Human Breast Milk Compound Alters Brain Growth in Mice

Human breast milk is a nutrient-rich mix that helps nurture newborns through an essential period of development. New evidence suggests that one particular compound derived from breast milk, the sugar myo-inositol, might play an important role in the maturation of the newborn brain.

The research  was published in PNAS.

A vital period for the developing brain

Human milk helps the human body develop through a period of unrivalled change. Over the first year of life, babies usually triple  their body weight. To encourage this growth, milk contains proteins and important fats and carbohydrates, alongside a rich cocktail of immune-boosting molecules like cytokines and antibodies .

The first 12 months of an infant’s life is also a transformative period for the brain. Researchers have noted that in this early stage of life, the barriers between the gut, bloodstream and brain are unusually fragile, suggesting that what babies consume is likely to have an outsize impact on how their brains develop.

In a new study, a multi-institution team analyzed the rich milieu of breast milk stored during the Global Exploration of Human Milk study. Using samples from Mexico City, Shanghai and Cincinnati, the team looked at how molecular contributions to breast milk changed over the first year of life, with the aim of analyzing the ingredients that might be most prominent during important periods of infant brain growth. During the first few weeks after birth, the human brain starts rapidly forming neuronal connections, imprinting circuits that will serve the brain throughout life.

In breast milk sampled from mothers while their infants were in this early stage of life, the team noted that levels of the sugar myo-inositol were consistently high, before dropping off towards the end of the first year, a change which mimics the density of synaptic connections in the growing brain. Similar levels of the sugar were seen across all three sample sites.

Milk for mice

The team decided to assess myo-inositol’s effect on the brain using a handful of different lab techniques. First, they showed that human neurons exposed to myo-inositol exhibited higher levels of a marker called Homer, which is linked to the development of post-synaptic connections. No such effect was seen for an equivalent pre-synaptic marker called Bassoon.

The effects appeared to be stronger in mouse neurons exposed to myo-inositol – these cells showed increases of roughly 40% in levels of both Homer and Bassoon.

The researchers then took their work a step further, by feeding newborn mouse pups a myo-inositol supplement everyday from birth to postnatal day 35. At this point, their visual cortexes, a region of the brain that rapidly develops after birth, were examined for markers of synaptic growth. While the density of these markers did not change in myo-inositol-fed pups, the size of each marker seen increased. This, say the authors, further supports the theory that myo-inositol can increase branching in the developing brain.

Excitingly, a final experiment showed that myo-inositol is also able to exert its effects on mature brain tissue samples. The authors want to further explore their findings in future research, writing, “it will be of interest to determine whether myo-inositol’s effects on synapses in the maturing cortex are sustained over time.”