Bone Structure and Volumetric BMD in Overweight Children: A Longitudinal Study

Authors

  • Rachel J Wetzsteon,

    1. Department of Pediatrics, Division of Nephrology, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
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  • Moira A Petit,

    Corresponding author
    1. School of Kinesiology, Laboratory for Musculoskeletal Health, University of Minnesota, Minneapolis, Minnesota, USA
    • Address reprint requests to: Moira Petit, PhD, University of Minnesota, School of Kinesiology, 1900 University Avenue, 111 Cooke Hall, Minneapolis, MN 55455, USA
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  • Heather M Macdonald,

    1. Department of Mechanical and Manufacturing Engineering, Calgary, Canada
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  • Julie M Hughes,

    1. School of Kinesiology, Laboratory for Musculoskeletal Health, University of Minnesota, Minneapolis, Minnesota, USA
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  • Thomas J Beck,

    1. Department of Radiology, Johns Hopkins University, Baltimore, Maryland, USA
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  • Heather A McKay

    1. Faculty of Medicine, Department of Orthopaedics, University of British Columbia, Vancouver, Canada
    2. Faculty of Medicine, Department of Family Practice, University of British Columbia, Vancouver, Canada
    3. Centre for Hip Health and Musculoskeletal Research, Vancouver Coastal Health Research Institute, Vancouver, Canada
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  • The authors state that they have no conflicts of interest.

Abstract

The effect of excess body fat on bone strength accrual is not well understood. Therefore, we assessed bone measures in healthy weight (HW) and overweight (OW) children. Children (9–11 yr) were classified as HW (n = 302) or OW (n = 143) based on body mass index. We assessed total (ToD) and cortical (CoD) volumetric BMD and bone area, estimates of bone strength (bone strength index [BSI]; stress-strain index [SSIp]), and muscle cross-sectional area (CSA) at the distal (8%), midshaft (50%), and proximal (66%) tibia by pQCT. We used analysis of covariance to compare bone outcomes at baseline and change over 16 mo. At baseline, all bone measures were significantly greater in OW compared with HW children (+4–15%; p ≤ 0.001), with the exception of CoD at the 50% and 66% sites. Over 16 mo, ToA increased more in the OW children, whereas there was no difference for change in BSI or ToD between groups at the distal tibia. At the tibial midshaft, SSIp was similar between groups at baseline when adjusted for muscle CSA, but low when adjusted for body fat in the OW group. At both sites, bone strength increased more in OW because of a greater increase in bone area. Changes in SSIp were associated with changes in lean mass (r = 0.70, p < 0.001) but not fat mass. In conclusion, although OW children seem to be at an advantage in terms of absolute bone strength, bone strength did not adapt to excess body fat. Rather, bone strength was adapted to the greater muscle area in OW children.

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