All ETDs from UAB

Advisory Committee Chair

Krista Casazza

Advisory Committee Members

Barbara Gower

Timothy Garvey

Suzanne Judd

Stephenie Wallace

Document Type

Dissertation

Date of Award

2015

Degree Name by School

Doctor of Philosophy (PhD) School of Health Professions

Abstract

Impaired insulin sensitivity as a consequence of childhood obesity has been implicated as a contributor to skeletal fragility. There is a need to understand the interrelationships among insulin sensitivity and skeletal parameters (i.e. cortical, trabecular, marrow) in obesity during the pubertal transition. Further, calorie restricted weight loss to stabilize these relationships warrants investigation as well. The goal of this project was to examine the relationships among body composition, skeletal parameters, and insulin sensitivity. The first aim was to evaluate the relationships among total body fat, bone mineral content (BMC) and femoral bone marrow adipose tissue (BMAT) during childhood and underlying metabolic determinants. Additional aims investigated the relationship among bone parameters and weight (tibia) and non-weight (radius) bearing sites, circulating bone turnover markers, and measures of insulin sensitivity before and after weight loss in overweight/obese early pubertal girls. Aim 1 included 59 healthy girls aged 4-10 years who underwent dual-energy x-ray absorptiometry (DXA) to assess total body fat and bone mineral content (BMC) and magnetic resonance imaging (MRI) for bone marrow adipose tissue (BMAT), and provided a fasting blood sample to assess metabolic factors (i.e. insulin, adiponectin, leptin). For aim 2, 53 overweight/obese girls aged 7-11 years underwent DXA to assess total body fat and BMC, peripheral quantitative computed tomography (pQCT) to assess skeletal parameters, and a liquid meal test to calculate whole body insulin sensitivity index (WBISI) and homeostasis model assessment of insulin utilization (HOMA-IR). For aim 3, 21 of the original 53 overweight/obese girls repeated the DXA, pQCT, and liquid meal test after 18 weeks on a calorie restricted weight loss intervention. Results from these studies revealed positive relationships among body fat, BMC, and BMAT that may be influenced by difference metabolic mechanism according to race. Also, greater IR may negatively influence skeletal remodeling processes that govern bone density, yet may promote areal growth processes (i.e. modeling) perhaps via elevated circulating insulin. Further, no detrimental influence of weight loss on bone growth was observed, and improvement in insulin sensitivity via weight loss may stabilize growth processes by slowing areal growth and promoting mineralization.

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