Bone mineral density (BMD) and soft-tissue composition of the total body and major subregions were measured with dual-energy x-ray absorptiometry (DEXA). Total body scans were made in 12 young adults (6 male, 6 female) on five occasions at both a medium speed (20 min) and a fast speed (10 min). There were no significant differences in mean results or in precision errors between the two speeds. The precision errors (1 SD) for total body BMD, percent fat in soft tissue (% Fat), fat mass, and lean tissue mass were less than 0.01 g/cm2, 1.4%, 1.0 kg, and 0.8 kg, respectively. These results corresponded to a relative error of 0.8% for total body BMD and 1.5% for lean body mass. Regional BMD and soft-tissue values (arms, legs, trunk) were determined with slightly higher precision errors. Skeletal mineral was 5.8 +/- 0.5% of lean tissue mass (r = 0.96, p less than 0.001). DEXA provides precise composition analysis with a low radiation exposure (less than 0.1 microGy).
In postmenopausal women, treatment with tamoxifen is associated with preservation of the bone mineral density of the lumbar spine. Whether this favorable effect on bone mineral density is accompanied by a decrease in the risk of fractures remains to be determined.
The effects of age, calcium, smoking, and physical activity on appendicular and axial bone mineral density (BMD) were evaluated in a 2-y study of 200-300 healthy young women aged 20-39 y. There was no cross-sectional change of BMD with age or longitudinal change with bone loss. No effect of birth-control pills on BMD was seen. There also was no association of calcium intake with BMD and/or with BMD changes. Current calcium intake was not a significant influence on BMD in this age group. Daily activity had no effect on BMD and there was no apparent additive interaction of activity and calcium intake on BMD. Smokers had significantly lower spine BMD and a tendency for lower BMD at other sites. Body weight was a better predictor of BMD than was any other factor. There was no association of BMD or BMD changes with both urinary calcium and hydroxyproline normalized for creatinine.
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