HISTOMORPHOMETRIC ASSESSMENT OF BONE MASS STRUCTURE, AND REMODELING -A COMPARISON BETWEEN HEALTHY BLACK-AND-WHITE PREMENOPAUSAL WOMEN

While noninvasive studies of bone mass and turnover in blacks and,whit es abound, histologic evaluations are very rare. We have performed a c omparative bone histomorphometric study of iliac biopsies from 55 heal thy, premenopausal women including 21 blacks (mean age 33.4 + 1.2 year s) and 34 whites (mean age 32.5 + 0.8 years) of comparable age, weight , body composition, education, and lifestyle. Biochemical indices of m ineral metabolism: parathyroid hormone, 25-hydroxyvitamin D, 1,25-dihy droxyvitamin D, serum ionized calcium, serum phosphorus, and urinary c alcium/creatinine were measured in the fasting state. Blacks had lower 25-hydroxyvitamin D (31.5 +/- 3.36 vs. 63.21 +/- 3.79 nmol/l, p = 0.0 001). Histomorphometric indices of bone volume, structure, and connect ivity were not different between groups. The following indices of bone remodeling were also similar in both groups: eroded perimeter, osteoi d width, mineralizing perimeter, tissue-based bone formation rate, ost eoid maturation time, active formation period, and activation frequenc y. However, osteoid perimeter (black [B] = 15.85 +/- 1.30 vs. white [W ] = 9.49 +/- 0.70%, p = 0.0002), osteoid area (B = 2.55 +/- 0.32 vs. W = 1.39 +/- 0.12%, p = 0.003): single-labeled perimeter (B = 5.46 +/- 0.54 vs. W = 4.04 +/- 0.33%, p = 0.03), mineralization lag time (B = 3 8.18 +/- 4.04 vs. W = 21.83 +/- 1.60 days, p < 0.009), and total forma tion period (B = 148.15 +/- 19.70 vs. W = 84.04 +/- 7.62 days, p = 0.0 056) were higher in blacks than in whites. The quiescent perimeter (B = 76.91 +/- 1.30 vs. W = 84.25 +/- 0.91%, p = 0.0001), mineral apposit ion rate (B = 0.70 +/- 0.02 vs. W = 0.75 +/- 0.02 mu m/day, p = 0.066) , mineralizing osteoid perimeter (B = 0.49 +/- 0.04 vs. W = 0.75 +/- 0 .04%, p = 0.0001) and adjusted apposition rate (B = 0.35 +/- 0.04 vs. W = 0.58 +/- 0.04 mu m(3)/mu m(2)/day, p = 0.0001) were all lower in b lacks than in whites. These results indicate that there are no differe nces in bone volume, microstructure, or turnover between black and whi te premenopausal women. However, there are significant differences in the mechanism of bone formation between the two groups, with a lower r ate of mineralized matrix apposition within each remodeling unit and a longer total formation period in blacks than in whites. The differenc es appear to be the result of more frequent and/or longer inactive per iods in the life span of the bone formation units in blacks. These dif ferences may allow a greater overall deposition of bone mineral in bla ck women and therefore help explain a higher bone mass and perhaps bet ter bone quality in black than white women.