Long-term longitudinal studies and implications for the development of an international growth reference for children and adolescents

This report reviews 21 long-term, longitudinal studies of physical growth as background for the International Growth Reference for Children and Adolescents (IGRCA) initiative. Longitudinal studies form a large share of the evidence base for much of the knowledge on normal growth of children, and the collective experience from their long history is instructive relative to future studies that may result from the IGRCA. Many of the studies were initiated in the 1920s and 1930s when some current techniques, such as the use of doubly labeled water for the assessment of energy expenditure or dual-energy x-ray absorptiometry (DEXA) for the study of body composition, were not available. Nevertheless, many well-established protocols for anthropometry and for assessment of somatic maturation are as important today as they were in the past. With some important exceptions, few of the studies collected detailed information on dietary intake or child health and illness. Genetic or familial factors were limited as well. Many lessons can be drawn from the past experience with prominent longitudinal growth studies. Nevertheless, the exact design, sampling, and measurement protocols chosen for future growth studies emanating from the IGRCA effort must be carefully linked to specific research questions and the explicit purposes for which the resultant data will be used.