Laura A. Milliken

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.

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.

Body Composition Modulates the Effects of Hormone Replacement Therapy on Growth Hormone and Insulin-Like Growth Factor-I Levels in Postmenopausal Women

Objective: To examine the relationships of body composition with basal serum estrone, estradiol, androstenedione, cortisol, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels in 73 postmenopausal women. Design: Cross-sectional study of hormone levels and body composition determined by dual-energy X-ray absorptiometry and anthropometry in women who were not taking oral hormone replacement therapy (HRT) and women taking HRT. Because high adiposity may modify hormone levels, subjects were grouped by fatness into obese (BMI >25 kg/m2 and waist circumference >80 cm) and lean groups, as well as by HRT use. Results: Total levels of estrone, estradiol, GH and cortisol were significantly higher and IGF-1 was lower in HRT users. In HRT users, estradiol levels were higher and GH levels were lower in obese than lean women. IGF-1 levels were lower in obese HRT users than lean nonusers. Total cortisol levels were significantly higher in lean HRT users than lean nonusers and obese users. GH and IGF-1 were significantly inversely correlated with trunk fat and percent body fat. Multiple regression revealed that only trunk fat was a significant (negative) determinant of GH and IGF-1 levels, whereas HRT use positively and negatively predicted GH and IGF-1, respectively. Percent body fat significantly predicted estradiol levels. Body composition did not differ by HRT use. Conclusions: Our results suggest that trunk fat attenuates the HRT-induced increase on GH levels. In addition, trunk fat is a significant determinant of low IGF-1 levels in postmenopausal women, and IGF-1 levels decline more with HRT use.