Child growth: Plasticity and environment

Abstract

The evolution of the human growth curve is characterized primarily by an attenuation of childhood, followed by a relatively brief, intense adolescent spurt. The primary selective pressure underlying this evolutionary trend is not certain; however, the extended period of biological immaturity relative to other mammalian species is associated with high environmental sensitivity and growth plasticity. The sensitivity of human growth to the environment is demonstrated both by the processes of stunting and wasting in response to poor nutrition and of compensatory growth during environmental improvements following episodes of stress. There are many common environmental influences on growth of children and adolescents. Known environmental factors that influence growth, body size, and body composition of children post-natally include nutrition, infection, psychosocial stress, food contaminants, pollution, and hypoxia. Most of these factors are conditioned historically, culturally, and politically by poverty and socio-economic status.

Adolescent growth is sensitive to nutritional deficit and surfeit, although the impacts of infection are of much lesser importance, because the immune system has matured and adaptive immunity is largely in place by adolescence. The two exceptions are HIV-1 and Heliobacter pylori infections. Exposure of adolescents to environmental pollutants also influences pubertal development in differing ways, while many high altitude populations experience delayed sexual maturation. In the latter case, the importance of hypoxia to delayed skeletal and sexual maturation is low relative to nutritional stress. Known impacts of psychological stress on pubertal growth include advanced pubertal growth and earlier age at menarche.