Changes in soft tissue composition are the primary predictors of 4-year bone mineral density changes in postmenopausal women.

UNLABELLED: Changes in body weight influence bone mineral density, but the role of body composition is not clear in postmenopausal women. Body weight and soft tissue composition predicted bone changes independent of calcium supplementation and exercise frequency, indicating that soft tissue composition should be measured in clinical trials. INTRODUCTION: The purpose of this study was to examine the relationship between changes in body weight and composition and changes in 4-year bone mineral density (BMD) after accounting for age, 4-year exercise frequency (EX), and 4-year calcium supplement intake (CA) in postmenopausal women with and without hormone therapy (HT). METHODS: Postmenopausal women (aged 40-65 years) either using HT (for 1-3.9 years) or not using HT (for > or =1 year) were recruited to the study. EX and CA was monitored throughout the study and 167 women completed 4 years. BMD and soft tissue composition measurements were made using dual-energy X-ray absorptiometry. Regression was used to predict 4-year BMD changes from EX, CA, age, baseline and 4-year changes in body weight and composition. HT users (n = 115, 55.3 +/- 4.3 years) and non-users (n = 52, 57.5 +/- 4.7 years) were analyzed separately. RESULTS: The models predicting regional BMD changes that included soft tissue composition changes explained the most variation compared with those with body weight or EX and CA alone. Larger amounts of variation in BMD changes were explained in the no HT group. CONCLUSION: Body composition changes are important positive predictors of BMD changes independent of EX and CA supplementation, but their contribution varies according to bone site and with HT use.

Effects of exercise training on bone remodeling, insulin-like growth factors, and bone mineral density in postmenopausal women with and without hormone replacement therapy.

The purpose of this study was to determine the effects of 12 months of weight bearing and resistance exercise on bone mineral density (BMD) and bone remodeling (bone formation and bone resorption) in 2 groups of postmenopausal women either with or without hormone replacement therapy (HRT). Secondary aims were to characterize the changes in insulin-like growth factors-1 and -2 (IGF-1 and -2) and IGF binding protein 3 (IGFBP3) in response to exercise training. Women who were 3-10 years postmenopausal (aged 40-65 years) were included in the study. Women in the HRT and no HRT groups were randomized into the exercise intervention, resulting in four groups: (1) women not taking HRT, not exercising; (2) those taking HRT, not exercising; (3) those exercising, not taking HRT; and (4) women exercising, taking HRT. The number of subjects per group after 1 year was 27, 21, 25, and 17, respectively. HRT increased BMD at most sites whereas the combination of exercise and HRT produced increases in BMD greater than either treatment alone. Exercise training alone resulted in modest site-specific increases in BMD. Bone remodeling was suppressed in the groups taking HRT regardless of exercise status. The bone remodeling response to exercise training in women not taking HRT was not significantly different from those not exercising. However, the direction of change suggests an elevation in bone remodeling in response to exercise training, a phenomenon usually associated with bone loss. No training-induced differences in IGF-1, IGF-2, IGF-l:IGF-2 (IGF-1 : IGF-2), and IGFBP3 were detected.

Effects of variations in regional composition on soft tissue measurements by dual-energy X-ray absorptiometry.

OBJECTIVE: To assess the effect of variations in regional composition on the accuracy of dual-energy X-ray absorptiometry (DXA) in humans by placing packets of lard, water and ground beef, to simulate fat, very lean tissue and high density lean material, on the thighs and abdomen. SUBJECTS: 28 healthy males and females (mean age: 25 y; mean % fat: 24.6%). METHODS: Up to six consecutive total body DXA scans (baseline plus five scans with added packets) at 16 cm/s were performed on each subject (Lunar DPX-L, software version 1.3y). Eight conditions were examined: one lard packet (n = 18), two stacked lard packets, one ground beef packet and one water packet (all n = 10) alternately placed on the thighs and abdomen. Masses (kg) and percentage fats (% fat) of the lard, water and ground beef packets were 1.45 and 90%, 2.80 and 4% and 1.80 and 24%, respectively. RESULTS: Differences between actual (baseline plus packet) and measured composition were assessed using paired t-tests (p < 0.05). Under all conditions except with two abdominal lard packets, actual and measured total mass were similar (p > 0.05). Percentage fat of one lard packet was significantly underestimated when placed on the abdomen (90% actual vs 52% measured). The % fat of two lard packets was underestimated when placed on the thighs (90% vs 77%) and abdomen (90% vs 47%) while the % fat of the water packet was overestimated in both locations. CONCLUSION: The Lunar DXA underestimates the % fat of lard placed over the abdomen moreso than when placed over the thighs and overestimates % fat of water in both locations independent of thickness. Ground beef is accurately detected.

Practical techniques for assessing body composition in middle-aged and older adults.

The purpose of this study was to compare the relationships of anthropometric, bioelectrical impedance analysis (BIA), and near infrared interactance (NIR) measurements with a multiple-component (MC) criterion estimate of body composition derived from body density (D), body water (W), and bone mineral (B) in 48 white adults aged 49-80 yr. Relative errors of predicting the MC criterion from the practical measurements were determined by simple regressions within gender and calculated as the SEE divided by the criterion mean and expressed as a percentage. Relative errors were lowest for the BIA variable, height2/resistance (4.8-5.0%), higher for body mass index and the sum of 10 skinfold thicknesses (7.0-14.5%), and highest for NIR-derived optical density readings at the biceps and the sum of 10 sites (10.8-15.8%). Due to the low relative prediction error for height2/resistance, sex-specific BIA formulas for estimating fat-free mass from D, W, and B (FFM-DWB) were developed. The SEEs for predicting FFM-DWB from BIA, weight, and age were both 1.5 kg in women and men. Because BIA is not limited to ambulatory subjects, it is concluded that BIA may be a particularly useful, practical technique for estimating body composition in older adults.