Elsevier

The Lancet

Volume 378, Issue 9799, 8–14 October 2011, Pages 1325-1338
The Lancet

Series
Inequality in early childhood: risk and protective factors for early child development

https://doi.org/10.1016/S0140-6736(11)60555-2Get rights and content

Summary

Inequality between and within populations has origins in adverse early experiences. Developmental neuroscience shows how early biological and psychosocial experiences affect brain development. We previously identified inadequate cognitive stimulation, stunting, iodine deficiency, and iron-deficiency anaemia as key risks that prevent millions of young children from attaining their developmental potential. Recent research emphasises the importance of these risks, strengthens the evidence for other risk factors including intrauterine growth restriction, malaria, lead exposure, HIV infection, maternal depression, institutionalisation, and exposure to societal violence, and identifies protective factors such as breastfeeding and maternal education. Evidence on risks resulting from prenatal maternal nutrition, maternal stress, and families affected with HIV is emerging. Interventions are urgently needed to reduce children's risk exposure and to promote development in affected children. Our goal is to provide information to help the setting of priorities for early child development programmes and policies to benefit the world's poorest children and reduce persistent inequalities.

Introduction

In a 2007 Series in The Lancet we estimated that more than 200 million children younger than 5 years from low-income and middle-income countries were not attaining their developmental potential, primarily because of poverty, nutritional deficiencies, and inadequate learning opportunities.1, 2 Economic recession and climate change will probably increase the number of children affected.3, 4 Biological and psychosocial risk factors associated with poverty lead to inequalities in early child development, which undermine educational attainment and adult productivity, thereby perpetuating the poverty cycle.5 In this Series, we review new evidence on the mechanisms and causes of developmental inequality and economic implications and strategies to promote early child development. In this report we summarise evidence from developmental neuroscience on how experiences in early life affect the structure and functioning of the brain, and subsequent child development. We review evidence on risks and protective factors for development, updating evidence on previously identified risks (panel 1),1 and highlight risks not previously identified. Our focus is on modifiable risks that affect large numbers of children younger than 5 years in low-income and middle-income countries.

Key messages

  • Exposure to biological and psychosocial risks affects the developing brain and compromises the development of children

  • Inequalities in child development begin prenatally and in the first years of life

  • With cumulative exposure to developmental risks, disparities widen and trajectories become more firmly established

  • Reducing inequalities requires early integrated interventions that target the many risks to which children in a particular setting are exposed

  • The most effective and cost-efficient time to prevent inequalities is early in life before trajectories have been firmly established

  • Action or lack of action will have lifetime consequences for adult functioning, for the care of the next generation, and for the wellbeing of societies

Section snippets

Risk, stress, and brain development

The foundations of brain architecture are laid down early in life through dynamic interactions of genetic, biological, and psychosocial influences, and child behaviour. Biological and psychosocial influences affect the timing and pattern of genetic expression, which can alter brain structure and function,6 and behaviour.7 Through bidirectional effects, children's behaviour affects brain development directly and by modifying the effects of biological and psychosocial influences.8

Childhood risks

Maternal nutrition

There is maternal undernutrition (body-mass index <18·5 kg/m2) in 10–19% of women in most low-income and middle-income countries, with higher prevalence in sub-Saharan Africa and south Asia. Maternal pre-pregnancy body-mass index and weight gain during pregnancy predict birthweight, and balanced energy–protein supplementation benefits birthweight and reduces births that are small for their gestational age. However, there is little information on associations between maternal nutritional status

Infant and child nutrition

In low-income and middle-income countries, 16% of births are LBW with rates as great as 27% in south Asia, most of these births being intrauterine growth restriction (IUGR)-LBW. A Guatemalan study28 showed associations between birth size adjusted for gestational age and development at 6 and 24 months, supporting earlier conclusions that IUGR is associated with early developmental risk.1

Evidence for longer-term effects of IUGR is less consistent. Significant effects of birthweight unadjusted for

Infectious diseases

Previous evidence of the effect of diarrhoea on child development was inconclusive. Additional studies in Brazil noted associations between the number of diarrhoea episodes before age 2 years, late school entry,55 deficits in semantic fluency, and verbal learning,56 adjusting for socioeconomic status and present nutritional status. Adjustment for stunting before age 2 attenuates the association between diarrhoea and intellectual performance.29 A multicountry study showed that each episode of

Environmental toxins

Children might be exposed to environmental toxins prenatally—through maternal exposure—and postnatally—through breastmilk, food, water, house dust, or soil. We previously identified lead as a risk factor for young children from low-income and middle-income countries.1 Recent evidence from Poland has shown that prenatal exposure to very low concentrations of lead (<5 μg/dL) can result in poor mental development in young children.80

Evidence from low-income and middle-income countries on the

Disabilities

In a survey of disability in 18 low-income and middle-income countries, 23% of children aged 2–9 years had, or were at risk for, disabilities. Besides being a marker for compromised development, childhood disabilities can reduce access to school or health services, and increase risk of caregiver stress and depression89, 90 (webappendix p 40). Studies from south Asia suggest that learning and social integration is also limited by social stigma89 and overprotection by parents.90

Although

Early learning and caregiver–child interaction

Learning opportunities that facilitate early cognitive development include caregiver activities and materials that promote age-appropriate language and problem-solving skills. Caregiver–child interactions that facilitate early social–emotional development include caregiver positive emotionality, sensitivity, and responsiveness toward the child, and avoidance of harsh physical punishment. Lack of early learning opportunities and appropriate caregiver–child interactions contribute to loss of

Protective influences

Protective factors attenuate adverse consequences of risk factors. Although risk and protective factors are conceptually distinct, many protective factors are the inverse of risk factors (eg, insecure attachment vs secure attachment). Studies in high-income countries have identified biological, psychosocial, and behavioural protective factors for young children, but there are few studies from low-income and middle-income countries. The protective effects of breastfeeding and early cognitive and

Conclusions

Major advances in neuroscience show how exposure to biological and psychosocial risk factors, prenatally and during early childhood, affects brain structure and function and compromises children's development and subsequent developmental trajectory. We summarise in figure 2 how risk and protective factors encountered before age 5 years compromise children's development. The greater the exposure to cumulative risks the greater the inequality, suggesting that early interventions that prevent

Search strategy and selection criteria

We searched relevant databases (eg, PubMed, PsychInfo, Cochrane Review) with multiple search terms for articles published since 2005. The search terms we used were linked to each of the risk or protective factors: “child development”, “child behaviour”, “infant behaviour”, “cognition”, “social”, “emotional”, “intelligence”, “language”, and “motor development”. We searched citation lists of articles retrieved and review articles published since the last Series for further references. We included

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