Critical periods in human growth and their relationship to diseases of aging

Abstract

It has long been recognized that there are "critical periods" during mammalian development when exposure to specific environmental stimuli are required in order to elicit the normal development of particular anatomical structures or their normal functioning. The responses of the organism to these stimuli depend on a specific level of anatomical maturation and a state of rapid anatomical and/or functional change. This discussion of critical periods in growth is not confined to the classic definition of a narrow time frame of development during which a particular environmental threshold or limit must exist for normal growth and function to ensue. Using both auxological and epidemiological approaches, we suggest a lifespan perspective which encompasses accumulating and interacting risks that are manifest from prenatal life onward. By understanding the process of growth and development, and by scrutinizing the growth process, early variations that lead to later disease can be identified. Here we review a significant amount of the evidence that links exposure during growth to later morbidity and mortality.The fetus appears to respond to insults during the prenatal period through the process of "programming," which has short-term survival advantages but may have a longterm disadvantage in that it is associated with cardiovascular disease, hypertension, type II diabetes, and later obesity. Low birth weight combined with rapid postnatal growth during infancy also appears to be associated, for instance, with later childhood and adult sequelae in terms of glucose tolerance and obesity. Independent of birth weight, the timing of adiposity rebound during mid-childhood also predicts later obesity. The timing, magnitude, and duration of adolescent growth and maturation are associated with critical body composition changes, including the normal acquisition of body fat and bone mineralization. In particular, the acquisition of appropriate peak bone mass is critical in determining the later risk of osteoporosis.A putative causal mechanism linking early growth variation to later chronic disease risk through telomeric attrition is discussed. The obligatory loss of telomeric DNA with each cell division serves as a mitotic clock and marks the rate of growth and repair processes in the cell. Although much more work is required, existing studies support the notion that telomere shortening is not only a clock of cellular division, but also marks relative growth rate, as well as contributing to common degenerative processes of aging through its impact on cellular senescence. Yrbk Phys Anthropol 45: 159 -184, 2002.

A Life Course Perspective on Body Size and Cardio-metabolic Health

“…The focus in the natural sciences was originally on the requirement of specific environmental stimuli to elicit the normal development and functioning of some body part or system (Cameron and Demerath 2002). In contrast, epidemiology focuses on the environmental exposures that result in anatomical and physiological adaptations that have longterm implications for cardio-metabolic health .…”

A Translational Model of Incomplete Catch‐Up Growth: Early‐Life Hypoxia and the Effect of Physical Activity

“…The traditional research interest in compensatory growth has focused on malnutrition and endocrine disorders 29. However, there is a growing body of research on the long‐term growth effects of hypoxia spurred, in part, by the increasing number of premature babies that survive chronic lung disease of prematurity, and by the recognition that disease or deleterious environmental factors (like hypoxia) occurring during critical periods of growth and development will impact health across the lifespan 30, 31. Earlier theories of whole‐organism, homeostatically controlled regulation of growth32 have, under the weight of experimental evidence given way to a (still rudimentary) model of compensatory growth in which tissue‐ and organ‐specific proliferative capacities, rather than some whole‐body set points, ultimately control the compensatory response to growth‐inhibiting diseases or noxious stimuli.…”

New analytic approaches in auxology

“…A uxologists have always recognized the importance of stature growth as an indicator of child health and wellbeing, but recent associations between growth and health later in life have made understanding the ecology of human development more important than ever (1)(2)(3)(4). It seems obvious that variation in stature growth may be attributed to differences in both genes and environmental exposures (5,6); however, teasing apart their relative effects and assessing interactions can be a significant challenge (6,7).…”