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Is BMI a valid measure of obesity in post-menopausal women?
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March 2018
Source: Menopause. 25(3):307-313
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Alternative Title:Menopause
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Personal Author:
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Description:Objective
Body mass index (BMI) is a widely used indicator of obesity status in clinical settings and population health research. However, there are concerns about the validity of BMI as a measure of obesity in post-menopausal women. Unlike BMI, which is an indirect measure of obesity and does not distinguish lean from fat mass, dual energy x-ray absorptiometry (DXA) provides a direct measure of body fat and is considered a gold standard of adiposity measurement. The goal of this study is to examine the validity of using BMI to identify obesity in post-menopausal women relative to total body fat percent measured by DXA scan.
Methods
Data from 1329 post-menopausal women participating in the Buffalo OsteoPerio study were used in this analysis. At baseline, women ranged in age from 53 years to 85 years. Obesity was defined as BMI >30kg/m2 and body fat percent (BF%) greater than 35%, 38% or 40%. We calculated sensitivity, specificity, positive predictive value and negative predictive value to evaluate the validity of BMI defined obesity relative BF%. We further explored the validity of BMI relative to percent body fat using graphical tools, such as scatterplots and receiver operating characteristic (ROC) curves. Youden’s J index was used to determine the empirical optimal BMI cut point for each level of BF% defined obesity.
Results
The sensitivity of BMI-defined obesity was 32.4% for 35% body fat, 44.6% for 38% body fat and 55.2% for 40% body fat. Corresponding specificity values were 99.3%, 97.1% and 94.6%, respectively. The empirical optimal BMI cut-point to define obesity is 24.9kg/m2 for 35% BF, 26.49 kg/m2 for 38% BF and 27.05 kg/m2 for 40% BF according to the Youden Index.
Conclusions
Results demonstrate that a BMI cut-point of 30 kg/m2 does not appear to be an appropriate indicator of true obesity status in post-menopausal women. Empirical estimates of the validity of BMI from this study may be used by other investigators to account for BMI-related misclassification in older women.
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Pubmed ID:29135897
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Pubmed Central ID:PMC5821529
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