Longitudinal changes in basal metabolism in man

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Abstract
In a recent cross-sectional study of aging in adult men all of the age-related differences in whole-body basal .ovrhdot.VO2 [O2 consumption] (WB.ovrhdot.VO2) were attributable to differences in skeletal muscle mass (creatinine excretion). The findings on 355 adult men on whom 5 or more paired determinations of WB.ovrhdot.VO2 and muscle mass were obtained over a mean of 10.7 yr were extended. Individual rates of change were calculated by the least-squares method. The overall mean was -0.82 ml O2 .cntdot. min-1 .cntdot. yr-1 and was similar to cross-sectional data. Mean slopes of WB.ovrhdot.VO2, summarized by age-decade groups, were all negative, not different from each other and consistent with the cross-sectional trend. Slopes for nonmuscle .ovrhdot.VO2 (NM.ovrhdot.VO2) were positive for the 6 older groups but not consistent with the unchanging cross-sectional trend. Reassessment of the subject population revealed that 48 men had died some time (mean 1.9 yr) after their last measurements. Cancer and cardiovascular disease accounted for 46 deaths. As a group all decedents had significantly higher mean slopes for NM.ovrhdot.VO2. Muscle mass decrement and the resulting decrease in aerobic requirement accounted for aging decrements in WB.ovrhdot.VO2 in the absence of these terminal diseases. When these conditions were present the overall decline was slowed or even reversed by gradual increases in NM.ovrhdot.VO2. In longitudinal studies this may be mistakenly interpreted as a stabilization of the aging trend.

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