Banack Hailey R, Wactawski-Wende Jean, Hovey Kathleen M, Stokes Andrew
Department of Epidemiology and Environmental Health, School of Public Health and Health Professions, University at Buffalo, The State University of New York, Buffalo, NY.
Department of Global Health and Center for Global Health and Development, Boston University School of Public Health, Boston, MA.
Menopause. 2018 Mar;25(3):307-313. doi: 10.1097/GME.0000000000000989.
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 postmenopausal 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 postmenopausal women relative to total body fat percent measured by DXA scan.
Data from 1,329 postmenopausal women participating in the Buffalo OsteoPerio Study were used in this analysis. At baseline, women ranged in age from 53 to 85 years. Obesity was defined as BMI ≥ 30 kg/m 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 BF% using graphical tools, such as scatterplots and receiver-operating characteristic curves. Youden's J index was used to determine the empirical optimal BMI cut-point for each level of BF% defined obesity.
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 24.9 kg/m for 35% BF, 26.49 kg/m for 38% BF, and 27.05 kg/m for 40% BF according to the Youden's index.
Results demonstrate that a BMI cut-point of 30 kg/m does not appear to be an appropriate indicator of true obesity status in postmenopausal 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.
体重指数（BMI）是临床环境和人群健康研究中广泛使用的肥胖状况指标。然而，人们对BMI作为绝经后女性肥胖衡量指标的有效性存在担忧。与BMI不同，BMI是肥胖的间接衡量指标，无法区分瘦体重和脂肪量，而双能X线吸收法（DXA）可直接测量体脂，被认为是肥胖测量的金标准。本研究的目的是检验相对于通过DXA扫描测量的全身脂肪百分比，使用BMI来识别绝经后女性肥胖的有效性。
本分析使用了来自参与布法罗骨质疏松牙周研究的1329名绝经后女性的数据。在基线时，女性年龄在53至85岁之间。肥胖定义为BMI≥30kg/m²且体脂百分比（BF%）大于35%、38%或40%。我们计算了灵敏度、特异度、阳性预测值和阴性预测值，以评估BMI定义的肥胖相对于BF%的有效性。我们还使用散点图和受试者工作特征曲线等图形工具进一步探讨了BMI相对于BF%的有效性。约登指数用于确定每个BF%定义肥胖水平的经验性最佳BMI切点。
对于35%体脂，BMI定义肥胖的灵敏度为32.4%；对于38%体脂，灵敏度为44.6%；对于40%体脂，灵敏度为55.2%。相应的特异度值分别为99.3%、97.1%和94.6%。根据约登指数，定义肥胖的经验性最佳BMI切点对于35%BF为24.9kg/m²，对于38%BF为26.49kg/m²，对于40%BF为27.05kg/m²。
结果表明，30kg/m²的BMI切点似乎不是绝经后女性真正肥胖状况的合适指标。本研究中BMI有效性的经验性估计可被其他研究者用于考虑老年女性中与BMI相关的错误分类。
