Increased fat mass is associated with increased bone size but reduced volumetric density in pre pubertal children

Recent studies have shown that obesity is associated with an increased risk of fracture in both adults and children. It has been suggested that, despite greater bone size, obese individuals may have reduced true volumetric density; however this is difficult to assess using two dimensional techniques such as DXA. We evaluated the relationship between fat mass, and bone size and density, in a population cohort of children in whom DXA and pQCT measurements had been acquired. We recruited 530 children at 6 years old from the Southampton Women's Survey. The children underwent measurement of bone mass at the whole body, lumbar spine and hip, together with body composition, by DXA (Hologic Discovery, Hologic Inc., Bedford, MA, USA). In addition 132 of these children underwent pQCT measurements at the tibia (Stratec XCT2000, Stratec Biomedical Systems, Birkenfeld, Germany). Significant positive associations were observed between total fat mass and both bone area (BA) and bone mineral content (BMC) at the whole body minus head, lumbar spine and hip sites (all p<0.0001). When true volumetric density was assessed using pQCT data from the tibia, fat mass (adjusted for lean mass) was negatively associated with both trabecular and cortical density (β=-14.6 mg/mm(3) per sd, p=0.003; β=-7.7 mg/mm(3) per sd, p=0.02 respectively). These results suggest that fat mass is negatively associated with volumetric bone density at 6 years old, independent of lean mass, despite positive associations with bone size.     

Cross-Calibration of Prodigy and Horizon A Densitometers and Precision of the Horizon A Densitometer

We performed this study to enable a reliable transition for clinical study participants and patients from a GE Lunar Prodigy to a Hologic Horizon A dual-energy X-ray absorptiometry (DXA) scanner and to assess the reproducibility of measurements made on the new DXA scanner. Forty-five older adults had one spine, hip, and total body scan on a Prodigy dual-energy X-ray absorptiometry (DXA) scanner and 2 spine, hip, and total body scans, with repositioning, on a new Hologic Horizon A DXA scanner. Linear regression models were used to derive cross calibration equations for each measure on the 2 scanners. Precision (group root-mean-square average coefficient of variation) of bone mineral density (BMD) of the total hip, femoral neck, and lumbar spine (L1-L4), and total body fat, bone, and lean mass, appendicular lean mass, and trabecular bone score (TBS) was assessed using the International Society of Clinical Densitometry's (ISCD's) Advanced Precision Calculation Tool. Correlation coefficients for the BMD and body composition measures on the 2 scanners ranged from 0.94 to 0.99 (p<0.001). When compared with values on the Prodigy, mean BMD on the Horizon A was lower at each skeletal site (0.136 g/cm² lower at the femoral neck and 0.169 g/cm² lower at the lumbar spine (L1-4)), fat mass was 0.47 kg lower, and lean mass was 4.50 kg higher. Precision of the Horizon A scans was 1.60% for total hip, 1.94% for femoral neck, and 1.25% for spine (L1-4) BMD. Precision of TBS was 1.67%. Precision of total body fat mass was 2.16%, total body lean mass was 1.26%, appendicular lean mass was 1.97%, and total body bone mass was 1.12%. The differences in BMD and body composition values on the 2 scanners illustrate the importance of cross-calibration to account for these differences when transitioning clinical study participants and patients from one scanner to another.     

Reproducibility of DXA in obese women.

Dual-energy X-ray absorptiometry (DXA) measurements were analyzed using two versions of software (Hologic V8.1a and V8.21) to compare the short- and long-term precisions of the measurements. Software V8.21 was designed by the manufacturer to better address magnification effects on estimations of soft tissue lean mass. Twenty weight-stable, obese postmenopausal Caucasian women aged 40-70 yr participated in the study. Total and regional body composition measurements were obtained at baseline and after 3 mo, using a fan beam Hologic QDR 4500A absorptiometer. For the estimation of precision, duplicate scans obtained on the same day for nine women were analyzed using both versions of the software. The correlations between duplicate scans ranged from 0.886 to 0.998 and were similar between software versions. The CVs for fat and lean weights and bone mineral content (BMC) were 1.2%, 1.1%, and 1.7%, respectively, for software V8.21 compared to 1.3%, 1.3%, and 2.1%, respectively, for V8.1a. Systematic differences were found between software versions with higher values for fat and lean weights for software version V8.21. The 3-mo, long-term reproducibility of body composition estimates from DXA was only slightly less than short-term reproducibility for both software versions (coefficient of variation [CV] range from 1.3% for BMC weight to 11.0% for arm fat). Software V8.21 yielded smaller percentage mean differences between scale and DXA-estimated weights (-2.4% and -7.2% at baseline and -2.9% and -7.6% at 3 mo, respectively) and higher fat and lean weights (49.12 and 47.1 kg and 49.6 and 44.6 kg, respectively) than V8.1a. Reproducibility of all variables was comparable between software versions.     

Assessing Agreement of Lateral Leg Muscle and Bone Composition Using Dual X-ray Absorptiometry

Background: Recently, a lateral-view dual X-ray absorptiometry (DXA) scanning method for measuring leg total, lean, and fat masses demonstrated accuracy vs the standard whole-body frontal DXA scanning view on the GE Lunar iDXA. The current study examined the lateral scanning method's agreement using a Hologic Horizon A DXA scanner. Methodology: Thirty healthy college-age participants (16 female; X̅_age = 21.5 ± 1.7 yr) received 3 DXA scans (1 whole-body, 2 lateral leg scans) to quantify leg composition in the frontal and lateral plane. To mark regions of interest for postscan analysis, metallic markers were placed at 60% of the length above and below each leg's lateral epicondyle. Using lateral subject positioning, leg composition was measured with participants lying on their right and left sides. Paired t tests examined the lateral DXA scanning method's agreement when quantifying total, fat, and lean masses, bone mineral content, and bone mineral density compared to measurements of equal area in the whole-body frontal scanning view. Results: Comparisons of frontal and lateral view DXA scan measurements for right leg total mass (7.12 ± 0.91kg vs 6.39 ± 0.85kg), fat mass (1.70 ± 0.44kg vs 1.36 ± 0.33kg), lean mass (5.14 ± 1.05kg vs 4.77 ± 0.92kg), bone mineral content (0.28 ± 0.06kg vs 0.23 ± 0.05kg), and bone mineral density (1.39 ± 0.14g/cm²vs 1.36 ± 0.15g/cm²), respectively, were significantly different (p < 0.001–0.028). Similarly, comparisons of frontal and lateral left leg total mass (7.12 ± 0.97kg vs 6.38 ± 0.92kg), fat mass (1.70 ± 0.44kg vs 1.39 ± 0.36kg), lean mass (5.15 ± 1.12kg vs 4.76 ± 0.97kg), bone mineral content (0.28 ± 0.06kg vs 0.24 ± 0.06kg), and bone mineral density (1.39 ± 0.15g/cm²vs 1.36 ± 0.17g/cm²), respectively, were significantly different (p < 0.001–0.046). Conclusion: Unlike a previous study in which agreement of lateral vs frontal leg composition measurements of equal area was reported utilizing the GE Lunar iDXA, agreement was not observed using the Hologic Horizon A DXA scanner. Therefore, lateral view assessment may not be reliably performed on DXA scanner models produced by different manufacturers.     

Pediatric Reference Centiles of Bone Mineral Density and Body Composition of Lower Limbs

Localized neurological diseases such as spina bifida are often accompanied by normal upper limb and spinal bone mineral density (BMD), whereas regional BMD of the lower limbs may be decreased. Therefore, regional BMD measurements may be more accurate to quantify regional bone health. Until now, no pediatric reference centiles of bone mineral density and body composition of the lower extremities are available for Hologic DXA systems. The objective was to generate age-and sex specific reference centiles of DXA scans of lower limbs for Hologic DXA systems. Data from the National Health and Nutrition Examination Survey of the period 1999–2004 (age 8 – 20 years) were used to generate age-specific and sex-specific reference centiles for the non-Hispanic Black, non-Hispanic White and Mexican-American NHANES study population. The LMS method was used to calculate the reference centiles. Data of DXA scans of 2233 non-Hispanic black children (880 females), 1869 non-Hispanic white children (803 females) and 2350 Mexican American children (925 females) were used to create age-specific and sex-specific reference curves. We presented age-and sex-specific reference centiles for regional bone mineral density, bone mineral content, lean body mass and fat mass at the lower limbs for children and adolescents which were ethnicity specific and directly applicable to Hologic QDR-4500A fan-beam densitometer.     

Bone mineral density in prepubertal obese and control children: relation to body weight,lean mass,and fat mass

The aim of the study was to determine the influence of obesity on bone status in prepubertal children. This study included 20 obese prepubertal children (10.7 +/- 1.2 years old) and 23 maturation-matched controls (10.9 +/- 1.1 years old). Bone mineral area, bone mineral content (BMC), bone mineral density (BMD), and calculation of bone mineral apparent density (BMAD) at the whole body and lumbar spine (L1-L4) and body composition (lean mass and fat mass) were assessed by DXA. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the calcaneus were measured with a BUA imaging device. Expressed as crude values, DXA measurements of BMD at all bone sites and BUA (69.30 versus 59.63 dB/MHz, P < 0.01) were higher in obese children. After adjustment for body weight and lean mass, obese children displayed lower values of whole-body BMD (0.88 versus 0.96 g/cm2, P < 0.05) and BMC (1190.98 versus 1510.24 g, P < 0.01) in comparison to controls. When results were adjusted for fat mass, there was no statistical difference between obese and control children for DXA and ultrasound results. Moreover, whole-body BMAD was lower (0.086 versus 0.099 g/cm3, P < 0.0001), whereas lumbar spine BMAD was greater (0.117 versus 0.100 g/cm3, P < 0.001) in obese children. Thus, it was observed that, in obese children, cortical and trabecular bone displayed different adaptation patterns to their higher body weight. Cortical bone seems to enhance both size and BMC and trabecular bone to enhance BMC. Finally, considering total body weight and lean mass of obese children, these skeletal responses were not sufficient to compensate for the excess load on the whole body.     

First all-solid pediatric phantom for dual X-ray absorptiometry measurements in infants.

Manufacturer-supplied lumbar spine phantoms are normally used for quality control of dual X-ray absorptiometry (DXA) instruments. Presently, there is no pediatric phantom for whole-body mineralization and softtissue composition DXA measurements. We designed blocks of acrylic (for fat mass), polyvinyl chloride (for lean mass), and aluminum (for bone mass) whose combination provides five whole-body phantoms ("Inphants") that mimic body weight and composition during the first year of life and help solve problems that require repeated scans in stable conditions. Inphants were scanned using an Hologic QDR 2000. Comparisons were made between values obtained with and without the table pad, using infant software. Then we compared data obtained using infant and adult softwares successively in the same phantoms. The table pad significantly influenced DXA measurements. We observed significant differences in fat mass (p = 0.04) and lean mass (p = 0.03) with the smaller Inphant (3 kg) and in bone mineral content (BMC) (p = 0.02) with the larger Inphant (13 kg). BMC was three to five times lower with adult than with infant software. Adult software yielded systematically significantly lower fat masses but higher lean masses than infant software. Because there was no overlap with larger Inphants, we calculated conversion formulae between values of infant and adult software. The results suggest guidelines for scan acquisition and analysis in young subjects.     

Effect of Chemotherapy on Dual-Energy X-ray Absorptiometry (DXA) Body Composition Precision Error in Head and Neck Cancer Patients

Background: Precision error in dual-energy X-ray absorptiometry (DXA) is defined as difference in results due to instrumental and technical factors given no biologic change. The aim of this study is to compare precision error in DXA body composition scans in head and neck cancer patients before and 2 months after chemotherapy. Methodology: A total of 34 male head and neck cancer patients with normal body mass index (BMI) were prospectively enrolled and all patients received 2 consecutive DXA scans both before and after 2 months of chemotherapy for a total of 4 scans. The precision error of 3 DXA body composition values (lean mass, fat mass, and bone mineral content) was calculated for total body and 5 body regions (arms, legs, trunk, android, and gynoid). Precision errors before and after treatment were compared using generalized estimating equation model. Results: There was no significant change in precision error for the DXA total body composition values following chemotherapy; lean mass (0.33%–0.40%, p = 0.179), total fat mass (1.39%–1.70%, p = 0.259) and total bone mineral content (0.42%–0.56%, p = 0.243). However, there were significant changes in regional precision error; trunk lean mass (1.19%–1.77%, p = 0.014) and android fat mass (2.17%–3.72%, p = 0.046). Conclusions: For head and neck cancer patients, precision error of DXA total body composition values did not change significantly following chemotherapy; however, there were significant changes in fat mass in the android and lean mass in the trunk. Caution should be exercised when interpreting longitudinal DXA body composition data in those body parts.     

Simulated change in body fatness affects Hologic QDR 4500A whole body and central DXA bone measures.

Changes in body fatness may impact the accuracy of dual energy X-ray absorptiometry (DXA) measures of bone mineral content (BMC) and bone mineral density (BMD). The aim of this study was to determine if DXA can accurately assess BMC and BMD with changes in exogenous fat (lard) placed to simulate weight change. Whole body (WB), lumbar spine (LS), and proximal femur (PF) DXA scans (Hologic QDR 4500A) were performed on 30 elderly (52-83 yr) and 60 young (18-40 yr) individuals (i.e., 45 females and 45 males) of varying body mass index (mean+/-standard deviation: 26.1+/-4.9 kg/m2). When scans were repeated with lard packets (2.54 cm thick, 25.4x17.8 cm, 1 kg), WB BMD decreased 1.1% and 1.6% after chest and thigh packet placement, respectively (p=0.001), PF BMD increased 0.7% (p=0.02) and LS BMD decreased 1.6% (p=0.001) primarily due to a 2.2% reduction in LS BMC (p<0.001). Initial LS BMC and trunk mass were related to error in LS BMC measures due to lard-loading (r=0.64 and 0.45, respectively, p<0.001). We conclude that on average simulated weight change minimally impacts PF bone measures and moderately impacts WB and LS bone measures; however, individual variability in measurement error was noteworthy and may be impacted by body thickness.     

Relationships of acylated and des-acyl ghrelin levels to bone mineralization in obese children and adolescents

AimsBodyweight is a significant predictor of bone mass. Hormonal factors are thought to play a role in the mechanisms controlling the association of body weight and fat mass with bone mass. Very recently, the orexigenic hormone ghrelin has also been implicated in bone metabolism. In this study we examined the associations of circulating acylated and des-acyl ghrelin concentrations with measures of bone in a group of obese children and adolescents as well as in a group of healthy control children. We also determined whether the associations were independent of body composition, chronological age, gender, Tanner stage, and leptin, glucose, insulin and insulin-like growth factor (IGF)-1 levels.MethodsWe performed a prospective cross-sectional study of 100 obese children [age, 8.9 (8.3 to 9.4); BMI-Standard Deviation Score (SDS), 2.2 (2.0 to 2.3)], and 100 age-matched lean healthy subjects. Fasting insulin, leptin, IGF-1, acylated and total ghrelin were measured by radioimmunoassay. Des-acyl ghrelin values were calculated as total ghrelin minus acylated ghrelin. Whole body (WB) and lumbar spine (LS) BMD, and BMC as well as body composition were assessed by DXA (Hologic QDR-4500W). LS volumetric BMD (BMAD) was estimated using the formula of Katzman (BMC/area^1.5), while WB BMC data were expressed as BMC/height.ResultsBackward linear regression analysis was performed for individual groups, with age, gender, Tanner stage, weight, height, body composition (lean and fat mass), acylated ghrelin, des-acyl ghrelin, leptin, glucose, insulin, and IGF-1, entered into the model. In healthy children, acylated ghrelin was a significant and independent negative predictor of WB BMD, and WB BMC/height, while lean mass was positively associated significantly with these bone measures. In contrast, in obese children, a positive significant association was observed between des-acyl ghrelin and WB BMD as well as WB BMC/height, along with lean mass, and to a lesser degree, with fat mass. Acylated as well as des-acyl ghrelin were not significant predictors of LS BMD and LS BMAD in obese as well as control children.ConclusionsThe results of this investigation indicate that the influence of the two distinct isoforms of ghrelin on BMD is mediated by specific body composition parameters in obese and control healthy children.     

Body Composition by Dual-Energy X-ray Absorptiometry in Black Compared with White Women

Dual-energy X-ray absorptiometry (DXA) has recently been applied to the measurement of body composition using a three-compartment model consisting of fat, lean and bone mineral. The mass of skeletal muscle may be approximated by measurement of the lean tissue mass of the extremities. In addition, body fat distribution can be estimated by determining the ratio of fat in the trunk to the fat in the extremities. In the current study, DXA was used to compare body composition and fat distribution between black (n= 162) and white women (n= 203). Black women had a higher mineral mass and a higher skeletal muscle mass. The ratio of mineral to muscle mass was higher in black women, even when the data were adjusted for age, height and weight. Both total body bone mineral and muscle mass declined with age in both races, with evidence for an accelerated loss of bone mineral after menopause. Body size (height and weight) was generally a significant variable in developing regressions of each compartment against age. Their higher musculoskeletal mass may lead to misclassification of 12% of black women as obese if body mass index is used as an index of obesity. Body fat distribution (trunk/leg) did not differ between races in the raw data. However, for women of the same age, height and weight, white women have a significantly higher trunk/leg fat ratio. Body composition values for fat, lean and bone mineral obtained from DXA should be adjusted not only for gender but also for age, height, weight and ethnicity. Received: 23 September 1998 / Accepted: 4 January 1999     

Interpretation of whole body dual energy X-ray absorptiometry measures in children: comparison with peripheral quantitative computed tomography

The assessment of bone health in children requires strategies to minimize the confounding effects of bone size on dual energy X-ray absorptiometry (DXA) areal bone mineral density (BMD) results. Cortical bone composes 80% of the total skeletal bone mass. The objective of this study was to develop analytic strategies for the assessment of whole body DXA that describe the biomechanical characteristics of cortical bone across a wide range of body sizes using peripheral quantitative computed tomography (pQCT) measures of cortical geometry, density (mg/mm³), and strength as the gold standard. Whole body DXA (Hologic QDR 4500) and pQCT (Stratec XCT-2000) of the tibia diaphysis were completed in 150 healthy children 6–21 years of age. To assess DXA and pQCT measures relative to age, body size, and bone size, gender-specific regression models were used to establish z scores for DXA bone mineral content (BMC) for age, areal BMD for age, bone area for height, bone area for lean mass, BMC for height, BMC for lean mass, and BMC for bone area; and for pQCT, bone cross-sectional area (CSA) for tibia length and bone strength (stress-strain index, SSI) for tibia length. DXA bone area for height and BMC for height were both strongly and positively associated with pQCT CSA for length and with SSI for length (all P < 0.0001), suggesting that decreases in DXA bone area for height or DXA BMC for height represent narrower bones with less resistance to bending. DXA BMC for age (P < 0.01) and areal BMD (P < 0.05) for age were moderately correlated with strength. Neither DXA bone area for lean mass nor BMC for lean mass correlated with pQCT CSA for length or SSI for length. DXA BMC for bone area was weakly associated with pQCT SSI for length, in females only. Therefore, normalizing whole body DXA bone area for height and BMC for height provided the best measures of bone dimensions and strength. DXA BMC normalized for bone area and lean mass were poor indicators of bone strength.     

Usefulness of Reflection Scanning in Determining Whole-Body Composition in Broadly Built Individuals Using Dual-Energy X-ray Absorptiometry

Whole-body composition analysis by dual-energy X-ray absorptiometry (DXA) requires subjects to fit within the width limits of the DXA bed. To overcome this limitation, the aim of this study was to validate a partial scanning technique at which the upper left limb is deliberately left unscanned and measurements are “reflected” from the right-side upper limb. A Hologic Explorer-W densitometer was used in a sample of 189 participants, including athletes and nonathletes, ranging from underweight to obese (body mass index: 17.0–40.1 kg/m²). A whole-body scan was analyzed as the reference procedure to determine bone mineral content (BMC), lean soft tissue (LST), and fat mass (FM), and reanalyzed using a partial reflection scanning (RS) technique. RS estimates of BMC were associated with athletic status and differed significantly from reference estimates (p < 0.05). Also, the RS estimates of LST and FM were different (p < 0.05) from those of the reference whole-body scan, although differences were small (0.17 kg, ?0.02 kg, and ?0.10% for BMC, LST, and FM, respectively). The alternative procedure explained more than 99% of the reference scan variance with low limits of agreement (BMC: ?13.8 to 23.9 g [athletes] and ?6.3 to 18.0 g [nonathletes]; LST: ?0.11 to 0.45 kg; FM: ?0.22 to 0.17 kg). Regardless of body mass index, athletic status, and gender, RS is a useful and simple solution to be used in individuals wider than the DXA scan area. However, individual errors for BMC may be higher in athletes engaged in lateral dominant sports practice.     

Body Composition Measurements by Dual-Energy X-ray Absorptiometry Differ Between Two Analysis Modes

This study was undertaken to determine to what extent body-composition measurements by dual-energy X-ray absorptiometry (DXA) differed between two analysis modes (standard vs extended). Whole-body bone mineral density (BMD), bone mineral content (BMC), bone area (BA), fat mass (FM), lean mass (LM), and percentage of fat (%fat) of 263 women, aged 20-74 yr, were measured by DXA, with each scan analyzed by both the standard and extended analysis modes. The standard mode had significantly higher values for BMD, BMC, BA, and %fat, and significantly lower values for LM than extended mode (p < 0.05). The measurement error of BMC was highly correlated with the measurement error of BA (r = 0.93), thereby indicating the possibility of bone-edge instability by different analysis modes. Body mass index (BMI) was also significantly correlated with the measurement error of BMC (r = 0.75). The degree of obesity might be tightly associated with the occurrence of the measurement error. Caution is recommended when different analysis modes are used for making multicenter comparisons or assessing intervention-induced changes.     

Too Tall for the DXA Scan? Contributions of the Feet and Head to Overall Body Composition

Accurate assessment of total body composition in tall (>1.96m) individuals using dual energy x-ray absorptiometry (DXA) scans is problematic due to current height restrictions of the scan table. The aim of this investigation was to quantify absolute and relative contributions of fat, bone and lean mass, of the feet and head regions, to whole-body composition DXA scan totals. Whole-body DXA scans were performed in collegiate athletes. Athlete DXA scans were included in data analyses if the entire body fit within the confines of scan table area. The feet region of interest (ROI) was delineated at the ankle joint mortise, marked superiorly by the inferior margin of the tibial plafond and encompassing all inferior anatomical structures. The head region was calculated by the DXA scan software. Both absolute (kg) and relative (feet/whole-body x 100 = feet mass %) contributions to body composition were calculated. Data presented as mean±SD. 132 National Collegiate Athletic Association (NCAA) athletes (85 female) underwent DXA scans which met the inclusion criteria. The feet region represented: 1.9±0.3kg (2.6±0.3%) of total mass; 0.4±0.3kg (2.6±0.5%) of fat mass; 1.3±0.3kg (2.5±0.3%) of lean mass; and 0.14±0.0kg (5.4±0.6%) of bone mineral content (BMC). The head region represented: 4.8±0.5kg (6.9±0.8%) of total mass; 1.2±0.2kg (8.2±3.0%) of fat mass; 3.2±0.5kg (6.1±0.9%) of lean mass; and 0.48±0.07kg (18.7±2.7%) of BMC. Significant negative relationships were found between head% versus whole-body BMC (r=-0.54;p < 0.0001), lean mass (r=-0.57;p<0.0001), and fat mass (r=-0.81;p<0.0001) and between feet% versus fat mass (r=-0.68;p<0.0001). A significant positive relationship was noted between feet% versus whole-body BMC (r=0.18;p=0.04) but not versus lean mass (r=0.15;p=0.09). Removing the feet from whole-body composition analyses reduces lean, fat and bone mass compartment totals by 3%-5%. Removing the head region reduces body composition compartments by 6%-19%, from whole-body DXA scan totals.     

Bone density interpretation and relevance in Caucasian children aged 9-17 years of age: insights from a population-based fracture study.

The interpretation of bone density measurement in children is difficult due to a number of factors including rapid change in body size and uncertain clinical significance of bone density in children. This study asked two questions. (1) Is there a preferred bone density measurement site or type for fracture risk in children? (2) What is the best way to interpret bone density in children? This population-based case control study included 321 upper limb fracture cases and 321 class- and sex- matched randomly selected controls. Bone density at the hip, spine, and total body (including the arm) was measured by a Hologic QDR2000 densitometer (Waltham, MA) and examined as bone area (BA), bone mineral content (BMC), bone mineral density (BMD), bone mineral apparent density (BMAD), and BMC/lean mass (BMCLM). The only dual-energy X-ray absorptiometry (DXA) variables that were consistently associated with fracture risk in both boys and girls were spine BMD and BMAD for total upper limb fractures, and spine and hip BMAD for wrist and forearm fractures. No significant associations were observed for BA and BMCLM and inconsistent associations for BMC and other BMD sites. Five-yr fracture risk varied from 15–24% depending on site and gender in a child with a Z-score of -3. In the controls, all DXA variables were associated with age, height, and weight, but the weakest associations were with BMAD. In conclusion, in this study the spine BMAD had the strongest and most consistent association with upper limb fracture risk in children. The associations with age and body size imply that age specific Z-scores will be the most convenient for interpretation of DXA measures in children. Five-yr wrist and forearm fracture risk has potential as a clinical endpoint of immediate relevance.     

Does the Severity of Obesity Influence Bone Mineral Density Values in Premenopausal Women?

The aim of this study was to compare bone mineral content (BMC), bone mineral density (BMD), and geometric indices of hip bone strength among 3 groups of adult obese premenopausal women (severely obese, morbidly obese, and super morbidly obese). This study included 65 young adult premenopausal women whose body mass index (BMI) > 35 kg/m². They were divided into 3 groups using international cut-offs for BMI. Body composition and bone variables were measured by DXA. DXA measurements were completed for the whole body (WB), lumbar spine, total hip (TH), and femoral neck (FN). Geometric indices of FN strength (cross-sectional area, cross-sectional moment of inertia [CSMI], section modulus [Z], strength index [SI], and buckling ratio) were calculated by DXA. Results showed that age and height were not significantly different among the 3 groups. WB BMC values were higher in super morbidly obese women compared to severely and morbidly obese women. WB BMD, L1-L4 BMD, total hip BMD, FN BMD, cross-sectional area, CSMI, Z, and buckling ratio values were not significantly different among the 3 groups. SI values were lower in super morbidly obese compared to morbidly and severely obese women. In the whole population (n = 65), body weight, BMI, lean mass, fat mass, and trunk fat mass were positively correlated to WB BMC and negatively correlated to SI. Weight and lean mass were positively correlated to WB BMD and CSMI. Our findings suggest that the severity of obesity does not influence BMD values in premenopausal women.     

Bone Mineral Accrual Across Growth in a Mixed-Ethnic Group of Children: Are Asian Children Disadvantaged from an Early Age?

We investigated the contribution of ethnicity, physical activity, body composition, and calcium intake to bone accrual across 7 years of growth. We assessed 80 Caucasian and 74 Asian boys and 81 Caucasian and 64 Asian girls at baseline and retained 155 children across all 7 years. Ethnicity, physical activity, and calcium intake were assessed by questionnaire; fat mass, lean mass, and bone mineral content (BMC) of the whole body (WB), lumbar spine (LS), total proximal femur (PF_TOT), and femoral neck (FN) were measured using DXA (Hologic QDR 4500). We aligned children on peak height velocity and utilized multilevel modeling to assess bone mineral accrual. Height and lean mass accounted for 51.8% and 44.1% of BMC accrual in children. There was a significant difference in physical activity, calcium intake, and lean mass between Asians and Caucasian boys and girls at baseline and conclusion (p < 0.05). In boys, physical activity and ethnicity significantly predicted BMC accrual at the FN. In girls, Asians had significantly lower PF_TOT and FN BMC. Calcium was a significant predictor of WB BMC accrual in boys and girls. In conclusion, our findings highlight the importance of accounting for ethnicity in pediatric studies. Physical activity, dietary calcium, and lean mass positively influence bone accrual and are lower in Asian compared to Caucasian children from a very young age.     

Bone mass in young women is dependent on lean body mass.

Relationships between bone mineral density (BMD) and body mass, height, fat mass, and lean mass have been reported. This study examined the relationship between body size and composition on bone density in young premenopausal women. In this study, a cross-sectional design was used. Seventy-one healthy women aged between 24 and 36 yr selected to have a wide range of boy habitus (mean body mass index, 22.7+/-3.0) underwent a dual-energy X-ray absorptiometry (DXA) whole-body bone density scan (Hologic QDR 2000). Their bone density and soft tissue body composition and anthropometric parameters (skinfolds, girths, limb lengths, bone breadths, height, and body mass) were analyzed, and their body composition was assessed by underwater weighing (UWW). Bone-free lean mass (BFLM) determined by DXA was correlated with both bone mineral content (BMC) and BMD (r=0.74, p<0.001; r=0.48, p<0.001, respectively). In addition, fat-free mass (FFM) determined by UWW was correlated with BMC and BMD (r=0.80, p<0.001; r=0.48, p<0.001, respectively). Controlling for height in the model removed most of the correlations with whole-body BMD, with the exception of FFM, BFLM, and shoulder breadth (r=0.39, p<0.001; r=0.37, p<0.01; and r=0.34, p<0.01, respectively). No correlation was found between fat mass by DXA, UWW, and sum of skinfolds and BMD. These results indicate that bone mass in premenopausal women is dependent on lean body mass.     

Comparison of Body Composition by Bioelectrical Impedance and Dual-Energy X-Ray Absorptiometry in Overweight/Obese Postmenopausal Women

The purpose of this study was to compare the Rudolph J. Liedtke (RJL) Sciences Quantum II system bioelectrical impedance analyzer (BIA) with the fan beam Hologic dual-energy X-ray absorptiometry (DXA, software V8.26a) for assessing body composition in postmenopausal obese women. Thirty-three postmenopausal overweight/obese females (mean age: 53.9 ± 6.0 yr; mean weight: 91.3 ± 17.5 kg; and mean body mass index [BMI]: 33.1 ± 5.7 kg/m²) were evaluated for comparison of body weight (BW), fat mass (FM), percent FM (%FM), and fat free mass (FFM). The comparison was assessed by RJL Quantum 2 Cyprus 2.6© (Clinton Township, MI) BIA vs fan beam DXA Hologic QDR-4500A software V8.26a (ODR 4500 Hologic, Inc., Waltham, Mass). RJL-BIA and DXA measurements were performed at the same time. BW was measured using a balance scale (Detecto; Web City, MO) and these results were used for the RJL-BIA analysis. Balance weight was compared with DXA BW. Correlations between DXA and RJL-BIA for BW, FM, %FM, and FFM were 0.998, 0.980, 0.782, and 0.926 (p < 0.01), respectively. Bland-Altman plots demonstrated general agreement between methods for BW, FM, %FM, and FFM. However, for the latter 3 metrics of body composition, one unit change using BIA does not correspond to one unit change using DXA, as there were systematic disagreements at either end of the range of values. But RJL-BIA could be a valid method for assessing body composition of overweight/obese postmenopausal women once appropriate validated regression equations have been developed.