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Serum osmolarity and haematocrit do not modify the association between the impedance index (Ht²/Z) and total body water in the very old: The Newcastle 85+Study

Lookup NU author(s): Dr Mario Siervo, Dr Carla Prado, Dr Joanna Collerton, Dr Karen Davies, Dr Andrew KingstonORCiD, Professor John Mathers, Emeritus Professor Thomas Kirkwood, Emerita Professor Carol Jagger

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Abstract

Purpose of the research: Bioelectrical impedance is a non-invasive technique for the assessment of body composition; however, information on its accuracy in the very old (80 + years) is limited. We investigated whether the association between the impedance index and total body water (TBW) was modified by hydration status as assessed by haematocrit and serum osmolarity.Materials and methods: This was a cross-sectional analysis of baseline data from the Newcastle 85 + Cohort Study. Anthropometric measurements [weight, height (Ht)] were taken and body mass index (BMI) calculated. Leg-to-leg bioimpedance was used to measure the impedance value (Z) and to estimate fat mass, fat free mass and TBW. The impedance index (Ht2/Z) was calculated. Blood haematocrit, haemoglobin, glucose, sodium, potassium, urea and creatinine concentrations were measured. Serum osmolarity was calculated using a validated prediction equation.Principal results: 677 men and women aged 85 years were included. The average BMI of the population was 24.3 +/- 4.2 kg/m2 and the prevalence of overweight and obesity was 32.6% and 9.5%, respectively. The impedance index was significantly associated with TBW in both men (n = 274, r = 0.76, p < 0.001) and women (n = 403, r = 0.96, p < 0.001); in regression models, the impedance index remained associated with TBW after adjustment for height, weight and gender, and further adjustment for serum osmolarity and haematocrit. The impedance index values increased with BMI and the relationship was not modified by hydration status in women (p = 0.69) and only marginally in men (p = 0.02).Major conclusions: The association between the impedance index and TBW was not modified by hydration status, which may support the utilisation of leg-to-leg bioimpedance for the assessment of body composition in the very old. (C) 2014 Elsevier Ireland Ltd. All rights reserved.

Publication metadata

Author(s): Siervo M, Prado C, Hooper L, Munro A, Collerton J, Davies K, Kingston A, Mathers JC, Kirkwood TBL, Jagger C

Publication type: Article

Publication status: Published

Journal: Archives of Gerontology and Geriatrics

Year: 2015

Volume: 60

Issue: 1

Pages: 227-232

Print publication date: 01/01/2015

Online publication date: 17/09/2014

Acceptance date: 09/09/2014

ISSN (print): 0167-4943

ISSN (electronic): 1872-6976

Publisher: Elsevier

URL: http://dx.doi.org/10.1016/j.archger.2014.09.004

DOI: 10.1016/j.archger.2014.09.004

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