Elsevier

The Lancet

Volume 369, Issue 9556, 13–19 January 2007, Pages 145-157
The Lancet

Series
Child development: risk factors for adverse outcomes in developing countries

https://doi.org/10.1016/S0140-6736(07)60076-2Get rights and content

Summary

Poverty and associated health, nutrition, and social factors prevent at least 200 million children in developing countries from attaining their developmental potential. We review the evidence linking compromised development with modifiable biological and psychosocial risks encountered by children from birth to 5 years of age. We identify four key risk factors where the need for intervention is urgent: stunting, inadequate cognitive stimulation, iodine deficiency, and iron deficiency anaemia. The evidence is also sufficient to warrant interventions for malaria, intrauterine growth restriction, maternal depression, exposure to violence, and exposure to heavy metals. We discuss the research needed to clarify the effect of other potential risk factors on child development. The prevalence of the risk factors and their effect on development and human potential are substantial. Furthermore, risks often occur together or cumulatively, with concomitant increased adverse effects on the development of the world's poorest children.

Introduction

The first paper in this series showed that more than 200 million children under 5 years of age in developing countries are not fulfilling their developmental potential.1 In this paper, we review biological and psychosocial risk factors that contribute to these adverse outcomes. We use the term risk factor to refer to biological and psychosocial hazards that can compromise development.

Figure 1 shows pathways from poverty to poor child development. Development consists of linked domains of sensori-motor, cognitive-language, and social-emotional function.2 Poverty and the socio-cultural context increase young children's exposure to biological and psychosocial risks that affect development through changes in brain structure and function, and behavioural changes. Although we consider risks individually in this paper, children are frequently exposed to multiple and cumulative risks.3 As risks accumulate, development is increasingly compromised. Data from Guatemala4 (figure 2) show a linear decrease in adolescents' school achievement and cognition with an increase in risk factors encountered by age 3 years.

As discussed in the first paper in this series,1 children's ability on school entry is an important component in determining their progress in school. We therefore focus on risk factors in early childhood that affect readiness for school and subsequent school performance. School readiness is affected by cognitive ability, social-emotional competence (affects classroom behaviour and peer relations), and sensori-motor development (affects critical skills such as writing).5

We first review the effect on development of individual biological and psychosocial risk factors. Based on this review we identify key risk factors which should be the main focus for interventions. The remaining risks are grouped into those where the evidence is sufficient to warrant implementation of interventions and those where additional information is needed.

Section snippets

Intrauterine growth restriction

Intrauterine growth restriction indicates constraints in fetal nutrition during a crucial period for brain development. In developing countries, intrauterine growth restriction is mainly due to poor maternal nutrition and infections. This review is restricted to infants at term with low birthweight (birthweight <2500 g; ≥37 weeks' gestation), which makes up 11% of births in developing countries.10

At age 12 months, low-birthweight infants with intrauterine growth restriction in Brazil had lower

Psychosocial risk factors

Research from developed countries has identified three aspects of parenting that are consistently related to young children's cognitive and social-emotional competence: cognitive stimulation, caregiver sensitivity and responsiveness to the child, and caregiver affect (emotional warmth or rejection of child).112 The effect of these factors is sensitive to contextual factors such as poverty, cultural values and practices.3 Nonetheless, these child-rearing dimensions affect children from developed

Developmental risk factors

In table 3 we present those risk factors where the existing evidence is strong enough to recommend implementation of strategies to reduce or prevent the effect of these risks on young children's development. We base our conclusions on the consistency of the evidence, the numbers of children affected, and the size of the effect on development. The first four risk factors in table 3 each affect at least 20–25% of children in developing countries, and the evidence for their effect on development

Research implications

The evidence for the developmental consequences of the risks listed in table 3 is substantial, although questions remain. Future research should investigate mechanisms, the importance of timing, duration, and severity of exposure, and reversibility of effects. Additionally, most of the research concerns the effect on developmental levels in early childhood and on later cognitive outcomes, and most of the effect sizes shown in table 3 relate to cognitive deficits. However social-emotional

Conclusions

Currently available evidence shows that specific risks encountered by young children in developing countries compromise their development. The numbers of children affected are enormous; in some countries 40–50% of children under 5 years are stunted. The risks described in this paper, all of which are modifiable, prevent millions of children from benefiting fully from the educational opportunities to which they have access. Education is vital for both individuals and nations to emerge from

Search strategy and selection criteria

We included only risk factors that could be addressed by interventions or public policy. We focused on risk factors to which children are exposed from birth (and in utero) up to 5 years of age and that affect large numbers of young children in developing countries.

Both associational studies and studies that allow greater inference of causality (eg, intervention studies) were reviewed. We used multiple search terms to search relevant databases (eg, PubMed, PsychInfo). We also reviewed

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