Greater lean tissue and skeletal muscle mass are associated with higher bone mineral content in children

Karen B Dorsey,Steven B Heymsfield,John C Thornton,Dympna Gallagher

doi:10.1186/1743-7075-7-41

Abstract

BackgroundTo compare the relationship of skeletal muscle mass with bone mineral content in an ethnically diverse group of 6 to 18 year old boys and girls.Methods175 healthy children (103 boys; 72 girls) had assessments of body mass, height, and Tanner stage. Whole body bone mineral content, non-bone lean body mass (nbLBM), skeletal muscle mass, and fat mass were assessed using dual-energy X-ray absorptiometry (DXA). Muscle mass was estimated from an equation using appendicular lean soft tissue measured by DXA, weight and height. Estimates of skeletal muscle mass and adipose tissue were also assessed by whole body multi-slice magnetic resonance imaging (MRI). Linear regression was used to determine whether skeletal muscle mass assessed by DXA or by MRI were better predictors of bone mineral content compared with nbLBM after adjusting for sex, age, race or ethnicity, and Tanner stage.ResultsGreater skeletal muscle mass was associated with greater bone mineral content (p < 0.001). The skeletal muscle mass assessed by MRI provided a better fitting regression model (determined by R2 statistic) compared with assessment by DXA for predicting bone mineral content. The proportion of skeletal muscle mass in nbLBM was significantly associated with greater bone mineral content adjusted for total nbLBM.ConclusionsThis study is among the first to describe and compare the relationship of skeletal muscle to bone using both MRI and DXA estimates. The results demonstrate that the use of MRI provides a modestly better fitting model for the relationship of skeletal muscle to bone compared with DXA. Skeletal muscle had an impact on bone mineral content independent of total non-bone lean body mass. In addition, Hispanics had greater bone mineral content compared to other race and ethnic groups after adjusting for sex, age, adipose tissue, skeletal muscle mass, and height.

Highlights

To compare the relationship of skeletal muscle mass with bone mineral content in an ethnically diverse group of 6 to 18 year old boys and girls
Estimates of non-bone lean body mass were consistently higher compared with estimates of skeletal muscle mass (SMMDXA and skeletal muscle mass from MRI (SMMMRI)) as nbLBM contains organ and non-muscle soft tissue in addition to muscle (Figure 2)
Estimates of skeletal muscle based on magnetic resonance imaging (MRI) (SMMMRI) provided the best fitting model for predicting bone mineral content (BMC) using simple linear regression followed by nbLBM (SMMMRI R2 = 0.948, β = 0.90, p < 0.001; nbLBM R2 = 0.936, β = 1.16, p < 0.001)

Summary

Introduction

To compare the relationship of skeletal muscle mass with bone mineral content in an ethnically diverse group of 6 to 18 year old boys and girls. In a 1992 review of human studies, Weinsier et al reported that as children grow bone is consistently 50% of fat-free body mass. In 2006, Kim et al described a new method for estimating skeletal muscle mass from whole body DXA scans and compared these estimates with skeletal muscle mass measured by whole body magnetic resonance imaging[2]. The assessment of skeletal muscle mass from DXA or MRI allows for the isolation of skeletal muscle mass from total nbLBM in the limbs and whole body respectively. These new techniques make it possible to determine how changes in skeletal muscle mass as a component of nbLBM relate to changes in bone mineral content in children[3]

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