By Michael Georgieff, MD, FAAP
Every child has a right to optimal cognitive, social and emotional behavioral development. Since behavior is the efferent expression of the brain, medical stakeholders — including pediatricians — have a stake in ensuring brain health across the lifespan. Brain health begins prenatally and likely even pre-conceptionally, implying that the first point of education/prevention may be in non-pregnant women of child-bearing age. Many of the principles of developmental (i.e., fetal) origins of adult metabolic health (obesity, type 2 diabetes, hypertension) apply to adult health (e.g., depression, anxiety, schizophrenia). Thus, the metabolic and structural brain development that occurs early in life provides a scaffold for complex adult mental capabilities. New brain/behavior assessment tools have allowed identification of important environmental events that promote or pose risks to normal brain development and identify critical and sensitive periods for these environmental effects.
The First 1,000 Days: A Critical Period
From a policy perspective, a greater emphasis has been recently placed on the first 1,000 days because of recognition of the enormous potential for doing good (and harm) in this period of rapid brain growth and development. The brain is not a homogenous organ. Rather, it contains multiple regions, all on different developmental trajectories. While some areas display broad trajectories across childhood, a remarkably large amount of brain development takes place before the age of 3 years. The trajectories of major neural systems such as the hippocampus, the dopaminergic neurotransmitter system and myelination begin prenatally. Thus, the timing of interventions is as important as the nature of the interventions. While the young brain is very vulnerable, it is also highly plastic. Nevertheless, vulnerability outweighs plasticity and thus the wisest policy is prevention.
Environmental factors that play a particularly important role in early brain development influence include nutrition, avoidance of toxic stress, and social enrichment. The mechanisms by which each of these factors work are well understood from the molecular to the behavioral level and include epigenetic modification of important genes that regulate behavior and stress responses across the lifespan.
Effect of Nutrition and Diet
Nutrients show a particularly early time window of effect (i.e., the first 1000 days). Certain nutrients have a greater influence early on. These include protein, calories, long-chain poly-unsaturated fatty acids, iron, zinc, folate, iodine, copper, vitamin A, vitamins B6 and 12, and choline. Each demonstrates a sensitive or critical period, where if the nutrient is in deficit, long-term brain and behavioral changes occur. The fetus and newborn can be somewhat protected from certain maternal nutrient deficits by active placental or mammary gland transport mechanisms. In contrast, a 1- to 3-year-old is particularly vulnerable because they are at the mercy of their parent’s diet. From a policy standpoint, disparities in access to quality food for pre-conceptional, pregnant and lactating women and their offspring from 1 to 3 years need to be addressed. From a practice standpoint, obtaining dietary histories and active teaching of parents (often through RDs) are crucial.
Impact of Toxic Stress
Toxic stress, which is characteristic of poverty, abuse, and unstable homes, has direct and collateral effects on the developing brain. Direct effects on the developing brain include activation of endocrine (e.g., cortisol) and immune (e.g., pro-inflammatory cytokines) systems with resultant truncation of neuronal dendrites and compromise of cerebral white matter. The effects of toxic stress occur on a broader timescale than nutrient effects. Maternal stress is co-morbid with poverty, anxiety and depression. While the placenta can partially protect the fetus, brain effects are still evident. From a policy standpoint, reduction of stress must begin pre-conceptionally, continuing throughout pregnancy and postnatally. Postpartum depression screening, community partnerships, home nurse visits and other early intervention programs and services can help minimize toxic stress.
Influence of Social Connections
Early social enrichment, especially programs to support attachment and language development, are key. The latter half of the first year is a sensitive period for promoting secure attachment. Infants are particularly responsive to interventions that improve the quality of parenting — effects that have long-term cognitive-academic benefits. Language exposure through contact with humans (i.e., not projected images) demonstrates a sensitive period between 8 to 14 months. Social enrichment has a later and longer sensitive period than nutrients. From a policy standpoint, a shift to earlier assessment and support (before the age of 3 years) is crucial. It is important to emphasize that early and late intervention are not mutually exclusive, but that the task of altering the brain’s trajectory gets more difficult with increasing age.
