AGING AND BONE METABOLISM IN AFRICAN-AMERICAN AND CAUCASIAN WOMEN

There is limited information concerning bone mineral density (BMD) and its determinants across a wide spectrum of ages in African American f emales (AAF). Therefore, we have performed a cross-sectional study of 54 AAF and 39 Caucasian females (CF), aged 20-90 yr, to quantify femor al and lumbar bone mineral density, total body calcium, as well as the potential determinants of bone density.BMD decreased with age in all sites after age 40 yr in both racial groups. Bone density was greater in AAF than in CF, although there was considerable overlap between the two groups. There was no significant difference in the rate of age-re lated bone loss between the two groups. At the femoral neck, BMD was b elow the fracture threshold in 28% of the postmenopausal AAF compared to 47% of postmenopausal CF. L1-L4 BMD was below the fracture threshol d in 8% of postmenopausal AAF and 11% of postmenopausal CF. Serum-25 h ydroxyvitamin D (25OHD) was inversely related to age in both ethnic gr oups and lower (P < 0.05) in premenopausal AAF than CF. Twenty-four pe rcent of the AAF and 22% of the CF had serum 25OHD levels of 8 ng/L or less. Serum PTH was directly related to age (r = 0.43; P = 0.003 in A AF and r = 0.55; P = 0.002 in CF), and 25OHD was inversely related to age (r = -0.43; P = 0.003 in AAF and r = -0.65; P < 0.001 in CF). PTH was higher (P < 0.05) in postmenopausal AAF than in CF. Serum testoste rone was greater in AAF than in CF (P < 0.05). Serum estradiol was gre ater in premenopausal AAF than in CF. Serum dehydroepiandrosterone sul fate was inversely related to age (r = 0.42; P = 0.004 in AAF and r = 0.51; P = 0.005 in CF). Serum osteocalcin was related to age in AAF (r = 0.47 P = 0.001), but not in CF. There was also a trend for an incre ase in urinary dipyridinoline (expressed per 100 mg urinary creatinine ) with age (r = 0.31; P = 0.055 in AAF and r = 0.37; P = 0.066 in CF). Both lean and fat mass were major determinants of femoral neck BMD in AAF. Femoral BMD was directly related to body weight and body mass in dex in both races. Serum 25OHD and dehydroepiandrosterone sulfate appr oached statistical significance as independent predictors of femoral B MD in AAF. We conclude that in AAF, 1) bone density is higher than in CF, but there is a significant risk of fracture in a substantial numbe r of subjects on the basis of BMD; 2) there is no difference in rates of age-related bone loss compared to those in CF; 3) both lean and fat mass are significant determinants of bone density; 4) serum estradiol and testosterone were higher than those in CF; and 5) aging is associ ated with increased bone turnover, 25OHD deficiency, and secondary hyp erparathyroidism in both races. The absence of a difference in rates o f bone loss between AAF and CF despite higher serum levels of PTH is c ompatible with the concept of a relative skeletal resistance to PTH in AAF.