Relationships among body mass, its components, and bone

The influence of ghrelin, adiponectin, and leptin on bone mineral density in healthy postmenopausal women

The association of body fat mass (FM) with bone mineral mass (BMC) and bone mineral density (BMD) has been attributed to a mechanical load exerted on the skeleton by FM and by the effect of different hormones. The aim of the present study was to determine whether there is a relationship between ghrelin, adiponectin, and leptin with BMC and BMD in healthy postmenopausal women (n = 88; age, 68.9 +/- 6.8 years; body mass index, 27.4 +/- 3.6 kg/m(2)). Body composition, BMC, and BMD were derived by dual-energy X-ray absorptiometry. Waist-to-hip (WHR) and waist-to-thigh (WTR) ratios were also obtained. Ghrelin was associated with total BMC (beta = -0.945; P = 0.0001), total BMD (beta = -0.959; P = 0.0001), lumbar spine BMD (beta = -0.945; P = 0.0001), and femoral neck BMD (beta = -0.957; P = 0.0001), and remained associated (P < 0.041) in different analyses that controlled for measured body composition and hormonal and insulin resistance values. However, the associations between ghrelin and measured bone mineral values were no longer significant (P > 0.149) when adjusted for body fat distribution values (WHR, WTR). Adiponectin was significantly related to total BMC (beta = -0.931; P = 0.0001), total BMD (beta = -0.940; P = 0.0001), lumbar spine BMD (beta = -0.937; P = 0.0001), and femoral neck BMD (beta = -0.940; P = 0.0001) values, and these relationships remained significant (P < 0.019) after adjusting for measured body fat, hormonal, and insulin resistance values but not when adjusted for fat-free mass (FFM; P > 0.106). In addition, significant associations of leptin with total BMC (beta = 0.912; P = 0.0001), total BMD (beta = 0.907; P = 0.0001), lumbar spine BMD (beta = 0.899; P = 0.0001), and femoral neck BMD (beta = 0.906; P = 0.0001) were found. These associations remained significant (P < 0.010) in different analyses that controlled for hormonal and insulin resistance values, but the associations between leptin and bone mineral values were no longer significant (P > 0.145) when adjusted for specific body composition values (WHR, WTR, FM, and FFM). In conclusion, it appears that the influence of plasma ghrelin, adiponectin, and leptin levels on BMC and BMD values is mediated or confounded by the specific body composition parameters in healthy postmenopausal women.

Low bone mineral density and decreased bone turnover in Duchenne muscular dystrophy

This cross-sectional study examined bone mineral density, bone turnover, body composition and calciotropic hormones in 24 boys with Duchenne muscular dystrophy (DMD) (2.3-19.7 years), most of whom were being treated with prednisolone, and 24 age-matched healthy boys. Our study demonstrated lower bone mineral density in the DMD group for total body, spine, hip, heel and forearm measurements. These differences between DMD patients and controls increased with increasing age. Biochemical markers of both bone formation and resorption revealed reduced bone turnover in DMD patients. The fracture rate was not higher in DMD patients. The DMD group had low vitamin D levels but high leptin levels in comparison with the control group. Muscle strength correlated with bone mineral density assessed at the hip and heel in the DMD group. Interventions that increase bone formation should be considered, as DMD patients have reduced bone turnover in addition to their low bone mineral density.

CLINICAL Review # : low body weight mediates the relationship between HIV infection and low bone mineral density: a meta-analysis

CONTEXT

HIV infection has been associated with low bone mineral density (BMD) in many cross-sectional studies, although longitudinal studies have not demonstrated accelerated bone loss. The cross-sectional studies may have been confounded by the failure to control for low body weight in HIV-infected patients.

OBJECTIVE

Our objective was to determine whether low body weight might explain the association of HIV infection with low BMD.

DATA SOURCES

MEDLINE and EMBASE were searched for English language studies published from 1966 to March 2007, and conference abstracts prior to 2007 were hand-searched.

STUDY SELECTION

All studies reporting BMD and weight or body mass index in adult patients with HIV and a healthy age- and sex-comparable control group were included. Nine of 40 identified studies and one of 68 identified abstracts were eligible.

DATA SYNTHESIS

We adjusted for the between-groups weight differences using regression coefficients from published cohorts of healthy men and women. On average, HIV-infected patients were 5.1 kg [95% confidence interval (CI), -6.8, -3.4; P < 0.001] lighter than controls. At all skeletal sites, unadjusted BMD was lower by 4.4-7.0% in the HIV-infected groups than the controls (P < 0.01). After adjustment for body weight, residual between-groups differences in BMD were small (2.2-4.7%) [lumbar spine, -0.02 (95% CI, -0.05, 0.01) g/cm2; P = 0.12; total hip, -0.02 (95% CI, -0.04, 0.00) g/cm2; P = 0.031; femoral neck, -0.04 (95% CI, -0.07, -0.01) g/cm2; P = 0.013; and total body, -0.03 (95% CI, -0.07, 0.01) g/cm2, P = 0.11].

CONCLUSION

HIV-infected patients are lighter than controls and low body weight may largely account for the high prevalence of low BMD reported in HIV-infected patients. However, in the setting of current treatment practice, HIV infection per se is not a risk factor for low BMD.

Polymorphisms in the CYP19 gene that influence bone mineral density

Osteoporosis is a prevalent disease with a strong genetic component. Estrogens play a critical role in bone homeostasis. The aromatization of androgenic precursors is the main source of estrogens in men and postmenopausal women. Thus, aromatase is an attractive osteoporosis candidate gene. In this paper the influence of aromatase activity and aromatase gene variants on skeletal homeostasis is reviewed. The results of studies regarding the association between some common polymorphisms of the aromatase gene and bone mineral density and the risk of osteoporotic fractures are described. The mechanisms involved and the potential usefulness of those genetic data in the prevention and management of osteoporosis are discussed.

Bone mineral density in adults with the metabolic syndrome: analysis in a population-based U.S. sample

BACKGROUND

The metabolic syndrome is associated with low-grade inflammation. It has been suggested that proinflammatory cytokines and low-grade systemic inflammation activate bone resorption and may lead to reduced bone mineral density (BMD), but no previous studies have evaluated the association between the metabolic syndrome and BMD. We examined this relationship in a representative U.S. population-based sample from the Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994).

METHODS

We identified adult subjects enrolled in NHANES III with the metabolic syndrome as defined by the criteria of the Adult Treatment Panel III. We conducted a cross-sectional analysis of femoral neck BMD (FN-BMD) for subjects with and without the metabolic syndrome. Analyses were adjusted for relevant covariates and stratified by quintile of body mass index.

RESULTS

Among 8,197 persons at least 20 yr old who underwent FN-BMD measurement, 1773 (22%) had the metabolic syndrome. After multivariable adjustment, FN-BMD was higher among subjects with the metabolic syndrome (0.86 g/cm(2)) than those without (0.80 g/cm(2); P < 0.0001). When stratified by body mass index, FN-BMD was similar between subjects with and without the metabolic syndrome. Adjusted FN-BMD increased with additional components of the metabolic syndrome (P < 0.0001 for trend), and there was a significant positive association with abdominal obesity (P < 0.0001). A subgroup of subjects with diabetes had higher FM-BMD than those without, independent of abdominal obesity.

CONCLUSIONS

In NHANES III, the metabolic syndrome was not associated with reduced FN-BMD.

Effects of bisphosphonate treatment on bone repair under immunosuppression using cyclosporine A in adult rats

The effect of cyclosporine A on bone turnover remains unclear. Using adult rats with vascularized bone transplantation, we show that long-term cyclosporine A administration increases bone turnover and zoledronic acid treatment enhances the reconstruction of cyclosporine A-administered skeleton. Bisphosphonates might be efficacious in human bone repair under immunosuppression using cyclosporine A.

INTRODUCTION

Bisphosphonate treatment effectively prevents bone loss after transplantation. However, recent evidence from gain- and loss-of-function experiments has indicated that calcineurin inhibitors, such as cyclosporine A (CsA), reduce bone turnover, and severely suppressed bone turnover might delay the union of human fractured bone. The purpose of this study was to investigate the effects of bisphosphonate treatment on the repair of CsA-administered skeleton.

METHODS

After skeletal reconstruction by vascularized tibial grafting, adult recipient rats were treated with intramuscular CsA (10 mg/kg/day) and low-dose (0.2 microg/kg/week) or high-dose (2 microg/kg/week) subcutaneous zoledronic acid alone or in combination for 8 weeks. Biochemical parameters were measured in blood and urine. The reconstructed skeleton was analyzed using soft X-ray, histology, dual energy X-ray absorptiometry, and three-point bending test.

RESULTS

CsA induced mild renal dysfunction, hyperparathyroidism and high bone turnover. High-dose zoledronic acid delayed cortical bone union at the distal host-graft junction, but its combination with CsA did not cause such a delay. High-dose zoledronic acid prevented CsA-induced bone loss and bone fragility in the reconstructed skeleton.

CONCLUSION

In this rat model, long-term CsA administration increases bone turnover, at least partly, through hyperparathyroidism and high-dose zoledronic acid treatment does not impair the union of CsA-administered bone.

Walking intensity for postmenopausal bone mineral preservation and accrual

INTRODUCTION

Mechanical stresses on the bone are an important aspect of physical activity that promotes bone preservation and increases in bone mass. Exercise intensities leading to bone preservation and accrual have not been adequately defined for humans in general, and postmenopausal women in particular.

MATERIALS AND METHODS

To quantify parameters of effective walking intensity for preservation and accrual of bone mineral, healthy postmenopausal women engaged in 30 weeks of supervised walking, 4.8 km per day, 4 days a week at intensities of 102% or 123% of the ventilatory threshold (VT) equivalent to 67% and 86% of maximal effort (VO2 max). Subjects were matched by age, body mass, hormone replacement status (HRT) and VT. Areal bone mineral density (aBMD) determined by DXA (n=25) and bone formation markers osteocalcin (OC), and bone-specific alkaline phosphatase (bALP) (n=43), were measured at the outset and at 15-week intervals. Peak vertical forces at corresponding intensities were measured (n=9) on a force plate.

RESULTS

aBMD of legs and whole body, but not of other sites, and lean mass of legs, but not of arms, increased after 15 weeks of high intensity, compared to moderate losses for low intensity training. Leg and total body aBMD was preserved and slightly increased with loads greater than 872.3 newtons (N) with a walking intensity above 115% of VT or 74% of VO2 max, speeds above 6.14 km/h, and heart rates above 82.3% of age-specific maximum. OC and bALP did not correlate with training-induced changes in aBMD.

CONCLUSIONS

At exercise intensities above 115% of VT or 74% of VO2 max, and walking speeds above 6.14 km/h, mechanical loading of 872.3 N or 1.22 times body weight is sufficient for increases in leg muscle mass and preservation of BMD in postmenopausal women.

Muscle mass deficits are associated with bone mineral density in men with idiopathic vertebral fracture

INTRODUCTION AND HYPOTHESIS

The causes of idiopathic vertebral fractures (IVF) in men are poorly understood. We hypothesised that in IVF, areal bone mineral density (aBMD) deficits would be associated with reduced muscle mass.

METHODS

In this case-control study, 48 men (61.5 +/- 12.1 years old) presenting with symptomatic IVF were compared with 48 healthy controls matched for age (+/-5 years) and stature (+/-5 cm). The aBMD and soft-tissue body composition were determined by dual energy X-ray absorptiometry (DXA). Muscle mass was defined as the ratio of appendicular lean mass to the square of height (ALMI). Sex hormones, IGF-I and its binding protein IGFBP-3 were measured by immunoassay.

RESULTS

ALMI was significantly lower in IVF patients (8.27 +/- 0.90 vs 8.65 +/- 0.88 kg/m(2), t = 2.193, df = 47, P = 0.033 by paired sample t-test). Hierarchical regression analysis revealed that for IVF patients, ALMI explained the greatest proportion of variance in BMD at the lumbar spine, femoral neck and total hip (R (2) (change) = 16.4-22.7%, P = 0.012-0.002) and only IGFBP-3 explained variance in ALMI (R (2) (change) = 19.9%, P = 0.006).

CONCLUSIONS

In men with IVF, ALMI was reduced and associated with IGFBP-3. ALMI was identified as a novel factor that explained a greater proportion of variance in BMD than either fat mass or serum biochemistry.

Relationships between bone mineral density and cell size in cervical smears, serum estradiol levels, and anthropometric characteristics

OBJECTIVE

To evaluate relationships between bone mineral density and morphometric characteristics of squamous cells in cervical smears, serum estradiol levels, body weight, and body mass index.

METHOD

Dual X-ray absorptiometry measurements were performed in 107 women who had recently undergone routine screening for cervical cancer. Serum estradiol levels were determined. Mean areas for squamous cells, squamous cell nuclei, and squamous cell cytoplasm were calculated, as well as the nucleus area to cytoplasm area ratio.

RESULTS

The mean cell and cytoplasmic areas were significantly lower in women with lower T scores for femoral neck and lumbar spine (P<0.001). Mean T scores were significantly lower for the women with atrophic cells than for those with mature cells (P<0.001). A correlation between estradiol levels and T scores was found for the lumbar spine (P<0.05) but not for the femoral neck. Multiple linear regression analysis showed the cytoplasmic area to be the most significant predictor of T scores for the total hip, followed by BMI and age, and to be the only significant predictor of T scores for the total spine.

CONCLUSION

Relationships were found between bone mineral density and both the total cell and cytoplasmic areas of squamous cells obtained from cervical smears.

The impact of obesity on the musculoskeletal system

Obesity is associated with a range of disabling musculoskeletal conditions in adults. As the prevalence of obesity increases, the societal burden of these chronic musculoskeletal conditions, in terms of disability, health-related quality of life, and health-care costs, also increases. Research exploring the nature and strength of the associations between obesity and musculoskeletal conditions is accumulating, providing a better understanding of underlying mechanisms. Weight reduction is important in ameliorating some of the manifestations of musculoskeletal disease and improving function.

Adiponectin is a predictor of bone mineral density in middle-aged premenopausal women

Adipose-modulated biochemical signal that explains some of the association between fat mass and bone mineral density (BMD) is adiponectin. The results demonstrated an independent association between adiponectin and BMD, while the influence of adiponectin on bone mineral content is mediated by fat free mass in middle-aged women.

INTRODUCTION

Positive association between fat mass (FM) and bone mineral density (BMD) is mediated by biochemical factors.

METHODS

The relationship between plasma adiponectin concentration and BMD in 98 sedentary premenopausal women aged 38-49 years with a body mass index range of 20.0-42.1 kg/m(2) was examined. Different body composition and blood biochemical parameters were measured to adjust for possible confounding variables.

RESULTS

The association between adiponectin and BMD values (total BMD: beta = -0.919; p = 0.0001, femoral neck BMD: beta = -0.925; p = 0.0001 and lumbar spine BMD: ss = -0.912; p = 0.0001) was independent of the influences that measured body composition, hormonal and insulin resistance factors may exert on BMD (p < 0.02). However, adiponectin explained only 3-12% of the variations in measured BMD variables. Similarly, adiponectin was associated with total bone mineral content (BMC; beta = -0.911; p = 0.0001) and remained associated in different analyses that controlled for possible confounding parameters (p < 0.01). However, the association between adiponectin and total BMC was no longer significant when adjusted for fat free mass (FFM; p > 0.21).

CONCLUSIONS

Adiponectin is an independent predictor of BMD, while its independent contribution to the interindividual variance in measured values is only modest. The influence of adiponectin on total BMC is mediated or confounded by FFM in middle-aged premenopausal women.

Effects of dietary calcium intake on body weight and prevalence of osteoporosis in early postmenopausal women

BACKGROUND

High calcium intakes seem to be ineffective at reducing bone loss in early postmenopausal women. However, the inverse relation between calcium intake and body weight can attenuate the negative effect of a low dietary calcium intake.

OBJECTIVE

The objective was to assess the role of dietary calcium and body mass index (BMI) on osteoporosis, defined according to World Health Organization criteria as a lumbar bone density >2.5 SD below the T score.

DESIGN

This was a cross-sectional, retrospective, observational study conducted in 1771 healthy, early postmenopausal women, who were not taking calcium supplements at the first densitometric evaluation. Weekly frequency of dairy food consumption was used to estimate the relative intake of dietary calcium. Total dairy intake was classified into 4 categories by quartile cutoffs. Multiple logistic regression analyses were used to study this sample.

RESULTS

BMI and prevalence of overweight showed significant inverse trends with increasing dairy intake. Calcium intake was not associated with osteoporosis when overweight was not considered. However, when overweight was considered in the analysis, women with the lowest calcium intake were more likely to have osteoporosis (odds ratio: 1.46; 95% CI: 1.12, 1.89; P = 0.008) than were women with the highest calcium intake.

CONCLUSIONS

In early postmenopausal women, a low dietary calcium intake may increase the risk of osteoporosis, but its negative effect can be offset by the greater BMI found in women with a low calcium intake.

Linkage of genes to total lean body mass in normal women

BACKGROUND

Total lean body mass (LEAN-tot) is one of the three major components of body weight. Its deterioration is a risk factor for frailty. Despite this, there are few studies examining the contribution of genetic factors.

OBJECTIVE

Our objective was to examine the contribution of genetic factors for LEAN-tot variation, including a genome-wide search for the genes.

RESEARCH METHODS

Dual-energy x-ray absorptiometry measurements of LEAN-tot were obtained from each of the 3180 United Kingdom females (509 monozygotic and 1081 dizygotic twin pairs). Contribution of genetic factors was assessed using variance component analysis. A genome-wide linkage analysis was performed on the dizygotic twins using a modified version of the Haseman-Elston method.

RESULTS

Age, body height, total fat, and bone mass were correlated with LEAN-tot, and commonly explained 52% of the LEAN-tot variation. The crude heritability estimate was 74.0 +/- 4.0%, after adjustment for the aforementioned factors; 65.2 +/- 4.6% was attributable to independent genetic effects. Significant (P < 0.001) genetic correlations were found between LEAN-tot and bone mass, and LEAN-tot and total fat. Adjusted only for age, LEAN-tot showed no significant linkage. After adjustment for all covariates, significant linkage (LOD = 4.49 and 3.62) was observed at chromosome 12q24.3 and 14q22.3, respectively. Additional peaks of interest were on 7p15.3-15.1 (LOD = 2.86) and 8p22 (LOD = 2.83).

CONCLUSIONS

LEAN-tot measured by dual-energy x-ray absorptiometry is highly heritable, independent of other body measures. This first genomic search for genes associated with the lean component of body mass suggests significant linkage to quantitative trait loci on chromosomes 12 and 14.

Bone mineral density remains stable in HAART-treated HIV-infected men over 2 years

OBJECTIVE

Recently we reported that human immunodeficiency virus (HIV)-infected Caucasian men treated with highly active antiretroviral therapy (HAART) have normal weight-adjusted bone mineral density (BMD), in contrast to most other cross-sectional analyses, which have reported low BMD in HIV-infected patients. We have now addressed the question of whether there is accelerated BMD loss over time in HIV-infected men.

DESIGN

A 2-year, prospective, longitudinal study.

SUBJECTS

Twenty-three HAART-treated, HIV-infected men and 26 healthy controls.

MEASUREMENTS

All participants had measurements of BMD and bone-related laboratory parameters at baseline, and a repeat measurement of BMD at 2 years.

RESULTS

In the HIV-infected men the mean age was 47 years, the mean duration of infection was 8.2 years, and the mean duration of HAART was 54 months. Over 2 years of follow-up, BMD increased from baseline in the HIV-infected men by 2.6% at the lumbar spine (P = 0.05 vs. baseline), and remained stable at the total hip (mean change 0.1%, P > 0.99) and total body (mean change 0.6%, P = 0.39). Mean changes in BMD in the control group were 1.4% at the lumbar spine, -0.1% at the total hip, and -0.8% at the total body. The HIV-infected men lost less total body BMD than the control group (P = 0.01). In the HIV-infected men, body weight remained stable over 2 years while fat mass decreased and lean mass tended to increase, whereas in the controls, body weight and fat mass increased while lean mass remained stable.

CONCLUSIONS

Accelerated bone loss does not occur in HIV-infected men treated with HAART. Monitoring of BMD in HIV-infected men may not be necessary.

Age-related changes in trabecular architecture differ in female and male C57BL/6J mice

We used microCT and histomorphometry to assess age-related changes in bone architecture in male and female C57BL/6J mice. Deterioration in vertebral and femoral trabecular microarchitecture begins early, continues throughout life, is more pronounced at the femoral metaphysis than in the vertebrae, and is greater in females than males.

INTRODUCTION

Despite widespread use of mice in the study of musculoskeletal disease, the age-related changes in murine bone structure and the relationship to whole body BMD changes are not well characterized. Thus, we assessed age-related changes in body composition, whole body BMD, and trabecular and cortical microarchitecture at axial and appendicular sites in mice.

MATERIALS AND METHODS

Peripheral DXA was used to assess body composition and whole body BMD in vivo, and microCT and histomorphometry were used to measure trabecular and cortical architecture in excised femora, tibia, and vertebrae in male and female C57BL/6J mice at eight time-points between 1 and 20 mo of age (n = 6-9/group).

RESULTS

Body weight and total body BMD increased with age in male and female, with a marked increase in body fat between 6 and 12 mo of age. In contrast, trabecular bone volume (BV/TV) was greatest at 6-8 wk of age and declined steadily thereafter, particularly in the metaphyseal region of long bones. Age-related declines in BV/TV were greater in female than male. Trabecular bone loss was characterized by a rapid decrease in trabecular number between 2 and 6 mo of age, and a more gradual decline thereafter, whereas trabecular thickness increased slowly over life. Cortical thickness increased markedly from 1 to 3 mo of age and was maintained or slightly decreased thereafter.

CONCLUSIONS

In C57BL/6J mice, despite increasing body weight and total body BMD, age-related declines in vertebral and distal femoral trabecular bone volume occur early and continue throughout life and are more pronounced in females than males. Awareness of these age-related changed in bone morphology are critical for interpreting the skeletal response to pharmacologic interventions or genetic manipulation in mice.

Extreme obesity reduces bone mineral density: complementary evidence from mice and women

OBJECTIVE

To evaluate the effects of body adiposity on bone mineral density in the presence and absence of ovarian hormones in female mice and postmenopausal women.

RESEARCH METHODS AND PROCEDURES

We assessed percentage body fat, serum leptin levels, and bone mineral density in ovariectomized and non-ovariectomized C57BL/6 female mice that had been fed various calorically dense diets to induce body weight profiles ranging from lean to very obese. Additionally, we assessed percentage body fat and whole body bone mineral density in 37 overweight and extremely obese postmenopausal women from the Women's Contraceptive and Reproductive Experiences study.

RESULTS

In mice, higher levels of body adiposity (>40% body fat) were associated with lower bone mineral density in ovariectomized C57BL/6 female mice. A similar trend was observed in a small sample of postmenopausal women.

DISCUSSION

The complementary studies in mice and women suggest that extreme obesity in postmenopausal women may be associated with reduced bone mineral density. Thus, extreme obesity (BMI > 40 kg/m2) may increase the risk for osteopenia and osteoporosis. Given the obesity epidemic in the U.S. and in many other countries, and, in particular, the rising number of extremely obese adult women, increased attention should be drawn to the significant and interrelated public health issues of obesity and osteoporosis.

Type I diabetic bone phenotype is location but not gender dependent

Bone is highly dynamic and responsive. Bone location, bone type and gender can influence bone responses (positive, negative or none) and magnitude. Type I diabetes induces bone loss and increased marrow adiposity in the tibia. We tested if this response exhibits gender and location dependency by examining femur, vertebrae and calvaria of male and female, control and diabetic BALB/c mice. Non-diabetic male mice exhibited larger body, muscle, and fat mass, and increased femur BMD compared to female mice, while vertebrae and calvarial bone parameters did not exhibit gender differences. Streptozotocin-induced diabetes caused a reduction in BMD at all sites examined irrespective of gender. Increased marrow adiposity was evident in diabetic femurs and calvaria (endochondrial and intramembranous formed bones, respectively), but not in vertebrae. Leptin-deficient mice also exhibit location dependent bone responses and we found that serum leptin levels were significantly lower in diabetic compared to control mice. However, in contrast to leptin-deficient mice, the vertebrae of T1-diabetic mice exhibit bone loss, not gain. Taken together, our findings indicate that TI-diabetic bone loss in mice is not gender, bone location or bone type dependent, while increased marrow adiposity is location dependent.

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.

Dlk1/FA1 is a novel endocrine regulator of bone and fat mass and its serum level is modulated by growth hormone

Fat and bone metabolism are two linked processes regulated by several hormonal factors. Fetal antigen 1 (FA1) is the soluble form of dlk1 (delta-like 1), which is a member of the Notch-Delta family. We previously identified FA1 as a negative regulator of bone marrow mesenchymal stem cell differentiation. Here, we studied the effects of circulating FA1 on fat and bone mass in vivo by generating mice expressing high serum levels of FA1 (FA1 mice) using the hydrodynamic-based gene transfer procedure. We found that increased serum FA1 levels led to a significant reduction in total body weight, fat mass, and bone mass in a dose-dependent manner. Reduced bone mass in FA1 mice was associated with the inhibition of mineral apposition rate and bone formation rates by 58 and 72%, respectively. Because FA1 is colocalized with GH in the pituitary gland, we explored the possible modulation of serum FA1 by GH. Serum levels of IGF-I and IGF binding proteins did not change in FA1 mice, whereas increasing serum GH in normal mice using hydrodynamic-based gene transfer procedure dramatically reduced serum FA1 levels by 60%. Conversely, serum FA1 was increased 450% in hypophysectomized mice, and this high level was reduced by 40% during GH treatment. In conclusion, our data identify the FA1 as a novel endocrine factor regulating bone mass and fat mass in vivo, and its serum levels are regulated by GH. FA1 thus provides a novel class of developmental molecules that regulate physiological functions of the postnatal organisms.

DXA in vivo BMD methodology: an erroneous and misleading research and clinical gauge of bone mineral status, bone fragility, and bone remodelling

The seemingly unqualified reliance and near-universal dependence upon in vivo dual-energy X-ray absorptiometric (DXA) methodology to provide accurate, quantitative, and meaningful in vivo (in situ cadaveric) bone mineral areal density ("BMD") determinations are proven to be unwarranted and misplaced. The underlying systematics of sizable, inherently unavoidable and un-correctable inaccuracies in the DXA output values of in vivo "BMD" are shown to be quantitatively consistent with being the root cause of unreliable, misdirected, and misinterpreted aspects of consensual knowledge of bone fragility, osteoporotic diagnostics/prognostics, and remodelling therapies. The "BMD" label that DXA ascribes to the output values of in vivo (in situ cadaveric) bone densitometry scans is shown to be a misnomer and an erroneous and invalid measure of bone mineral material. The DXA-derived "BMD" value does not correctly represent the areal density of bone mineral material, as it is contaminated by sizable, unavoidable, inextricable, independent soft tissue contributions. Due to intra- and extra-osseous soft tissue X-ray absorptiometric effects, it is unknown (and unknowable) exactly what DXA in vivo "BMD" is a measure of in any given case, or what proportion of the "BMD" value represents the actual bone mineral material areal density present in the DXA scan region of interest (ROI) of any predominantly trabecular bone-site (e.g., lumbar vertebrae, proximal femora). This inherent fundamental defect in DXA in vivo bone mineral areal density methodology adversely compromises both the validity and reliability of patient-specific diagnostic/prognostic evaluations, cross sectional and prospective studies, and DXA-based interpretations of bone quality and bone fragility. It further undermines the WHO characterizations (and definitions) of 'normal', 'osteopenic', and 'osteoporotic' classifications. It is also seen to make equivocal the qualitative and quantitative epidemiological estimates of the proportion of the population that is, or is deemed to become, osteoporotic. The present quantitative exposition shows DXA-measured in vivo "BMD" methodology to be an intrinsically flawed and misleading indicator of bone mineral status and an erroneous gauge of relative fracture risk.

Expression and regulation of resistin in osteoblasts and osteoclasts indicate a role in bone metabolism

The adipose tissue is the site of expression and secretion of a range of biologically active proteins, called adipokines, for example, leptin, adiponectin, and resistin. Leptin has previously been shown to be expressed in osteoblasts and to promote bone mineralization, whereas adiponectin expression is enhanced during osteoblast differentiation. In the present study we explored the possible role of resistin in bone metabolism. We found that resistin is expressed in murine preosteoclasts and preosteoblasts (RAW 264.7, MC3T3-E1), in primary human bone marrow stem cells and in mature human osteoblasts. The expression of resistin mRNA in RAW 264.7 was increased during differentiation and seemed to be regulated through PKC- and PKA-dependent mechanisms. Recombinant resistin increased the number of differentiated osteoclasts and stimulated NFkappaB promoter activity, indicating a role in osteoclastogenesis. Resistin also enhanced the proliferation of MC3T3-E1 cells in a PKA and PKC-dependent manner, but only weakly interfered with genes known to be upregulated during differentiation of MC3T3-E1 into osteoblasts. All together, our results indicate that resistin may play a role in bone remodeling.

Biphasic fracture risk in diabetes: a population-based study

Diabetes is associated with increased fracture rates but the effect size, time course and modifying factors are poorly understood. This study was undertaken to assess the effect of diabetes on fracture rates and possible interactions with age, duration of diabetes and comorbidity. A retrospective, population-based matched cohort study (1984-2004) was performed using the Population Health Information System (POPULIS) for the Province of Manitoba, Canada. The study cohort consisted of 82,094 diabetic adults and 236,682 non-diabetic matched controls. Diabetes was subclassified as long term, short term, and newly diagnosed. Number of ambulatory diagnostic groups (ADGs) was an index of comorbidity. Poisson regression was used to study counts of combined hip, wrist and spine (osteoporotic) fractures (5691 with diabetes and 16,457 without diabetes) and hip fractures (1901 with diabetes and 5224 without diabetes). Independent effects of longer duration of diabetes (p-for-trend<0.0001) and number of ADGs (p-for-trend<0.0001) were observed on fracture rates. Newly diagnosed diabetes showed a reduction in osteoporotic fractures (rate ratio [RR] 0.91 [95% CI, 0.86-0.95]) and hip fractures (RR 0.83 [0.75-0.92]). Long-term diabetes showed an increase in osteoporotic fractures (RR 1.15 [CI, 1.09-1.22]) and hip fractures (RR 1.40 [1.28-1.53]). We conclude that long-term diabetes is associated with increased fracture risk, whereas newly diagnosed diabetes shows a reduction in fractures. It is hypothesized that the opposing effects of overweight/obesity and diabetes-related complications contribute to the observed biphasic fracture risk, though causality cannot be proven from this observational study.

Relationship of obesity with osteoporosis

CONTEXT

The relationship between obesity and osteoporosis has been widely studied, and epidemiological evidence shows that obesity is correlated with increased bone mass. Previous analyses, however, did not control for the mechanical loading effects of total body weight on bone mass and may have generated a confounded or even biased relationship between obesity and osteoporosis.

OBJECTIVE

The objective of this study was to reevaluate the relationship between obesity and osteoporosis by accounting for the mechanical loading effects of total body weight on bone mass.

METHODS

We measured whole body fat mass, lean mass, percentage fat mass, body mass index, and bone mass in two large samples of different ethnicity: 1988 unrelated Chinese subjects and 4489 Caucasian subjects from 512 pedigrees. We first evaluated the Pearson correlations among different phenotypes. We then dissected the phenotypic correlations into genetic and environmental components with bone mass unadjusted or adjusted for body weight. This allowed us to compare the results with and without controlling for mechanical loading effects of body weight on bone mass.

RESULTS

In both Chinese and Caucasian subjects, when the mechanical loading effect of body weight on bone mass was adjusted for, the phenotypic correlation (including its genetic and environmental components) between fat mass (or percentage fat mass) and bone mass was negative. Further multivariate analyses in subjects stratified by body weight confirmed the inverse relationship between bone mass and fat mass, after mechanical loading effects due to total body weight were controlled.

CONCLUSIONS

Increasing fat mass may not have a beneficial effect on bone mass.

Bone mass, biochemical markers and growth in children with chronic kidney disease: a 1-year prospective study

AIM

This study was designed to investigate bone mineral density (BMD), growth parameters and biochemical markers in children with chronic kidney disease (CKD).

METHODS

Sixteen patients, 4-18 years, with CKD were prospectively followed for 1 year. Auxological data, body composition, BMD by dual-energy X-ray absorptiometry, bone age, bone turnover markers, vitamin D, parathyroid hormone (PTH), leptin, osteoprotegerin, insulin-like growth factor-I (IGF-I) and IGF binding protein-3 were measured. A questionnaire regarding bone health and diet was also performed.

RESULTS

Delayed bone age was observed (n = 11) and the BMD Z-scores for total body were below zero in seven patients. However, total body BMD (TBBMD) increased in 12 patients. Most patients had increased osteocalcin and carboxy-terminal telopeptide of type I collagen, but normal alkaline phosphatase, type I procollagen intact amino-terminal propeptide and tartrate-resistant acid phosphatase 5b. Ten patients had increased PTH. Most children had normal levels of leptin, osteoprotegerin, IGF-I and IGFBP-3. Leptin, at baseline, correlated with differences in TBBMD over 1 year.

CONCLUSIONS

Only seven (44%) had negative Z-scores and TBBMD increased over 1 year. Bone markers at baseline did not predict the longitudinal changes in BMD.

Association of a single-nucleotide variation (A1330V) in the low-density lipoprotein receptor-related protein 5 gene (LRP5) with bone mineral density in adult Japanese women

Low-density lipoprotein receptor-related protein 5 (LRP5), a co-receptor of Wnt signaling, is an important regulator of bone development and maintenance. Recently we identified correlation between an intronic single-nucleotide polymorphism (SNP) in the LRP5 gene and vertebral bone mineral density (BMD), indicating that a genetic ground exists at this locus for determination of BMD. In the study reported here, we searched for nucleotide variation(s) that might confer susceptibility to osteoporosis among an extended panel of 387 healthy subjects recruited from the same hospital (Group-A), as well as among 384 subjects from the general population in eastern Japan (Group-B). We basically focused on two potentially functional variations, Q89R (c.266A > G) and A1330V (c.3989C > T), whose functional effects by the amino-acid changes were estimated by the SIFT software program; it predicted the 1330 V allele as deleterious ("intolerant") although the minor allele of Q89R was questionable. By analyzing associations between the variant alleles and the BMD, reproducible association of the minor variant of A1330V to lower adjusted BMD levels was detected; i.e., In Group-A subjects 1330-V significantly associated with the spinal BMD Z-score (P = 0.034), and in Group-B it associated with low radial BMD (P = 0.019). From haplotype and linkage disequilibrium (LD) analysis for 29 SNPs, we detected two separate LD blocks within the entire 137-kb LRP5 locus, basically consistent with a previous report on Caucasians. One of the second block haplotype significantly associated with adjusted BMD (r = 0.15, P = 0.004). Possible combined effect of Q89R and A1330V belonging to different LD blocks was denied by multiple regression analyses. Our results indicate that genetic variations in LRP5 are important factors affecting BMD in adult women and that 1330 V may contribute to osteoporosis susceptibility, at least in Japanese.

Impact of increased overweight on the projected prevalence of osteoporosis in older women

INTRODUCTION

Overweight is increasing worldwide, but particularly in the United States of America. Higher body weight is associated with higher bone density, so our goal was to estimate whether the higher prevalence of overweight is likely to reduce osteoporosis among older women.

METHODS

We calculated the prevalence of osteoporosis by weight status in older women using data from the third National Health and Nutrition Examination Survey (NHANES III, 1988-94). We defined overweight as a body mass index (BMI) >or=25 and osteoporosis as a femur neck bone mineral density (BMD) value 2.5 standard deviations or more below the mean of that of young women. To estimate the expected prevalence of osteoporosis, we applied the prevalence of osteoporosis by weight status from NHANES III to the corresponding weight status prevalence from NHANES 1999-2002.

RESULTS

Of older women in NHANES 1999-2002, 68% were overweight compared to 62% in NHANES III. Overweight status was significantly related to osteoporosis prevalence (P < 0.001). However, the expected prevalence of osteoporosis in NHANES 1999-2002 was only slightly lower than that seen in NHANES III (16.8% vs 18.1%, respectively).

CONCLUSIONS

The increasing prevalence of overweight among older US women appears unlikely to be accompanied by a significant reduction in osteoporosis.

Relative contribution of body composition to bone mineral density at different sites in men and women of South Korea

We examined the relative contribution of body composition to bone mineral density (BMD) at various sites in 1406 Korean rural men and women, aged 19-80 years, from July to August 2004. The BMD was measured at peripheral (distal forearm and calcaneus) and central (lumbar spine at L1-L4, femoral neck, trochanter, and Ward's triangle) using dual-energy X-ray absorptiometry. In multivariate analyses, the linear regression models were adjusted for relevant covariates. In premenopausal women, only lean mass had a significant positive correlation with BMD at all sites. In postmenopausal women, fat mass was significantly positively correlated with BMD at all sites, except the Ward's triangle; fat mass was the only determinant of BMD at the lumbar, distal forearm, and calcaneus sites, whereas both lean and fat mass contributed to BMD at the hip, with the effect of lean mass being slightly greater than that of fat mass. In younger men, lean mass had a significant positive contribution to BMD at all sites, whereas fat mass appeared to contribute negatively to BMD at all sites, except the calcaneus. In older men, lean mass made a significant positive contribution to the BMD at all sites; fat mass also made a significant positive contribution to the BMD at the forearm and calcaneus. These data indicate that in the Korean rural population, lean mass may be an important determinant of the BMD, whereas fat mass may contribute positively to BMD only in postmenopausal women and older men.

Fat mass is not beneficial to bone in adolescents and young adults

CONTEXT

Although muscle mass is beneficial to bone, studies on the effect of fat mass on bone have yielded conflicting results.

OBJECTIVE

The aim of this study was to assess the relations between lean and fat mass and bone structure.

DESIGN

This study was cross-sectional.

SETTING

The study was conducted in a general community.

SUBJECTS

Subjects included 300 healthy sexually mature adolescents and young adults (150 males and 150 females) between the ages of 13 and 21 yr.

MAIN OUTCOME MEASURE

We investigated the relation between dual-energy x-ray absorptiometry (DXA) measures of total body fat and lean mass and bone values obtained with DXA (legs and lumbar spine bone mineral density and bone mineral content) and computed tomography (CT) (cross-sectional and cortical bone areas of the femurs and cross-sectional area and cancellous bone density of the vertebrae).

RESULTS

Simple and multiple linear regression analyses showed significant positive relations between DXA lean mass and all CT and DXA measures of bone in the axial and appendicular skeletons (all P < 0.005). In contrast, whereas Pearson correlations between DXA measures of fat mass and bone parameters were generally positive, multiple regression analyses showed that fat mass, after accounting for lean mass, trunk height/leg length, had a negative, or no, correlation with CT and DXA values for bone.

CONCLUSIONS

Our findings provide compelling evidence that, despite increased mechanical loading and independent of lean mass, adipose tissue is not beneficial to bone structure.

Relationship between body composition and bone mineral density in women with and without osteoporosis: relative contribution of lean and fat mass

To assess the relationship of total fat mass (TFM) and total lean mass (TLM) with bone mineral density (BMD) and bone mineral content (BMC), we studied 770 postmenopausal white women after total body measurements by dual-energy X-ray absorptiometry. Height-independent bone mineral density (HIBMD) was also tested. The effects of TFM and TLM on the dependent variables HIBMD, BMD, and BMC were assessed by the univariate general linear model (UGLM). Age, age at menopause, height, and bone area were entered in the models as controlling variables when appropriate. In the total population, TLM and TFM were associated with BMD, BMC, and HIBMD (P < 0.001). Taking the T-score cut-off as -2.5, women without (463) and with (307) osteoporosis were then tested separately. In nonosteoporotic women, TLM was significantly associated with BMD, BMC, and HIBMD (P < 0.001), while TFM was not. In osteoporotic women, both TLM and TFM were associated with BMD to the same extent (P < 0.05), but not with HIBMD. Women without osteoporosis were then tested according to whether their TFM/TLM fraction was less than or greater than 1. In those with TFM/TLM less than 1, both TLM (P < 0.001) and TFM (P < 0.01), tested separately, were associated with BMD and BMC, but not with HIBMD. When TLM and TFM were tested at the same time and assessed by the same UGLM, only TLM (P < 0.001) still affected these three bone parameters. In women with TFM/TLM greater than 1, testing the body components both separately and at the same time and using the UGLM showed that TFM affected both BMC and BMD (P < 0.05), while TLM did not. In conclusion, our data indicate that both TFM and TLM affect bone density, with different physiological/pathological conditions modulating this relationship.

Skeletal muscle mass, fat mass, and hip bone mineral density in elderly women with hip fracture

Soft tissue body composition strongly affects bone health. Our aim was to investigate the relationship between both skeletal muscle mass (SMM) and fat mass (FM) and femoral bone mineral density (BMD) in a sample of elderly women with hip fracture. We assessed 293 of 325 hip fracture women admitted consecutively to a rehabilitation hospital. Soft tissue body composition and BMD were assessed by dual-energy X-ray absorptiometry (DXA), 23.2 +/- 7.7 (mean +/- SD) days after fracture occurrence. BMD was measured at four sites (neck, total femur, trochanter, intertrochanteric area) in the unfractured femur. Appendicular lean mass (aLM) was calculated as the sum of LM in arms and legs. We used two approaches to adjust aLM for body size: aLM divided by height squared (aLM/ht(2)), and aLM adjusted for height and FM (residuals). Both FM and aLM were significantly correlated with femoral BMD. However, the correlation coefficients for aLM were lower than for FM; they further decreased after adjustment for height squared, and were no longer significant after correction for both height and FM (residuals). When FM, aLM/ht(2), age, and time spent between fracture occurrence and DXA assessment were included together as the independent variables in a regression model, FM was the only independent variable significantly associated with BMD. The coefficients of partial correlation ranged from 0.414 to 0.647 depending on the femoral region of BMD assessment (P < 0.001). FM, but not SMM emerged as a pivotal determinant of BMD in our sample of hip fracture women.

Preptin, another peptide product of the pancreatic beta-cell, is osteogenic in vitro and in vivo

Several hormones that regulate nutritional status also impact on bone metabolism. Preptin is a recently isolated 34-amino acid peptide hormone that is cosecreted with insulin and amylin from the pancreatic beta-cells. Preptin corresponds to Asp(69)-Leu(102) of pro-IGF-II. Increased circulating levels of a pro-IGF-II peptide complexed with IGF-binding protein-2 have been implicated in the high bone mass phenotype observed in patients with chronic hepatitis C infection. We have assessed preptin's activities on bone. Preptin dose-dependently stimulated the proliferation (cell number and DNA synthesis) of primary fetal rat osteoblasts and osteoblast-like cell lines at periphysiological concentrations (>10(-11) M). In addition, thymidine incorporation was stimulated in murine neonatal calvarial organ culture, likely reflecting the proliferation of cells from the osteoblast lineage. Preptin did not affect bone resorption in this model. Preptin induced phosphorylation of p42/p44 MAP kinases in osteoblastic cells in a dose-dependent manner (10(-8)-10(-10) M), and its proliferative effects on primary osteoblasts were blocked by MAP kinase kinase inhibitors. Preptin also reduced osteoblast apoptosis induced by serum deprivation, reducing the number of apoptotic cells by >20%. In vivo administration of preptin increased bone area and mineralizing surface in adult mice. These data demonstrate that preptin, which is cosecreted from the pancreatic beta-cell with amylin and insulin, is anabolic to bone and may contribute to the preservation of bone mass observed in hyperinsulinemic states such as obesity.

Adiposity, estradiol, and genetic variants of steroid-metabolizing enzymes as determinants of bone mineral density

OBJECTIVES

Bone mineral density (BMD) is a complex trait resulting from the interplay of genetic and acquired factors. The objective of this study was to explore the influence of several anthropometric, lifestyle, genetic, and hormonal factors on BMD and analyze the possible differences in men and women.

METHODS

We studied 572 individuals over 50 years of age (381 postmenopausal women and 191 men). Lumbar spine and femoral neck BMD were measured by dual energy x-ray absorptiometry. The free estrogen index (FEI) was calculated as the ratio of serum estradiol to sex hormone binding globulin in 241 individuals. Three polymorphisms in the genes coding for 17-hydroxylase/liase, sulfotransferase, and 5alpha-reductase were studied in DNA isolated from blood cells.

RESULTS

Body mass index was strongly correlated to spine and femoral BMD both in women and in men (r = 0.32-0.49; P < 0.001). FEI was also independently correlated with spine BMD in both sexes (r = 0.23 and 0.34, P < 0.01), and with femoral neck in women (r = 0.30). Women with G alleles of the sulfotransferase gene tended to have higher spine BMD than those with C alleles (P = 0.025). No other genotype-related differences in BMD were found.

CONCLUSIONS

In conclusion, the results of this study point toward body weight and estradiol levels as major factors determining BMD both in women and in men. A common polymorphism of the sulfotransferase gene also appears to be associated to spine BMD in women.

Systemic sclerosis and bone loss: the role of the disease and body composition

OBJECTIVES

Studies on body composition are not available in systemic sclerosis (SSc). As this variable may play an important role in bone loss we have analysed bone mineral density (BMD) and body composition in SSc patients and healthy controls.

METHODS

Forty-three postmenopausal SSc patients and 47 healthy postmenopausal women were studied. Patients with intestinal malabsorption, renal failure, current or past history of smoking or using osteopenic drugs were excluded. BMD and body composition was evaluated by dual X-ray absorptiometry (DXA).

RESULTS

A higher frequency of osteoporosis in the lumbar spine (32.5%) and femoral neck (51.1%) was observed in SSc patients when compared to controls (14.8% vs. 19.1%; p<0.01). Multiple linear regression analysis revealed an association between the presence of SSc and low BMD. Body composition showed a reduced lean mass (33.15 vs. 39.99 g; p<0.01) and fat mass (21.05 vs. 26.82 g; p<0.01) in SSc when compared to controls. Lean mass was an important factor related to BMD in the lumbar spine and femoral neck.

CONCLUSION

SSc may be an independent factor for low BMD. The low lean mass in these patients emphasizes the need for appropriate additional therapeutic measures to reduce bone loss in SSc patients.

Influence of insulin-like growth factor-1 and leptin on bone mineral content in healthy premenopausal women

The aim of the present investigation was to study the influence of plasma insulin-like growth factor-1 (IGF-1) and leptin levels on bone mineral mass (BMC) and bone mineral density (BMD) in premenopausal women and the relationship between IGF-1 and leptin levels. Two hundred and four healthy women participated in this study. All participants had a body mass index (BMI) <30 kg/m(2) and were matched for their level of mean daily energy expenditure. BMC and BMD were correlated with measured body composition and blood biochemical parameters. No association was observed between BMC and BMD values with measured physical performance characteristics. Leptin had a significant association with BMC (beta = 0.840; P = 0.0001), total BMD (beta = 0.833; P = 0.0001), femoral neck BMD (beta = 0.829; P = 0.0001), and lumbar spine BMD (beta = 0.833; P = 0.0001). However, these associations were no longer independent when adjusted for body fat mass (FM) and trunk fat:leg fat ratio (P > 0.385). IGF-1 was significantly related to BMC (beta = 0.920; P = 0.0001), total BMD (beta = 0.918; P = 0.0001), femoral neck BMD (beta = 0.921; P = 0.0001), and lumbar spine BMD (beta = 0.917; P = 0.0001), but did not remain significant when adjusted for fat free mass (FFM; P > 0.062). In addition, a significant association between IGF-1 and leptin was found (beta = 0.801; P = 0.0001), and it remained significant after controlling for age, FM, FFM, insulin, and fasting insulin resistance index (FIRI), but not when adjusted for BMC and body mass values. In conclusion, it appears that fasting IGF-1 and leptin concentrations have no direct effect on BMC and BMD values. In addition, if there is an important relationship between IGF-1 and leptin, it is mediated or confounded by BMC in premenopausal women.

Leptin is a negative independent predictor of areal BMD and cortical bone size in young adult Swedish men

The association between leptin and areal BMD has been controversial, and the predictive role of leptin on cortical volumetric BMD and bone size has not previously been studied. We show that leptin is a negative independent predictor of aBMD (DXA), at several measured sites, and of cortical bone size (pQCT) in a large population of young men.

INTRODUCTION

Recent findings suggest that both adipose tissue (AT) and bone mass are regulated by leptin. Previous reports studying the association between leptin and areal BMD (aBMD) have yielded conflicting results. The role of leptin on volumetric BMD (vBMD) and bone size of the cortical and trabecular bone compartments has not previously been studied.

MATERIALS AND METHODS

The Gothenburg Osteoporosis and Obesity Determinants (GOOD) study is a population-based study of 1068 men (age, 18.9 +/- 0.6 [SD] years). aBMD of the total body, lumbar spine, femoral neck, both radii, and trochanter, as well as total body AT and lean mass (LM) were measured using DXA, whereas cortical and trabecular vBMD and bone size were measured by pQCT.

RESULTS

Total body LM could explain a larger magnitude of the difference in the variation in aBMD and cortical bone size than what total body AT could (total body aBMD: LM 37.4% versus AT 8.7%; tibia cross-sectional area [CSA]: LM 46.8% versus AT 5.6%). The independent role of leptin on bone parameters was studied using a multiple linear regression model, including age, total body LM and AT, height, present physical activity, calcium intake, and smoking as covariates. Leptin was found to be a negative independent predictor of aBMD (total body: beta = -0.08, p = 0.01; lumbar spine: beta = -0.13, p < 0.01; trochanter: beta = -0.09, p = 0.01), as well as of the cortical bone size (CSA and thickness) of both the radius (CSA: beta = -0.12, p < 0.001) and tibia (CSA: beta = -0.08, p < 0.01), but not of the cortical or trabecular vBMD of these bones.

CONCLUSION

Our results indicate that LM has a greater impact on bone mass than AT. Our findings further show that leptin is a negative independent predictor of aBMD at several measured sites and of bone parameters reflecting cortical bone size, but not vBMD, in a large population of young Swedish men.

Effect of exercise on bone mineral density and lean mass in postmenopausal women

PURPOSE

To evaluate the effects of physical activity on bone mineral density, bone mineral content, and lean mass in postmenopausal, overweight/obese women.

METHODS

We conducted a 12-month randomized controlled aerobic exercise intervention versus control in 173 sedentary, overweight/obese, postmenopausal women, aged 50-75 yr. The exercise prescription consisted of >or=45 min of moderate-intensity aerobic exercise (60-75% of maximal heart rate), 5 d.wk for 12 months. Control participants attended 45-min stretching sessions once a week. Ninety-eight percent (N=170) completed the trial. Exercisers averaged 172 min.wk (SD=89) of exercise and expended 3828 kJ.wk (SD=2053). We assessed body fat, total lean mass, and total body bone mineral density and content using dual-energy x-ray absortiometry (DXA). We compared baseline with 12-month changes in exercisers versus controls.

RESULTS

Exercisers lost significantly more weight than stretchers (1.3-kg loss vs 0.1-kg gain, P=0.01). However, no differences between exercisers and controls in the change from baseline to 12 months were detected: exercisers' average bone mineral density increased by 0.005 g.cm and controls' by 0.003 g.cm (P=0.61). Similarly, no significant differences were detected for bone mineral content. Lean mass increased by 0.2 kg in both groups (P=0.84).

CONCLUSION

Overall, the results from this randomized controlled study suggest that a yearlong moderate-intensity aerobic exercise intervention does not affect total body bone mineral density, bone mineral content, or lean mass in overweight/obese postmenopausal women.

Mechanisms of disease: is osteoporosis the obesity of bone?

Osteoporosis and obesity, two disorders of body composition, are growing in prevalence. Interestingly, these diseases share several features including a genetic predisposition and a common progenitor cell. With aging, the composition of bone marrow shifts to favor the presence of adipocytes, osteoclast activity increases, and osteoblast function declines, resulting in osteoporosis. Secondary causes of osteoporosis, including diabetes mellitus, glucocorticoids and immobility, are associated with bone-marrow adiposity. In this review, we ask a provocative question: does fat infiltration in the bone marrow cause low bone mass or is it a result of bone loss? Unraveling the interface between bone and fat at a molecular and cellular level is likely to lead to a better understanding of several diseases, and to the development of drugs for both osteoporosis and obesity.

Hypothalamic regulation of cortical bone mass: opposing activity of Y2 receptor and leptin pathways

NeuropeptideY-, Y2 receptor (Y2)-, and leptin-deficient mice show similar anabolic action in cancellous bone but have not been assessed in cortical bone. Cortical bone mass is elevated in Y2(-/-) mice through greater osteoblast activity. In contrast, leptin deficiency results in reduced bone mass. We show opposing central regulation of cortical bone.

INTRODUCTION

Treatment of osteoporosis is confounded by a lack of agents capable of stimulating the formation of bone by osteoblasts. Recently, the brain has been identified as a potent anabolic regulator of bone formation. Hypothalamic leptin or Y2 receptor signaling are known to regulate osteoblast activity in cancellous bone. However, assessment of these pathways in the structural cortical bone is critical to understanding their role in skeletal health and their potential clinical relevance to osteoporosis and its treatment.

MATERIALS AND METHODS

Long bones of 16-week male ob/ob and germline and hypothalamic Y2(-/-) mice were assessed by QCT. Cortical osteoblast activity was assessed histologically.

RESULTS

The femora of skeletally mature Y2(-/-) mice and of leptin-deficient ob/ob and Y2(-/-)ob/ob mice were assessed for changes in cortical osteoblast activity and bone mass. Ablation of Y2 receptors increased osteoblast activity on both endosteal and periosteal surfaces, independent of leptin, resulting in increased cortical bone mass and density in Y2(-/-) mice along the entire femur. Importantly, these changes were evident after deletion of hypothalamic Y2 receptors in adult mice, with a 5-fold elevation in periosteal bone formation. This is in marked contrast to leptin-deficient models that displayed reduced cortical mass and density. These changes were associated with substantial differences in calculated strength between the Y2(-/-) and leptin-deficient mice.

CONCLUSIONS

These results indicate that the Y2-mediated anabolic pathway stimulates cortical and cancellous bone formation, whereas the leptin-mediated pathway has opposing effects in cortical and cancellous bone, diminishing the production of cortical bone. The findings from conditional hypothalamic Y2 knockout show a novel, inducible control mechanism for cortical bone formation and a potential new pathway for anabolic treatment of osteoporosis.

Change in lean body mass is a major determinant of change in areal bone mineral density of the proximal femur: a 12-year observational study

Our objective was to assess the contribution of lean body mass (LBM) and fat body mass (FBM) to areal bone mineral density (aBMD) in women during the years surrounding menopause. We used a 12-year observational design. Participants included 75 Caucasian women who were premenopausal, 53 of whom were available for follow-up. There were two measurement periods: baseline and 12-year follow-up. At both measurement periods, bone mineral content and aBMD of the proximal femur, posterior-anterior lumbar spine, and total body was assessed using dual-energy X-ray absorptiometry (DXA). LBM and FBM were derived from the total-body scans. General health, including current menopausal status, hormone replace therapy use, medication use, and physical activity, was assessed by questionnaires. At the end of the study, 44% of the women were postmenopausal. After controlling for baseline aBMD, current menopausal status, and current hormone replacement therapy, we found that change in LBM was independently associated with change in aBMD of the proximal femur (P = 0.001). The cross-sectional analyses also indicated that LBM was a significant determinant of aBMD of all three DXA-scanned sites at both baseline and follow-up. These novel longitudinal data highlight the important contribution of LBM to the maintenance of proximal femur bone mass at a key time in women's life span, the years surrounding menopause.

Bone mineral density is not reduced in HIV-infected Caucasian men treated with highly active antiretroviral therapy

OBJECTIVE

Recent studies have reported low bone mineral density (BMD) in patients infected with human immunodeficiency virus (HIV). Frequently these findings have been attributed to treatment with highly active antiretroviral therapy (HAART). We sought to determine whether BMD in HIV-infected men treated with HAART for at least 3 months is different from that in healthy controls, and, if so, what HIV-related factors might explain this finding.

DESIGN

Cross-sectional analysis.

PATIENTS

Fifty-nine HIV-infected Caucasian men treated with HAART, and 118 healthy community-dwelling controls. Each HIV-infected man was age-matched (within 5 years) to two controls.

MEASUREMENTS

All participants had measurements of BMD and bone-related laboratory parameters.

RESULTS

The mean duration of known HIV infection was 8.5 years, and of treatment with HAART was 52 months. There was no significant difference in mean BMD between groups at the lumbar spine (HIV group: 1.23 g/cm2, controls: 1.25 g/cm2; P = 0.53) or total body (HIV group: 1.18 g/cm2, controls: 1.20 g/cm2; P = 0.09). At the total hip the HIV-infected group had significantly lower BMD than the control group (HIV group: 1.03 g/cm2, controls: 1.09 g/cm2; P = 0.01). The HIV-infected group were, on average, 6.3 kg lighter than the controls. After adjusting for this weight difference, HIV infection was not an independent predictor of BMD at any site (lumbar spine P = 0.79; total hip P = 0.18; total body P = 0.76).

CONCLUSIONS

HIV-infected men treated with HAART are lighter than healthy controls. This weight difference is responsible for a small decrement in hip BMD. Overall, BMD is not significantly reduced in HIV-infected Caucasian men treated with HAART.

Age-related loss of muscle mass and bone strength in mice is associated with a decline in physical activity and serum leptin

The mechanisms underlying age-related loss of muscle and bone tissue are poorly understood but are thought to involve changes in sex hormone status, physical activity, and circulating levels of inflammatory cytokines. This study attempts to develop an animal model useful for evaluating these mechanisms in vivo. Male C57BL/6 mice were included for study at 3, 6, 12, 18, 24, and 29 months of age. Endocortical mineralizing surface, serum leptin, body weight, and percentage of body fat all increased between 6 and 12 months of age as activity level declined. Serum levels of the inflammatory marker IL-6 increased significantly after 12 months of age, following the observed increase in body weight and percent body fat. Hindlimb muscle mass declined significantly between 18 and 24 months of age, both absolutely and relative to total body mass, with a further decline ( approximately 15%) between 24 and 29 months. Loss of muscle mass after 18 months of age was accompanied by a significant increase in bone resorption, as indicated by serum pyridinoline cross-links, and a significant decrease in fat mass, serum leptin, bone strength, bone mineral density, and vertical cage activity. No significant changes in serum testosterone with aging were detected in the mice, as levels were essentially constant between 6 and 29 months. Our data show that mice lose a significant amount of muscle and bone tissue with age, and this loss of musculoskeletal tissue is accompanied by a drop in serum leptin and preceded by a significant decrease in physical activity.

Different skeletal regional response to continuous brain infusion of leptin in the rat

This study was designed to evaluate whether or not continuous intracerebroventricular infusion of leptin (1.5 microg/rat/24 h, for 28 days) produced different regional response on the skeleton of growing rats. Leptin reduce the accretion of total femoral bone mineral content (BMC) and density (BMD). This effect was related to a reduction of metaphyseal femur as no changes were detected in the diaphysis. Despite the reduced accretion in the volumetric of both femur and tibia compared to controls, leptin had no significant effects on the lumbar vertebrae. Urine deoxypyrydinoline and serum osteocalcin remained more elevated in the leptin-treated group as compared to controls. The results demonstrate that long-term central infusion of leptin activates bone remodeling with a negative balance. Leptin induces distinct responses in the different structure of bone and in the axial and appendicular skeleton.

The impact of childhood obesity on musculoskeletal form

Despite the greater prevalence of musculoskeletal disorders in obese adults, the consequences of childhood obesity on the development and function of the musculoskeletal system have received comparatively little attention within the literature. Of the limited number of studies performed to date, the majority have focused on the impact of childhood obesity on skeletal structure and alignment, and to a lesser extent its influence on clinical tests of motor performance including muscular strength, balance and locomotion. Although collectively these studies imply that the functional and structural limitations imposed by obesity may result in aberrant lower limb mechanics and the potential for musculoskeletal injury, empirical verification is currently lacking. The delineation of the effects of childhood obesity on musculoskeletal structure in terms of mass, adiposity, anthropometry, metabolic effects and physical inactivity, or their combination, has not been established. More specifically, there is a lack of research regarding the effect of childhood obesity on the properties of connective tissue structures, such as tendons and ligaments. Given the global increase in childhood obesity, there is a need to ascertain the consequences of persistent obesity on musculoskeletal structure and function. A better understanding of the implications of childhood obesity on the development and function of the musculoskeletal system would assist in the provision of more meaningful support in the prevention, treatment and management of the musculoskeletal consequences of the condition.

Epidemiology of osteoporosis

Osteoporosis and related fractures represent a major, and growing, public health concern for the United States and worldwide. The pathogenesis of osteoporosis is complex, requiring attention to the different life phases involved in growth, maintenance, and loss of bone, in addition to non-skeletal factors associated with falls and fractures. While the current clinical definition is based upon bone density measurements, other determinants of skeletal strength, particularly bone quality, are important to identify for future areas of research and prevention efforts. This epidemiologic review describes the definition, pathogenesis, and risk factors, as well as the frequency and impact of osteoporosis, with particular emphasis upon hip fracture.

Gender differences in relationships between body composition components, their distribution and bone mineral density: a cross-sectional opposite sex twin study

Numerous studies indicate that bone mineral density (BMD) is closely related to body mass and its components. Most studies have examined these relationships in women with little attention given to how these relationships differ by gender. The aims of the present study were to use the opposite sex twin model to determine if there were gender differences in the relationship between body composition and its relation to BMD and how any such differences were influenced by age. We measured body composition and bone mass by dual energy X-ray absorptiometry in 93 pairs of opposite sex twins. To examine the effect of age, they were divided into two age groups: under 50 years old (45 pairs) and over 50 years old (48 pairs). Lean mass (LM) had stronger positive relationships with the most bone variables than fat mass in both genders at all ages. Fat mass (FM) had positive relationships with total body and hip BMD in women under age 50, but not over 50. There was no significant relationship between FM and total or regional BMD in men under age 50, but men over 50 showed positive relationships between FM measures and total and some regional BMD measures. Central adiposity showed a positive relationship with BMD in men over 50 and women under 50. Fat mass (FM) and lean mass (LM) and their distribution in the body have different relationships with regional BMD in men and women that differ by age.

Increased bone density and decreased bone turnover, but no evident alteration of fracture susceptibility in elderly women with diabetes mellitus

Bone density, bone turnover and fracture susceptibility were evaluated in 1,132 randomly recruited women, all 75 years old. Seventy-four of the women had diabetes, while 1,058 women did not. Areal bone mineral density (aBMD) of the hip and lumbar spine was investigated by dual energy X-ray absorptiometry (DXA), and bone mass of the calcaneus was measured by ultrasound. Urinary deoxypyridinoline/creatinine (U-DPD/Crea) and serum C-terminal cross-linked telopeptide of type 1 collagen (S-CTX) were assessed as markers of bone resorption. Serum bone-specific alkaline phosphatase (S-bone ALP) and serum osteocalcin (S-OC) were assessed as markers of bone formation. Also, serum 25(OH) vitamin D and serum parathyroid hormone (S-PTH) were assessed. Fracture susceptibility was evaluated retrospectively and prospectively for up to 6.5 years. In diabetic women, the aBMD of the femoral neck was 11% higher (p<0.001), and BMD of the lumbar spine was 8% higher (p=0.002) than in non-diabetic women. There was no difference in bone mass by ultrasound of the calcaneus. Women with diabetes had higher BMD of the femoral neck (p<0.001) and lumbar spine (p=0.03) also after correction for differences in body weight. In diabetic women, U-DPD/Crea, S-CTX, and S-OC were decreased when compared with non-diabetic women (p=0.001 or less). After correction for covariance of body weight and plasma creatinine, S-CTX (p<0.001) and S-OC (p<0.001) were still lower in the diabetic women. Diabetic patients had hypovitaminosis D (p=0.008), a difference explained by differences in time spent outdoors and body weight. S-PTH did not differ between the groups. Women with diabetes had no more lifetime fractures (52%) than women without diabetic disease (57%), (p=0.31). This study shows that elderly women with diabetes and without severe renal insufficiency have high bone mass and low bone turnover. The high bone mass and low bone turnover is not likely to have a strong influence on fracture susceptibility.

Reference charts for the relationships between dual-energy X-ray absorptiometry-assessed bone mineral content and lean mass in 3,063 healthy men and premenopausal and postmenopausal women

Correlations between dual-energy X-ray absorptiometry (DXA)-assessed bone mineral content and lean mass (BMC-LM curves), and between BMC/LM ratio and age ([BMC/LM]-age curves), were analyzed in the whole body (WB), the upper limbs (ULs) and the lower limbs (LLs) of 3,063 healthy Hispanic adults. Groups of 472 men aged 25-87 years, 1,035 premenopausal (pre-MP) women aged 27-54 years, and 1,556 post-menopausal (post-MP) women aged 48-93 years were studied with a GE-Lunar DPX-Plus device. BMC-LM curves confirmed previous observations that BMC and LM masses always correlate linearly, with similar slopes within each region, but differing in intercepts according to gender and hormonal status. Multiple regression tests showed little or no independent interaction of body weight or height with those relationships. [BMC/LM]-age curves were flat in men but showed the positive influence of estrogens throughout the age range in women. Z-scored graphs of all the corresponding relationships were compiled, showing the confidence intervals for means +/-1, +/-2, and +/-3 SDs of the data (+/-1, +/-2, +/-3 z-scores) along BMC-LM and [BMC/LM]-age curves. These charts are proposed as references for assessing how well bone mass (as assessed by BMC) and muscle mass (assumed proportional to LM) follow the natural anthropometric/biomechanical proportionality in Hispanic men and women within the age range studied, employing similar devices. Charts for LLs, showing the lowest variance amongst the studied correlations and approaching the origin as an exclusive feature, could provide the most accurate reference curves. Differences between data from ULs and LLs may provide information about any eventual interaction of body-weight bearing with the general results. The proposed analysis may provide useful information for approaching a differential diagnosis between disuse-related and other types of osteopenias employing only DXA.

Contribution of lean tissue mass to the urban-rural difference in bone mineral density

While the urban-rural difference in bone mineral density (BMD) has been shown in some, but not all, Western populations, such a difference and the reason for the difference is largely unknown, particularly in developing countries. This cross-sectional, epidemiologic study was designed to examine the hypothesis that differences in measures of body composition such as lean mass (LM) and fat mass (FM) contribute to the urban-rural difference in BMD. Lean mass, fat mass, lumbar spine and femoral neck BMD were measured by DXA (GE Lunar Corp, Wis.) in 411 urban (Bangkok city) and 436 rural (Khon Kaen province) Thai subjects, aged 20-84 years. Rural men and women had significantly higher LM and lower FM than their urban counterparts. In multiple linear regression analysis, age, LM, menopausal status (in women) and residence were independent determinants of BMD. After adjusting for age, menopause and LM, rural subjects were found to have significantly higher femoral neck BMD, but not lumbar spine BMD, than urban subjects. Furthermore, to alleviate the potential effect of multicolinearity of LM and FM, each rural subject was matched with each urban subject for FM and age, which resulted in 46 pairs of men and 91 pairs of women. In this matched-pair analysis, the femoral necks in rural men and women were, respectively, 7.3+/-2.1% (mean+/-SE; P<0.01) and 6.3+/-2.8% (P<0.02) higher than in urban men and women. The urban-rural difference in LM accounted for approximately 23 and 5% of the urban-rural difference in femoral neck BMD in men and women, respectively. These data are thus consistent with the hypothesis that the urban-rural difference in BMD at a weight-bearing site is in part associated with the urban-rural difference in lean mass.