Albertine Donker

Iron Function and Iron Handling from Fetus to Adult 59 2 IRON IS PARAMOUNT FROM FETUS TO ADULT Iron and Growth Human growth occurs in phases; the infancy-childhood-puberty (ICP) model Children are not small adults; they differ in many aspects. Opposite to the steady state of adulthood, childhood is characterized by growth and development. Children going through childhood and adolescence grow tremendously from and average weight of 3.5 kg and 50 cm at birth 52 to an average length of 72 kg and 184 cm for boys and 60 kg and 171 cm for girls at the age of 18 years (children of Dutch origin). 53 Growth and development are dynamic processes, driven by age- and gender- dependent genetic, environmental, dietary, socioeconomic, developmental, behavioral, nutritional, metabolic, biochemical factors, and hormonal factors. 54 Starting at the time of conception, the child transits through different stages and achieves multiple milestones regarding growth and development on the road from fetus to adult. 5,6,55,56 The infancy-childhood-puberty (ICP) model describes this process as three additive and partly superimposed stages that strongly reflect the different hormonal phases involved in human growth. 5,6,54-57 While growth during infancy (0 to 2-3 years) is largely nutrition dependent and closely linked to insulin- growth-factor 1 (IGF1), growth in childhood (2-3 to 11-12 years) is associated with the setting of the growth hormone (GH) – IGF1 axis. During this phase, growth largely depends on the activity of both GH and thyroid hormone. 6,57 The start of puberty (11- 12 years) is a function of the hypothalamic–pituitary–gonadal (HPG) axis maturation, resulting in the production of gonadal steroids that cause the typical growth spurt of adolescense by both a direct effect on bone formation and also by a synergistic effect since sex hormones stimulate GH secretion. 5,6,54-57 The hormonal mechanisms involved in growth and development have to activate physical, psychological and behavioural traits at the right time in the right context as the child transits through the different phases from infant to adult. Adaptive plasticity plays an important role in this timing, in order to cope with environmental challenges. 58 Both organic (e.g. undernutrition) and non-organic (e.g. child abuse) threats may result in a delay in transition from infancy to childhood or from childhood to adolescense, leading to a short stature at reaching adulthood, outside the target