APPLIED NUTRITIONAL INVESTIGATION Migration of the Bioelectrical Impedance Vector in Healthy Elderly Subjects Roberto Buffa, PhD, Giovanni Floris, MD, and Elisabetta Marini, PhD From the Department of Experimental Biology, Anthropological Science Section, University of Cagliari, Cagliari, Italy OBJECTIVE: We describe the effects of aging on the bioelectrical impedance vectors in healthy men and women. METHODS: Resistance (R) and reactance (Xc; standard, tetrapolar analysis at 50-kHz frequency) were measured in 201 volunteers (97 men and 104 women) aged 60 to 89 y. Criteria of exclusion from the sample were hospitalization within 3 mo before the survey, current medical treatment, physical handicaps, or other pathologies that might influence the measurements. Stature, weight, and four body circumfer- ences were also measured, and body mass index was calculated. The values of R and Xc were normalized for stature (H) and adjusted for body circumferences by means of covariance analysis. Age- and sex-dependent bioelectrical changes were evaluated by two-factor analysis of variance and Hotelling’s T 2 test. RESULTS: The bioelectrical data of the sample agreed well with the normal reference values of the Italian population. R/H showed a significant increase with age in both sexes, whereas Xc/H and the phase angle significantly decreased. The greatest changes occurred in the 70- to 79-y to the 80- to 89-y groups. After adjustment of the bioelectrical values for body circumferences, only Xc/H and the phase angle showed significant differences that decreased with age. CONCLUSIONS: The impedance vectors of healthy individuals showed a clear trend in the elderly, in both sexes, and particularly after age 80 y. The bioelectrical parameters indicated a reduction of soft tissue mass with age, as they tended to approach values typical of pathologically lean subjects (cachetic and anorexic states). After adjustment for the circumferences, the changes in the vector concerned only the Xc component, a measure of the capacitance produced by cell membranes of soft tissues. Therefore, in addition to the quantitative change, the electrical properties of the tissues may also change. Nutrition 2003;19:917–921. ©Elsevier Inc. 2003 KEY WORDS: body composition, bioelectrical impedance, elderly INTRODUCTION Bioelectrical impedance analysis (BIA) is useful for evaluation of the nutritional state in the elderly. Like anthropometry, BIA is a simple non-invasive technique and is particularly suitable for the determination of body composition in epidemiologic investiga- tions and in routine clinical use. The most frequent method of estimation of the body compart- ments by BIA is the use of regression equations. These equations generally make use of the predictive power of the resistance index (stature 2 /resistance) because it is proportional to the mass of con- ductive tissue in the body. 1 In the literature, there are numerous BIA equations for the estimation of body composition, but most of them have been developed from samples of young adults of normal weight. Be- cause various studies have demonstrated that the predictive effi- cacy of the BIA equations are significantly influenced by age, 2,3 several investigators have proposed specific equations for the estimation of body composition in the elderly. 4–6 However, even the use of age-specific equations could lead to substantial estimation errors. 7 Indeed, there is great individual variability in the density of mineral mass, hydration, and protein content of fat-free mass (FFM), and this variability is particularly evident in elderly subjects. 8,9 Moreover, the predictive accuracy of the BIA equations is highly dependent on the body composition of the reference population and on the method of validation. To avoid the multiplication of population-, sex-, and age- specific BIA equations to predict body composition, which would diminish the comparative value of the results, Piccoli et al. 10 proposed the direct use of resistance (R) and reactance (Xc) normalized for stature (H). Bioelectrical impedance vector analysis (BIVA) allows the semiquantitative examination of body compo- sition and provides an evaluation of tissue hydration and nutri- tional state without the need for descriptive models of the electrical properties of the human body. 11 In fact, the length and inclination of the Z impedance vector in the plane delimited by the variables R/H and Xc/H varies according to the state of hydration and soft tissue mass. 10 Comparison of the Z vector of an individual or group of individuals with the reference standards of the healthy population 12–14 allows one to evaluate the affinity between the bioelectrical characteristics of the individual or group and those of the population. Moreover, the position of the Z vector in the RXc plane permits a clinical evaluation of an individual. For example, peculiar im- pedance characteristics have been described for renal pathologies, liver disease, obesity, cachexia, and anorexia. 14 BIVA is particu- This research was financially supported by M.I.U.R. 40% and 60% contributions. Correspondence to: Giovanni Floris, MD, Department of Experimental Biology, Anthropological Science Section, Cittadella Universitaria Mon- serrato, 09042 Monserrato (Cagliari), Italy. E-mail: floris@unica.it 0899-9007/03/$30.00 Nutrition 19:917–921, 2003 ©Elsevier Inc., 2003. Printed in the United States. All rights reserved. doi:10.1016/S0899-9007(03)00180-1