Bone volumetric density, geometry and strength in young adults

Introduction: Osteoporosis and related fractures are significant societal health burdens. Healthy and strong bones in old age depend upon many factors (such as hormones and mechanical loading) that influence changes in bone tissue throughout life. It is important to understand how these factors affect bone strength during the young adult years to generate effective prevention strategies, which may reduce the risk for osteoporosis later in life.;Aim: The primary aim was to explore bone volumetric density, geometry and strength in young adult females. Specifically, 1) how these parameters change over time, 2) how mechanical loading influences the parameters and 3) to provide a functional bone health perspective as it relates to common findings of low areal bone mineral density in amenorrheic athletes.;Methods: Design and Participants: The first study was a prospective, ancillary study of a randomized controlled trial (Women in Steady Exercise Research, WISER). 141 females were assessed at baseline and 49 had follow-up measures. Bone strength and influential factors were assessed at baseline and at 2 years. A subset of this baseline group (N=30) served as sedentary female control participants in the second study. The second study compared bone outcomes of these sedentary women to eumenorrheic or oligomenorrheic runners (N=38) from local area running teams and clubs. A male group included 21 runners from local area running teams or clubs. Sedentary age-matched University of Minnesota students served as male controls (N=17). Male groups were included to address our original research question assessing bone strength differences in mechanically loaded bones regardless of sex. Bone Measurements: Dual energy x-ray absorptiometry was used in the first study population body composition changes. Tibia and radius bone strength was assessed with peripheral quantitative computed tomography in both studies.;Results: 2-year Change in Inactive Young Adult Females After adjusting for age and limb length, follow-up bone strength was 3.5% greater at the distal 4% radius site and 1.5 to 2.9% greater at the 4% and 66% tibia sites. Strength changes were primarily due to increases in volumetric bone mineral density and bone content. Change in tibia bone strength and bone content at both the 4% and the 66% sites was correlated with follow-up muscle cross sectional area.;Bone Strength in Female and Male Runners After adjusting for age, weight and limb length, tibia bone strength was 17 to19% greater at the distal 4%, the 50% and the 66% measurement sites. Volumetric BMD was not different at the 4% site and was 2% lower in female runners than controls at the 50 and 66% sites. At the radius, bone strength at the 50% site was 13% greater in female runners compared to controls due to 9% greater total area. There were no differences in strength outcomes at the radius site, however total area was 11% greater in female runners compared to female controls. In Male participants, after adjusting for age, weight and limb length, runners had 8 to 14% greater tibia cortical thickness and tibia cortical area than controls at both the 50 and 66% sites. There were no adjusted tibia or radius bone strength differences between the male groups.;Summary: These study findings demonstrate muscle cross sectional area and mechanical load are important for bone strength and suggest it may be important to utilized the role of muscle to prevent the natural loss of bone that occurs with aging.;An Editorial: Low Bone Mass and Density in Female Athletes-Is there really cause for concern? Areal bone mineral density has been shown to be lower in amenorrheic athletes than their eumenorrheic or control counterparts. We discuss the evidence that supports a functional bone adaptation theory and in light of this, encourage future studies in this population to address bone structure. Further, we hypothesis that if structural components are assessed, these individuals may still be found to have low aBMD but their strength will have adapted to be as strong as necessary for customary loads.