Bone Geometry, Body Composition and Sex Hormones in Men

描述（申请人提供）：骨质疏松症的特征是骨强度降低，导致骨折风险增加，在美国，1-2百万50岁或以上的男性受骨质疏松症影响。骨密度降低对骨质疏松症和骨折风险的影响是众所周知的。然而，注意力已经转向骨几何形状作为另一种可能影响骨折风险的骨骼特征。骨几何形状由骨内表面和骨外表面上组织的相对量决定。从生物力学的角度来看，骨强度在很大程度上取决于几何形状。老年男性中影响骨几何形状和骨强度的特征实际上是未知的。骨的生长和吸收是通过生物学途径来调节的，这些生物学途径涉及来自肌肉力量的机械负荷以及非机械因素，如内分泌效应。因此，我们假设老年男性髋部和脊柱的骨几何形状与腹部身体成分以及内源性睾酮和雌二醇水平相关。腹部肌肉可能直接影响髋关节和脊柱的机械负荷。腹部脂肪组织可能影响整体负荷模式或可能对骨骼产生内分泌影响。在老年男性中，睾酮似乎刺激骨骼生长，雌二醇可能抑制骨质流失。为了检验假设的相关性，我们建议使用来自1,800名年龄在65岁及以上的美国男性的现有数据，他们是男性骨质疏松性骨折（MrOS）队列的参与者。在该队列中进行了定量计算机断层扫描（QCT）。髋关节和脊柱中的骨几何结构测量以及腹部身体组成测量源自这些扫描。还对这些参与者进行了睾酮和雌二醇测定。我们将采用横断面设计，量化髋部和脊柱骨几何结构与腹部身体成分、睾酮和雌二醇的相关性。该项目将产生有关影响老年男性骨骼几何形状的因素的新信息。

DESCRIPTION (provided applicant): Osteoporosis is characterized by reduced bone strength that results in an increased risk of fracture, in the US, 1-2 million men ages 50 years or older are affected by osteoporosis. The contribution of reduced bone density to osteoporosis and fracture risk is well known. However, attention has turned toward bone geometry as another skeletal feature that may influence fracture risk. Bone geometry is determined by the relative amounts of tissue on the inner and outer bone surfaces. From a biomechanical perspective, bone strength is vitally dependent on geometry. The characteristics among older men that influence bone geometry and bone strength are virtually unknown. Bone growth and resorption are regulated through biologic pathways that involve mechanical loading from muscle forces, as well as non-mechanical factors such as endocrine effects. Therefore, we hypothesize that bone geometry in the hip and spine among older men will be associated with abdominal body composition and with endogenous levels of testosterone and estradiol. Abdominal muscles may directly affect mechanical loads on the hip and spine. Abdominal adipose tissues may affect overall loading patterns or may exert endocrine influences on bone. In older men, testosterone appears to stimulate bone growth and estradioi may inhibit bone loss. To test the hypothesized associations, we propose to use existing data from 1,800 US men ages 65 years and older who are participants in the Osteoporotic Fractures in Men (MrOS) cohort. Quantitative computed tomography (QCT) scans have been performed in this cohort. Bone geometry measures in the hip and spine and abdominal body composition measures are derived from these scans. Assays for testosterone and estradiol have also been performed for these participants. We will quantify the associations of bone geometry in the hip and spine with abdominal body composition, testosterone and estradiol using a cross-sectional design. The proposed project will yield new information about factors that influence bone geometry among older men.