TO WHAT EXTENT IS BONE MASS DETERMINED BY FAT-FREE OR FAT MASS

One hundred sixty-four healthy black and white women aged 24-79 y were studied to determine to what extent bone mass is determined by fat-fr ee mass (FFM). A multicomponent approach to body composition, with tec hniques that are not interdependent, was used. The measurements includ ed dual x-ray absorptiometry (DXA), prompt gamma-neutron-activation an alysis, inelastic neutron scattering, tritiated water dilution, and wh ole-body counting. Univariate correlations showed significant relation ships of all the fat-free measures and most of the fat measures with b one mass measured by total body calcium (TBCa). Data from pre- and pos tmenopausal women were analyzed separately. The average FFM by itself explained 50-55% of the variability in TBCa whereas the average fat ma ss by itself explained only 5-18% of the variability. The contribution of fat mass was consistently greater in postmenopausal than in premen opausal women. When stepwise multiple regression with TBCa was perform ed to determine the influence of adding fat mass, height, and race to the relationship of FFM with TBCa, the variation explained by average FFM was 56% premenopausal, 50% postmenopausal; by height 3% premenopau sal, 6% postmenopausal; by race 4% premenopausal, 8% postmenopausal; a nd average fat mass was not significant. Average values for fat mass a nd FFM were obtained by averaging all the methods used. In conclusion, in black and white healthy women, although bone mass may be partially influenced by fatness or race, the major determinant of bone mass is FFM. Fat mass may play a more important role in postmenopausal women.