Total body bone mineral in healthy adults.

Total body bone mineral (TBBM) was measured by dual photon absorptiometry (DPA) using a gadolinium 153 source in 135 healthy women aged 21 to 77 years and 101 healthy men aged 20 to 74 years. Among several predictor variables, including lean body mass measured by DPA, weight, and height, only normalization for the projected skeletal area (i.e., calculation of the total body bone density) had an appreciable effect on reduction of TBBM variation. In regression analysis of TBBM, raw and normalized, vs. age, a menopause-adjusted age was used for interpretation of data in women. Regardless of the normalization procedure, the best fit of TBBM vs. menopause-adjusted age was obtained by a polynomial regression of the third degree or a combined linear (premenopausal)--exponential (postmenopausal) regression. In men bone loss was linear with age (0.2% to 0.3% per year). In women, no significant premenopausal bone loss was found. The postmenopausal exponential loss was 4%, 0.44%, and 0.03% per year from TBBM 1 year, 10 years, and 20 years after the menopause. This amounts to a negative calcium balance of 100 mg calcium per day during the first postmenopausal year, and returning to zero after 20 years of menopause, when about 20% of premenopausal bone is lost.