technical brief 4- nutrition and brain development in early life

8/3/2019 Technical Brief 4- Nutrition and Brain Development in Early Life

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Summary o main points

1) Adequate nutrition during pregnancy

and the rst two years is necessary

or normal brain development, laying

the oundation or uture cognitive

and social ability, school success, and

productivity.

2) Undernutrition may inuence

brain development both directly and

indirectly. Nutrient deciencies directly aect

neurodevelopmental processes. Undernutrition aects childrens

experiences and behavior, which in

turn inuence brain development.

3) Priority should be given to the

prevention o severe acute malnutrition

(very low weight or height), chronic

malnutrition (as evidenced by

intrauterine growth retardation and

linear growth retardation or stunting),

iron-deciency anemia, and iodine

deciency. There is strong evidence

that they aect the developing

brain and compromise long-termcognitive, motor, and socio-emotional

development.

4) There is growing evidence that

breasteeding promotion, pre- and

post-natal multiple micronutrient

supplementation, pre- and post-natal

supplementation with essential atty

acids, and ortied ood supplements

provided during pregnancy and to the

child rom 6 to 24 months o age can

have benecial eects on early child

development. Few data exist on the

long-term eects o these interventions.

5) An integrated approach is likely to be

most eective or promoting optimal

child development, i.e., interventions

that combine improved nutrition with

other strategies such as enhancing the

home environment and the quality o

caregiver-child interaction.

Adequate nutrition or pregnant mothersand inants is necessary or normal braindevelopment. Pregnancy and inancy areimportant periods or the ormation o thebrain, laying the oundation or the devel-opment o cognitive, motor, and socio-emotional skills throughout childhoodand adulthood. Children with restricteddevelopment o these skills during early

lie are at risk or later neuropsychologi-cal problems, poor school achievement,early school drop out, low-skilled employ-ment, and poor care o their own children,thus contributing to the intergenerationaltransmission o poverty.

Many mothers and children in both low-and high-income countries are at riskor moderate undernutrition. Decreasedetal nutrition can be caused by poverty,maternal dieting, teenage pregnancy, anduterine vascular problems. Inadequate

Insight

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nutrition during inancy can result rompoor inant eeding practices and/or thelack o physical or economic access to nu-tritious oods to complement breasteed-ing. Many children worldwide ace theseconditions. For example, in 2010, 925 mil-lion people in the world experienced oodinsecurity,1 and birth rates among teenagegirls (age 15-19) ranged rom an average

o 103 per 1000 women in the lowest-income countries to 21 per 1000 women inhigher-income countries.2

An estimated 200 million children underage ve in low- and middle-income coun-tries are at risk o ailing to reach theirdevelopmental potential in cognitive, mo-tor, and socio-emotional abilities, partlydue to undernutrition3 (see Figure 1). Tistechnical brie reviews the evidence or theeect o undernutrition rom conceptionthrough the rst two years o lie on brain

Nutrition and brain

development in early lie

A&T Technica

Issue 4, January

Elizabeth Prado and Kathryn Dewey

Figure 1. Estimated percentage o children under 5 ailing to ulll their

developmental potential by country in 2004. Grantham-McGregor et al. (2007)

Missing or excluded

0-20%

20-40%

40-60%

60% and above


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Box 1. Brain development and the

childs experiences and environment

The brain develops its structural orm and

unctional capacity through dynamic bi-

directional inuences between biological

actors (such as nutrition), genetic actors,

the childs experiences, and the childs

own behavior.

Experience can aect brain development

in at least two ways. Certain

developmental processes have been

called experience-expectant because

the brain relies on them or normal

development.104 For example, the brainexpects visual input through the optic

nerve or the normal development o the

visual cortex.104

The absence o these expected

experiences impairs the

neurodevelopmental processes that

depend on them. These experience-

development and on both the short-termand long-term development o cogni-tive, motor, and socio-emotional skills.Appendix 1 denes these three domainso development and provides exampleso tests that are commonly used to assess

them in inants and older children.

Mechanisms or the efect o inadequate

nutrition on brain development

Undernutrition may inuence braindevelopment by directly aecting brainprocesses or indirectly by aecting chil-drens experiences and behavior. First,inadequate availability o nutrients duringgestation and inancy aects the structuraand unctional development o the brain.Gestation and inancy are periods orapid brain development. Te neural tubebegins to orm 16 days aer conceptionand within 7 months takes on a orm thatresembles the adult brain.4

Nutrients are required or many o thebiological processes that drive this trans-ormation. For example, they are neededor the creation o new neurons. A neuron

nsight

Early child growth

2

Figure 2. Structure o a neuron

expectant processes have been

distinguished rom experience-dependent processes.104 The latter

reers to the way the brain develops in

response to an individuals experiences

and acquired skills. For example, a

neuroimaging study demonstrated that

the rear hippocampus, a part o the brain

that underlies spatial memory, was larger

in London taxi drivers than age-matched

comparison subjects, presumably due to

their memory o the complex layout o

the London city streets.105

These experience-dependant processes

enable individuals to adapt to and thrivein their specic culture and environment.

Whereas experience-expectant processes

are more likely to occur early in lie,

experience-dependent processes continue

throughout lie, suggesting that neuronal

connections can re-organize in response to

experiences and that new neuronal growth

beyond inancy is possible.

The eects o undernutrition must be

understood in the context o thesemultiple biological and environmental

inuences as well as the interactions

between them. For example, low birth

weight inants born into amilies with

high socio-economic status are at lower

risk or poor developmental outcomes

than those born into disadvantaged

environments.19 Thus, protective

environmental actors can, in some

cases, buer the potential negative

eects o undernutrition. Conversely,

undernourished children rom

disadvantaged homes where protective

actors are lacking may show moreresponse to nutrition (and other orms o)

interventions.

Moreover, several studies have ound that

nutrition and psychosocial stimulation

together result in greater improvements

in child development than either

intervention alone.106

Neuron: one o the cells that constitutes nervous

tissue that is able to transmit and receive nervous

impulses, also called a nerve cell

Axon: a long projection o the neuron that

conducts nerve impulses away rom the nerve cell

body

Dendrite: a branching projection o the neuron

that conducts nerve impulses toward the nerve

cell body

Synapse: the place between nerve cells through

which nerve impulses pass rom one neuron to

another; this process is called neurotransmission

Neurotransmitter: a substance that transmits

nerve impulses across a synapse, or example,

acetylcholine and dopamine

Myelin: a sot white material o lipid and protein

that covers axons to insulate and accelerate

nerve impulses


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A&T Technica

Issue 4, January

is pictured in Figure 2. Nutrients are also

needed or the growth o axons and den-drites (also see Figure 2), the ormation osynapses, and the covering o axons withmyelin, which is atty matter that acceler-ates the speed o nerve impulses travelingrom one cell to another. Inadequate avail-ability o energy, protein, atty acids, andmicronutrients impairs these neurodevel-opmental processes.5 Tese nutrients arealso important or brain unction through-out childhood and adulthood, or example,or the maintenance o brain tissue andor neurotransmitter synthesis.6, 7 Most

o the evidence or these direct eectson the brain comes rom animal modelso nutrient deciency. A recent paperreported that moderate (30%) reductionin maternal ood intake during the rsthal o pregnancy in baboons negativelyaected etal brain development eventhough etal weight was not aected andmaternal weight was only slightly aected.Tis suggests that the brain can be aectedby moderate undernutrition during thisperiod even in the absence o overt signso undernutrition.8

Second, nutrition may aect braindevelopment indirectly through inu-encing childrens experiences. Childrensexperiences and environment are criticalactors in the development o the brainand the development o cognitive, motor,and socio-emotional abilities (see Box 1).

Undernutrition aects physical growth,

motor development, and physical activity,which in turn may inuence brain devel-opment through both caregiver behaviorand child interaction with the environ-ment9 (see Figure 3). Tat is, caregiversmay treat children who are small or theirage as younger than they actually are,which would result in less appropriatestimulation and thereore altered braindevelopment in an undernourished child.Undernourished children may also berequently ill and thereore ussy, irritable,and withdrawn. Tis could also lead care-

givers to treat them more negatively thanthey would treat a happy, healthy child.Additionally, lower activity levels wouldlimit the undernourished childs explora-tion o the environment and initiation ocaregiver interactions, which could alsolead to poor brain development. Someevidence suggests that these mechanismsmay contribute to delayed motor and cog-nitive development in inants and childrenwith protein-energy malnutrition10 andiron-deciency anemia.11, 12

An implication o the model presented inFigure 3 is that interventions targeting boththe child and the caregiver can operate atmultiple levels.13 For example, an inter-

vention that improves the childs nutrientintake may improve the childs physicalgrowth, activity levels, and behavior. Tiswould then enable the child to elicit and

receive age-appropriate care and positiveinteraction rom the caregiver and improvecognitive development. On the other hand,an intervention that improves the caregiv-ers sensitivity and appropriate response tochildrens cues, or example or hunger and

satiety, may improve the nutritional statuso the child. Tis would eed back into thechilds behavior and ability to elicit appro-priate interaction rom the caregiver. Tus,interventions aimed at either the child orthe caregiver may have cumulative andcascading eects over time.

Long-term consequences o

undernutrition in early lie

Severe acute malnutrition (low weight or

height) in early lie can have long-lastingconsequences on brain development evenaer nutritional rehabilitation. Many stud-ies have compared school-age childrenwho had suered rom an episode o severeacute malnutrition in the rst ew years olie to matched controls or siblings whohad not. Tese studies generally ound thatthose who had suered rom early mal-nutrition had poorer IQ levels, cognitiveunction, and school achievement, as wellas greater behavioral problems.14 o treatmalnourished children, WHO recom-

mends providing structured activities topromote cognitive development in additionto nutrition and health care. wo studiesin Uganda and Bangladesh have shownthat providing such stimulation can helpimprove mental and motor development inseverely malnourished inants.15

Chronic malnutrition, as measured bypoor physical growth, is also associ-ated with reduced cognitive and motordevelopment. From the rst year o liethrough school age, children who are

short or their age (stunted) or under-weight or their age perorm more poorlythan their normal-sized peers (on aver-age) in cognitive and motor tasks andin school achievement.16 Longitudinalstudies have also consistently shown thatchildren who had been stunted (heightor age < -2 SD below norm values) in

Figure 3. Potential mechanisms or the efect o nutrient deciency on childrens

cognitive, motor, and socio-emotional development

Adapted rom Levitsky & Barnes (1972) and Pollitt (1993)

Caregiver

behavior, parent-

child interaction

Brain

development and

unction

Nutritional

status

Cognitive, motor, and

socio-emotional

development

Level o child

interaction with the

environment

Physical

growth

Physical

activity

Illness


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the rst 2 years o lie continued to showdecits in cognition and school achieve-ment rom age 5 years to adolescence.16Tus, chronic undernutrition in early lieseems to have long-lasting consequencesor brain development.

Growth altering can begin beore birth,and the evidence indicates that being bornsmall or gestational age is associated withmild to moderately low perormance inschool during childhood and adolescence,and with lower psychological and intel-lectual perormance in young adulthood.17However, studies that have examined therelationship between low birth weight (

technical brief 4- nutrition and brain development in early life

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