Abstract
BackgroundThe relative contribution of lean and fat to the determination of bone mineral density (BMD) in postmenopausal women is a contentious issue. The present study was undertaken to test the hypothesis that lean mass is a better determinant of BMD than fat mass.MethodsThis cross-sectional study involved 210 postmenopausal women of Vietnamese background, aged between 50 and 85 years, who were randomly sampled from various districts in Ho Chi Minh City (Vietnam). Whole body scans, femoral neck, and lumbar spine BMD were measured by DXA (QDR 4500, Hologic Inc., Waltham, MA). Lean mass (LM) and fat mass (FM) were derived from the whole body scan. Furthermore, lean mass index (LMi) and fat mass index (FMi) were calculated as ratio of LM or FM to body height in metre squared (m2).ResultsIn multiple linear regression analysis, both LM and FM were independent and significant predictors of BMD at the spine and femoral neck. Age, lean mass and fat mass collectively explained 33% variance of lumbar spine and 38% variance of femoral neck BMD. Replacing LM and FM by LMi and LMi did not alter the result. In both analyses, the influence of LM or LMi was greater than FM and FMi. Simulation analysis suggested that a study with 1000 individuals has a 78% chance of finding the significant effects of both LM and FM, and a 22% chance of finding LM alone significant, and zero chance of finding the effect of fat mass alone.ConclusionsThese data suggest that both lean mass and fat mass are important determinants of BMD. For a given body size -- measured either by lean mass or height --women with greater fat mass have greater BMD.
Highlights
The relative contribution of lean and fat to the determination of bone mineral density (BMD) in postmenopausal women is a contentious issue
While a majority of studies have found a positive association between lean mass and BMD [9,10,11,12,13,14,15,16,17,18], few studies have shown that fat mass (FM) is an important determinant of BMD [1922]
By using an appropriate adjustment for body size, we have shown in this study that both lean and fat mass were significantly associated with BMD, with the former being a stronger predictor than the latter
Summary
The relative contribution of lean and fat to the determination of bone mineral density (BMD) in postmenopausal women is a contentious issue. Several prospective studies in the last three decades have consistently indicated that bone mineral density (BMD) is the best indicator of fracture risk [1,2]. BMD is highly related to body weight, such that individuals with higher body weight have higher BMD [5] and reduced fracture risk [6]. Body weight explains approximately 30% of variance in BMD, making it one of the best determinants of BMD [7,8]. Body weight is largely made up of two components: fat mass (FM) and lean mass (LM, or fat-free mass). The inconsistency of findings may relate to the expression of bone mass as an areal BMD or apparent BMD, and the collinearity between FM and LM [9]
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