Body mass index versus bioelectrical impedance analysis for classifying physical function impairment in a racially diver
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ORIGINAL ARTICLE
Body mass index versus bioelectrical impedance analysis for classifying physical function impairment in a racially diverse cohort of midlife women: the Study of Women’s Health Across the Nation (SWAN) Bradley M. Appelhans1,2 · Brittney S. Lange‑Maia1 · Kelley Pettee Gabriel3,4,5 · Carrie Karvonen‑Gutierrez6 · Kelly Karavolos1 · Sheila A. Dugan7 · Gail A. Greendale8 · Elizabeth F. Avery1 · Barbara Sternfeld9 · Imke Janssen1 · Howard M. Kravitz1,2 Received: 18 June 2019 / Accepted: 13 September 2019 © Springer Nature Switzerland AG 2019
Abstract Background Body composition strongly influences physical function in older adults. Bioelectrical impedance analysis (BIA) differentiates fat mass from skeletal muscle mass, and may be more useful than body mass index (BMI) for classifying women on their likelihood of physical function impairment. Aims This study tested whether BIA-derived estimates of percentage body fat (%BF) and height-normalized skeletal muscle mass (skeletal muscle mass index; SMI) enhance classification of physical function impairment relative to BMI. Method Black, White, Chinese, and Japanese midlife women (N = 1482) in the Study of Women’s Health Across the Nation (SWAN) completed performance-based measures of physical function. BMI (kg/m2) was calculated. %BF and SMI were derived through BIA. Receiver-operating characteristic (ROC) curve analysis, conducted in the overall sample and stratified by racial group, evaluated optimal cutpoints of BMI, %BF, and SMI for classifying women on moderate–severe physical function impairment. Results In the overall sample, a BMI cutpoint of ≥ 30.1 kg/m2 correctly classified 71.1% of women on physical function impairment, and optimal cutpoints for %BF (≥ 43.4%) and SMI (≥ 8.1 kg/m2) correctly classified 69% and 62% of women, respectively. SMI did not meaningfully enhanced classification relative to BMI (change in area under the ROC curve = 0.002; net reclassification improvement = 0.021; integrated discrimination improvement = − 0.003). Optimal cutpoints for BMI, %BF, and SMI varied substantially across race. Among Black women, a %BF cutpoint of 43.9% performed somewhat better than BMI (change in area under the ROC curve = 0.017; sensitivity = 0.69, specificity = 0.64). Conclusion Some race-specific BMI and %BF cutpoints have moderate utility for identifying impaired physical function among midlife women. Keywords Physical function · Body composition · Body mass index · Skeletal muscle mass
Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40520-019-01355-8) contains supplementary material, which is available to authorized users. * Bradley M. Appelhans [email protected] Extended author information available on the last page of the article
Physical function, which denotes the capacity to complete physical tasks in daily life, is an important domain of health that impacts quality of life, disability, morbidity, and mortality risk. Physical function generally declines with
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