Does Time Spent Upright Moderate the Influence of a Weighted Vest on Change in Bone Mineral Density During Weight Loss among Older Adults? A Secondary Analysis of the INVEST in Bone Health Randomized Controlled Trial

Jason Fanning^1*Daniel P. Beavers¹Shirley M. Bluethmann²S. Delanie Lynch²Ashley A. Weaver²Cassidy Guida²Kristen M. Beavers²

• ¹Wake Forest University, Winston-Salem, United States
• ²Wake Forest University School of Medicine, Winston-Salem, United States

Introduction: The INVEST in Bone Health randomized controlled trial examined whether one year of weight loss paired with resistance training (WL+RT) or weighted vest use (WL+VEST) sustained bone mineral density (BMD) at the hip better than weight loss alone (WL). All groups lost similar amounts of body weight, but neither those wearing the vest nor those engaging in structured resistance training retained greater bone density relative to those in the weight loss-only condition. One possible reason for the absence of a group difference may be that the bone-sparing benefits of the weighted vest may relate to the amount of time one spends standing and therefore exposed to additional loading Purpose: The purpose of this secondary analysis was to determine whether the time an individual spent upright moderated the effect of the intervention on BMD at the hip. Methods: Older adults (mean age 66.9±4.8 years) were eligible if they were living with obesity or who were both overweight with an indication for weight loss. Participants were randomized to one of the three WL interventions. Participants completed quantitative computed tomography (CT) and dual energy x-ray absorptiometry (DXA) assessments of hip BMD and wore an ActivPAL accelerometer to measure upright time for one week at baseline, 6, and 12 months. Results: In total 131 participants had sufficient DXA data and 132 and sufficient CT data for inclusion in linear mixed effects models. The model for DXA-derived hip areal BMD (aBMD) revealed a significant interaction between upright time and group assignment (p=0.023) such that upright time was positively associated with baseline-adjusted change in aBMD in WL+VEST, but the opposite was true for WL (p=0.009). The relationship between upright time and change in aBMD likewise differed significantly between WL+RT and WL (p=0.043), as WL+RT demonstrated a less negative relationship than did WL. There were no significant interactions between group assignment and upright time for CT-derived measures of BMD. Conclusion: These results suggest a need for research investigating the efficacy of a weighted vest intervention paired with a focus on improving daily upright time for sustaining bone health among older adults as they lose weight.