Differences in skeletal and muscle mass with aging in black and white women

Previous cross-sectional studies using delayed gamma neutron activation ana lysis and whole body counting suggested that the relationship of total body calcium (TBCa) to total body potassium (TBK) (muscle mass, body cell mass) remained constant with age. This led to the hypothesis that the muscle mas s and skeletal mass compartments are integrated in their response to aging. It had also been hypothesized that loss of skeletal and muscle mass was si milar between races. In the current study, delayed gamma neutron activation analysis and whole body counting were performed on 90 black and 143 white women 20-69 yr of age. Black women had higher TBCa and TBK values than whit e women, even when the data were adjusted for age, height, and weight. TBCa was correlated with height and TBK with weight. The estimated decline of s keletal mass (TBCa) from 20 to 70 yr was 18% in black women and 19% in whit e women. However, the lifetime decline of TBK was only 8% for black women, compared with 22% for white women. Black women may lose TBK more slowly tha n TBCa with aging, compared with white women. In particular, correlation of TBCa and age was similar for blacks and whites (r = -0.44 and r = -0.54, r espectively). However, for TBK these correlations were r = -0.14 and r = -0 .42. These data confirm a higher musculoskeletal mass in black women and su ggest that the loss of muscle mass with age may be lower in black than in w hite women. These ethnic differences do not support the hypothesis of an in tegrated musculoskeletal system, so that these two components should be con sidered separately. A prospective study is needed to confirm these findings .