Peak bone mass, which can be defined as the amount of bony tissue present at the end of the skeletal maturation, is an important determinant of osteoporotic fracture risk.Measurement of bone mass development. The bone mass of a given part of the skeleton is directly dependent upon both its volume or size and the density of the mineralized tissue contained within the periosteal envelope. The techniques of single-1 and dual-energy photon or X-ray absorptiometry measure the so-called ‘areal’ or ‘surface’ bone mineral density (BMD), a variable which has been shown to be directly related to bone strength.Bone mass gain during puberty. During puberty the gender difference in bone mass becomes expressed. This difference appears to be essentially due to a more prolonged bone maturation period in males than in females, with a larger increase in bone size and cortical thickness. Puberty affects bone size much more than the volumetric mineral density. There is no significant sex difference in the volumetric trabecular density at the end of pubertal maturation. During puberty, the accumulation rate in areal BMD at both the lumbar spine and femoral neck levels increases to four- to sixfold over a 3-and 4-year period in females and males, respectively. Change in bone mass accumulation rate is less marked in long bone diaphyses. There is an asynchrony between the gain in statural height and bone mass growth. This phenomenon may be responsible for the occurrence of a transient period of a relative increase in bone fragility that may account for the pattern of fracture incidence during adolescence.Variance in peak bone mass. At the beginning of the third decade there is a large variability in the normal values of areal BMD in the axial and appendicular skeleton. This large variance, which is observed at sites particularly susceptible to osteoporotic fractures such as lumbar spine and femoral neck, is barely reduced after correction for statural height, and does not appear to increase substantially during adult life. The height-independent broad variance in bone mass develops during puberty at sites such as lumbar spine and femoral neck, where the accretion rate is markedly increased.Time of peak bone mass attainment. Despite the fact that a majority of studies did not indicate that bone mass continues to accumulate significantly during the third and fourth decades, it has been generally accepted that peak bone mass at any skeletal site is attained in both sexes during the mid-thirties. However, recent studies indicate that in healthy Caucasian females with apparently adequate intakes of energy and calcium, bone mass accumulation can virtually be completed before the end of the second decade, for both lumbar spine and femoral neck. It is possible that both genetic and environmental factors could influence the time of peak bone mass achievement.Determinants of peaks bone mass. Several variables, more or less independent, are supposed to influence bone mass accumulation during growth; heredity, sex, dietary components, endocrine factors, mechanical forces, and exposure to risk factors. Quantitatively, the most prominent factor appears to be the genetic determinant, as estimated by studies comparing monozygotic and dizygotic twins. That heredity is not to be the only determinant of peak bone mass is of practical interest, since environmental factors can be modified. With respect to nutrition, the quantitative importance of calcium intake in bone mass accumulation during growth, particularly at sites prone to osteoporotic fractures, remains to be clearly determined. The same can be said for the impact of physical activity. Finally, the crucial years when these external factors will be particularly effective on bone mass accumulation remain to be determined by longitudinal prospective studies in order to produce credible and well targeted recommendations for the setting up of osteoporosis prevention programs aimed at maximizing peak bone mass.
Bone fragility Bone mineral density Bone size Cortical bone Osteoporosis Puberty Sex difference Statural height Trabecular bone
1.Division of Clinical Pathophysiology, World Health Organization Collaborating Center for Osteoporosis and Bone Disease, Department of Medicine, and Division of Nuclear Medicine, Department of RadiologyUniversity HospitalGenevaSwitzerland