Nutrition

Adequate nutrition is necessary for normal brain development. Nutrition is especially important during pregnancy and infancy, which are crucial periods for the formation of the brain, laying the foundation for the development of cognitive, motor, and socio-emotional skills throughout childhood and adulthood. Thus, nutritional deficiencies during pregnancy and infancy are likely to affect cognition, behavior, and productivity throughout the school years and adulthood. Focusing on this early period for the prevention of nutrient deficiencies may have long-term and widespread benefits for individuals and societies.

Role of Nutrients in Brain Development

Approximately 22 days after conception, the neural plate begins to fold inward, forming the neural tube, which eventually becomes the brain and spinal cord. Adequate nutrition is necessary from the beginning, with the formation of the neural plate and neural tube affected by nutrients such as folic acid, copper, and vitamin A. Seven weeks after conception, cell division begins within the neural tube, creating nerve cells (neurons) and glial cells (cells that support neurons). After a neuron is created, it migrates to its place in the brain, where it then grows axons and dendrites projecting out from its cell body. These branching projections make connections with other cells, called synapses, through which nerve signals travel from one cell to another. These neurodevelopmental processes begin during gestation and continue throughout infancy.

Groups of neurons form pathways, which are refined through the programmed elimination of cells and connections. About half of all the cells that are produced in the brain are subsequently eliminated throughout childhood and adolescence. Synapses are also overproduced and then selectively eliminated. Some of this refining of neural pathways depends on the child's experience, or in other words, input from the child's environment. Cells and connections that are activated are retained and strengthened while those that are not used are eliminated. This is thought to be one of the primary mechanisms of brain plasticity, allowing the brain to organize itself to adapt to the environment and reorganize itself to recover from injury during development.

Although the necessity of nutrients for brain development is evident, the extent to which nutrient deprivation during gestation and infancy results in long-term effects on brain function in free-living human populations is not yet clear. The actual impact depends on several factors, including 1) the child's experience and input from the environment, 2) the timing of nutrient deprivation, 3) the degree of nutrient deficiency, and 4) the possibility of recovery.

Experience and input from the environment

Adequate nutrition can be considered an aspect of the environment that is expected by the brain for normal development. An environment with poor quality and a variety of sensory and social input. impairs some of the same neurodevelopmental processes as nutrient deprivation during early development.

Timing of nutrient deprivation or supplementation

Nutrient deficiency is more likely to impair brain development if the deficiency occurs during a time period when the need for that nutrient for neurodevelopment is high. Various nutrients are necessary for specific neurodevelopmental processes. Each process occurs in different, overlapping time periods in different brain areas. Future studies that examine precise hypotheses related to specific nutrients, neurodevelopmental processes, timing, and brain areas are needed to clarify the relationship between nutrition and brain development and its mechanisms.

Degree of nutrient deficiency

Much evidence shows that brain development may be compromised when nutrient deficiency is severe to moderate but spared when deficiency is mild to moderate. A number of homeostatic mechanisms protect the developing fetus and the developing brain from nutrient deficiency to a certain degree. For example, in the case of placental insufficiency, when insufficient nutrients and oxygen are available, fetal cardiac output is redistributed such that blood flow to the peripheral tissues decreases and blood flow to the brain, adrenal glands, and heart increases. This leads to brain sparing, or the sparing of brain growth even when overall fetal growth is reduced. Another mechanism that protects the fetus from iron deficiency to a certain degree is the increased transfer of iron across the placenta as maternal levels decrease. For each nutrient, there is likely to be a threshold at which deficiency results in impairment for the child. Exactly where this line is drawn is an important question that must be answered for each nutrient individually. In summary, greater severity of nutritional deficiency increases both the likelihood of negative effects on brain development and the likelihood of positively responding to nutritional supplementation.

Possibility of recovery

The brain's potential for recovery from early damage has been widely studied in the context of neurological injury during development. When a certain part of the brain is damaged during early life, recovery happens in three ways, depending on the timing of the injury and subsequent experience. First, there are changes in the organization of the remaining intact circuits in the brain that were left uninjured, involving the generation of new synapses in existing pathways. Second, new circuitry that did not exist before the injury develops. Third, neurons and glia are generated to replace the injured neurons and glia. In the case of brain alterations caused by nutrient deficiency, recovery is plausible if nutrients become available during the time that the affected growth process is still occurring. In addition to nutrient repletion, enhanced sensory, linguistic, and social interactions may also facilitate recovery.

Data from the study of undernourished Korean orphans under the age of 2, and children experiencing nutrient deprivation in utero but adequate nutrition and health care thereafter both suggest that improved conditions earlier rather than later in childhood provide a greater benefit and that some, but not all, of the negative effects of early undernutrition on brain development, can be reversed through subsequent improvement in nutrition, health care, and enriched environments.

Conclusion

When a child is adequately nourished from conception through infancy, the essential energy, protein, fatty acids, and micronutrients necessary for brain development are available during this foundational period, establishing the basis for lifetime brain function. The well-nourished child is also better able to interact with his or her caregivers and environment in a way that provides the experiences necessary for optimal brain development. Children who are not adequately nourished are at risk for failing to reach their developmental potential in cognitive, motor, and socioemotional abilities. These abilities are strongly linked to academic achievement and economic productivity. Therefore, preventing or reversing developmental losses in early childhood is crucial for fostering economic development in low- and middle-income areas as well as reducing economic disparities in high-income areas.

The following interventions are examples of strategies that have been found to be effective in preventing or improving these conditions: salt iodization to prevent iodine deficiency, provision of iron via home fortification (e.g., with micronutrient powders) to prevent IDA, and educational interventions in conjunction with food supplementation in food-insecure populations. Strategies to promote exclusive breastfeeding during the first 6 months of life and continued breastfeeding thereafter, along with adequate complementary feeding, are also likely to improve cognitive development.

The following interventions are promising for preventing developmental loss: supplementation with iron and folic acid and/or multiple micronutrients during pregnancy, provision of multiple micronutrients (in addition to iron) during infancy, supplementation with essential fatty acids during pregnancy and infancy, fortified food supplements provided during pregnancy and infancy. Interventions to improve the home environment and the quality of caregiver-infant interaction are also recommended to complement and enhance the effect of improved nutrition.

Integrated strategies targeting multiple risk factors, including nutrition, are necessary to reduce inequality and promote cognitive, motor, and socioemotional development in disadvantaged children worldwide, ensuring that all children have the opportunity to fulfill their developmental potential.