EFFECTS OF ETHNICITY AND AGE OR MENOPAUSE ON OSTEOBLAST FUNCTION, BONE MINERALIZATION, AND OSTEOID ACCUMULATION IN ILIAC BONE

We measured histologic indices of osteoblast function, bone mineraliza tion, and osteoid accumulation separately on the cancellous, endocorti cal, and intracortical subdivisions of the endosteal envelope and on t he combined total surface in transiliac biopsies obtained after double tetracycline labeling in 142 healthy women, aged 20-74 years, 34 who were black (19 pre- and 15 postmenopausal) and 108 white (32 pre- and 66 postmenopausal). The data were subjected to two-way analysis of var iance of the four groups defined by age/menopause and ethnicity. Also, linear regressions of selected variables on age and between functiona lly related bur independently measured variables were examined. None o f the interaction terms mas significant, and none of the regression sl opes on age differed between blacks and whites, indicating that, as fo r the previously reported structural and remodeling indices, the effec ts of ethnicity and of age/menopause are independent, Accordingly, the data were analyzed separately for the effects of ethnicity (pre-and p ostmenopausal combined) and age/menopause (blacks and whites combined) . The analyses led to the following conclusions (1) Osteoid surface an d volume were higher and adjusted apposition rate and osteoid minerali zation rate lower in postmenopausal than in premenopausal subjects, bu t none of the indices of osteoid accumulation differed between blacks and whites. (2) Each index of osteoid accumulation was significantly c orrelated with its primary independently measured kinetic determinant (osteoid thickness with adjusted apposition rate, osteoid surface/bone surface with activation frequency, and osteoid volume/bone volume wit h bone formation rate/bone volume). None of the regression parameters differed significantly between blacks and whites, (3) The ratio of min eralizing surface to osteoid surface (MS/OS) was substantially lower i n all demographic groups than could be accounted for toy the later ons et of mineralization than of matrix apposition at individual hone form ing sites. (4) The low values for MS/OS can be explained by terminal m ineralization being too slow to trap enough tetracycline molecules to produce detectable fluorescence, and do not require that mineralizatio n be interrupted. (5) MS/OS was about 25% lower in blades than in whit es on all surfaces with corresponding differences in derived indices b ased on MS/OS, including adjusted apposition rate, mineralization lag time, and formation period. (6) The lower values for MS/OS in blacks a re most likely due to slower terminal mineralization, This could not b e accounted for by a lower serum level of calcidiol, but is consistent with the reported effect of reduced bone blood flow, (7) All differen ces in bane cell function between blacks and whites that Ne have obser ved could be the result of the ethnic, and presumably genetic, differe nce in bone accumulation during growth, Higher bone mass would result in less fatigue microdamage, less need for repair by directed bone rem odeling, lower bone turnover, lower bone blood flow, and slower termin al mineralization. (8) If this explanation is correct, there are no fu ndamental differences in the biology of bone remodeling between ethnic groups.