Assessment of age-related bone loss in normal South African women by means of the Hologic QDR 1000 system

The aim of this study was to evaluate age-related changes in cortical and trabecular bone mineral density (BMD) in South African subjects, and to develop a local reference database for dual energy X-ray absorptiometry with the QDR 1000 densitometer. A questionnaire was used to recruit volunteers. Age, years since menopause, use of medications and medical diseases were recorded. Men were excluded. Only whites and coloureds were studied. Three hundred and eleven women had single measurements over a 2-year period. Seven sets of subjects were defined according to age (18-44; 45-49; 50-54; 55-59; 60-64; 65-69; >70 years) (N = 163; 32; 35; 23; 25; 16; 17 respectively). Height and weight did not change significantly with age. There were significant differences in lumbar and femoral BMD (Ward's) compared with those of American subjects in the different age categories. Both the lumbar and total femoral BMD began to fall significantly between the ages of 60 and 65 years (P < 0,01). Ward's triangle showed a significant fall in BMD between 45 and 50 years of age (P < 0,01). Ward's BMD predicted 36% of the variation in lumbar BMD at 45 years but 10% at 70 years. Ward's triangle is a useful predictor of femoral bone loss in later years. The fracture threshold at the lumbar vertebrae was 0,822 g/cm2; at Ward's triangle it was 0,443 g/cm2. This gave a 16% prevalence of osteopenia in the lumbar region and a prevalence of 24% at Ward's area.