Specific bioelectrical impedance vector reference values for assessing body composition in the Italian elderly

Abstract

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=1.1H.

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.

Keywords: Aging; BIA; BIVA; Bioelectrical values; Body composition; Classic BIVA; DXA; ECW/ICW; FFM; FFMI; FM; FM%; FMI; R; Rsp; SMI; Specific BIVA; Tolerance ellipses; Xc; Xcsp; Z; Zsp; bioelectrical impedance analysis; bioelectrical impedance vector analysis; dual-energy X-ray absorptiometry; extracellular/intracellular water ratio; fat mass; fat mass index; fat mass percentage; fat-free mass; fat-free mass index; impedance; impedivity; reactance; reactivity; resistance; resistivity; skeletal muscle mass index.