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Specific bioelectrical impedance vector reference values for assessing body composition in the Italian elderly
Experimental Gerontology 50 (2014) 52–56
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Specific bioelectrical impedance vector reference values for assessing body composition in the Italian elderly Bruno Saragat a, Roberto Buffa a, Elena Mereu a, Marina De Rui b, Alessandra Coin b, Giuseppe Sergi b, Elisabetta Marini a,⁎ a b
Department of Environmental and Life Sciences, University of Cagliari, Cittadella Universitaria, 09042 Monserrato, Italy Department of Medicine-DIMED, Geriatrics Division, University of Padova, via Giustiniani 2, 35128 Padova, Italy
a r t i c l e
i n f o
Article history: Received 28 July 2013 Received in revised form 15 October 2013 Accepted 26 November 2013 Available online 3 December 2013 Section Editor: Andrzej Bartke Keywords: Bioelectrical values Tolerance ellipses Classic BIVA Specific BIVA Aging Body composition
a b s t r a c t Objective: To obtain specific bioelectrical impedance vector reference values for the healthy elderly Italian population, and to study age- and sex-related differences in body composition. Design: The study group consisted of 560 healthy individuals (265 men and 295 women) aged 65 to 100 y, whose anthropometric (height, weight, and calf, arm and waist circumferences) and bioelectrical measurements (resistance [R] and reactance [Xc], at 50 kHz and 800 μA) were recorded. R (Ω) and Xc (Ω) values were standardized for stature (H, m) to obtain the classic bioelectrical values. Specific values (resistivity [Rsp] and reactivity [Xcsp], Ω · cm) were obtained by multiplying R and Xc by a correction factor (A/L) that includes an estimate of the cross-sectional area of the body (A = 0.45 arm area + 0.10 waist area + 0.45 calf area), where L = 1.1 H. Results: Descriptive statistics were: Rsp (391.8 ± 57.9), Xcsp (42.6 ± 9.9), Zsp (394.2 ± 58.2), phase angle (6.2° ± 1.2) in men; Rsp (462.0 ± 80.1), Xcsp (47.9 ± 11.2), Zsp (464.6 ± 80.5), phase angle (5.9° ± 1.0) in women. The Xcsp and phase angle values showed a significant age-related decrease in both sexes, but especially in men, possibly relating to a gradual loss of muscle mass. Women's Rsp and Zsp values tended to drop, attributable to their declining proportion of fat mass. A declining sexual dimorphism was also apparent. Conclusions: Specific tolerance ellipses can be used for reference purposes for the Italian population when assessing body composition in gerontological practice and for epidemiological purposes. © 2013 Elsevier Inc. All rights reserved.
1. Introduction Normal aging is characterized by changes in body mass and composition (Buffa et al., 2011) that can impair an individual's health status and functionality, with the possible onset of geriatric syndromes, such as frailty (Fried et al., 2001), sarcopenia (Morley et al., 2001), and sarcopenic obesity (Baumgartner, 2000). Age-related body mass variations involve an initial tendency for it to increase, followed by a decline (Buffa et al., 2011). This latter reduction is mainly due to a loss of muscle mass (especially in men), total body water (particularly from the intracellular compartment), and skeletal mass (especially in women). The loss of fat mass (FM) is less marked and occurs at a later age. The combined changes in FM and fat-free mass (FFM) give rise to an initial increase in the percentage of body fat, which subsequently levels off (Ding et al., 2007).
Abbreviations: R, resistance; Xc, reactance; Z, impedance; Rsp, resistivity; Xcsp, reactivity; Zsp, impedivity; FM, fat mass; FFM, fat-free mass; BIA, bioelectrical impedance analysis; BIVA, bioelectrical impedance vector analysis; DXA, dual-energy X-ray absorptiometry; ECW/ICW, extracellular/intracellular water ratio; FFMI, fat-free mass index; FMI, fat mass index; SMI, skeletal muscle mass index; FM%, fat mass percentage. ⁎ Corresponding author. Tel.: +39 0706756607; fax: +39 0706756616. E-mail address: [email protected] (E. Marini). 0531-5565/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.exger.2013.11.016
Body composition screening and monitoring in the elderly is to be recommended to prevent the risk of malnutrition and related disorders (Cruz-Jentoft et al., 2010). Bioelectrical impedance vector analysis (BIVA) is a portable, noninvasive and low-cost method for assessing body cell mass and body hydration (Piccoli et al., 1994). The BIVA approach differs from traditional bioelectrical impedance analysis (BIA) in that it analyzes bioelectrical values directly, without referring to predictive equations. Resistance (R, Ω) and reactance (Xc, Ω), at 50 kHz and 800 μA, are normalized for an individual's height and plotted in a tolerance ellipse graph that enables the person's body characteristics to be assessed. BIVA thus avoids the potential error deriving from adopting BIA equations, which can lead to unreliable results in elderly individuals because of the physiological changes associated with aging, such as weight loss and muscle mass atrophy (Baumgartner et al., 1995; Lupoli et al., 2004). BIVA has been amply used in clinical practice (Barbosa-Silva et al., 2005; Norman et al., 2012) and validated for the purpose of assessing nutritional (Norman et al., 2012) and hydration status (Bronhara et al., 2012; Norman et al., 2012). The classic BIVA approach has proven weak, however, in terms of its ability to recognize differences in body composition compared to dual-energy X-ray absorptiometry (DXA) (Buffa et al., 2013; Marini et al., 2013). On the other hand, using the recently-proposed specific BIVA approach has resulted in an
B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
accurate assessment of variations in the proportion of fat mass (FM%) in samples of healthy elderly Italians (Marini et al., 2013) and U.S. American adults (Buffa et al., 2013). Specific BIVA differs from the classic approach in that the bioelectrical values are standardized on the basis of an estimated body volume (height and cross-sectional area) rather than just body height. This means that specific values (resistivity, reactivity and impedivity) are influenced not by body size and shape, but only by the tissues' properties. Specific BIVA has proven to be capable of distinguishing sarcopenic individuals from sarcopenic-obese individuals (Marini et al., 2012). Normal reference values for the elderly have yet to be published, however. The aim of this study was to establish standard specific BIVA values for Italian elderly people, suitable for use in screening programs and in gerontological practice to identify conditions of undernutrition, sarcopenia and sarcopenic obesity. We also aimed to study age-related changes in the specific vector (i.e. body composition) in a large sample of elderly individuals. 2. Subjects and methods 2.1. Subjects The study group consisted of 560 individuals (295 women and 265 men) aged 65 years or more (mean age 76.0 ± 7.1 in women and 77.0 ± 7.2 in men), all born in Italy and recruited on a voluntary basis in the Veneto region and Sardinia. The survey was performed by trained health technicians from the Geriatrics Department of Padova University and from the University of Cagliari. The following exclusion criteria were considered: pulmonary disease, severe cardiovascular or uncontrolled metabolic diseases (diabetes, anemia, or thyroid disease), electrolyte abnormalities, cancer, inflammatory conditions, and the
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use of any implanted electrical devices. In accordance with the Helsinki Declaration, as revised in 2008, all individuals who agreed to take part in the study were informed about the goals and methods of the research. 2.2. Measurements Anthropometric measurements (weight, height, and upper arm, waist and calf circumferences) were taken in agreement with international criteria (Lohman et al., 1988), and each individual's body mass index (BMI = weight/height2, kg/m2) was calculated. Impedance measurements (resistance, R; reactance, Xc) were obtained using a singlefrequency analyzer (BIA 101, Akern, Italy) with an operating frequency of 50 kHz at 800 μA. The whole procedure complied with international criteria (NIH, 1996), and participants avoided eating or drinking (for 4 h), intensive exercise or alcohol intake (for 12 h) before the test. The “specific BIVA standards 2013” database is available at the Cagliari University institutional repository (http://veprints.unica.it/904/). In a subgroup of 207 individuals, DXA fan-beam technology (QDR 4500 W; Hologic Inc., Bedford, MA) was used to estimate the fat-free mass index (FFMI) (i.e. the sum of lean soft tissue mass and bone mineral content, corrected for height squared [kg/m2]), and the fat mass index (FMI) (i.e. the fat mass corrected for height squared [kg/m2]). Individuals of different body mass and composition were classified using the BMI cutoffs proposed for the elderly by Sergi et al. (2005), and the quartiles
Table 1 Descriptive statistics of anthropometric and bioelectrical values, and correlation between bioelectrical impedance variables. Men
Women
Mean
s.d.j
Mean
s.d.j
77.0
7.2
76.0
7.1
Anthropometric variables Height (cm) Weight (kg) BMIb (kg/m2) Calf crf.c (cm) Arm crf.c (cm) Waist crf.c (cm)
162 69.5 26.4 34.6 28.0 95.7
8.5 11.1 3.3 3.4 3.3 9.2
150.2 60.1 26.6 33.8 28.2 92.2
8.0 11.0 4.1 3.7 3.8 10.9
Bioelectrical variables Rd (Ω) Xce (Ω) Rd/Hf (Ω/m) Xce/Hf (Ω/m) Phase (degrees) Zg/Hf (Ω/m) Rdsph (Ω · cm) Xcesph (Ω · cm) Zgsph (Ω · cm) ri Rd/Hf − Xce/Hf ri Rdsph − Xcesph
485.3 52.3 300.6 32.4 6.2 302.4 391.8 42.6 394.2 0.43⁎⁎ 0.59⁎⁎
64.3 9.5 44.9 6.2 1.2 44.9 57.9 9.9 58.2
554.8 57.1 370.4 38.1 5.9 372.4 462.0 47.9 464.6 0.44⁎⁎ 0.75⁎⁎
64.9 9.4 47.7 6.3 1.0 47.8 80.1 11.2 80.5
a
Age (y)
a
Year. Body mass index. c Circumference. d Resistance. e Reactance. f Height. g Impedance. h Specific. i Correlation. j Standard deviation. ⁎⁎ p b 0.01. b
Fig. 1. a. Specific tolerance ellipses for the elderly male population. b. Specific tolerance ellipses for the elderly female population.
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B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
Table 2 Descriptive statistics and two-factor ANOVA for comparisons by age and sex.g 65–70 ya Men
Women
(n = 59) Weight (kg) Height (cm) BMIb (kg/m2) Rcspd (Ω · cm) Xcespd (Ω · cm) Zfspd (Ω · cm) Phase (degrees)
77.1 167.8 27.3 389.4 46.0 392.2 6.7
71–80 ya
± ± ± ± ± ± ±
11.3 6.9 3.3 46.8 10.8 47.4 1.2
Men
(n = 73) 65.5 155.1 27.2 483.9 51.1 486.6 6.0
± ± ± ± ± ± ±
10.2 6.7 3.9 69.7 10.3 70.2 0.8
Women
(n = 134) 69.9 162.3 26.5 396.3 43.3 398.7 6.3
81–90 ya
± ± ± ± ± ± ±
9.7 8.1 3.2 58.0 9.6 58.3 1.1
Men
(n = 161) 60.4 150.6 26.6 458.2 48.3 460.8 6.1
± ± ± ± ± ± ±
N91 ya
9.6 6.3 3.7 82.8 10.8 83.1 1.0
Women
(n = 59) 62.9 157.3 25.4 381.4 39.1 383.5 5.9
± ± ± ± ± ± ±
8.4 6.9 3.1 70.1 8.6 70.2 1.0
Men
(n = 48) 54.6 143.5 26.5 451.9 43.9 454.0 5.5
± ± ± ± ± ± ±
11.1 6.9 5.1 84.9 12.1 85.5 0.8
(n = 13) 60.2 155.0 25.0 403.5 34.9 405.1 4.9
Fsex
Fage
Fsex × age
84.52⁎⁎ 236.4⁎⁎ 0.53 53.03⁎⁎ 13.80⁎⁎ 52.70⁎⁎ 4.20⁎
45.18⁎⁎ 61.42⁎⁎ 7.18⁎⁎
1.17 0.78 1.62 2.73⁎
Women
± ± ± ± ± ± ±
9.2 7.2 3.4 35.1 5.9 35.4 0.6
(n = 13) 45.3 141.0 22.7 424.1 38.4 425.9 5.2
± ± ± ± ± ± ±
7.7 4.0 3.5 58.9 7.3 59.0 0.9
1.91 15.70⁎⁎ 2.03 17.94⁎⁎
0.05 2.67⁎ 2.65⁎
a
Year. Body mass index. Resistance. d Specific. e Reactance. f Impedance. g Mean ± standard deviation. ⁎ p b 0.05. ⁎⁎ p b 0.01. b c
of the FFMI and FMI distribution in the Italian population (Coin et al., 2008). The following four groups were considered: 1. low weight (BMI ≤ 24 kg/m 2 ), low muscle mass (FFMI b 18.7 kg/m 2 ), and low fat mass (FMI b 4.2 kg/m2); 2. low weight (BMI ≤ 24 kg/m2), low muscle mass (FFMI b 18.7 kg/m 2 ), and normal fat mass (FMI N 4.2 kg/m 2 ); 3. normal weight (24 b BMI ≤ 28 kg/m2), low muscle mass (FFMI b 18.7 kg/m2), and high fat mass (FMI N 7 kg/m2); 4. high weight (BMI N 28 kg/m 2 ), normal or low muscle mass (FFMI b 21 kg/m2), and high fat mass (FMI N 7 kg/m2). This analysis was only performed in men because women showed too little body composition variability. Two other groups (of sarcopenic and sarcopenic-obese individuals), already analyzed by Marini et al. (2012), were considered for comparison. Sarcopenia (group 5) and sarcopenic obesity (group 6) were classified according to Baumgartner et al. (1998), and based on the median FM% values for the male elderly sample analyzed by Marini et al. (2012). Descriptive statistics were calculated for the whole sample, grouped by gender and age bracket (65 to 70 y, 71 to 80 y, 81 to 90 y, and N91 y). The mean impedance vectors for the various groups were compared using two-factor analysis of variance with fixed effects, and by means of confidence ellipses and Hotelling's T2 test. Analyses were performed using BIVA software and the R program with the MASS library.
significant for both sexes (p b 0.001), and due mainly to a lower specific reactance and narrower phase angle. Fig. 1a (men) and b (women) shows the newly-proposed specific tolerance ellipses for our healthy elderly Italian sample, by gender. 3.1. Age, gender and body composition comparisons Table 2 shows the descriptive and two-factor analysis of variance statistics for the anthropometric measures (height, weight, BMI) and specific bioelectrical variables, by age group and gender. Fig. 2 shows the 95% confidence ellipses for each age group and gender. The mean impedance vectors differed significantly in all comparisons (T2 b 0.05), the only exception regarding women N91 y vis-à-vis women aged 81–90 y and men N 91 y. All bioelectrical variables showed gender-related differences, with higher Rsp, Xcsp and Zsp values in women, while phase angle was higher in men. The specific reactance and phase angle values dropped significantly with age. The specific resistance, Zsp and phase angle showed a significant interaction between gender and age, with different age-related trends in the two sexes, i.e. a more accentuated reduction in the phase angle in men and a tendency for Rsp and Zsp to drop only in women. These changes give rise to a
3. Results Table 1 shows the descriptive statistics for the anthropometric and bioelectrical variables in the sample, divided by gender. Age differences between the two genders were not significant (p N 0.05). The mean BMI values showed that both women and men were slightly overweight, based on the BMI N25 kg/m2 cutoff (World Health Organization, 1997). Waist circumference showed a mean tendency towards abdominal obesity in women (based on the 88 cm cutoff (World Health Organization, 1997), but not in men (102 cm cutoff (World Health Organization, 1997). The distribution of the bioelectrical values (R/H and Xc/H) was centered on the classic tolerance ellipses for the Italian population (Piccoli et al., 1995): 96.6% of cases fell within the 95% area (95.9% and 97.3%, respectively, when men and women were considered separately). On the other hand, the distribution of the specific bioelectrical values (Rsp and Xcsp) did not fit the specific tolerance ellipses for the adult U.S. population (Buffa et al., 2013): 27.6% of cases fell outside the 95% area, with a more accentuated divergence in men (34.0%) than in women (8.8%). The difference between the Italian elderly and U.S. adults was
Fig. 2. Confidence ellipses for the various groups divided by age and sex.
435.9 39.7 437.7 5.3 40.0 7.3 49.2 1.0 348.7 28.9 349.9 4.7
Mean Mean
Group 5 SMIh b 7.2 kg/m2 FM%i ≤ 23.8 (n = 10)
s.d.j
Group 6 SMIh b 7.2 kg/m2 FM%i N 23.8 (n = 8)
s.dj
subverted sexual dimorphism in “older-old” individuals, with sexrelated differences declining as people get older (65–70 y: T2 = 108.3, p b 0.001, D = 1.82; 71–80 y: T2 = 54.1, p b 0.001, D = 0.86; 81–90: T2 = 24.7, p b 0.001, D = 0.97; N91: T2 = 2.0, p b 0.406, D = 0.55). Fig. 3 shows the specific tolerance ellipses with the mean impedance vectors for the groups of men with different body compositions, as assessed by DXA. Table 3 shows the bioelectrical characteristics of the six groups. Men with a “low body weight, low FFM, and low FM” (group 1) showed the best-defined pattern, with specific bioelectrical characteristics very similar to those of sarcopenic individuals (group 5) towards the inferior pole of the ellipses, and differing from those of all the other groups (p b 0.001). Similarly, men with a “normal body weight, low FFM, and high FM” (group 3) were located near the sarcopenic-obese group (group 6), to the right of the ellipses. The men with a “high body weight, normal or low FFM, and high FM” (group 4) and those with a “low body weight, low FFM, and normal FM” (group 2) were centered and less differentiated from the others.
55 65.2 6.9 65.2 0.9
B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
49.4 9.1 49.9 0.8 419.6 44.0 422.0 6.0 54.7 6.9 54.5 1.1 454.4 40.8 456.3 5.2 26.3 6.2 26.5 0.8 383.3 38.2 385.2 5.7 41.0 7.2 41.2 1.0
j
i
h
g
f
e
d
c
Resistance. Specific. Reactance. Impedance. Body mass index. Fat-free mass index. Fat mass index. Skeletal muscle mass index. Fat mass percentage. Standard deviation. b
a
Mean s.d.j Mean s.d.j Mean s.d.j Mean
Group 4 BMIe N 28 kg/m2 FFMIf b 21 kg/m2 FMIg N 7 kg/m2 (n = 8) Group 3 24 b BMIe ≤ 28 kg/m2 FFMIf b 18.7 kg/m2 FMIg N 7 kg/m2 (n = 8) Group 2 BMIe ≤ 24 kg/m2 FFMIf b 18.7 kg/m2 FMIg N 4.2 kg/m2 (n = 7) Group 1 BMIe ≤ 24 kg/m2 FFMIf b 18.7 kg/m2 FMIg b 4.2 kg/m2 (n = 10)
323.0 28.0 324.2 4.9 Raspb (Ω · cm) Xccspb (Ω · cm) Zdspb (Ω · cm) Phase angle (degrees)
Fig. 3. Specific tolerance ellipses with the mean impedance vector of men characterized by different body mass and composition. Group 1: BMI ≤ 24 kg/m2, FFMI b 18.7 kg/m2, FMI b 4.2 kg/m2; group 2: BMI ≤ 24 kg/m2, FFMI b 18.7 kg/m2, FMI > 4.2 kg/m2; group 3: 24 b BMI ≤ 28 kg/m2, FFMI b 18.7 kg/m2, FMI N 7 kg/m2; group 4: BMI N 28 kg/m2, FFMI b 21 kg/m 2 , FMI N 7 kg/m 2 ; group 5: SMI b 7.2 kg/m 2 , FM% ≤ 23.8, 6: SMI b7.2 kg/m 2 , FM% N 23.8. Abbreviations: BMI: body mass index; FFMI: fat-free mass index; FMI: fat mass index; SMI: skeletal muscle mass index; FM%: fat mass percentage.
Table 3 Descriptive statistics of specific bioelectrical values in six groups of men with a different body mass and composition.
The bioelectrical data collected in this study for healthy elderly individuals are consistent with the classic vectorial reference values for the Italian 15–85 year-old population (Piccoli et al., 1995), confirming that such reference standards are also applicable to the elderly. Specific BIVA is a recently-proposed technique for assessing body composition (Buffa et al., 2013; Marini et al., 2013), and standard values are only available for U.S. adults from 21 to 49 years old (Buffa et al., 2013). Our elderly Italian sample was clearly not consistent with such American standards (especially as far as men were concerned), probably due partly to instrumental differences affecting the BIA measurements, and partly to population- and age-related bioelectrical variability. The present, newly-proposed specific tolerance ellipses are therefore the first to become available for elderly people, but whether or not they are applicable to populations outside Italy remains to be seen. On the matter of intra-sample variability, the bioelectrical and body composition variations observed in this research were consistent with the results of previous studies on samples of U.S. adults (Buffa et al., 2013), healthy elderly Italians (Marini et al., 2013), or sarcopenic and sarcopenic-obese individuals (Marini et al., 2012). Participants with a
s.d.j
4. Discussion
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B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
low FFM (groups 1, 3, 5, 6) were characterized by low specific reactance and phase angle values. Those with a low FM (groups 5, 6) featured a low specific resistance and impedivity, which gradually increased for people with a normal FM (group 2), or high FM (groups 3, 4). These last groups were distinguishable from specific reactance and phase angle values, which were higher for individuals with a normal FFM (group 4) than for those with a low FFM (group 3). People who were sarcopenic (groups 2, 5) or sarcopenic-obese (groups 3, 6) shared a low reactance and phase angle, but could be distinguished by the higher impedivity characterizing sarcopenic obesity. There was also evidence of sex- and age-related differences in specific bioelectrical values that can be interpreted in terms of changes in body composition. Based on specific BIVA, and consistently with the well-known expression of sexual dimorphism in body composition, the higher Rsp, Xcsp and Zsp values seen in the women in our sample are indicative of a greater relative quantity of fat mass (FM%) than in men. Similar gender-related bioelectrical differences were observed in the adult U.S. sample (Buffa et al., 2013). The higher phase angle seen in men, and already reported in the literature (Barbosa-Silva et al., 2005; BosyWestphal et al., 2006), is indicative of a greater body cell mass (Piccoli et al., 1994), and particularly of a greater skeletal muscle mass (Buffa et al., 2013). Age-related specific bioelectrical variations are due mainly to a reduction in Xcsp and phase angle, and they indicate a gradual increase in the ECW/ICW ratio, and a decrease in skeletal muscle mass (Buffa et al., 2013). Other research on bioelectrical variations in normal aging has shown a decline in phase angle (Barbosa-Silva et al., 2005; BosyWestphal et al., 2006; Buffa et al., 2003, 2010). These changes are consistent with what we know about body composition variations in the elderly, i.e. their gradual tendency towards sarcopenia (Morley et al., 2001), and loss of intracellular body water (Steen, 1997). This pattern is also confirmed by the significant decrease in weight and BMI with age observed in the present sample. An age-related vector migration is detectable in both sexes, but it follows a rather different trajectory in men and women. The more accentuated reduction in specific reactance and phase angle in men can be interpreted in the light of men's more severe loss of muscle mass (Buffa et al., 2011). The tendency for Rsp and Zsp to drop in women is attributable to their declining FM%. A declining sexual dimorphism is also apparent, due mainly to smaller differences in Rsp, and consequently in FM%. 5. Conclusions This study showed an age-related migration of the specific vector indicative of a loss of fat-free mass (especially in men) and a tendency towards a loss of fat mass in women. The specific reference values for healthy elderly people presented here could be used to assess the risk of malnutrition and sarcopenia in gerontological practice and for epidemiological purposes. More studies are needed to ascertain whether these Italian standards are applicable to other populations. Conflict of interest The authors have no conflict of interest to declare. Acknowledgements The Authors acknowledge the support of the volunteers who took part in the study. The Authors also thank Sandro Piludu and Valeria Succa (Department of Environmental and Life Sciences, University of
Cagliari) for technical assistance, and A. Piccoli and G. Pastori (Department of Medical and Surgical Sciences, University of Padova, Italy) for providing the BIVA software. This research received financial support from the “Regione Autonoma della Sardegna” through a research grant for funding the Project “POR Sardegna FSE 2007–2013, L.R.7/2007 Promozione della ricerca scientifica e dell'innovazione tecnologica in Sardegna”. References Barbosa-Silva, M.C., Barros, A.J., Wang, J., Heymsfield, S.B., Pierson, N.J., 2005. Bioelectrical impedance analysis: population reference values for phase angle by age and sex. Am. J. Clin. Nutr. 82 (1), 49–52. Baumgartner, R.N., 2000. Body composition in healthy aging. Ann. N. Y. Acad. Sci. 904, 437–448. Baumgartner, R.N., Heymsfield, S.B., Roche, A.F., 1995. Human body composition and the epidemiology of chronic disease. Obes. Res. 3 (1), 73–95. Baumgartner, R., Koehler, K., Gallagher, D., Romero, L., Heymsfield, S., Ross, R., et al., Apr 1998. 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Efficacy of specific bioelectrical impedance vector analysis (BIVA) for assessing body composition in the elderly. J Nutr Health Aging 17 (6), 515–521. Morley, J.E., Baumgartner, R.N., Roubenoff, R., Mayer, J., Nair, K.S., 2001. Sarcopenia. J. Lab. Clin. Med. 137, 231–243. NIH, 1996. Bioelectrical impedance analysis in body composition measurement: National Institutes of Health Technology Assessment Conference Statement. Am. J. Clin. Nutr. (64), 524S–532S. Norman, K., Stobäus, N., Pirlich, M., Bosy-Westphal, A., 2012. Bioelectrical phase angle and impedance vector analysis—clinical relevance and applicability of impedance parameters. Clin. Nutr. 31 (6), 854–861. Piccoli, A., Rossi, B., Pillon, L., Bucciante, G., 1994. A new method for monitoring body fluid variation by bioimpedance analysis: the RXc graph. Kidney Int. 46, 534–539. Piccoli, A., Nigrelli, S., Caberlotto, A., Bottazzo, S., Rossi, B., Pillon, L., et al., 1995. Bivariate normal values of the bioelectrical impedance vector in adult and elderly populations. Am. J. Clin. Nutr. 61 (2), 269. Sergi, G., Perissinotto, E., Pisent, C., Buja, A., Maggi, S., Coin, A., et al., 2005. An adequate threshold for body mass index to detect underweight condition in elderly persons: the Italian Longitudinal Study on Aging (ILSA). J. Gerontol. A Biol. Sci. Med. Sci. 60, 866–871. Steen, B., 1997. Body water in the elderly—a review. J Nutr Health Aging 1 (3), 142–145. World Health Organization, 1997. Obesity: preventing and managing the global epidemic. Report of a WHO Consultation of Obesity.
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Experimental Gerontology journal homepage: www.elsevier.com/locate/expgero
Short report
Specific bioelectrical impedance vector reference values for assessing body composition in the Italian elderly Bruno Saragat a, Roberto Buffa a, Elena Mereu a, Marina De Rui b, Alessandra Coin b, Giuseppe Sergi b, Elisabetta Marini a,⁎ a b
Department of Environmental and Life Sciences, University of Cagliari, Cittadella Universitaria, 09042 Monserrato, Italy Department of Medicine-DIMED, Geriatrics Division, University of Padova, via Giustiniani 2, 35128 Padova, Italy
a r t i c l e
i n f o
Article history: Received 28 July 2013 Received in revised form 15 October 2013 Accepted 26 November 2013 Available online 3 December 2013 Section Editor: Andrzej Bartke Keywords: Bioelectrical values Tolerance ellipses Classic BIVA Specific BIVA Aging Body composition
a b s t r a c t Objective: To obtain specific bioelectrical impedance vector reference values for the healthy elderly Italian population, and to study age- and sex-related differences in body composition. Design: The study group consisted of 560 healthy individuals (265 men and 295 women) aged 65 to 100 y, whose anthropometric (height, weight, and calf, arm and waist circumferences) and bioelectrical measurements (resistance [R] and reactance [Xc], at 50 kHz and 800 μA) were recorded. R (Ω) and Xc (Ω) values were standardized for stature (H, m) to obtain the classic bioelectrical values. Specific values (resistivity [Rsp] and reactivity [Xcsp], Ω · cm) were obtained by multiplying R and Xc by a correction factor (A/L) that includes an estimate of the cross-sectional area of the body (A = 0.45 arm area + 0.10 waist area + 0.45 calf area), where L = 1.1 H. Results: Descriptive statistics were: Rsp (391.8 ± 57.9), Xcsp (42.6 ± 9.9), Zsp (394.2 ± 58.2), phase angle (6.2° ± 1.2) in men; Rsp (462.0 ± 80.1), Xcsp (47.9 ± 11.2), Zsp (464.6 ± 80.5), phase angle (5.9° ± 1.0) in women. The Xcsp and phase angle values showed a significant age-related decrease in both sexes, but especially in men, possibly relating to a gradual loss of muscle mass. Women's Rsp and Zsp values tended to drop, attributable to their declining proportion of fat mass. A declining sexual dimorphism was also apparent. Conclusions: Specific tolerance ellipses can be used for reference purposes for the Italian population when assessing body composition in gerontological practice and for epidemiological purposes. © 2013 Elsevier Inc. All rights reserved.
1. Introduction Normal aging is characterized by changes in body mass and composition (Buffa et al., 2011) that can impair an individual's health status and functionality, with the possible onset of geriatric syndromes, such as frailty (Fried et al., 2001), sarcopenia (Morley et al., 2001), and sarcopenic obesity (Baumgartner, 2000). Age-related body mass variations involve an initial tendency for it to increase, followed by a decline (Buffa et al., 2011). This latter reduction is mainly due to a loss of muscle mass (especially in men), total body water (particularly from the intracellular compartment), and skeletal mass (especially in women). The loss of fat mass (FM) is less marked and occurs at a later age. The combined changes in FM and fat-free mass (FFM) give rise to an initial increase in the percentage of body fat, which subsequently levels off (Ding et al., 2007).
Abbreviations: R, resistance; Xc, reactance; Z, impedance; Rsp, resistivity; Xcsp, reactivity; Zsp, impedivity; FM, fat mass; FFM, fat-free mass; BIA, bioelectrical impedance analysis; BIVA, bioelectrical impedance vector analysis; DXA, dual-energy X-ray absorptiometry; ECW/ICW, extracellular/intracellular water ratio; FFMI, fat-free mass index; FMI, fat mass index; SMI, skeletal muscle mass index; FM%, fat mass percentage. ⁎ Corresponding author. Tel.: +39 0706756607; fax: +39 0706756616. E-mail address: [email protected] (E. Marini). 0531-5565/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.exger.2013.11.016
Body composition screening and monitoring in the elderly is to be recommended to prevent the risk of malnutrition and related disorders (Cruz-Jentoft et al., 2010). Bioelectrical impedance vector analysis (BIVA) is a portable, noninvasive and low-cost method for assessing body cell mass and body hydration (Piccoli et al., 1994). The BIVA approach differs from traditional bioelectrical impedance analysis (BIA) in that it analyzes bioelectrical values directly, without referring to predictive equations. Resistance (R, Ω) and reactance (Xc, Ω), at 50 kHz and 800 μA, are normalized for an individual's height and plotted in a tolerance ellipse graph that enables the person's body characteristics to be assessed. BIVA thus avoids the potential error deriving from adopting BIA equations, which can lead to unreliable results in elderly individuals because of the physiological changes associated with aging, such as weight loss and muscle mass atrophy (Baumgartner et al., 1995; Lupoli et al., 2004). BIVA has been amply used in clinical practice (Barbosa-Silva et al., 2005; Norman et al., 2012) and validated for the purpose of assessing nutritional (Norman et al., 2012) and hydration status (Bronhara et al., 2012; Norman et al., 2012). The classic BIVA approach has proven weak, however, in terms of its ability to recognize differences in body composition compared to dual-energy X-ray absorptiometry (DXA) (Buffa et al., 2013; Marini et al., 2013). On the other hand, using the recently-proposed specific BIVA approach has resulted in an
B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
accurate assessment of variations in the proportion of fat mass (FM%) in samples of healthy elderly Italians (Marini et al., 2013) and U.S. American adults (Buffa et al., 2013). Specific BIVA differs from the classic approach in that the bioelectrical values are standardized on the basis of an estimated body volume (height and cross-sectional area) rather than just body height. This means that specific values (resistivity, reactivity and impedivity) are influenced not by body size and shape, but only by the tissues' properties. Specific BIVA has proven to be capable of distinguishing sarcopenic individuals from sarcopenic-obese individuals (Marini et al., 2012). Normal reference values for the elderly have yet to be published, however. The aim of this study was to establish standard specific BIVA values for Italian elderly people, suitable for use in screening programs and in gerontological practice to identify conditions of undernutrition, sarcopenia and sarcopenic obesity. We also aimed to study age-related changes in the specific vector (i.e. body composition) in a large sample of elderly individuals. 2. Subjects and methods 2.1. Subjects The study group consisted of 560 individuals (295 women and 265 men) aged 65 years or more (mean age 76.0 ± 7.1 in women and 77.0 ± 7.2 in men), all born in Italy and recruited on a voluntary basis in the Veneto region and Sardinia. The survey was performed by trained health technicians from the Geriatrics Department of Padova University and from the University of Cagliari. The following exclusion criteria were considered: pulmonary disease, severe cardiovascular or uncontrolled metabolic diseases (diabetes, anemia, or thyroid disease), electrolyte abnormalities, cancer, inflammatory conditions, and the
53
use of any implanted electrical devices. In accordance with the Helsinki Declaration, as revised in 2008, all individuals who agreed to take part in the study were informed about the goals and methods of the research. 2.2. Measurements Anthropometric measurements (weight, height, and upper arm, waist and calf circumferences) were taken in agreement with international criteria (Lohman et al., 1988), and each individual's body mass index (BMI = weight/height2, kg/m2) was calculated. Impedance measurements (resistance, R; reactance, Xc) were obtained using a singlefrequency analyzer (BIA 101, Akern, Italy) with an operating frequency of 50 kHz at 800 μA. The whole procedure complied with international criteria (NIH, 1996), and participants avoided eating or drinking (for 4 h), intensive exercise or alcohol intake (for 12 h) before the test. The “specific BIVA standards 2013” database is available at the Cagliari University institutional repository (http://veprints.unica.it/904/). In a subgroup of 207 individuals, DXA fan-beam technology (QDR 4500 W; Hologic Inc., Bedford, MA) was used to estimate the fat-free mass index (FFMI) (i.e. the sum of lean soft tissue mass and bone mineral content, corrected for height squared [kg/m2]), and the fat mass index (FMI) (i.e. the fat mass corrected for height squared [kg/m2]). Individuals of different body mass and composition were classified using the BMI cutoffs proposed for the elderly by Sergi et al. (2005), and the quartiles
Table 1 Descriptive statistics of anthropometric and bioelectrical values, and correlation between bioelectrical impedance variables. Men
Women
Mean
s.d.j
Mean
s.d.j
77.0
7.2
76.0
7.1
Anthropometric variables Height (cm) Weight (kg) BMIb (kg/m2) Calf crf.c (cm) Arm crf.c (cm) Waist crf.c (cm)
162 69.5 26.4 34.6 28.0 95.7
8.5 11.1 3.3 3.4 3.3 9.2
150.2 60.1 26.6 33.8 28.2 92.2
8.0 11.0 4.1 3.7 3.8 10.9
Bioelectrical variables Rd (Ω) Xce (Ω) Rd/Hf (Ω/m) Xce/Hf (Ω/m) Phase (degrees) Zg/Hf (Ω/m) Rdsph (Ω · cm) Xcesph (Ω · cm) Zgsph (Ω · cm) ri Rd/Hf − Xce/Hf ri Rdsph − Xcesph
485.3 52.3 300.6 32.4 6.2 302.4 391.8 42.6 394.2 0.43⁎⁎ 0.59⁎⁎
64.3 9.5 44.9 6.2 1.2 44.9 57.9 9.9 58.2
554.8 57.1 370.4 38.1 5.9 372.4 462.0 47.9 464.6 0.44⁎⁎ 0.75⁎⁎
64.9 9.4 47.7 6.3 1.0 47.8 80.1 11.2 80.5
a
Age (y)
a
Year. Body mass index. c Circumference. d Resistance. e Reactance. f Height. g Impedance. h Specific. i Correlation. j Standard deviation. ⁎⁎ p b 0.01. b
Fig. 1. a. Specific tolerance ellipses for the elderly male population. b. Specific tolerance ellipses for the elderly female population.
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B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
Table 2 Descriptive statistics and two-factor ANOVA for comparisons by age and sex.g 65–70 ya Men
Women
(n = 59) Weight (kg) Height (cm) BMIb (kg/m2) Rcspd (Ω · cm) Xcespd (Ω · cm) Zfspd (Ω · cm) Phase (degrees)
77.1 167.8 27.3 389.4 46.0 392.2 6.7
71–80 ya
± ± ± ± ± ± ±
11.3 6.9 3.3 46.8 10.8 47.4 1.2
Men
(n = 73) 65.5 155.1 27.2 483.9 51.1 486.6 6.0
± ± ± ± ± ± ±
10.2 6.7 3.9 69.7 10.3 70.2 0.8
Women
(n = 134) 69.9 162.3 26.5 396.3 43.3 398.7 6.3
81–90 ya
± ± ± ± ± ± ±
9.7 8.1 3.2 58.0 9.6 58.3 1.1
Men
(n = 161) 60.4 150.6 26.6 458.2 48.3 460.8 6.1
± ± ± ± ± ± ±
N91 ya
9.6 6.3 3.7 82.8 10.8 83.1 1.0
Women
(n = 59) 62.9 157.3 25.4 381.4 39.1 383.5 5.9
± ± ± ± ± ± ±
8.4 6.9 3.1 70.1 8.6 70.2 1.0
Men
(n = 48) 54.6 143.5 26.5 451.9 43.9 454.0 5.5
± ± ± ± ± ± ±
11.1 6.9 5.1 84.9 12.1 85.5 0.8
(n = 13) 60.2 155.0 25.0 403.5 34.9 405.1 4.9
Fsex
Fage
Fsex × age
84.52⁎⁎ 236.4⁎⁎ 0.53 53.03⁎⁎ 13.80⁎⁎ 52.70⁎⁎ 4.20⁎
45.18⁎⁎ 61.42⁎⁎ 7.18⁎⁎
1.17 0.78 1.62 2.73⁎
Women
± ± ± ± ± ± ±
9.2 7.2 3.4 35.1 5.9 35.4 0.6
(n = 13) 45.3 141.0 22.7 424.1 38.4 425.9 5.2
± ± ± ± ± ± ±
7.7 4.0 3.5 58.9 7.3 59.0 0.9
1.91 15.70⁎⁎ 2.03 17.94⁎⁎
0.05 2.67⁎ 2.65⁎
a
Year. Body mass index. Resistance. d Specific. e Reactance. f Impedance. g Mean ± standard deviation. ⁎ p b 0.05. ⁎⁎ p b 0.01. b c
of the FFMI and FMI distribution in the Italian population (Coin et al., 2008). The following four groups were considered: 1. low weight (BMI ≤ 24 kg/m 2 ), low muscle mass (FFMI b 18.7 kg/m 2 ), and low fat mass (FMI b 4.2 kg/m2); 2. low weight (BMI ≤ 24 kg/m2), low muscle mass (FFMI b 18.7 kg/m 2 ), and normal fat mass (FMI N 4.2 kg/m 2 ); 3. normal weight (24 b BMI ≤ 28 kg/m2), low muscle mass (FFMI b 18.7 kg/m2), and high fat mass (FMI N 7 kg/m2); 4. high weight (BMI N 28 kg/m 2 ), normal or low muscle mass (FFMI b 21 kg/m2), and high fat mass (FMI N 7 kg/m2). This analysis was only performed in men because women showed too little body composition variability. Two other groups (of sarcopenic and sarcopenic-obese individuals), already analyzed by Marini et al. (2012), were considered for comparison. Sarcopenia (group 5) and sarcopenic obesity (group 6) were classified according to Baumgartner et al. (1998), and based on the median FM% values for the male elderly sample analyzed by Marini et al. (2012). Descriptive statistics were calculated for the whole sample, grouped by gender and age bracket (65 to 70 y, 71 to 80 y, 81 to 90 y, and N91 y). The mean impedance vectors for the various groups were compared using two-factor analysis of variance with fixed effects, and by means of confidence ellipses and Hotelling's T2 test. Analyses were performed using BIVA software and the R program with the MASS library.
significant for both sexes (p b 0.001), and due mainly to a lower specific reactance and narrower phase angle. Fig. 1a (men) and b (women) shows the newly-proposed specific tolerance ellipses for our healthy elderly Italian sample, by gender. 3.1. Age, gender and body composition comparisons Table 2 shows the descriptive and two-factor analysis of variance statistics for the anthropometric measures (height, weight, BMI) and specific bioelectrical variables, by age group and gender. Fig. 2 shows the 95% confidence ellipses for each age group and gender. The mean impedance vectors differed significantly in all comparisons (T2 b 0.05), the only exception regarding women N91 y vis-à-vis women aged 81–90 y and men N 91 y. All bioelectrical variables showed gender-related differences, with higher Rsp, Xcsp and Zsp values in women, while phase angle was higher in men. The specific reactance and phase angle values dropped significantly with age. The specific resistance, Zsp and phase angle showed a significant interaction between gender and age, with different age-related trends in the two sexes, i.e. a more accentuated reduction in the phase angle in men and a tendency for Rsp and Zsp to drop only in women. These changes give rise to a
3. Results Table 1 shows the descriptive statistics for the anthropometric and bioelectrical variables in the sample, divided by gender. Age differences between the two genders were not significant (p N 0.05). The mean BMI values showed that both women and men were slightly overweight, based on the BMI N25 kg/m2 cutoff (World Health Organization, 1997). Waist circumference showed a mean tendency towards abdominal obesity in women (based on the 88 cm cutoff (World Health Organization, 1997), but not in men (102 cm cutoff (World Health Organization, 1997). The distribution of the bioelectrical values (R/H and Xc/H) was centered on the classic tolerance ellipses for the Italian population (Piccoli et al., 1995): 96.6% of cases fell within the 95% area (95.9% and 97.3%, respectively, when men and women were considered separately). On the other hand, the distribution of the specific bioelectrical values (Rsp and Xcsp) did not fit the specific tolerance ellipses for the adult U.S. population (Buffa et al., 2013): 27.6% of cases fell outside the 95% area, with a more accentuated divergence in men (34.0%) than in women (8.8%). The difference between the Italian elderly and U.S. adults was
Fig. 2. Confidence ellipses for the various groups divided by age and sex.
435.9 39.7 437.7 5.3 40.0 7.3 49.2 1.0 348.7 28.9 349.9 4.7
Mean Mean
Group 5 SMIh b 7.2 kg/m2 FM%i ≤ 23.8 (n = 10)
s.d.j
Group 6 SMIh b 7.2 kg/m2 FM%i N 23.8 (n = 8)
s.dj
subverted sexual dimorphism in “older-old” individuals, with sexrelated differences declining as people get older (65–70 y: T2 = 108.3, p b 0.001, D = 1.82; 71–80 y: T2 = 54.1, p b 0.001, D = 0.86; 81–90: T2 = 24.7, p b 0.001, D = 0.97; N91: T2 = 2.0, p b 0.406, D = 0.55). Fig. 3 shows the specific tolerance ellipses with the mean impedance vectors for the groups of men with different body compositions, as assessed by DXA. Table 3 shows the bioelectrical characteristics of the six groups. Men with a “low body weight, low FFM, and low FM” (group 1) showed the best-defined pattern, with specific bioelectrical characteristics very similar to those of sarcopenic individuals (group 5) towards the inferior pole of the ellipses, and differing from those of all the other groups (p b 0.001). Similarly, men with a “normal body weight, low FFM, and high FM” (group 3) were located near the sarcopenic-obese group (group 6), to the right of the ellipses. The men with a “high body weight, normal or low FFM, and high FM” (group 4) and those with a “low body weight, low FFM, and normal FM” (group 2) were centered and less differentiated from the others.
55 65.2 6.9 65.2 0.9
B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
49.4 9.1 49.9 0.8 419.6 44.0 422.0 6.0 54.7 6.9 54.5 1.1 454.4 40.8 456.3 5.2 26.3 6.2 26.5 0.8 383.3 38.2 385.2 5.7 41.0 7.2 41.2 1.0
j
i
h
g
f
e
d
c
Resistance. Specific. Reactance. Impedance. Body mass index. Fat-free mass index. Fat mass index. Skeletal muscle mass index. Fat mass percentage. Standard deviation. b
a
Mean s.d.j Mean s.d.j Mean s.d.j Mean
Group 4 BMIe N 28 kg/m2 FFMIf b 21 kg/m2 FMIg N 7 kg/m2 (n = 8) Group 3 24 b BMIe ≤ 28 kg/m2 FFMIf b 18.7 kg/m2 FMIg N 7 kg/m2 (n = 8) Group 2 BMIe ≤ 24 kg/m2 FFMIf b 18.7 kg/m2 FMIg N 4.2 kg/m2 (n = 7) Group 1 BMIe ≤ 24 kg/m2 FFMIf b 18.7 kg/m2 FMIg b 4.2 kg/m2 (n = 10)
323.0 28.0 324.2 4.9 Raspb (Ω · cm) Xccspb (Ω · cm) Zdspb (Ω · cm) Phase angle (degrees)
Fig. 3. Specific tolerance ellipses with the mean impedance vector of men characterized by different body mass and composition. Group 1: BMI ≤ 24 kg/m2, FFMI b 18.7 kg/m2, FMI b 4.2 kg/m2; group 2: BMI ≤ 24 kg/m2, FFMI b 18.7 kg/m2, FMI > 4.2 kg/m2; group 3: 24 b BMI ≤ 28 kg/m2, FFMI b 18.7 kg/m2, FMI N 7 kg/m2; group 4: BMI N 28 kg/m2, FFMI b 21 kg/m 2 , FMI N 7 kg/m 2 ; group 5: SMI b 7.2 kg/m 2 , FM% ≤ 23.8, 6: SMI b7.2 kg/m 2 , FM% N 23.8. Abbreviations: BMI: body mass index; FFMI: fat-free mass index; FMI: fat mass index; SMI: skeletal muscle mass index; FM%: fat mass percentage.
Table 3 Descriptive statistics of specific bioelectrical values in six groups of men with a different body mass and composition.
The bioelectrical data collected in this study for healthy elderly individuals are consistent with the classic vectorial reference values for the Italian 15–85 year-old population (Piccoli et al., 1995), confirming that such reference standards are also applicable to the elderly. Specific BIVA is a recently-proposed technique for assessing body composition (Buffa et al., 2013; Marini et al., 2013), and standard values are only available for U.S. adults from 21 to 49 years old (Buffa et al., 2013). Our elderly Italian sample was clearly not consistent with such American standards (especially as far as men were concerned), probably due partly to instrumental differences affecting the BIA measurements, and partly to population- and age-related bioelectrical variability. The present, newly-proposed specific tolerance ellipses are therefore the first to become available for elderly people, but whether or not they are applicable to populations outside Italy remains to be seen. On the matter of intra-sample variability, the bioelectrical and body composition variations observed in this research were consistent with the results of previous studies on samples of U.S. adults (Buffa et al., 2013), healthy elderly Italians (Marini et al., 2013), or sarcopenic and sarcopenic-obese individuals (Marini et al., 2012). Participants with a
s.d.j
4. Discussion
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B. Saragat et al. / Experimental Gerontology 50 (2014) 52–56
low FFM (groups 1, 3, 5, 6) were characterized by low specific reactance and phase angle values. Those with a low FM (groups 5, 6) featured a low specific resistance and impedivity, which gradually increased for people with a normal FM (group 2), or high FM (groups 3, 4). These last groups were distinguishable from specific reactance and phase angle values, which were higher for individuals with a normal FFM (group 4) than for those with a low FFM (group 3). People who were sarcopenic (groups 2, 5) or sarcopenic-obese (groups 3, 6) shared a low reactance and phase angle, but could be distinguished by the higher impedivity characterizing sarcopenic obesity. There was also evidence of sex- and age-related differences in specific bioelectrical values that can be interpreted in terms of changes in body composition. Based on specific BIVA, and consistently with the well-known expression of sexual dimorphism in body composition, the higher Rsp, Xcsp and Zsp values seen in the women in our sample are indicative of a greater relative quantity of fat mass (FM%) than in men. Similar gender-related bioelectrical differences were observed in the adult U.S. sample (Buffa et al., 2013). The higher phase angle seen in men, and already reported in the literature (Barbosa-Silva et al., 2005; BosyWestphal et al., 2006), is indicative of a greater body cell mass (Piccoli et al., 1994), and particularly of a greater skeletal muscle mass (Buffa et al., 2013). Age-related specific bioelectrical variations are due mainly to a reduction in Xcsp and phase angle, and they indicate a gradual increase in the ECW/ICW ratio, and a decrease in skeletal muscle mass (Buffa et al., 2013). Other research on bioelectrical variations in normal aging has shown a decline in phase angle (Barbosa-Silva et al., 2005; BosyWestphal et al., 2006; Buffa et al., 2003, 2010). These changes are consistent with what we know about body composition variations in the elderly, i.e. their gradual tendency towards sarcopenia (Morley et al., 2001), and loss of intracellular body water (Steen, 1997). This pattern is also confirmed by the significant decrease in weight and BMI with age observed in the present sample. An age-related vector migration is detectable in both sexes, but it follows a rather different trajectory in men and women. The more accentuated reduction in specific reactance and phase angle in men can be interpreted in the light of men's more severe loss of muscle mass (Buffa et al., 2011). The tendency for Rsp and Zsp to drop in women is attributable to their declining FM%. A declining sexual dimorphism is also apparent, due mainly to smaller differences in Rsp, and consequently in FM%. 5. Conclusions This study showed an age-related migration of the specific vector indicative of a loss of fat-free mass (especially in men) and a tendency towards a loss of fat mass in women. The specific reference values for healthy elderly people presented here could be used to assess the risk of malnutrition and sarcopenia in gerontological practice and for epidemiological purposes. More studies are needed to ascertain whether these Italian standards are applicable to other populations. Conflict of interest The authors have no conflict of interest to declare. Acknowledgements The Authors acknowledge the support of the volunteers who took part in the study. The Authors also thank Sandro Piludu and Valeria Succa (Department of Environmental and Life Sciences, University of
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