Figure 1.

A, Bone loss begins in the third decade of life in both sexes. The data are from the Epidemiological Follow-up Study cohort of the First National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of noninstitutionalized civilians who were followed for a maximum of 22 yr. A cohort of 2879 Caucasian men (1437 in the bone density subsample) aged 45–74 yr at baseline (1971–1975) were observed through 1992. [From A. C. Looker et al.: Osteoporosis Int 8:468–489, 1998 (21). Reproduced with permission of the International Bone & Mineral Society and the IBMS BoneKEy where this graphic depiction of the data is provided online.] B, Age is a more critical determinant of fracture risk than bone mass in humans. Data are from a follow-up of 521 Caucasian women over an average of 6.5 yr with repeated bone mass measurements at the radius. A total of 138 nonspinal fractures in 3388 person-years were detected, and the incident fractures were cross-classified by age and bone mass. The incidence of fracture was then fitted to a log-linear model in age and bone mass. [From S. L. Hui et al.: J Clin Invest 81:1804–1809, 1988 (24). Reproduced with permission from The American Society for Clinical Investigation.]