INTRODUCTION

The human growth pattern is characterized by rapid growth in infancy, followed by an extensive period of childhood, and a relatively intense adolescent spurt (seeChapter 22 of this volume). The extended period of biological immaturity relative to other mammalian species is associated with high environmental sensitivity and growth plasticity (Johnston, 1998), illustrated by the processes of stunting and wasting in response to poor nutrition and infection (Waterlow, 1988) and of catch-up growth during environmental improvements following episodes of environmental stress (Prader et al., 1963).

Known environmental factors that influence growth, body size, and body composition of children postnatally include nutrition (Barclay and Weaver, 2006), infection (Bhan et al., 2001), interactions between the two (Ruel, 2001), psychosocial stress (Powell et al., 1967), food contaminants (Gong et al., 2004), pollution (Schell, 1991a), and hypoxia (Frisancho, 1977). Most of these factors are conditioned by poverty and socioeconomic status (Martorell et al., 1988). They are also conditioned historically, culturally, and politically (Ulijaszek, 2006), interacting with each other, but also with individual genotypes in the production of growth, body size, and body composition.

Diet, nutrition, disease, hypoxia, pollution, contamination, behavioral toxicants, deprivation, and psychosocial stress can be clustered as proximate environmental agents that can influence growth (Figure 23.1). They vary in importance according to circumstance and the age and stage in infancy, childhood, and adolescence. Culture, society, behavior, socioeconomic status, poverty, and political economy can also be clustered as structurally powerful but distal agents in the production of growth and body size outcomes, at all ages and stages of childhood and adolescence.