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Four-compartment model of body composition of normal elderly women

Age and Ageing, July, 1993 by H. Rico, M. Revilla, E.R. Hernandez, J.M. Gonzalez-Riola, L.F. Villa

Introduction

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Chumled and Baumgartner [1] have commented on the lack of information about changes in body composition in older individuals. They and Kueczmarski [2] suggested that these changes should be studied since some organs hypertrophy and others atrophy with age; for instance, soft-tissue mass, body water, and the mineral component decrease, while fat increases [3]. An understanding of these changes is of importance in the elderly population, since it enables a correct evaluation of nutritional state and the management of drugs, whose effectiveness and pharmacokinetics are affected by changes in body composition [4]. The four-compartment model [5], recognized as one of the best models for the study of body composition, defines fat (F), fat-free mass (FFM), total body bone mineral (TBBM) and water compartments. These compartments once were determined separately using different techniques [6-8], but now they all can be studied using the same technique since technological developments in dual-photon absorptiometry (DPA), originally used for bone density studies [9, 10], now permit evaluation of TBBM, FFM, and F. An additional improvement in this technique is dual-energy X-ray absorptiometry (DEXA) [11], which is considered more precise and delivers less radiation than DPA [12, 13]. Given that the water component is totally dependent on the fat-free compartment [14, 15], it can be calculated using the formula of Brozek et al. [16], recently corroborated by the excellent work of Heymsfield et al. [5].

To study the body composition of elderly subjects, we examined a group of 186 women using DEXA to determine the variations occurring in the four-compartment model with age.

Material and Methods

A sample of 186 women was recruited from outpatients of our general rheumatology clinic and their relatives. Their socioeconomic characteristics and urban sedentary life-style were representative of the normal active urban population of their age. The 186 women were considered to be normal after clinical and analytical studies, and the use of medications influencing water mineral and lipid metabolism was excluded. All were physically active but did not practice sports. Only 9% smoked, and none more than 10 cigarettes/day. Average calcium intake calculated using a 7-day diet survey was 500 to 950 mg/ day. None exhibited clinical lactose intolerance. The women were divided into three groups containing, respectively, 63, 62, and 61 women; the average ages in these three groups were 65.3 [+ or -] 4.4, 74.7 [+ or -] 5.5, and 80.9 [+ or -] 4.2 years, respectively. The women's personal characteristics and the values obtained for the four compartments are shown in the Table.

Body composition was determined during a non-intake period using a Norlan XR-26 densitometer (Norland Co., Fort Atkinson, Missouri, USA). Our coefficient of variation for this procedure in vivo is 1.2% for TBBM, 2.3% for F, and 1.3% for FFM, calculated as described in earlier papers [17]. The amount of water, in litres, in the FFM component was calculated using the Brozek et al. [16] formula. The standard errors of this technique are: 48 for TBBM, 0.89 for fat and 1.2 for fat-free mass. The usefulness and validation of DEXA for measurements of body composition were recently confirmed by Friedl et al. [17] and by Fuller et al. [18]. The values of bone mineral content, fat and fat-free mass are given directly by the software installed with the DEXA machine depending on the different densities of the cited tissues.

Statistical analysis of the differences was made using the Student's t test (average data+standard deviation) for paired groups of the different variables studied.

Results

The Table, which lists the four compartments, shows that mean fat diminished with age and was lowest in the 80-year-old group of women (p < 0.005). The soft-tissue compartment was greater in the 80-year-old women than in the 65-year-old group (p < 0.005). The mineral component did not vary between the three groups.

[TABULAR DATA OMITTED]

Discussion

Various methods are used to evaluate body composition, and in recent years several techniques have been validated for these studies [18, 19]. Densitometry is considered one of the most exact, but expensive, techniques [5, 20], and is the one we selected. Although this technique does not evaluate the water component, the water component is known to be totally dependent on the fat-free component [14, 15]. The studies of Heymsfield et al. [5] confirm that the proportion of water in the fat-free component is similar to that given by Brozek et al. [16], thus validating the calculation of water content from the fat-free tissue component.

In our group of women, mean body water decreased with age, which concurs with reports in the literature [21, 22], but, paradoxically, fat-free tissues did not decrease with age. Van Loan and Koehler [23] also reported the absence of changes in the fat-free mass, together with a slight reduction in the water compartment of subjects over 75 years of age.

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Four-compartment model of body composition of normal elderly women

Age and Ageing, July, 1993 by H. Rico, M. Revilla, E.R. Hernandez, J.M. Gonzalez-Riola, L.F. Villa

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