Hormonal Determinants and Disorders of Peak Bone Mass in Children 1

Abstract

PEAK BONE MASS can be defined as the maximal bone mineral density that is accrued during growth and development plus subsequent consolidation that continues during early adulthood (1). The precise age at which peak bone mineral density is acquired is still unknown and may be site dependent. It is generally accepted that maximal bone density is present during the third to fourth decade, but this assumption is based upon data derived from studies using densitometry techniques that are less precise than newer methods. Normative data are derived primarily from cross-sectional studies of adolescents and young adults, such as cohorts of the National Health and Nutrition Examination Survey (NHANES). Differences in absolute density depend on the various techniques used for assessing bone density [i.e. single photon absorptiometry, dual energy x-ray absorptiometry (DEXA), quantitative computed tomography (QCT)] and differences using the same method among different machines, emphasizing the importance of methodology, including the type of machine used when referencing normative databases. There are also ethnic differences in bone density, with blacks reported as having higher bone density than whites. There are gender differences in bone density during childhood and adolescence due to differences in the timing of growth and puberty, resulting in females reaching peak bone mass earlier than males, although bone density values at peak bone mass are similar between the sexes. An individual’s height, bone size, and skeletal age may all impact bone density values, particularly in growing children and adolescents. These variables should be considered when assessing the normality of an individual’s bone density, but unfortunately current reference data do not include information on these variables. More recent investigations have suggested that peak bone mass may be attained as early as late adolescence in the hip and spine (1). In healthy adolescents, bone mass increases throughout childhood, with maximal bone mass accrual occurring in early to midpuberty and slowing in late puberty (2–5). However, most published studies are cross-sectional and do not include individuals in sufficient numbers encompassing the entire age span of interest (i.e. teens to fourth decade) followed prospectively to definitively determine the age at which peak bone mass is attained. Longitudinal data from healthy girls demonstrate that the gain in bone mass is most pronounced between 11–14 yr of age and falls significantly after 16 yr of age and/or 2 yr after menarche, as shown in Fig. 1 (4, 5). These data suggest that there is a critical window in time to maximize bone density in early and midadolescence, and the majority of bone mass will accumulate by late adolescence. It has been shown in adult patients that each sd reduction in bone density is associated with a doubling of fracture risk. In children, as in adults, fracture rates have also been shown to be higher in individuals with a lower bone mineral content (6). Because an individual’s bone density is determined by peak bone density and the degree of later bone loss, an understanding of the factors responsible for maximizing peak bone mass is critical for preventing fractures in later life. In this review, the factors that influence the attainment of peak bone mass, particularly hormonal determinants and disorders, will be considered.