The Impact of Nutrition on Early Brain Development
During brain development, infancy and early childhood are particularly sensitive and characterized by rapid periods of brain growth that coincide with the emergence of nearly all cognitive, behavioral, and social-emotional functions. Moreover, throughout this period, brain’s networks are built and refined through processes that include axon growth, dendritic aborisation, synaptogenesis, and synaptic pruning and myelination. Therefore, providing the appropriate level of nutrition and the nutrients that support these physiological processes is key to guarantee optimal brain development.
Brain organization and plasticity
Ramòn y Cajal (1852–1934) was a pioneer in brain anatomy and basically is the father of modern neuroscience. Using light microscopy and tissue silver staining approaches, Ramon y Cajal generated extremely accurate drawings disclosing the cytoarchitecture of the key cellular elements of the brain, including neurons and glia cells. Based on these observations he proposed 4 hypotheses that shaped modern neuroscience:
the brain is composed of discrete individual signaling elements (neurons);
Information passes from neuron to neuron across gaps (synapses);
Information is polarized.
Moreover, very importantly, he proposed that the brain has not a static structure depending on experience.
The ability of the brain to alter its functional and structural organization as a results of experience is referred to brain plasticity. The brain architecture is also incredibly complex: it is estimated that the human brain contains more than 200 billion neurons and non-neuron cells, 1 quadrillion of connections, 100 km of nerve fibers and 600 km of blood vessels. Such dynamic abilities and complex architecture require outstanding energy needs. Indeed, the adult brain accounting for a mere 2% of body weight is estimated to be responsible for 20% of oxygen (O2) consumption and 20–25% of
As noted earlier, brain development is characterized by massive growth that is due to several physiological processes that hap-pen in overlapping waves. Neurogenesis and neural migrations happening first mainly before birth. And after birth, billions of neurons get connected by synaptogenesis, it is estimated that 700,000 synapses/second are formed. Myelination develops rapidly as well postnatal to enhance neuron communication throughout the entire brain. Moreover, early experience-dependent processes are triggering the plasticity and capacity for adaptation that is the hallmark of brain ability to adapt. We know that there are mainly 2 different factors that influence the brain development. Indeed, molecular processes can be either driven genetically but also influenced by environmental factors like social economic status, social interaction, urbanization, pollution, social mobility, stress and nutrition and food. Concerning the 2 later, it has been shown that the total white and gray matter’s volume of malnourished and non-malnourished children are significantly different suggesting that appropriate level of nutrients is key for proper brain and cognitive development.
Brain has specialized areas and functional net-work to support cognitive tasks through information integration. Indeed, different parts of the brain need to structurally and functionally connect to each other in order to fully integrate different sensory information and make sense out of it. Therefore, proper connectivity is key for proper brain and cognitive functions. High brain connectivity allows complex cognitive processes such as executive functions (EFs). EFs are a set of key mental skills that act as a command center in the brain to get it organize, manage information and control behavior.
Three core EFs are particularly important:
Inhibition: the ability to suppress automatized or predominant responses.
Cognitive fexibility: the ability to switch between cognitive sets or tasks.
Working memory: the ability to organize and mobilize information that is stored in memory and is crucial for planning, for example.
EFs are necessary for life and learning and
also for cognitive, social, and psychological development. Importantly EF are not genetically encoded, and children are not born with EFs, but rather are develop them along time. Therefore, nutrition may play a key role in promoting brain development and being especially important for optimal development of EF. Interestingly EFs involve different part of the brain and relies heavily on brain connectivity. Myelination that wraps around axons, and acts as insulators and lead to a dramatic increase of axonal conduction velocity and therefore information transmission is there-fore, extremely important to promote efficient communication between different brain areas.
Myelination is the process by which oligodendrocytes (OLs), specialized glial cells in the central nervous system (CNS), form a myelin sheath around axons and this is critical for proper brain connectivity. Myelin acts as an insulator by increasing axonal resistance and decreasing capacitance. Myelin sheath thickness, affects the conduction velocity of action potentials: compared to unmyelinated axon,
the velocity of information in a myelinated axon is increased by 20 fold (Fig. 1).
In humans, myelination starts at midgestation, peaks during the first years of life and continues into adulthood.
Interestingly, there is a strong overlap in the emergence of specific cognitive function and the myelination of brain regions and networks subserving these functions. (Dajani/Uddin, Trends Neurosci 2015)
Recent studies suggest that the level and presence of specific nutrient may have significant impact on myelination and eventually on cognitive performance during brain development. Comparing infants that have been either exclusively breast fed or formula fed in an observational study showed first that breast fed infants have higher level of myelination in some brain areas and performed better in specific cognitive task compared to formula fed infants. Moreover, these observational data show positive associations between lev- el of some nutrients present in breast milk and formula and myelination, like sphingomyelin DHA/ARA, choline, Vit B9, Vit B12 and iron
(Schneider et al., eNeuro 2019). Furthermore, we showed that the combination of these nu- trients enhances de novo myelination in vitro (Hauser et al., Nutritional Neuroscience 2019).
While the brain is, is mostly composed by water (77-78%), the brain is one of the rich- est in lipids (10-12%) among the body organs. Moreover, it has been estimated that there are around 100,000 different lipids in the brain, with different structures (Piomelli et al., Nat Rev. Neurosc. 2007). Lipids have three main functions: first they affect the cytoarchi- tecture of cells, organelles, and subcellular structures such as synapses, second they can act like signaling molecules, and finally lipids are used as a source of energy through beta-oxidation. Some of the lipids, called polar lipids, are especially important for brain development including synapse and myelin. Indeed, polar lipids such as sphingomyelin, and phospholipids are key to build brain connectivity and promote fast and efficient brain communication.
The first 1000 days of life are a rapid and dynamic period of brain development.
Brain connectivity is at the heart of high cognitive functions.
Myelination is key to promote proper brain connectivity, it accelerates signal transmission between cells and thus supports brain communication.
Myelin is mainly built during the first years of life and is modulated by specific nutrients.
Polar lipids play an important role in brain, myelin and cognitive development, particularly phospholipids and sphingomyelin.
Sphingomyelin is highly concentrated in the brain and naturally present in human milk.