The loss of bone mineral with aging and its relationship to risk of fracture.

Longitudinal studies have shown that individuals lose bone mineral at unequal rates with aging. It has been postulated that individuals with the more rapid rates of loss constitute a separate population having an increased risk for developing fractures, i.e., osteoporosis. To examine this postulate, we made a search for a separate population of elderly women using a precise and objective measurement technique of bone mineral, photon absorptiometry. Bone mineral content (BMC) was measured in the radius of 571 Caucasian females who were age 50 or older. It was found that BMC values adjusted for width had a normal distribution in all decades and the variation in BMC values did not increase with age. Subjects with vertebral fractures (n = 108) were estimated to be losing bone mineral at the same rate as those without vertebral fractures (n= 161). Thus evidence for a separate population of rapid losers of bone mineral was not found. Reconciliation of longitudinal studies which show unequal rates of loss with the present population survey, in which evidence for unequal rates was not found, would require that (a) the rate of loss of bone mineral for an individual is not constant and/or (b) the rate of mineral loss is proportional to the amount of mineral present at maturity. The incidence of vertebral fractures was inversely proportional to BMC values. In a group of 278 women followed for 470 subject-yr, the incidence of all fractures during the study (n = 31) was also inversely proportional to BMC. These data suggest that the BMC values of osteoporotics would be at the lower end of normally distributed values for the population.