Bone density in ageing Caucasian and African populations.

Fracture surveys in the Johannesburg metropolitan area showed that the rate of femoral-neck fractures rose sharply after the climacteric in Caucasians, whereas the incidence of such fractures in African Negroes of the same age was almost negligible. However, a parallel epidemiological survey of metacarpal bone density in random samples of the same populations showed that absolute values for skeletal mass and bone density were greater in the Caucasians through most of the age-range from 5 to 75 years. Also, although bone density increased more rapidly and reached higher maximum values in young Caucasians than in Africans, it fell more rapidly in the former from the fourth decade onwards. The differences in the pattern of bone density alone are unlikely to account for the large difference in the fracture rates in the two populations. Perhaps quantitative changes in bone mass associated with ageing are accompanied by qualitative changes which may be critical in determining the liability to fracture.