pramukhswami Medical
College, Karamsad, Anand, Gujarat, India; and
*University of Chicago, Chicago, Illinois, USA.
reast milk has a dynamic and a variable
composition during a single feed, diurnally, and differs in composition
according to gestation, chronological age of the infant, and health
status of the mother. The timing of expression of milk and storage can
also alter this composition . The difference between preterm and term
milk has been studied in great detail by researchers; a few studies have
focused on the changes that occur in these two kinds of milk over a
longitudinal period of time. A recent systematic review of these studies
did not find any study on preterm milk composition beyond two months of
chronological age . The pilot study by Dutta, et al. , in
this issue of Indian Pediatrics, explores an important area that
has not been evaluated well in previous studies, i.e. change in
composition of breast milk as the chronologic age advances and the other
feeds are added. The study provides some more information regarding
composition at 90 and 180 days . The duration of exclusive
breastfeeding in preterm infants is likely to be foreshortened due to
delay in initiation of breastfeeding, intensive care in neonatal period
and prolonged hospitalization. These infants are more likely to have
complementary feeding introduced before 6 months of corrected age and
hence are likely to be bereft of benefits of exclusive breastfeeding. In
this study, analysis of serial breast milk samples reveals that as the
chronologic age advances, there is an increase in the triglyceride and
sodium levels and progressive decline in the protein content. However,
to suggest that there is a possible cause-effect relationship in sodium
and triglycerides between exclusive breastfeeding mothers compared to
those who have introduced mixed feeding is a speculation, because of low
numbers and some methodology related issues. Limitations of the study
include sample collection time as fat content beyond three minutes is
expected to be more, and with increasing age the lipid concentration in
the initial milk is higher due to efficient breast emptying. The
information related to milk volume and other components of milk such as
trace elements, bioactive proteins, or anti-inflammatory substances have
not been collected. Future studies would benefit from tracking caloric
intake of infants, breastfeeding frequency in mothers, and
anthropometric data of infants. These parameters would inform us about
infant health and other important modifiers in addition to changes in
breast milk composition over a period of time. Authors speculate on the
pathophysiology behind differences in composition as the chronologic age
advances, such as involution of mammary gland or changes in the cellular
permeability. Although this is possible theoretically, one cannot make a
strong case for these physiologic attributes, unless there are data on
milk volumes, secretory rates, and the concentration of components
measured and analyzed using regression analysis. Human milk is
species-specific and it is uniquely superior for infant feeding .
This basic understanding raises the question whether the compositional
changes that occur over time are nature’s way of adapting the milk
constituents to suit the infant needs. The compositional changes in term
infants during weaning have been reported earlier in other studies
[5-7], but the pathophysiologic mechanisms that lead to these changes
have not been explored well. Various biologically active proteins such
as secretory immuno-globulin A, lysozyme, lactoferrin, adiponection, and
beta endorphin with the exception of leptin are seen in higher amounts
in preterm milk in the first month as compared to term neonates .
Whether this composition gives the preterm a better chance for combating
infection, can only be speculated but it will be interesting to detect
levels of these components in the first six months of life.
Understanding of RNA, DNA, gene expression of epithelial cells from
breast milk (including genes for cytokines, and other interleukins), and
genome wide evaluations would give better understanding of reasons
behind differences in composition. Breast milk is a rich source of
maternal genetic information. RNA and DNA from breast milk is an
appropriate source for conducting gene expression or epigenetic study
. Scientists interested in research in this area would be well served
by forming a coalition to conduct studies across communities with a
centralized laboratory given the task of analyzing bioactive components
as well as genomic data.
Funding: None; Competing interests: None
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