Milk makes a baby grow, including the baby’s brain. DHA, for example, is an omega-3 fatty acid that is a critical structural component of the brain. DHA, and other LCPUFA (long-chain poly unsaturated fatty acids), naturally occur in mother’s milk and are ingested by the infant during critical periods of neurodevelopment. More fatty acids are thought to enhance neurodevelopment which in turn produces better cognitive function. A number of studies supported these predictions and influenced companies to start adding fatty acids to infant formulas starting about a decade ago. But there is now a growing body of evidence that milk contains numerous bioactive micro-constituents beyond LCPUFA that are critical for the development of the infant’s brain.
For example, in their recent paper, Serpero and colleagues (2012) outlined the functional properties of “brain” proteins found in human breast milk- specifically Activin A and S100B. Activin A is important for brain cell growth and development. Additionally, Activin A shields brain cells from damage. S100B is part of the calcium-binding protein family and is also a brain specific protein that regulates communication between cells, as well as cellular energy metabolism and growth. In addition to characterizing the functions of Activin A and S100B, Serpero and colleagues address two important issues when thinking about milk and milk science applications;, developmental priorities of the neonate and enhancing milk formula.
Developmental Priorities of the Neonate
In each species, unique properties of milk are specific to the developmental needs of the infant of that species. For example, compared to other mammals our size, humans have a brain that is seven times larger. Most of our brain growth and development occurs during infancy when we are ingesting breast-milk or formula. Serpero and her co-authors revealed two important clues about the importance of these brain proteins for the human neonate. First, the concentration of both Activin A and S100B is higher in the mother’s milk than in her bloodstream. This means the high concentration of these proteins in milk is on purpose rather than a byproduct of the mother’s circulation and suggests Activin A and S100B are critically important for the human neonate to ingest. Secondly, the concentration of S100B in human breast milk is higher than in the milk of other domestic dairy animals. Differences in the concentration of the brain protein S100B in milk between human and non-human species likely reflect the greater post-natal neurodevelopment of the human neonate. Activin A may also be higher in humans, but data are not yet available.
Enhancing Milk Formula
Currently, the brain proteins Activin A and S100B are not detectable in commercial milk formula. The absence of Activin A and S100B could be a result of lower concentrations in cow’s milk to start with, but the amount of these proteins may also be diminished during commercial food processing. For example, bioactive properties of S100B are retained through pasteurization, but are degraded by spray-drying. Identifying the presence and abundance of bioactive constituents in human breast-milk, and their function in the developing infant, provides opportunities to better engineer commercial infant formula. After all, there was also a time when commercial formula lacked supplemental long-chain polyunsaturated fatty acids like DHA. Improvement of milk formula composition will come from advances in formula preparation and from the make-up of the milk that dairy animals produce. Researchers can now insert human DNA into transgenic, cloned dairy cows to express human-type lactoferrin and lysozyme in cow’s milk. Lactoferrin and lysozyme are immune constituents with anti-bacterial properties, and similarly to S100B, they are found in higher concentrations in human breast milk than in cow’s milk.
As a science, we still know very little about the mechanistic and functional outcomes of most milk constituents in isolation, not to mention their complex, synergistic interactions. However, we are clearly at the outset of significant advances in milk science because biochemical, microbiological, and genomic tools for investigating milk are exponentially expanding. With these tools, we can expect to better answer the questions, what exactly is milk, and how does it do a baby good?
Serpero LD, Frigiola A, Gazzolo D. 2012. Human milk and formulae: Neurotrophic and new biological factors. Early Human Development. 88:S9-S12.
Prof. Katie Hinde
Human Evolutionary Biology
Cambridge, Massachusetts, U.S.