The adult decline in lean body mass.

Abstract

Cross-sectional data reveal an apparent decline in the size of the lean body mass (LBM) during the adult years. We present longitudinal data on LBM as estimated by 40K counting, which show that this decline is for the most part biologic rather than secular in origin. The average rate of loss is about 3 kg per decade. Most data on body size in adult man are cross-sectional in nature. These show that older adults are shorter (National Center for Health Statistics, 1966), have a smaller skeletal mass (Trotter and Hixon, 1974), and a reduced muscle mass as judged from width of forearm muscles (Meema et al. 1973). They also have a smaller lean body mass (LBM) than young adults. This decline in LBM has been documented by several techniques for estimating the size of this body component, including potassium-40 assays, densitometry, assay of total body water, and estimates derived from direct assays of body fat (Allen et al. 1960; Woodward et al. 1960; Wagner et al. 1966; Burmeister and Bingert, 1967; Forbes and Reina, 1970; Novak, 1972; Shukla et al. 1973; Pierson et al. 1974; Brožek, 1952; Baker et al. 1962; Norris et al. 1963; Young et al. 1963; Myhre and Kessler, 1966; Lesser et al. 1971). The question is whether this observed decline is truly biologic, or merely secular in origin. Since children have been getting taller with each succeeding generation (Tanner, 1962), this secular trend could account for the apparent decline in height with advancing age, and possibly for the apparent decline in LBM as well. This question can be answered only by reference to longitudinal data. In this report I present longitudinal observations on LBM in adult man, which have been gathered from my laboratory and from the literature. These data speak in favor of a true decline in LBM during the adult years. Supported by grants from National Institute of Child Health and Human Development, and by the facilities of the Atomic Energy Project at the University of Rochester, Report No. UR-3490-686. 2Departments of Pediatrics and Radiation Biology, University of Rochester Medical Center, Rochester, New York 14642. Human Biology , February 1976, Vol. 48, No. 1, pp. 161-173. ° Wayne State University Press, 1976 This content downloaded from 207.46.13.169 on Sun, 14 May 2017 18:09:51 UTC All use subject to http://about.jstor.org/terms 162 Gilbert В. Forbes