No abstract

Many fractures occur in individuals without osteoporosis defined by areal bone mineral density (aBMD). Inclusion of other aspects of skeletal strength may be useful in identifying at-risk subjects. We used surrogate measures of bone strength at the radius and tibia measured by peripheral quantitative computed tomography (pQCT) to evaluate their relationships with nonvertebral fracture risk. Femoral neck (FN) aBMD, measured by dual-energy X-ray absorptiometry (DXA), also was included. The study population consisted of 1143 white men aged 69+ years with pQCT measures at the radius and tibia from the Minneapolis and Pittsburgh centers of the Osteoporotic Fractures in Men (MrOS) study. Principal-components analysis and Cox proportional-hazards modeling were used to identify 21 of 58 pQCT variables with a major contribution to nonvertebral incident fractures. After a mean 2.9 years of follow-up, 39 fractures occurred. Men without incident fractures had significantly greater bone mineral content, cross-sectional area, and indices of bone strength than those with fractures by pQCT. Every SD decrease in the 18 of 21 pQCT parameters was significantly associated with increased fracture risk (hazard ration ranged from 1.4 to 2.2) independent of age, study site, body mass index (BMI), and FN aBMD. Using area under the receiver operation characteristics curve (AUC), the combination of FN aBMD and three radius strength parameters individually increased fracture prediction over FN aBMD alone (AUC increased from 0.73 to 0.80). Peripheral bone strength measures are associated with fracture risk and may improve our ability to identify older men at high risk of fracture. © 2011 American Society for Bone and Mineral Research.

Design and MethodsSkeletal muscle adipose tissue (AT) infiltration (myosteatosis) increases with aging and may contribute to the development of type 2 diabetes mellitus (T2DM). It remains unclear if myosteatosis is associated to glucose and insulin homeostasis independent of total and central adiposity. We evaluated the association between intermuscular AT (IMAT) in the abdominal skeletal muscles (total, paraspinal and psoas) and fasting serum glucose, insulin, and homeostasis model assessment of insulin resistance (HOMA-IR) in 393 non-diabetic Caucasian men aged 65+. Abdominal IMAT, visceral (VAT) and subcutaneous (SAT) AT (cm3) were measured by quantitative computed tomography at the L4-L5 intervertebral space.ResultsIn age, study site, height and muscle volume adjusted regression analyses, total abdominal and psoas (but not paraspinal) IMAT were positively associated with glucose, insulin and HOMA-IR (all P < 0.003). The associations between total abdominal and psoas IMAT and insulin and HOMA-IR remained significant after further adjusting for lifestyle factors, as well as DXA total body fat, VAT or SAT in separate models (all P <0.009).ConclusionsOur study indicates a previously unreported, independent association between abdominal myosteatosis and hyperinsulinemia and insulin resistance among older Caucasian men. These associations may be specific for particular abdominal muscle depots, illustrating the potential importance of separately studying specific muscle groups.

African Caribbean males have the highest BMD on a population level ever reported. Lean mass was the single most important correlate. Variability in BMD/BMAD was also explained by age, mixed African ancestry, anthropometric, lifestyle, and medical factors.

The protective effect of total fat mass on bone mineral density (BMD) has been challenged with studies showing no or negative association after adjusting for weight. Subsequently, more studies have evaluated the relationship of regional adiposity with BMD, and findings were inconsistent for central obesity. Advancements in imaging techniques enable us to directly and noninvasively study the role of adiposity on skeletal health. Visceral adiposity measured by computed tomography (CT) has consistently been shown to have negative effects on bone. Availability of magnetic resonance spectroscopy (MRS) also allows us to noninvasively quantify bone marrow fat (BMF), which has been known to be associated with osteoporosis from histomorphometric studies. Using MRS along with dual energy x-ray absorptiometry, studies have reported a detrimental role of BMF on BMD. With the increase in aging and obesity of the population, it is important to continue this effort in identifying the contribution of adipose tissues to bone quality and fracture.

Our analyses suggest that despite lower total adiposity, skeletal muscle fat infiltration is greater among African than among Caucasian ancestry men and is associated with T2D in both ethnic groups. Additional studies are needed to determine the mechanisms contributing to ethnic differences in skeletal muscle adiposity and to define the metabolic and health implications of this fat depot.

Elevated vertebral bone marrow fat (BMF) among individuals with osteoporosis has been established in histomorphometric studies. Several studies have found a negative correlation between BMF and bone mineral density (BMD) at the spine in men and women across different age groups. Animal studies have also observed bone loss with increased BMF in mice with induced diabetes. Our study objective was to test the hypothesis that the association between BMF and BMD varies by diabetic status. We performed a cross-sectional study of 156 men aged 74–96 years from the Osteoporotic Fractures in Men study (MrOS) at the Pittsburgh clinical site. All men had spine BMF scans using proton magnetic resonance spectroscopy and spine and hip BMD scans by dual-energy x-ray absorptiometry. BMF was expressed as lipid to “lipid + water” ratio (%). Men were considered diabetic if they self-reported a physician diagnosis of diabetes, diabetes medication or had a fasting glucose ≥ 126mg/dl. Men with diabetes (n=38) had a significantly higher spine BMF (58.9 vs. 54.6 %, p=0.0035), spine BMD (1.20 vs. 1.10 g/cm2, P=0.007)) and total hip BMD (0.99 vs. 0.94 g/cm2, p=0.04) than those without, while no differences were observed for body weight, body mass index or waist circumference. Pearson correlation tests showed no significant correlation of spine BMF with age or BMD in non-diabetics. Significant inverse correlations were observed between BMF and BMD (−0.30 for femoral neck and −0.39 for total hip) among diabetic men. In conclusion, men with diabetes had a higher BMF compared to non-diabetic men. The correlation between BMF and BMD differed by diabetes status. Further investigation of the association of diabetes with BMF and BMD may provide a better understanding of the high fracture rates among individuals with diabetes despite their higher BMD.

QCT provides a measure of volumetric BMD (vBMD) and distinguishes trabecular from cortical bone. Few studies have determined the factors related to vBMD in men, especially among men of African heritage. This study evaluated the relationship of anthropometric, medical, and behavioral factors and vBMD in a population-based cohort of men of African ancestry (n = 1901) 40 yr of age who had undergone screening for prostate cancer for the first time. Trabecular and cortical vBMD were measured at the radius and tibia by pQCT. Multiple linear regression analysis identified age, height, body weight, cigarette smoking, history of diabetes, fracture, and prostate cancer as the independent correlates of vBMD. However, associations with several variables differed between cortical and trabecular vBMD and between the radius and tibia. Longitudinal studies are needed to gain a better understanding of the mechanisms underlying these differential associations that may show new insight into the etiology of trabecular and cortical bone loss in men.