ETHNIC-DIFFERENCES IN BONE-DENSITY IN FEMALE SOUTH-AFRICAN NURSES

In the United States, the higher prevalence of osteoporosis and the hi gher incidence of fractures in whites than in blacks may be attributed to the finding of lower bone density (ED) in both white children and adults. In South Africa, osteoporosis and fractures also occur more fr equently in whites than in blacks. Appendicular ED has been found to b e similar in black and white children in South Africa, but there is li ttle information available on ED of adults in South Africa. This cross -sectional study aimed to assess changes in ED with age in adult femal es in South Africa and to assess possible differences in peak ED and i n the rate of postmenopausal bone loss between blacks and whites. Data for 180 black and 184 white female nurses aged 20-64 years were analy zed. The distal radius bone density (RBD) was measured by single photo n absorptiometry. The lumbar spine bone density (SBD) and the femur bo ne density (FED) were measured by dual-energy X-ray absorptiometry. Bl acks were shorter than whites (p = 0.0001), and blacks' weight, body m ass index, and skinfold thickness increased with age. Peak SBD and RED were similar in blacks and whites, but peak FED was higher in blacks (p = 0.0001). This ethnic difference in peak FED became apparent in th e fourth decade. Peak FED was similar in black and white subjects with normal body mass indices (p = 0.09), but in overweight subjects peak FED was higher in blacks than in whites (p = 0.0001). SBD (p = 0.03), RED (p = 0.0002), and FED (p = 0.04) in whites, but not in blacks, dec reased after the menopause. Weight had a positive association with FED in premenopausal blacks (R(2) = 0.24, p = 0.0001) but not in whites. In the postmenopausal group, adiposity had a positive association with SBD and RED in blacks and with FED in both blacks and whites. These r esults suggest that weight-bearing is important in the attainment of p eak FED and that adiposity may be important in decreasing postmenopaus al bone loss. The finding of higher FED in blacks than in whites may e xplain the lower rate of femoral fractures in black South Africans. Ho wever, the similarity in SBD between blacks and whites in this study s uggests that factors other than bone density might contribute to the l ower vertebral fracture rate in black compared with white South Africa ns.