Genome-wide approaches for identifying genetic risk factors for osteoporosis

NEDD4 family E3 ligases in osteoporosis: mechanisms and emerging potential therapeutic targets

Osteoporosis is a systemic skeletal disorder characterized by reduced bone density and an increased risk of fractures, particularly prevalent in the aging population. Osteoporotic complications, including vertebral compression fractures, hip fractures, and distal forearm fractures, affect over 8.9 million individuals globally, placing a significant economic strain on healthcare systems. Recent advances have expanded our understanding of the mechanisms underlying osteoporosis, particularly the intricate regulatory networks involved in bone metabolism. A central player in these processes is ubiquitin-mediated proteasomal degradation, a crucial post-translational modification system that involves ubiquitin, the ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), ubiquitin ligase (E3), deubiquitinating enzymes, and the proteasome. Among the various E3 ligases, the NEDD4 family has emerged as a key regulator of both bone development and osteoporotic pathology. This review delineates the role of NEDD4 family in osteoporosis and identifies potential drug targets within these pathways, offering insights into novel therapeutic approaches for osteoporosis through targeted intervention.

Utilize polygenic risk score to enhance fracture risk estimation and improve the performance of FRAX in patients with osteoporosis

This study examined the use of polygenic risk scores (PGS) in combination with the Fracture Risk Assessment Tool (FRAX) to enhance fragility fractures risk estimation in osteoporosis patients. Analyzing data from over 57,000 participants, PGS improved fracture risk estimation, especially for individuals with intermediate to low risks, allowing personalized preventive strategies.

INTRODUCTION

Osteoporosis and fragility fractures are multifactorial, with contributions from both clinical and genetic determinants. However, whether using polygenic risk scores (PGS) may enhance the risk estimation of osteoporotic fracture in addition to Fracture Risk Assessment Tool (FRAX) remains unknown. This study investigated the collective association of PGS and FRAX with fragility fracture.

METHODS

We conducted a cohort study from the Taiwan Precision Medicine Initiative (TPMI) at Taichung Veterans General Hospital, Taiwan. Genotyping was performed to compute PGS associated with bone mineral density (BMD). Phenome-wide association studies were executed to pinpoint phenotypes correlated with the PGS. Logistic regression analysis was conducted to ascertain factors associated with osteoporotic fractures.

RESULTS

Among all 57,257 TPMI participants, 3744 (904 men and 2840 women, with a mean age of 66.7) individuals had BMD testing, with 540 (14.42%) presenting with fractures. The 3744 individuals who underwent BMD testing were categorized into four quartiles (Q1-Q4) based on PGS; 540 (14.42%) presented with fractures. Individuals with PGS-Q1 exhibited lower BMD, a higher prevalence of major fractures, and elevated FRAX-major and FRAX-hip than those with PGS-Q4. PGS was associated with major fractures after adjusting age, sex, and FRAX scores. Notably, the risk of major fractures (PGS-Q1 vs. Q4) was significantly higher in the subgroups of FRAX-major scores < 10% and 10-20%, but not in participants with a FRAX-major score ≧ 20%.

CONCLUSIONS

Our study highlights the potential of PGS to augment fracture risk estimation in conjunction with FRAX, particularly in individuals with middle to low risks. Incorporating genetic testing could empower physicians to tailor personalized preventive strategies for osteoporosis.

E3-ubiquitin ligases and recent progress in osteoimmunology

Ubiquitin-mediated proteasomal degradation is a post-transcriptional protein modification that is comprised of various components including the 76-amino acid protein ubiquitin (Ub), Ub-activating enzyme (E1), Ub-conjugating enzyme (E2), ubiquitin ligase (E3), deubiquitinating enzyme (DUB) and proteasome. We and others have recently provided genetic evidence showing that E3-ubiquitin ligases are associated with bone metabolism, the immune system and inflammation through ubiquitylation and subsequent degradation of their substrates. Dysregulation of the E3-ubiquitin ligase RNF146-mediated degradation of the adaptor protein 3BP2 (SH3 domain-binding protein 2) causes cherubism, an autosomal dominant disorder associated with severe inflammatory craniofacial dysmorphia syndrome in children. In this review, on the basis of our discoveries in cherubism, we summarize new insights into the roles of E3-ubiquitin ligases in the development of human disorders caused by an abnormal osteoimmune system by highlighting recent genetic evidence obtained in both human and animal model studies.

Osteoblasts and osteoclasts: an important switch of tumour cell dormancy during bone metastasis

Bone metastasis occurs when tumour cells dissociate from primary tumours, enter the circulation (circulating tumour cells, CTCs), and colonize sites in bone (disseminated tumour cells, DTCs). The bone marrow seems to be a particularly dormancy-inducing environment for DTCs, yet the mechanisms of dormancy initiation, reactivation, and interaction within the bone marrow have to be elucidated. Intriguingly, some evidence has suggested that dormancy is a reversible state that is switched 'on' or 'off' depending on the presence of various bone marrow resident cells, particularly osteoclasts and osteoblasts. It has become clear that these two cells contribute to regulating dormant tumour cells in bone both directly (interaction) and indirectly (secreted factors). The involved mechanisms include TGFβ signalling, the Wnt signalling axis, the Notch2 pathway, etc. There is no detailed review that specifically focuses on ascertaining the dynamic interactions between tumour cell dormancy and bone remodelling. In addition, we highlighted the roles of inflammatory cytokines during this 'cell-to-cell' communication. We also discussed the potential clinical relevance of remodelling the bone marrow niche in controlling dormant tumour cells. Understanding the unique role of osteoclasts and osteoblasts in regulating tumour dormancy in bone marrow will provide new insight into preventing and treating tumour bone metastasis.

Fragile Bones Secondary to SMURF1 Gene Duplication

Studies on mice have shown that the Smad Ubiquitin Regulatory Factor-1 (SMURF1) gene negatively regulates osteoblast function and the response to bone morphogenetic protein in a dose-dependent fashion (Chan et al. in Mol Cell Biol 27(16):5776-5789, https://doi.org/10.1128/MCB.00218-07, 2007; Yamashita et al. in Cell 121(1):101-113, https://doi.org/10.1016/j.cell.2005.01.035, 2005). In addition, a tumorigenic role for SMURF1 has been implicated due to the interference with apoptosis signals (Nie et al. in J Biol Chem 285(30):22818-22830, https://doi.org/10.1074/jbc.M110.126920, 2010; Wang et al. in Nat Commun 5:4901, https://doi.org/10.1038/ncomms5901, 2014). A 10-year-old girl with a history of severe developmental delay, infantile seizures, and B-cell lymphoma, in remission for approximately 3.5 years, was referred to the metabolic bone clinic for fractures and low bone mineral density. Array comparative genomic hybridization revealed a pathogenic microduplication in chromosome 7 at bands 7q21.3q22.1 that encompasses the SMURF1 gene. The clinical features of this child are congruous with the phenotype as ascribed excess Smurf1 mutations in mice. This is the first case description of osteoporosis in a child secondary to a microduplication involving SMURF1 gene.

Identification of novel variants and candidate genes associated with porcine bone mineral density using genome-wide association study

Pig leg weakness not only causes huge economic losses for producers but also affects animal welfare. However, genes with large effects on pig leg weakness have not been identified and suitable methods to study porcine leg weakness are urgently needed. Bone mineral density (BMD) is an important indicator for determining leg soundness in pigs. Increasing pig BMD is likely to improve pig leg soundness. In this study, porcine BMD was measured using an ultrasound bone densitometer in a population with 212 Danish Landrace pigs and 537 Danish Yorkshires. After genotyping all the individuals using GeneSeek Porcine 50K SNP chip, genetic parameter estimation was performed to evaluate the heritability of BMD. Genome-wide association study and haplotype analysis were also performed to identify the variants and candidate genes associated with porcine BMD. The results showed that the heritability of BMD was 0.21 in Landrace and 0.31 in Yorkshire. Five single-nucleotide polymorphisms on chromosome 6 identified were associated with porcine BMD at suggestive significance level. Two candidate quantitative trait loci (74.47 to 75.33 Mb; 80.20 to 83.83 Mb) and three potential candidate genes (ZBTB40, CNR2, and Lin28a) of porcine BMD were detected in this study.

High risk of lumbar spine osteoporosis with the RANK rs3018362 polymorphism

Osteoporosis is characterized by reduced bone mineral density (BMD) and quality, increasing the risk of fractures. A large number of genes involved in bone metabolism have been implicated in the genesis of osteoporosis; these include RANK and RANKL. Polymorphisms of these genes have been implicated in osteoporosis. The aim of this study was to determine the association of the RANK rs3018362 and RANKL rs12585014 polymorphisms with risk of osteoporosis. Four hundred Mexican women aged 40 years old or above were genotyped by real-time PCR and several demographic and risk factors were explored. The GA and AA genotypes of the rs3018362 polymorphism were associated with a high risk of osteoporosis in the dominant model (p=.0062; OR = 2.16, 95% CI: 1.24-3.78). In summary, the rs3018362 polymorphism in the RANK gene seems to be associated with osteoporosis of the lumbar spine while the RANKL rs12585014 is not, although more studies are needed to confirm these results.

Ginkgolide B promotes osteoblast differentiation via activation of canonical Wnt signalling and alleviates osteoporosis through a bone anabolic way

Osteoporosis has become a worldwide problem as the population ages. Although many advances have been made in the treatment of osteoporosis in the past few years, the outcome are sometimes disturbing because of the adverse effects of these treatments. Further studies are still needed to identify novel alternate agents to improve the therapeutic effect. Ginkgolide B (GB), a derivative of Ginkgo biloba leaves, has numerous pharmacological effects, including anticancer and anti-inflammation activities. However, the effect of GB on the regulation of osteoblast activity and bone formation effect has not yet been investigated. In this study, we showed the in vitro and in vivo effects of GB on osteoblast differentiation and bone formation. We found that GB promotes osteoblast differentiation of Bone Mesenchymal Stem Cells (BMSCs) and MC3T3-E1 cells in vitro in a Wnt/β-catenin-dependent manner. In an in vivo study, we constructed a cranial defect model in rats and treated with GB. Histomorphometric and histological analyses confirmed that the usage of GB significantly promotes bone formation. Further study on ovariectomy (OVX) rats demonstrated that GB is capable of alleviating ovariectomy-induced bone loss by enhancing osteoblast activity. Our findings indicate that GB is a potential therapeutic agent of osteoporosis through an anabolic way in bone.

Regulation of Skeletal Homeostasis

Landmark advances in skeletal biology have arisen mainly from the identification of disease-causing mutations and the advent of rapid and selective gene-targeting technologies to phenocopy human disease in mice. Here, we discuss work on newly identified mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, and crosstalk between bone and vital organs as these relate to the therapeutic targeting of the skeleton.

A Prospective, Controlled, Multicenter Study to Evaluate the Clinical Outcome of Implant Treatment in Women with Osteoporosis/Osteopenia: 5-Year Results

The impact of osteoporosis on implant treatment is still a matter of debate in the scientific community, as it may possibly lead to higher failure rates. As long-term controlled trials are missing, the aim of this study was to verify the long-term outcome of implants placed in patients with systemic osteoporosis. Postmenopausal women in need of implants underwent bone mineral density measurements in hip and spine, using dual X-ray absorptiometry scans. Based on T-scores, they were divided into 2 groups: group O (osteoporosis group) with a T-score ≤-2 or group C (control group) with a T-score of ≥-1. Implants were placed in a 2-stage manner and loaded 4 to 8 wk after abutment surgery. Six months after loading and thereafter yearly, clinical and radiographical parameters were assessed. In total, 148 implants were placed in 48 patients (mean age: 67 y [range, 59-83]). Sixty-three implants were placed in 20 patients (group O) and 85 implants in 28 patients (group C). After 5 y, 117 implants (38 in group O and 79 in the group C) in 37 patients were assessed. Cumulative survival rate on an implant level was 96.5% (group O: 91.5%; group C: 100.0% [ P < 0.05]) and 95.7% (group O: 89.2%; group C: 100.0% [ P > 0.05]) on a patient level. The overall marginal bone-level alterations, after 5 y of loading, were -0.09 ± 0.78 mm (group O: -0.15 ± 0.50 mm; group C: -0.06 ± 0.89 mm) on an implant level and -0.09 ± 0.54 mm (group O: -0.18 ± 0.43 mm; group C: 0.06 ± 0.58 mm) on a patient level ( P > 0.05). Oral implant therapy in osteoporotic patients is a reliable treatment option with comparable osseointegration rates, implant survival, and marginal bone-level alterations after 5 y of functional loading (ClinicalTrials.gov NCT00745121).

The emerging role of microRNAs in bone remodeling and its therapeutic implications for osteoporosis

Osteoporosis, a common and multifactorial disease, is influenced by genetic factors and environments. However, the pathogenesis of osteoporosis has not been fully elucidated yet. Recently, emerging evidence suggests that epigenetic modifications may be the underlying mechanisms that link genetic and environmental factors with increased risks of osteoporosis and bone fracture. MicroRNA (miRNA), a major category of small noncoding RNA with 20–22 bases in length, is recognized as one important epigenetic modification. It can mediate post-transcriptional regulation of target genes with cell differentiation and apoptosis. In this review, we aimed to profile the role of miRNA in bone remodeling and its therapeutic implications for osteoporosis. A deeper insight into the role of miRNA in bone remodeling and osteoporosis can provide unique opportunities to develop a novel diagnostic and therapeutic approach of osteoporosis.

Maternal nutrition and the developmental origins of osteoporosis in offspring: Potential mechanisms and clinical implications

Osteoporosis, the most frequent metabolic disorder of bone, is a complex disease with a multifactorial origin that is influenced by genes and environments. However, the pathogenesis of osteoporosis has not been fully elucidated. The theory of "Developmental Origins of Health and Disease" indicates that early life environment exposure determines the risks of cardiometabolic diseases in adulthood. However, investigations into the effects of maternal nutrition and nutrition exposure during early life on the development of osteoporosis are limited. Recently, emerging evidence has strongly suggested that maternal nutrition has long-term influences on bone metabolism in offspring, and epigenetic modifications maybe the underlying mechanisms of this process. This review aimed to address maternal nutrition and its implications for the developmental origins of osteoporosis in offspring. It is novel in providing a theoretical basis for the early prevention of osteoporosis. Impact statement Our review aimed to address maternal nutrition and its implications for the developmental origins of osteoporosis in offspring, that can novelly provide a theoretical basis for the early prevention of osteoporosis.

VDR, RANKL and OPG polymorphisms as possible predisposing cofactors of postmenopausal osteoporosis: explorative study in Italian population

Postmenopausal osteoporosis (PO) has a strong genetic component. Presently, the published evidence on the association between the main single-nucleotide polymorphisms (SNPs) of the receptor activator of nuclear factor-kb ligand (RANKL), osteoprotegerin (OPG) and vitamin D receptor (VDR) and bone mass density (BMD) are scarce, mostly considering Italian population. This study sought to determine whether OPG (rs2073618), RANKL (rs9525641) and the VDR (rs2228570) SNPs were associated with BMD in a sample of 139 North-Italian postmenopausal women. The allelic distribution of rs9525641 in women with PO or osteopenia (OP + OPE group) differed from controls (p < 0.05), suggesting that this allele might confer a greater susceptibility to bone resorption. Concerning rs2228570, CC genotype was associated with OP + OPE women, with a worst total hip BMD. Notably, the combined genotype RANK (CT)-VDR (TT) was significantly associated to spine BMD (p < 0.05). In conclusion, this pilot study showed that rs9525641 and rs2228570 polymorphisms might contribute, separately or in combination, in determining BMD phenotype in selected postmenopausal populations.

The relationship between osteoporosis and body composition in pre- and postmenopausal women from different ethnic groups in China

OBJECTIVE

To investigate the ethnic differences in osteoporosis (OP) and body composition (BC) and their relationship in the Maonan, Mulam, Hmong, and Yao minorities in China.

DESIGN

A total of 860 Maonan, Mulam, Hmong, and Yao women were included in this cross-sectional study. Demographic, health history, and lifestyle information was collected using questionnaires. BC was measured through bioelectrical impedance analysis, and bone mineral density (BMD) was assessed via calcaneal quantitative ultrasound.

RESULTS

Compared with premenopausal women, postmenopausal women exhibited a lower fat-free mass (FFM), muscle mass (MM), limb muscle mass, and T-score but a higher waist-to-hip ratio and prevalence of OP in each minority (p < .05). After adjustment for age, Hmong women displayed the highest body mass index, fat mass, percentage of body fat, visceral fat, and subcutaneous fat contents, while Yao women presented the highest T-scores and lowest prevalence of OP among the four minorities (p < .05). Having a greater number of children and an older age were significant risk factors for OP in all ethnic groups (p < .05, OR > 1). In addition, our results revealed that FFM and MM exhibited exactly the same weak positive relationship with the T-score (r = 0.081, p < .05) after adjusting for menopausal status and age in all of the participants. Furthermore, significant ethnic differences in the relationship between BC and the T-score existed in the four minorities studied here.

CONCLUSIONS

BC and OP prevalence varied by menopausal status and ethnic group, and ethnic-specific relationships between BC and BMD were present in the four minorities. More research is needed to further investigate the ethnic differences in BC, OP, and risk factors for lower BMD to develop targeted prevention strategies to reduce the burden of OP across different ethnic groups in China.

Rapid phenotyping of knockout mice to identify genetic determinants of bone strength

The genetic determinants of osteoporosis remain poorly understood, and there is a large unmet need for new treatments in our ageing society. Thus, new approaches for gene discovery in skeletal disease are required to complement the current genome-wide association studies in human populations. The International Knockout Mouse Consortium (IKMC) and the International Mouse Phenotyping Consortium (IMPC) provide such an opportunity. The IKMC generates knockout mice representing each of the known protein-coding genes in C57BL/6 mice and, as part of the IMPC initiative, the Origins of Bone and Cartilage Disease project identifies mutants with significant outlier skeletal phenotypes. This initiative will add value to data from large human cohorts and provide a new understanding of bone and cartilage pathophysiology, ultimately leading to the identification of novel drug targets for the treatment of skeletal disease.

The genetics of bone mass and susceptibility to bone diseases

Osteoporosis is characterized by low bone mass and an increased risk of fracture. Genetic factors, environmental factors and gene-environment interactions all contribute to a person's lifetime risk of developing an osteoporotic fracture. This Review summarizes key advances in understanding of the genetics of bone traits and their role in osteoporosis. Candidate-gene approaches dominated this field 20 years ago, but clinical and preclinical genetic studies published in the past 5 years generally utilize more-sophisticated and better-powered genome-wide association studies (GWAS). High-throughput DNA sequencing, large genomic databases and improved methods of data analysis have greatly accelerated the gene-discovery process. Linkage analyses of single-gene traits that segregate in families with extreme phenotypes have led to the elucidation of critical pathways controlling bone mass. For example, components of the Wnt-β-catenin signalling pathway have been validated (in both GWAS and functional studies) as contributing to various bone phenotypes. These notable advances in gene discovery suggest that the next decade will witness cataloguing of the hundreds of genes that influence bone mass and osteoporosis, which in turn will provide a roadmap for the development of new drugs that target diseases of low bone mass, including osteoporosis.

The analysis of DKK1 polymorphisms in relation to skeletal phenotypes and bone response to alendronate treatment in Chinese postmenopausal women

Aim: To investigate the correlation between DKK1 polymorphisms with bone phenotypes and response to alendronate treatment. Materials & methods: Five tag single nucleotide polymorphisms of DKK1 were analyzed in 639 Chinese postmenopausal women with osteoporosis or osteopenia. Bone mineral density (BMD), β-CTX and ALP were measured before and after alendronate treatment. Results: Genotypes at rs1896367, rs1528877 and rs2241529 correlated to baseline BMD (p < 0.05). rs1528877 and rs2241529 polymorphisms correlated to baseline β-CTX levels (p < 0.05). rs2241529 polymorphisms of DKK1 had a small influence on the skeletal response to alendronate treatment (p < 0.05). Conclusion: DKK1 polymorphisms may correlate to baseline BMD and serum β-CTX levels, but present a weak effect on the response to alendronate.

MULTIFACTORIAL PATHOGENESIS OF OSTEOPOROSIS AND THE ROLE OF GENES OF CANONICAL WNT-SIGNALING PATHWAY

Nowadays, multifactorial nature of osteoporosis does not raise any doubts. Besides, it should be noted that about 90% disease cases are determined genetically. In 1990-s a number of candidate genes mutations were established which increase the risk of osteoporosis development. VDR, ESR1, ESR2, COLIA1, PTH, CT, CTR, BGP, AR, GCCR, TGFB1, IL-6, IGF1, IL-1ra, OPG were considered to be this kind of genes. New genetic analysis technologies (GWAS, etc.) gave the opportunity to expand our conception about multi genomic pathogenesis of osteoporosis and to point out a new group of genes candidate - a canonical Wnt-signaling pathway genes (CTNNB1, SOST, FOXC2, FOXL1, LRP4, LRP5, WNT1, WNT3, WNT16, DKK1, AXIN1, JAG1, etc.). Extreme importance of canonical Wnt-signaling pathway and genes given above in skeleton formation and its strength necessitate the need for further scientific research and opens perspective to improve osteoporosis diagnostics, treatment and prognosis.

Association of the I264T variant in the sulfide quinone reductase-like (SQRDL) gene with osteoporosis in Korean postmenopausal women

To identify novel susceptibility variants for osteoporosis in Korean postmenopausal women, we performed a genome-wide association analysis of 1180 nonsynonymous single nucleotide polymorphisms (nsSNPs) in 405 individuals with osteoporosis and 722 normal controls of the Korean Association Resource cohort. A logistic regression analysis revealed 72 nsSNPs that showed a significant association with osteoporosis (p<0.05). The top 10 nsSNPs showing the lowest p-values (p = 5.2×10-4-8.5×10-3) were further studied to investigate their effects at the protein level. Based on the results of an in silico prediction of the protein's functional effect based on amino acid alterations and a sequence conservation evaluation of the amino acid residues at the positions of the nsSNPs among orthologues, we selected one nsSNP in the SQRDL gene (rs1044032, SQRDL I264T) as a meaningful genetic variant associated with postmenopausal osteoporosis. To assess whether the SQRDL I264T variant played a functional role in the pathogenesis of osteoporosis, we examined the in vitro effect of the nsSNP on bone remodeling. Overexpression of the SQRDL I264T variant in the preosteoblast MC3T3-E1 cells significantly increased alkaline phosphatase activity, mineralization, and the mRNA expression of osteoblastogenesis markers, Runx2, Sp7, and Bglap genes, whereas the SQRDL wild type had no effect or a negative effect on osteoblast differentiation. Overexpression of the SQRDL I264T variant did not affect osteoclast differentiation of the primary-cultured monocytes. The known effects of hydrogen sulfide (H2S) on bone remodeling may explain the findings of the current study, which demonstrated the functional role of the H2S-catalyzing enzyme SQRDL I264T variant in osteoblast differentiation. In conclusion, the results of the statistical and experimental analyses indicate that the SQRDL I264T nsSNP may be a significant susceptibility variant for osteoporosis in Korean postmenopausal women that is involved in osteoblast differentiation.

WNT3A gene polymorphisms are associated with bone mineral density variation in postmenopausal mestizo women of an urban Mexican population: findings of a pathway-based high-density single nucleotide screening

Osteoporosis (OP) is a common skeletal disorder characterized by low bone mineral density (BMD) and is a common health problem in Mexico. To date, few genes affecting BMD variation in the Mexican population have been identified. The aim of this study was to investigate the association of single nucleotide polymorphisms (SNPs) located in genes of the Wnt pathway with BMD variation at various skeletal sites in a cohort of postmenopausal Mexican women. A total of 121 SNPs in or near 15 Wnt signaling pathway genes and 96 ancestry informative markers were genotyped in 425 postmenopausal women using the Illumina GoldenGate microarray SNP genotyping method. BMD was measured by dual-energy X-ray absorptiometry in total hip, femoral neck, Ward's triangle, and lumbar spine. Associations were tested by linear regression for quantitative traits adjusting for possible confounding factors. SNP rs752107 in WNT3A was strongly associated with decreased total hip BMD showing the highest significance under the recessive model (P = 0.00012). This SNP is predicted to disrupt a binding site for microRNA-149. In addition, a polymorphism of the Wnt antagonist DKK2 was associated with BMD in femoral neck under a recessive model (P = 0.009). Several LRP4, LRP5, and LRP6 gene variants showed site-specific associations with BMD. In conclusion, this is the first report associating Wnt pathway gene variants with BMD in the Mexican population.

Relationship of body composition with bone mineral density in northern Chinese men by body mass index levels

Osteoporosis and obesity are severe public health problems in an aging society, and as we all know, bone mineral density (BMD) is closely related to fat mass (FM) and fat distribution. However, studies have long focused on pre- or post-menopausal women, and its presence in men has been underestimated. To investigate the differential impact of fat on BMD, we characterized body composition of northern Chinese men and examined the relationship with BMD according to body mass index (BMI) levels.

METHODS

A cross-sectional study was conducted on 502 healthy northern Chinese men aged 20-89 screened from the participants in a community-based osteoporosis prevention study conducted by the Research Center of Qianfoshan Hospital of Shandong University from 2009 to 2010. The qualified subjects were stratified according to BMI levels as normal weight (18.5 ≤ BMI < 24 kg/m(2), n = 137), overweight (24 ≤ BMI < 28 kg/m(2), n = 225), and obesity (BMI ≥ 28 kg/m(2), n = 140). Total body, left femur, lumbar spine BMD and lean mass (LM), FM, percent body fat (%BF) were measured by dual-energy X-ray absorptiometry. Pearson correlation and age-adjusted partial correlation analyses between body composition-related parameters and BMD were performed. Multiple regression analysis was performed to examine the relationship of BMD with LM, FM and %BF.

RESULTS

Height and weight had positive associations with BMD at all sites, although age had negative associations. Of all subjects, LM and FM were positively correlated with BMD at almost sites (P < 0.01). However, when the subjects were divided into normal weight, overweight and obesity, no relations were reflected between FM and BMD. %BF showed negative correlations with BMD at arm and leg (P < 0.01) in overweight, and with BMD at total body, arm, leg, hip (P < 0.01) in obesity. In regression models, both FM and LM showed statistically positively significant relations with total body and regional BMD in all subjects (all P < 0.05). LM was positively correlated with BMD at almost site (all P < 0.05) in groups, while FM had no association. Interestingly, percent body fat (%BF) had negative associations with BMD at total body, arm, leg and total femur in overweight and obesity.

CONCLUSIONS

The relationship between LM and BMD was certain in northern Chinese men while fat-bone relationship was complicated. %BF had a significantly negative association with total body and regional BMD in overweight and obese men.